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THE POWER AND UTILITY OF MORPHOLOGICAL CHARACTERS INSYSTEMATICS: A FULLY RESOLVED PHYLOGENY OF XENOSAURUSAND ITS FOSSIL RELATIVES (SQUAMATA: ANGUIMORPHA)
B.-A. S. BHULLAR1
ABSTRACT. Xenosaurus is an enigmatic clade ofMexican and Central American lizards distinguishedby knob-like scalation and flattening of the head andbody associated with living in cracks within cliff faces.The position of Xenosaurus within the larger cladeAnguimorpha is difficult to determine owing to acombination of primitive features and a unique, highlymodified anatomy that obscures useful characters.Evidently, the phylogenetic stem of Xenosaurusrepresents a long independent history of evolution.Fortunately, several fossil taxa exist that can elucidatethis history. These taxa include the extinct Exostinuslancensis (Cretaceous), Exostinus serratus (Oligocene),and Restes rugosus (Paleocene), the latter two knownfrom substantial, cranial material (Bhullar, 2007; 2010).Using osteological and alcohol-preserved specimens,fossils, and high-resolution x-ray CT scans thereof, Iattempted to reconstruct the relationships of the threefossil taxa and the six extant species of Xenosaurus thatare available in U.S. collections.
Despite the considerable phylogenetic importance ofXenosaurus and its stem, this is the first phylogeneticanalysis of the group. An exhaustive search of theskeleton, including osteoderms embedded in theskin visualized using CT scanning, yielded 274 newcharacters, substantially more than have been usedpreviously in gross anatomy–based analyses of such arestricted group of reptiles. The great number ofcharacters is largely the result of the availability ofdisarticulated skeletal material, CT scans showinginternal bone structure and bones embedded in theskin, and attention to subtle anatomical differenceswhose validity could be assessed in terms of intraspe-cies variation because of the availability of large samplesizes for certain taxa.
My results suggested that R. rugosus is sister to theother xenosaurs, resolving a polytomy with otherAnguimorpha recovered by previous work. Exostinus
lancensis is problematic in that it may represent severaldistinct taxa, but it was recovered as sister to E.serratus + Xenosaurus, making Exostinus paraphyletic.Exostinus serratus emerged as sister to Xenosaurus.Xenosaurus comprises a northern clade consisting ofXenosaurus newmanorum and Xenosaurus platyceps;the remaining taxa are united as a southern clade.Within the southern clade, Xenosaurus agrenon andXenosaurus rectocollaris are sister to Xenosaurusgrandis and Xenosaurus rackhami. North–south splitswithin Xenosauridae mirror those of several otherlizard clades and may be the legacy of the equatorialcontraction of early Tertiary tropical forests. The fullyresolved nature of the phylogeny and the congruenceof the extant portion with molecular results indicatesthe continued relevance and efficacy of morphologicalsystematics when an exhaustive anatomical analysis isperformed to search for new characters.
Key words: Xenosaurs, Xenosauridae, squamates,lizards, extinct, paleontology, Anguimorpha, systemat-ics, Shinisaurus
INTRODUCTION
Phylogenetic analysis using gross mor-phological characters, while once the stan-dard approach to systematics, has in the lasttwo decades been complemented by thehuge number of characters (albeit with avery limited number of character states)available from the morphology of nucleicacids, or ‘‘molecular’’ data. Ancient fossiltaxa, of course, can generally be included inphylogenetic analyses only when morpho-logical data are in play, but for extantorganisms the huge number of individualcharacters available from DNA sequencescompared with the characters available fromgross morphology has led to suggestions thatmorphological analyses are woefully inaccu-rate and obsolete (Scotland et al., 2003).
1 Department of Geological Sciences, Jackson Schoolof Geosciences, The University of Texas at Austin,Austin, Texas; and Department of Organismic andEvolutionary Biology, Harvard University, 16 DivinityAvenue, Bio Labs Room 4110, Cambridge, Massachu-setts 02138 ([email protected]).
Bull. Mus. Comp. Zool., 160(3): 65–181, December, 2011 65
Indeed, early morphology-based analyses inparticular often utilized only a few dozencharacters—but still their resolving powercould be considerable (Gauthier et al.,1988). However, far longer character listsand far better resolution can be achievedwith the detailed consideration of the near-infinite aspects of organismal morphology atall scales. Here, I employ an exhaustivesearch for the characters most relevant tofossil taxa—those derived from skeletalanatomy—in an attempt to resolve thephylogeny of the enigmatic clade Xeno-saurus and its fossil relatives.
Xenosaurus (‘‘knob-scaled lizards’’) con-sists of unusual flat-bodied crevice-dwellinglizards distributed throughout Mexico andnorthern Central America. The relation-ships of the species within Xenosaurus andextinct taxa with affinities to the clade havenot been treated in a published phylogenet-ic analysis. Two studies, by Gauthier (1982)and Conrad (2008; see also Conrad et al.,2011), presented hypotheses of relation-ships along the phylogenetic stem of Xeno-saurus, although both dealt primarily withrelationships within the larger clade Angu-imorpha as a whole. In the first of thesestudies, Gauthier (1982) suggested that theOligocene fossil taxon Exostinus serratus issister to Xenosaurus to the exclusion of theCretaceous Exostinus lancensis and thePaleocene Restes rugosus (Exostinus rugo-sus prior to reassignment in that work) butleft the relationships of the latter two taxaunresolved. These taxa are described fullyunder Materials and Methods. A preferredhypothesis in which R. rugosus is sister tothe remaining taxa and E. lancensis is sisterto E. serratus was provided by Conrad(2008). Finally, an unpublished master’sthesis (Canseco Marquez, 2005) included ahypothesis of relationships among theextant species of Xenosaurus based onsquamation. That study included morespecies of Xenosaurus than were availableto me, but for those which were included byCanseco Marquez (2005) and by me in thisstudy, the phylogenetic hypotheses recov-ered for relationships within Xenosaurus is
identical. I did not include the charactersfrom that study here in deference to theauthor of the work, who is preparing it forpublication.
Hypotheses of the phylogeny of Angui-morpha as a whole were provided byMcDowell and Bogert (1954) and Gauthier(1982). Those hypotheses were not explicitlytested by the authors, although Gauthier(1982) presented his hypothesis with anexplicitly cladistic frame of reference. An-guimorpha was subjected to explicit phylo-genetic analysis by several authors, some ofwhom used gross anatomical characters(Rieppel, 1980; Estes et al., 1988; Lee,1998; Evans and Barbadillo, 1998; Gao andNorell, 1998; Conrad, 2005, 2008; Conradet al., 2011) and others of whom usednucleic acid structure (Macey et al., 1999;Wiens and Slingluff, 2001; Townsend et al.,2004; Conrad et al., 2011).
In a cladistic framework, the phylogenyposited by McDowell and Bogert (1954) hasan initial split between Varanoidea (herePlatynota) and Diploglossa, the latter ofwhich includes the remainder of Anguimor-pha. The arrangement suggested that Var-anoidea is split between Heloderma andLanthanotus borneensis + Varanus, whereasDiploglossa is split between Diploglossinaeand a trichotomy of Gerrhonotinae +Anguinae + Xenosauridae. Xenosauridaewas used in the sense of Shinisauruscrocodilurus + Xenosaurus. A similar phy-logeny was presented by Rieppel (1980),with Varanoidea sister to a clade whose firstsplit is between Gerrhonotinae and all othertaxa, with the latter then split into Xeno-sauridae and Diploglossinae + Anguinae.Xenosauridae was not nested within Angu-idae in the topology presented by Gauthier(1982). Instead, he posited a trichotomy ofVaranoidea, Xenosauridae, and Anguidae,the last consisting of Anguinae and Ger-rhonotinae + Diploglossinae. The trichoto-my was resolved by Estes et al. (1988) toAnguidae on one branch and Xenosauridae+ Varanoidea on the other. The sametopology was recovered by Lee (1998).According to Evans and Barbadillo (1998),
66 Bulletin of the Museum of Comparative Zoology, Vol. 160, No. 3
the initial split is between Xenosauridae andthe remaining anguimorphs (in addition,Gekkota is nested within Anguimorpha, anunusual result that was not recovered inother studies). This topology, without thenested Gekkota, was also recovered by Gaoand Norell (1998), as was the placement ofthe Mongolian taxon Carusia intermedia(Borsuk-Bialynicka, 1984) as the sister toXenosauridae. Finally, a similar topologywas recovered by Conrad (2005, 2008), savethat S. crocodilurus and its extinct relativeBahndwivici ammoskius are sister to Var-anoidea, leaving the initial split in Angui-morpha between Xenosaurus plus its alliedextinct taxa and the remainder of Angui-morpha. Carusia intermedia emerged in the2005 study as the sister taxon to Anguimor-pha, and in the 2008 and 2011 studies as thesister to Xenosaurus and its extinct relatives.Within Anguidae, Anguinae and Diploglos-sinae are sister taxa to the exclusion ofGerrhonotinae.
Among the studies based on nucleic acidstructure, the same data set was used byMacey et al. (1999) and Wiens and Slingluff(2001). Both groups recovered the sameoverall topology for Anguimorpha. Theinitial split according to those studies is atrichotomy among Varanus, Heloderma, andthe remainder of Anguimorpha. The latterclade is split between S. crocodilurus andXenosaurus + Anguidae. Within Anguidae,Anguinae and Gerrhonotinae are sister taxato the exclusion of Diploglossinae. Severalyears after the publications of those focusedstudies on Anguimorpha, the first molecularstructure–based phylogenies of all of Squa-mata appeared (Townsend et al., 2004; Vidaland Hedges, 2005). In general, most of thetrees recovered in those analyses have theinitial split in Anguimorpha between S.crocodilurus + Varanidae and Anguidae +Heloderma + Xenosaurus in some combina-tion. An Anguidae + Heloderma cladeappears more often than a Heloderma +Xenosaurus clade. The molecular structure–based phylogenies are thus broadly congru-ent with the newest gross anatomy–basedphylogenies, save for the unprecedented
nonmonophyly of Varanoidea, a clade sup-ported by numerous gross anatomical apo-morphies (summarized by Gao and Norell,1998; Conrad, 2005, 2008; Conrad et al.,2011).
Regarding outgroups to Anguimorpha,the gross anatomy–based and molecularstructure–based phylogenies differ striking-ly. All of the gross anatomy–based phylog-enies have Anguimorpha as part of amonophyletic Scleroglossa (sensu Estes etal., 1988), with Iguania sister to that largeclade. The appropriate outgroups to Angui-morpha would thus be found within‘‘Scincomorpha’’ (whose monophyly is notuniversally supported), at least a part ofwhich is, in most gross anatomy–basedphylogenies, more closely related to Angui-morpha than is Gekkota. The molecularstructure–based phylogenies, on the otherhand, generally recover Iguania as moreclosely allied to Anguimorpha than any‘‘scincomorph’’ clade, sometimes with Ser-pentes intervening.
Given the potential importance of Xeno-saurus and its extinct relatives to resolvingthe phylogeny of Anguimorpha and therebyof Squamata as a whole, this study isdirected at resolving the problematic rela-tionships within the highly autapomorphiccrown clade and its stem. The extinct taxaare particularly important to my analysesbecause they can break up the phylogenetic‘‘long branch’’ leading to Xenosaurus (Gau-thier et al., 1988). Two other factors wereimportant to the viability of the study. First,museum collections in the United Stateshave sufficient skeletal and wet-preservedspecimens of extant Xenosaurus to allow areasonable sampling of taxa and someassessment of intraspecific variation. Fur-thermore, some of the skeletal specimens Iused were disarticulated. Many of thecharacters identified here would have beenimpossible to see in articulated skeletons.Finally, high-resolution CT scanning tech-nology allowed the digital disarticulation offossils in matrix and the visualization ofosteoderms within the skin of extant spec-imens.
XENOSAUR PHYLOGENY N Bhullar 67
MATERIALS AND METHODS
Ingroup
The focus of the present study is Xeno-saurus and its extinct relatives, also referredto herein as ‘‘xenosaurs’’ (Shinisaurus andits extinct relatives are likewise called‘‘shinisaurs’’). The term Xenosauridae isused exclusively to refer to the ‘‘traditional’’clade, including xenosaurs and shinisaurs assister taxa, a topology only supported by oneof the two analyses performed here. Thecharacters included are limited in large partto those pertinent to relationships within thexenosaur ingroup. Most of the 274 charac-ters I describe and score (Table 1) are newor newly defined; derivation from previousliterature is noted in the character descrip-tions. The extinct taxa are particularlyimportant in light of the highly derivednature of the crown clade; they provide theopportunity to break up ‘‘long branches’’and resolve problematic clades (Rowe,1986; Gauthier et al., 1988).
Xenosaurus. Twelve extant species ofXenosaurus were included in the unpub-lished external anatomy–based phylogeneticanalysis by Canseco Marquez (2005); two ofthose are undescribed, and I was unable toobtain four—Xenosaurus arboreus, Xeno-saurus sanmartinensis, Xenosaurus phalar-oanthereon, and Xenosaurus penai—fromU.S. collections. Most species of Xenosauruswere once classified as subspecies of Xeno-saurus grandis Gray 1856. Summaries of thetaxonomic history of the group were pro-vided by King and Thompson (1968),Ballinger et al. (2000), and Canseco Mar-quez (2005). The taxa used in my study (seeTable 1) are Xenosaurus newmanorum Tay-lor 1949 (Fig. 1), Xenosaurus platycepsKing and Thompson 1968 (Fig. 2), Xeno-saurus rackhami King and Thompson 1968(as Xenosaurus grandis rackhami) (Fig. 3),X. grandis (Fig. 4), Xenosaurus agrenonKing and Thompson 1968 (as Xenosaurusgrandis agrenon), and Xenosaurus rectocol-laris Smith and Iverson 1993 (Fig. 5).Alcoholic specimens were available for alltaxa, and skeletal material was available for
all but X. rectocollaris. To supplement theskeletal material, I used high-resolution x-ray CT scans of the heads and bodies of allspecies save X. agrenon, for which the wet-preserved specimens were filled with metalshot that interfered with the scanningprocess. The scans were performed at theHigh-Resolution CT Scanning Facility atThe University of Texas at Austin (UTCT)and allowed visualization of the articulatedskeletons with the osteodermal armor inplace.
Exostinus serratus. The included speci-mens, from the Oligocene of Colorado andWyoming, were described by Bhullar (2008;2010), as was the history of this taxon.
Exostinus lancensis. This is the mostproblematic taxon included in the study. Itwas described by Gilmore (1928) and Estes(1964) on the basis of fragmentary materialfrom the Late Cretaceous of Wyoming andMontana. A summary of the history of thetaxon until 1983 was provided by Estes(1983). Following that work, the onlyadditional information on the anatomy ofthe taxon was provided by Gao and Fox(1996) on the basis of specimens from thewestern interior of Canada. Scoring here isbased on those descriptions and on anumber of undescribed specimens fromthe western United States in the collectionsof the American Museum of NaturalHistory. For the purposes of this study, allof these disparate specimens are assumed torepresent the same taxon. However, E.lancensis requires additional study. Inparticular, most of the American Museumspecimens from the Lance Formation ofWyoming conform well to the descriptionsof E. lancensis in the literature. However,frontals that are clearly associated with thecharacteristic parietals based on size, osteo-dermal sculpturing, and fit of the articularsurfaces are large and unfused, whereasGao and Fox (1996) described the anteriorportion of a fused frontal that is nearly thesame size. For the purposes of this study,frontal fusion is assumed to be ontogenet-ically variable in E. lancensis, but work onthis taxon continues.
68 Bulletin of the Museum of Comparative Zoology, Vol. 160, No. 3
Restes rugosus. This taxon was describedas Exostinus rugosus by Gilmore (1942) andfurther by Estes (1965). It was renamed R.rugosus by Gauthier (1982). It is knownprimarily from a single well-preserved butdisarticulated specimen, YPM PU 14640from the late Paleocene of Wyoming.Isolated frontals that Gauthier (1982) re-ferred to the taxon were suggested to belonginstead to a shinisaur or a platynotan bySmith (2006b). Restes rugosus was neverfully described, nor has it been examinedsince the work of Gauthier (1982). Theanalysis here utilizes a low-resolution CTscan of the YPM PU 14640 block, which Ifound to contain a surprising amount ofunexposed material. I had access to oneadditional specimen, an anterior section of amaxilla (UMMP 73565) from the Paleoceneof Wyoming.
Outgroup
Anguimorpha. Because of the unresolvedstate of the larger clade Anguimorpha, itwas necessary to use a variety of angui-morph taxa in the analysis. In general, thefocus was upon extant taxa to minimizemissing data, and because I was notattempting to resolve anguimorph relation-ships definitively. However, because S.crocodilurus was traditionally allied toXenosaurus in Xenosauridae, the analysisincludes two described fossil shinisaurs—B.ammoskius from the Eocene of Wyoming(Conrad, 2005, 2008) and Merkurosaurusornatus from the Miocene of the CzechRepublic (Klembara, 2008). These are theonly included taxa that I scored entirelyfrom the literature. I also included threeanguids—the diploglossine Celestus ennea-grammus (part of the clade sister to all otherdiploglossines; Macey et al., 1999), theanguine Ophisaurus ventralis, and thegerrhonotine Elgaria multicarinata. I ex-cluded the problematic glyptosaurs (seeConrad, 2005, 2008) and Anniella (Wiensand Slingluff, 2001; Conrad, 2005, 2008).Within Varanidae, L. borneensis and themonitor lizard species Varanus niloticus and
Varanus exanthematicus were used (Fulleret al., 1998; Ast, 2001; Pianka and King,2004). Helodermatidae is scored as acomposite taxon. Heloderma suspectumsuffices for scoring most characters of thisclade. However, for two characters (96 and97), the derived nature of H. suspectumaffected the resolution of xenosaur phylog-eny. The anterior (frontal and pre-orbital)skull roof osteoderms of extant Helodermaare highly domed, but those of Primadermanessovi Nydam 2000, Gobiderma pulchraBorsuk-Bialynicka 1984, and Eurhelodermagallicum, primitive taxa on the stem ofHeloderma, are flat and plate-like (Hoff-stetter, 1957; Gao and Norell, 2000; Nydam,2000). The domed state of the extant taxarendered ambiguous the nature of theflattened skull roof osteoderms of R. rugo-sus, whereas scoring the primitive state forthe helodermatid lineage results in a mostparsimonious hypothesis that R. rugosus isprimitive relative to Xenosaurus + E.lancensis and pulls it out of a trichotomywith those taxa. In these cases, as noted,scoring was performed as though theancestral states for the entire helodermatidlineage were being considered. When great-er access to the skeletal material of thesestem taxa is possible, they should be brokenout and scored separately.
Outside of Anguimorpha. One non-angui-morph was used as an outgroup. A possiblechoice according to Conrad (2005) wouldbe C. intermedia (Gao and Norell, 1998,2000). However, C. intermedia is notuniversally agreed to lie outside of Angui-morpha and still cannot be as thoroughlyscored as an extant taxon. Because of theoverwhelming molecular scale support foran Anguimorpha + Iguania clade, I chosethe iguanian Pristidactylus torquatus as myadditional outgroup. No previous gross ana-tomical phylogenetic analysis has used thistopology.
Variation
The assessment of intraspecies variation,including but not limited to ontogenetic
XENOSAUR PHYLOGENY N Bhullar 69
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70 Bulletin of the Museum of Comparative Zoology, Vol. 160, No. 3
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TA
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.
XENOSAUR PHYLOGENY N Bhullar 71
Xen
osau
rus
spp
.12
512
612
712
812
913
013
113
213
313
413
513
613
713
813
914
014
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214
314
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614
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72 Bulletin of the Museum of Comparative Zoology, Vol. 160, No. 3
Xen
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rus
spp
.18
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818
919
019
119
219
319
419
519
619
719
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320
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XENOSAUR PHYLOGENY N Bhullar 73
variation, is an important but often over-looked aspect of character discovery forphylogenetic analysis (Barahona and Barba-dillo, 1998; Wible, 2003; Bever, 2005, 2006,2008). Large sample sizes representing agood sample of the populations of thespecies were not possible to obtain for alltaxa here examined, but such samples wereavailable for enough taxa to phylogeneticallybracket several clades. Specifically, samplesof 10 or more specimens, spanning most ofpostnatal ontogeny, were available for V.exanthematicus, E. multicarinata, H. suspec-tum, X. platyceps, and X. grandis. I also had alarge sample of X. rackhami (see Supple-mentary Information), although very youngindividuals were lacking. When statementsare made in the character descriptionsregarding ontogenetic variation, they referto the taxa listed above as being present aslarge samples or clades bracketed by them.
Observed variation is noted in the charac-ter descriptions. For most taxa scored,multiple specimens were available for exam-ination (see specimen list in SupplementaryInformation). As might be expected, ingeneral, sample sizes were low for the extincttaxa—one in the cases of R. rugosus (save fora small fragment of maxilla, UMMP 73565)and B. ammoskius. The weakest part of theextant ingroup in terms of variation assess-ment was the X. agrenon + X. rectocollarisclade. For each of these taxa, I had only asingle skeletal specimen (but multiple wetspecimens). However, I discovered multipleunique synapomorphies for the clade, andtheir position in my results is consistent, asmentioned above, with that recovered byother researchers using different sources ofdata from gross anatomy. In general, I wasconservative in defining characters; most ofthe characters described in this work varylittle within species for which multipleindividuals were available. Any variation thatwas present is noted.
Another aspect of variation is the assess-ment of the relative ontogenetic age of thespecimens examined, which affects thescoring of some characters. Within Squa-mata and more specifically Anguimorpha,X
enos
auru
ssp
p.
249
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74 Bulletin of the Museum of Comparative Zoology, Vol. 160, No. 3
several general ontogenetic trends can bebracketed as ancestral for the clade (Beveret al., 2005; Bhullar, 2006; Bhullar andSmith, 2008, for Anguimorpha). Ontogenet-ic age can thus be inferred for fossils andextant specimens without age data. Merkur-osaurus ornatus specimens range from‘‘subadults’’ with unfused frontals and pro-portionally shorter supratemporal processesof the parietal to large, mature adults withfused frontals, heavy osteodermal sculptur-ing, and long supratemporal processes(Klembara, 2008). The single known spec-imen of B. ammoskius appears to be arelatively mature adult based on the prom-inent osteodermal sculpturing on the skullroof and the proportionally great length ofthe supratemporal processes. The Yale R.
rugosus likewise has fully fused frontals andstrong osteodermal sculpturing upon boththe frontal and the maxillae, suggesting thatit is a large, mature individual. Mostspecimens of E. lancensis have parietalsthat are heavily sculptured and rectangularin overall outline and are large comparedwith those of other xenosaurs, suggestingfairly advanced ontogenetic stages, but thefrontals are unfused save in a few individ-uals, indicating immaturity (taking intoaccount the cautionary notes regarding thistaxon made earlier). Finally, the knownspecimens of E. serratus are approximatelythe same size as adults of other xenosaursand bear heavy osteodermal sculpturing andgenerally ‘‘mature adult’’ proportions of thecranial elements.
Figure 1. Cranium of Xenosaurus newmanorum, CT scan of UMMZ 126056. A, Dorsal, anterior to the left. B, Ventral, anterior tothe left. C, Left lateral, anterior to the left. Illustrates characters 114(1), 151(0), 184(0), 247(1), 248(1), 249(0), 251(0), 252(0),255(1), 256(0), 257(0), 258(3), 259(0), 260(0), 261(1), 262(0), 263(0), 264(2).
XENOSAUR PHYLOGENY N Bhullar 75
Analyses
Instead of a single preferred startinghypothesis, I use two, generating resultsreferred to as Analysis 1 and Analysis 2 inthe descriptions and discussions that follow.Starting conditions for Analysis 1 wereinspired by phylogenies of Anguimorphaon the basis of nucleic acid structure,notably that of Townsend et al. (2004),which remains the most thorough andthoughtful analysis of these data. To gener-ate Analysis 1, I used a constraint tree fixingextant taxa in the topology discussed previ-ously for molecular studies (with an Angui-dae + Helodermatidae clade instead of aHelodermatidae + Xenosaurus clade or atrichotomy) and leaving relationships among
xenosaurs, as well as among Shinisaurus andits extinct relatives, free to vary. To generateAnalysis 2, I initially intended to constrainrelationships based on a preferred grossanatomy–based phylogenetic hypothesis forAnguimorpha, but I found that my charac-ters alone, with P. torquatus specified as theoutgroup, generated a hypothesis identicalto that of Conrad (2005, 2008), with onemajor difference: Shinisaurus and its extinctrelatives are not sister to Varanoidea but areunited with xenosaurs in the traditionalXenosauridae. This result obtained withoverwhelming support even after the exper-imental addition of the characters unitingshinisaurs with varanoids in Conrad’s anal-yses (2005, 2008; results not shown).
Figure 2. Cranium of Xenosaurus platyceps, CT scan of UTA 23594, courtesy of Deep Scaly Project (2007; images from originaldata processing). A, Dorsal, anterior to the left. B, Ventral, anterior to the left. C, Left lateral, anterior to the left. Illustratescharacters 26(1), 248(0), 250(0), 253(0), 254(1), 258(4), 260(1), 262(1), 263(1).
76 Bulletin of the Museum of Comparative Zoology, Vol. 160, No. 3
Both analyses proceeded using the parsi-mony heuristic search option in PAUP* v.4.0b10, with default options save that treebisection and reconnection (TBR) branchswapping was enabled with 1,000 randomaddition sequences (Swofford, 2001). Boot-strap analyses were run with default settingssave the parsimony settings noted above andthe specification of 200 replicates. Each setof conditions yielded a single most parsimo-nious tree under all three character stateoptimization options, mercifully obviatingcalculations of consensus.
Ingroup relationships were identical inthe results of Analysis 1 and Analysis 2.Because Analysis 2 was essentially uncon-strained save for the specification of anuncontroversial outgroup, I was able touse a nonparametric Wilcoxon signed ranks
test (Templeton test), automated throughPAUP*, to assess whether the overall treetopologies (including the outgroups) weresignificantly different in terms of charactersupport and evolution (Templeton, 1983;Larson, 1994).
Inapplicable and unknown data wereboth scored as ? under the default settingsin PAUP* v. 4.0b10. Failing to distinguishbetween the two can be problematic be-cause character states from applicable taxacan ‘‘bleed’’ to inapplicable taxa duringoptimization, but the alternative strategy of‘‘absence coding’’ is also problematic(Strong and Lipscomb, 1999). Specifically,in such a case, inapplicability can beoptimized as a synapomorphy when multi-ple taxa are scored as inapplicable for asingle character. In several cases within this
Figure 3. Cranium of Xenosaurus rackhami, CT scan of UTEP 4555. A, Dorsal, anterior to the left. B, Ventral, anterior to the left.C, Left lateral, anterior to the left. Illustrates characters 28(0), 123(0), 133(1), 135(2), 249(6), 252(3), 256(3), 264(3).
XENOSAUR PHYLOGENY N Bhullar 77
analysis, this presence/absence scoringwould be redundant with another character.
Multistate characters are discretizationsof quantitative continua (counts or mea-surements) and were run as ordered,although the unordered setting was usedto test the robusticity of the results.Mesquite v. 2.01 (Maddison and Maddison,2008) was used to construct the charactermatrix and to trace character evolution. Theprocess of discretizing continua necessarilyleads to artificial bins, and the cutoffs foreach character state are different to capturedifferent levels of quantitative distinctionamong taxa. However, when more than twocharacter states exist, the intervals are even.Even intervals prevent ‘‘cooking’’ of the databy selectively expanding some bins to
encompass extra taxa. I first described mostof the characters expressed as numericalvalues in less precise or more ‘‘qualitative’’terms (all valid ‘‘qualitative’’ characters canbe expressed in quantitative terms; seeWiens, 2001). The numerical values serveto give additional precision to these differ-ences; essentially, after describing the dif-ferences in the states of a character in com-parative or ‘‘qualitative’’ terms, I searchedfor a numerical expression of these differ-ences. This process explains why the cutoffsfor different values are not always ‘‘stan-dard’’ intervals of 5 or 10, for instance(though, as noted, they are always regularintervals). The logical next step would be toattempt quantification of all characters andto score them using more advanced numer-
Figure 4. Cranium of Xenosaurus grandis, CT scan of FMNH 123704, courtesy of Deep Scaly Project (2007; images fromoriginal data processing). A, Dorsal, anterior to the left. B, Ventral, anterior to the left. C, Left lateral, anterior to the left. Illustratescharacters 135(1), 248(3), 250(1), 251(1), 252(2), 253(2), 256(2), 260(3).
78 Bulletin of the Museum of Comparative Zoology, Vol. 160, No. 3
ical methods such as gap-weighting (Wiens,2001). For the purposes of the present study,however, this analysis takes a middle ground.
Institutional Abbreviations
AMNH, American Museum of NaturalHistory, New York; CAS, California Acade-my of Sciences, San Francisco; NAUQSP-JIM, Northern Arizona University Quater-nary Sciences Program, Jim I. Mead collec-tion (now housed at East Tennessee StateUniversity, Johnson City); FMNH, FieldMuseum of Natural History, Chicago; MCZ,Harvard Museum of Comparative Zoology,Cambridge; MVZ, Museum of VertebrateZoology, The University of California atBerkeley; TMM, Vertebrate PaleontologyLaboratory, Texas Natural Science Center,
The University of Texas at Austin; UF,Florida Museum of Natural History, Gains-ville; TNHC, Texas Natural History Collec-tions, The University of Texas at Austin;UMMZ, University of Michigan Museum ofZoology, Ann Arbor; USNM, NationalMuseum of Natural History, Washington,DC; UTA, The University of Texas atArlington Herpetological Collections, Ar-lington; UTEP, The University of Texas atEl Paso Natural History Collections, ElPaso; YPM, Yale Peabody Museum ofNatural History, New Haven, Connecticut.
CHARACTER DESCRIPTIONS
Extended descriptions of characters andtheir distribution are contained in theelectronic supplementary material. All char-
Figure 5. Cranium of Xenosaurus rectocollaris, CT scan of UF 51443. A, Dorsal, anterior to the left. B, Ventral, anterior to the left.C, Left lateral, anterior to the left. Illustrates characters 87(1), 123(1), 135(0), 165(2), 248(2), 249(3), 252(1), 253(1), 254(0),255(0), 256(1), 257(1), 258(2), 259(1), 260(2), 264(4).
XENOSAUR PHYLOGENY N Bhullar 79
acters refer to the condition in relativelylarge ‘‘adult’’ individuals, except wherenoted. Measurements are given to definesome character states; most states, however,are illustrated, and the figures should beused as primary guides in scoring speci-mens. Intraspecific variation was accountedfor by measurements of additional individ-uals and by simple visual comparison whenpossible. Where angles to a plane or an edgeare given, the acute component is provided.
Comments on variation follow the charac-ter descriptions when variation that wouldaffect scoring was evident. Given the lowsample sizes of some of the taxa included inthis study, the comments are certainly incom-plete. An intensive study of variation in thecharacters used in this study is warranted butbeyond the scope of the current work.
Description of the evolution of charactersreferences both terminal taxa and clades thatare supported by both resultant phylogenetichypotheses (Figs. 6, 7), i.e., Anguimorpha,Anguidae, Varanidae, S. crocodilurus + B.ammoskius + M. ornatus, and all subcladeswithin the clade Xenosaurus + E. serratus.Varanus exanthematicus + Varanus niloticusis referred to as Varanus where scorings donot differ in Varanus salvator, a taxon on theother branch from the basal split of Varanus(Fuller et al., 1998; Ast, 2001). Bahndwiviciammoskius was scored based on the descrip-tion by Conrad (2006), and M. ornatus fromthat by Klembara (2008).
When character states are identified assynapomorphies of various clades, these state-ments are to be understood given thelimitations of the taxon sampling for this study;
Figure 6. Analysis 1 tree with bootstrap values greater than 50%.
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thus, most stated synapomorphies of cladesoutside of Xenosaurus and its stem are likely torepresent synapomorphies of more inclusiveclades or may not be valid with the inclusion ofthe vast array of additional extant and extincttaxa within Anguimorpha (Conrad et al., 2011).Most characters are new; if a version of thecharacter appeared in a previous analysis, theoriginal analysis is cited parenthetically afterthe short description. The only characters thatappeared in some form in previous analysesare 62, 91, 117, 124, 134, 145, 149, 189, 218,224, 231, 246, and 272. Of those, only 91, 149,and 189 are essentially unmodified. The fulltaxon–character matrix is depicted in Table 1.
Dentition, General
1. Dentition: Tooth form (0) entirely uni-cuspid with pointed apices (Fig. 8A); (1)
chisel-shaped (see Gao and Fox, 1996);(2) chisel-shaped, some bicuspidity(Fig. 8B).
Variation. Considerable ontogeneticvariation occurs in tooth form. Bicus-pidity develops during postnatal ontog-eny in Xenosaurus and in Anguidae.However, whereas early (postnatal)-stage anguid teeth are nearly conical,in early-stage Xenosaurus, the chiselshape already obtains. The teeth ofiguanians in general do not undergo aunicuspid-to-multicuspid transition dur-ing postnatal ontogeny, although theextremity of development of the cuspsmay increase with ontogenetic age.Moreover, in no observed taxon do theteeth progress during ontogeny frommulticuspid to unicuspid. Thus, thefossils with bicuspid teeth R. rugosus
Figure 7. Analysis 2 tree with bootstrap values greater than 50%.
XENOSAUR PHYLOGENY N Bhullar 81
and E. serratus are scored as such andthe inferred late ontogenetic stages ofthe fossil shinisaurs are beyond those atwhich the transition from unicuspid tomulticuspid occurs in any observedextant specimen. Little variation occursacross broad ontogenetic stages in thegeneral form of the teeth.
Evolution. Under both phylogeneticanalyses, state (0), unicuspid teeth, isplesiomorphic within Anguimorpha assuggested by Gauthier (1982). Further-more, under most hypotheses for theplacement of Anguimorpha that havebeen suggested, having unicuspid teethis a synapomorphy along the angui-
morph stem. If C. intermedia is on theanguimorph stem as suggested by Con-rad (2005) and if the blunt, multicuspidstate of the teeth of that taxon (Gao andNorell, 1998) is homologous to that ofmost other Scleroglossa, then this syn-apomorphy can be constrained to theinternode between C. intermedia andAnguimorpha. However, various Meso-zoic squamates with unicuspid teeth areplaced by some phylogenetic analyses as asister clade to all other Scleroglossa(Evans et al., 2005; but see Conrad,2008), potentially complicating the opti-mization of unicuspidity. The chisel shapeof the tooth crowns is a synapomorphy of
Figure 8. A, Right dentary of Shinisaurus crocodilurus MVZ 204291, medial, anterior to the left. Illustrates character 1(0). B, Leftdentary of Xenosaurus newmanorum uncatalogued NAUQSP-JIM specimen, medial, anterior to the right. Illustrates character1(2). C, Premaxilla of Elgaria multicarinata TMM-M 8993, ventral, anterior to the top. Illustrates characters 2(0), 14(0). D,Premaxilla of Xenosaurus newmanorum uncatalogued NAUQSP-JIM specimen, ventral, anterior to the top. Illustrates characters2(1), 14(1).
82 Bulletin of the Museum of Comparative Zoology, Vol. 160, No. 3
Xenosaurus and its fossil relatives. Thepresence of chisel-shaped teeth withoutbicuspidity in E. lancensis is either aprimitive character of that taxon withbiscupidity a synapomorphy of Xeno-saurus and an autapomorphy of R.rugosus, or the chisel-shaped state lackingbicuspidity is an autapomorphy of E.lancensis with the bicuspid chisel-shapedmorphology as a synapomorphy of Xeno-saurus + Retes rugosus.
Premaxilla
The premaxilla is unknown for R. rugosusand E. lancensis.
2. Premaxilla: Curvature of rostral arc inhorizontal plane (0) relatively broad(Fig. 8C); (1) relatively acute (Fig. 8D).
Variation. The premaxillae of mosttaxa become slightly less acute duringontogeny, but even early neonates ofnon-xenosaurs do not show the acutemorphologies of adult Xenosaurus.
Evolution. Acute curvature is a synapo-morphy of Xenosaurus under bothanalyses.
3. Premaxilla: Height of dentigerous arc atsuture of dermal surface to lateral(dermal) surface of maxilla: (0) dorso-ventrally short, about one-fifth or less ofmediolateral width between contralateralsutures (Fig. 9A); (1) tall, aboutone quarter or more of mediolateralwidth between contralateral sutures(Fig. 9B).
Evolution. Under Analysis 1, twoalternative hypotheses of character evo-lution each require three steps. In thefirst hypothesis of character evolution,the proportional tallness of the dentig-erous arc is a synapomorphy of Angui-morpha. The shortness of the dentiger-ous arc is then a synapomorphy ofAnguidae + Helodermatidae and ofVaranus. In the second hypothesis ofcharacter evolution, relative tallness isindependently a synapomorphy of Xe-
nosaurus + E. serratus, S. crocodilurus +M. ornatus, and L. borneensis. UnderAnalysis 2, relative tallness is a synapo-morphy of Xenosauridae, independentlyof L. borneensis.
4. Premaxilla: Angle to the horizontal intransverse plane of lateral edges ofrostral body connecting portion (0)low, 40u or lower (Fig. 9A); (1) high,greater than 40u (Fig. 9C).
Evolution. Taking into account therelatively vertical condition in P. torqua-tus and the wide distribution of thatcondition in other non-anguimorphSquamata and sphenodontians (Evans,1980; Fraser, 1982; Whiteside, 1986), alow angle to the horizontal of the lateraledges is a synapomorphy of Anguimor-pha under both analyses. According toAnalysis 1, a high angle to the horizontalwithin Aguimorpha is independently asynapomorphy of E. serratus + Xeno-saurus and of S. crocodilurus + M.ornatus. According to Analysis 2, a highangle to the horizontal is a synapomor-phy of Xenosauridae.
5. Premaxilla: Dorsolateral angle of den-tigerous arc (0) formed by meeting ofrelatively straight edges, not producedinto wedge (Fig. 9A); (1) produced intosmall wedge (Fig. 9B).
Variation. The degree of developmentof the produced wedges varies withinbroad ontogenetic stages of X. rackhamiand X. grandis but is always greater thanthat of the taxa scored as (0).
Evolution. Under both analyses, pro-duction into wedges is a synapomorphyof X. grandis + X. rackhami and of S.crocodilurus + M. ornatus.
6. Premaxilla: Major premaxillary ethmoidcanals (0) partially or completely bound-ed by connective tissue only, not fullysurrounded by ossified premaxilla(Fig. 9D, left side); (1) bony, surround-ed by ossified premaxilla (Fig. 9D, rightside).
XENOSAUR PHYLOGENY N Bhullar 83
Variation. The enclosure does nottransform during postnatal ontogeny,but its does vary to some extent withintaxa. Specifically, in one S. crocodilurusspecimen examined, UF 71623, theenclosure is incomplete on one side.Enclosure is also present on one side in asingle very large individual of E. multi-carinata, TMM-M 8993 (Fig. 9D). Ingeneral, extremely large individuals, atleast within anguimorphs, tend to devel-op extra flanges of bone that sometimesclose previously open grooves for nervesand vasculature (personal observation).
Evolution. Under Analysis 1, enclo-sure of the medial ethmoidal canals is asynapomorphy of Xenosaurus + E. serra-
tus and of S. crocodilurus + Varanidae.Under Analysis 2, enclosure is a synap-omorphy of Xenosauridae and an auta-pomorphy of L. borneensis. The hypoth-esis that Varanidae and its stemancestrally showed enclosure of thecanals is complicated by the existence oftaxa along the stems of the two varanoidlineages (and perhaps Varanoidea as awhole) from the Cretaceous of Mongoliaand the early Paleogene of Europe,including Estesia mongoliensis, Aiolo-saurus oriens, G. pulchra, and Necro-saurus sp., that do not appear to show themorphology (Estes, 1983; Borsuk-Bialy-nicka, 1984; Norell et al., 1992; Norelland Gao, 1997; Gao and Norell, 1998,
Figure 9. A, Premaxilla of Heloderma suspectum TMM-M 9001, anterior. Illustrates characters 3(0), 4(0), 5(0), 7(0), 8(0), 9(0),21(0). B, Premaxilla of Xenosaurus grandis NAUQSP-JIM 1460, anterior. Illustrates characters 3(1), 5(1), 7(2), 9(2), 10(1), 11(2),12(1). C, Premaxilla of Exostinus serratus, CT scan of USNM v16565, anterior. Illustrates characters 4(1), 8(3), 9(1), 11(1), 12(0),13(0). D, Premaxilla of Elgaria multicarinata TMM-M 8993, posterior. Illustrates characters 6(0), 6(1), 19(0).
84 Bulletin of the Museum of Comparative Zoology, Vol. 160, No. 3
2000). However, the issue is resolved ifVaranoidea is not monophyletic, as inAnalysis 1, and most or all of these taxa liealong the helodermatid stem, as wassuggested for E. mongoliensis and G.pulchra (Norell and Gao, 1997; Gao andNorell, 1998; Conrad, 2004, 2005, 2008).
7. Premaxilla: Number of anterior forami-na collinear with main row of maxillarylabial foramina (0) none (Fig. 9A); (1)two (Fig. 10A); (2) more than two(Fig. 9B).
Variation. Other than the variation inthe degree of enclosure noted for Char-acter 6, the number of lower foraminadoes not vary in observed specimens of
those taxa scored as possessing two (butsee variation in upper foramina notedunder Character 8). Slight variation oc-curs in the number of foramina within thespecies of Xenosaurus—from three to five,for example, in X. rackhami. No variationthat would affect scoring was evident.
Evolution. Under both analyses, thepossession of several lower anterior fo-ramina is a synapomorphy of E. serratus +X. grandis. Under Analysis 1, the ances-tral state for the entire group, forXenosaurus + Anguidae, and for S.crocodilurus + Varanidae is ambiguousbetween no foramina and two foramina.The ancestral state for Anguidae +Helodermatidae is no foramina. Under
Figure 10. A, Premaxilla of Shinisaurus crocodilurus UF 72805, anterior. Illustrates characters 7(1), 9(0), 11(0). B, Premaxilla ofXenosaurus newmanorum uncatalogued NAUQSP-JIM specimen, anterior. Illustrates characters 8(4), 10(0), 13(1). C, Premaxillaof Xenosaurus newmanorum uncatalogued NAUQSP-JIM specimen, posterior. Illustrates characters 15(0), 16(1), 17(1), 18(1),22(2), 23(1). D, Premaxilla of Xenosaurus grandis NAUQSP-JIM 1460, posterior. Illustrates characters 15(1), 16(0), 18(0), 19(1).
XENOSAUR PHYLOGENY N Bhullar 85
Analysis 2, a lack of foramina is ancestralfor the entire group and for Anguimorphaand two foramina is a synapomorphy ofVaranidae; the ancestral state for Xeno-sauridae is ambiguous between no foram-ina and two foramina.
8. Premaxilla: Number of anterior forami-na dorsal to main row of maxillary labialforamina (0) none (Fig. 9A); (1) one; (2)two; (3) three (Fig. 9C); (4) four or more(Fig. 10B).
Evolution. Under both analyses, thepresence of one to three dorsal foraminais a synapomorphy of E. serratus +Xenosaurus and an increased numberof such foramina is a further synapo-morphy of Xenosaurus. Absence offoramina is an autapomorphy of X.rectocollaris.
9. Premaxilla: Anterior surface of premax-illa just dorsal to teeth (0) flush withremainder of anterior surface (Fig. 9A);(1) raised into supradental thickening(Fig. 9C); (2) supradental thickeningpronounced (Fig. 9B).
Variation. Little noticeable variationwas evident, save that very youngindividuals of Xenosaurus have a slightlyless pronounced thickening.
Evolution. Under both analyses,the presence of the premaxillary supra-dental thickening is a synapomorphyof Xenosaurus + E. serratus. The pres-ence of a more pronounced thickening isa synapomorphy of Xenosaurus.
10. Premaxilla: Surface ventral to rostralosteoderm (0) rugose (Fig. 10B); (1)bearing discrete fused osteoderms(Fig. 9B).
Variation. Osteoderms fuse to thepremaxilla during postnatal ontogeny,but are present in mid-sized and largespecimens within the species that pos-sess them.
Evolution. Under both analyses, ru-gosity of the surface ventral to the
rostral osteoderm is a possible synapo-morphy of E. serratus + Xenosaurus;fusion of osteoderms in this region is asynapomorphy of the southern clade ofXenosaurus.
11. Premaxilla: Rostral osteoderm (0) absent(Fig. 10A); (1) oval and mediolaterallynarrow (Fig. 9C); (2) rounded andmediolaterally wide (Fig. 9B).
Variation. Other than the ontogeneticfusion of osteoderms to the premaxilla, Iobserved no intraspecific variation inthis character.
Evolution. Under both analyses,presence of a narrow rostral osteodermis a synapomorphy of E. serratus +Xenosaurus. A rounded shape to theosteoderm is a synapomorphy of thesouthern clade of Xenosaurus.
12. Premaxilla: Distinct flanking osteo-derms dorsolateral to rostral osteoderm(0) present (Fig. 9C); (1) absent(Fig. 9B).
Evolution. Under both analyses, thepresence of flanking osteoderms is asynapomorphy of E. serratus + Xeno-saurus. Their absence is a synapomor-phy of the southern clade of Xeno-saurus.
13. Premaxilla: Rostral osteoderm and flank-ing osteoderms (when present) (0)smoothly domed or weakly keeled(Fig. 9C); (1) strongly keeled (Fig. 10B).
Variation. The keel appears to formfirst during osteoderm development (un-published observation), and as evidencedby juvenile X. platyceps, this characterdoes not transform postnatally.
Evolution. Under both analyses, arelatively smooth and rounded morphol-ogy is the primitive state for the rostralosteoderm, with strong keeling a synap-omorphy of the northern clade ofXenosaurus.
14. Premaxilla: Medial edges of vomerineprocesses oriented in a horizontal plane
86 Bulletin of the Museum of Comparative Zoology, Vol. 160, No. 3
(0) more mediolaterally (Fig. 8C); (1)more anteroposteriorly (Fig. 8D).
Evolution. Under Analysis 1, medio-lateral orientation is a synapomorphy ofAnguidae and of S. crocodilurus (or amore inclusive shinisaur-related clade).Under Analysis 2, more ambiguity exists.With one possible hypothesis of charac-ter evolution, an anteroposterior orien-tation is ancestral, with a mediolateralorientation an autapomorphy of S.crocodilurus. A mediolateral orientationis then either a synapomorphy ofAnguidae + Varanoidea with an antero-posterior orientation a synapomorphy ofVaranidae, or a mediolateral orientationis a synapomorphy of Anguidae and anautapomorphy of Helodermatidae. Thesecond hypothesis of character evolutionis that a mediolateral orientation isancestral. An anteroposterior orientationis thus an autapomorphy of P. torquatusand a synapomorphy of E. serratus +Xenosaurus on the one hand andVaranidae on the other.
15. Premaxilla: Medial edges of vomerineprocesses near midline convergence (0)straight, without dorsoventral bow(Fig. 10C); (1) with dorsoventral bow(Fig. 10D).
Evolution. Under both analyses, thebowing or inflection is a synapomorphyof X. rackhami + X. grandis.
16. Premaxilla: Stalk of incisive process (0)relatively long, length similar to orgreater than diameter (Fig. 10D); (1)relatively short, length shorter thandiameter (Fig. 10C).
Variation. Some variation does occuracross ontogenetic stages within taxa;in particular, a few individuals ofX. rackhami and X. grandis show shorterprocesses. However, the vast majorityof specimens where adequate samplesare available have incisive processesof approximately uniform relativelength.
Evolution. Under both analyses,shortness of the stalk of the incisive processis a synapomorphy of the northern clade ofXenosaurus and an autapomorphy of X.rectocollaris. Under Analysis 1, shortness isa synapomorphy of Helodermatidae +Anguidae and an autapomorphy of L.borneensis. Under Analysis 2, shortness isa synapomorphy of Anguidae + Varanoi-dea. Within this clade, a longer morphol-ogy is a synapomorphy of Varanus.
17. Premaxilla: Accessory processes dorsalto vomerine processes (0) absent(Fig. 11A); (1) present (Fig. 10C).
Evolution. Under both analyses, pres-ence of the accessory dorsal processes isa synapomorphy of Xenosaurus.
18. Premaxilla: Accessory processes dorsalto vomerine processes (0) relativelyshort, nub-like (Fig. 10C); (1) relativelylong and slender (Fig. 10D).
Evolution. Under both analyses, rela-tive length of the processes is a synap-omorphy of the northern clade ofXenosaurus.
19. Premaxilla: Fossa for rostral process ofnasal septum (0) relatively mediolateral-ly narrow (Fig. 9D); (1) relatively me-diolaterally wide (Fig. 10D).
Variation. Although the shape ofthe fossa varies somewhat among indi-viduals, no variation so great as to affectthe scoring of the character was evident.
Evolution. Under both analyses, rela-tively great width of the fossa is a synapo-morphy of E. serratus + Xenosaurus.
20. Premaxilla: Angle of rise of nasal processin sagittal plane (0) relatively low(Fig. 11B); (1) intermediate (Fig. 11C);(2) relatively great (Fig. 11D).
Evolution. Under both analyses, amoderate angle is ancestral and a highangle is a synapomorphy of S. crocodi-lurus + M. ornatus and an autapomorphyof Helodermatidae. Also under bothanalyses, a low angle is a synapomorphy
XENOSAUR PHYLOGENY N Bhullar 87
of the northern clade of Xenosaurus andof Varanus. Under Analysis 1, a low angleis a synapomorphy of E. multicarinata +O. ventralis. Under Analysis 2, a low angleis either a synapomorphy of Anguidaewith a moderate angle an autapomorphyof C. enneagrammus or an autapomorphyof E. multicarinata and of O. ventralis.
21. Premaxilla: Mediolateral width of nasalprocess at base (0) two to three toothpositions (Fig. 9A); (1) between fourand five tooth positions (Fig. 12A); (2)five tooth positions (Fig. 11A); (3) be-tween five and six tooth positions(Fig. 10D); (4) six or more tooth posi-tions (Fig. 10C).
Variation. The values scored for thischaracter are approximate; it can bedifficult to determine precisely whetherall or most of a tooth lies within the spanof the nasal process. The character mayneed refining in the future. Neverthe-less, at least comparatively, the scoringsare sound.
Evolution. Under both analyses, awidth of about five tooth positions isancestral. This is largely a consequenceof the state in P. torquatus and mayseem unusual given the classical grossanatomy–based hypothesis of squamatephylogeny, in that many non-angui-morph scleroglossans have narrow nasal
Figure 11. A, Premaxilla of Exostinus serratus, CT scan of USNM v16565, posterior. Illustrates characters 17(0), 22(1), 23(0),24(1). B, Premaxilla of Elgaria multicarinata TMM-M 8993, left lateral, anterior to the left. Illustrates character 20(0). C, Premaxillaof Exostinus serratus, CT scan of USNM v16565, left lateral, anterior to the left. Illustrates character 20(1). D, Rostrum ofShinisaurus crocodilurus MVZ 204291, left lateral, anterior to the left. Illustrates character 20(2).
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processes. However, in support of theinference here presented, a relativelywide-based nasal process is shared by ahost of primitive iguanians on the onehand (Polychrotinae, Corytophaninae,Hoplocercinae, Leiolepis, and Uromas-tyx, among others) and by C. interme-dia, sometimes suggested to be theextinct sister taxon to Anguimorpha(Gao and Norell, 1998, 2000; Conrad,2005, 2008). Under both analyses, awidth of between five and six toothpositions is a synapomorphy of Xeno-saurus and six or more is a synapomor-phy of the northern clade of Xenosaurus,as well as an autapomorphy of L.borneensis. Under Analysis 1, a width
of two to three tooth positions is asynapomorphy of Anguidae, and a widthof between four and five tooth positionsis an autapomorphy of E. multicarinata.A width of between four and five toothpositions is also a synapomorphy ofVaranus, and a width of two to three anautapomorphy of V. niloticus. However,this result might be skewed by theunusual width of the snout of V. ex-anthematicus. Under Analysis 2, a widthof between four and five tooth positionsis a synapomorphy of Anguidae + Var-anoidea; a width of two to three is asynapomorphy of O. ventralis + C.enneagrammus and an autapomorphy ofboth Helodermatidae and V. niloticus.
Figure 12. A, Premaxilla of Elgaria multicarinata TMM-M 8958, posterior and slightly left lateral. Illustrates characters 21(1),22(0), 24(0). B, Rostrum of Shinisaurus crocodilurus MVZ 204291, dorsal, anterior to the left. Illustrates characters 26(0), 67(0). C,Left nasal of Xenosaurus grandis NAUQSP-JIM 1460, ventral, anterior to the left. Illustrates character 27(0). D, Left nasal ofXenosaurus platyceps UF 45622, dorsal, anterior to the left. Illustrates characters 27(1), 28(1), 29(2).
XENOSAUR PHYLOGENY N Bhullar 89
22. Premaxilla: Dorsolateral flare at con-tact with dermal surface of nasal (0)absent or minimal (Fig. 12A); (1)present with distinct dorsal wedgeseparated (Fig. 11A); (2) pronounced(Fig. 10C).
Evolution. Under both analyses, apronounced premaxillary flare is a syn-apomorphy of the northern clade ofXenosaurus. Under Analysis 1, theflaring morphology is a synapomorphyof E. serratus + Xenosaurus. Additional-ly, either the flare is a synapomorphy ofM. ornatus + S. crocodilurus and noflare is an autapomorphy of B. ammos-kius, or the flare is an autapomorphy ofboth M. ornatus and S. crocodilurus.Under Analysis 2, the flaring morphol-ogy is a synapomorphy of Xenosauridae,and the lack of a flare is an autapomor-phy of B. ammoskius.
23. Premaxilla: Anterior portions of nasalfacets (0) shallowly impressed (Fig. 11A);(1) deeply impressed (Fig. 10C).
Evolution. Under both analyses,deep impression is a synapomorphy ofXenosaurus and an autapomorphy of M.ornatus.
24. Premaxilla: Keel between nasal facets(0) dorsoventrally extensive (Fig. 12A);(1) restricted to dorsal portion of nasalprocess (Fig. 11A).
Evolution. Under Analysis 1, relativelygreat extent of the keel is unambiguous-ly a synapomorphy of E. multicarinata +O. ventralis. At the initial split of thetree, the ancestral state is ambiguous. Ifthe ancestral state is great extent, thenrestriction is either a synapomorphy ofAnguimorpha with great extent an auta-pomorphy of Varanidae, or restriction isa synapomorphy of both Anguidae +Xenosaurus and S. crocodilurus + M.ornatus. If the ancestral state is restric-tion, then great extent is an autapomor-phy of P. torquatus and a synapomorphyof Varanidae. Under Analysis 2, greatextent is ancestral and restriction is a
synapomorphy of Xenosauridae and anautapomorphy of both C. enneagram-mus and Helodermatidae.
25. Premaxilla: Tooth position count, aver-age rounded to nearest integer, (0) 7; (1)8; (2) 9; (3) more than nine.
Variation. Premaxillary tooth positioncount does vary, and the characterscored is the average value for theindividuals examined. However, evenin those taxa whose count did vary, thevariants always possessed one fewertooth position than the average (andmodal) number. Furthermore, thesenonmodal variants were rare.
Evolution. Under both analyses, hav-ing more than nine tooth positions is anautapomorphy of L. borneensis. UnderAnalysis 1, the ancestral state is ambig-uous. If it is eight or nine toothpositions, then having seven tooth posi-tions is an autapomorphy of P. torqua-tus, and the other transformations are asdescribed below for the case in whicheight or nine is ancestral for Anguimor-pha. If seven tooth positions is theancestral state, an increased number isa synapomorphy either of Anguimorphaor of Anguidae + Xenosaurus. Twopossibilities obtain if an increased num-ber of either eight or nine is a synapo-morphy of Anguimorpha. If eight, thenhaving nine tooth positions is a synapo-morphy of Anguidae + Xenosaurus andof Varanidae, and having seven toothpositions is a synapomorphy of S.crocodilurus + M. ornatus. If nine, thenonly the two-step transformation alongthe Shinisaurus stem need occur.
Nasal
The nasal is unknown for E. lancensis, R.rugosus, and M. ornatus.
26. Nasal: Contacts contralateral nasal atdermal surface (0) extensively, along atleast a quarter of its medial margin(Fig. 12B); (1) barely or not at all (Fig. 2A).
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Variation. In younger individuals ofV. exanthematicus, the nasals are barely incontact, but in medium to large individ-uals, they show extensive contact. Thenasals of Varanus in general are unusualin their morphology and their contacts,concomitantly with the retracted narescharacteristic of the clade (McDowell andBogert, 1954; Estes et al., 1988).
Evolution. Under both analyses, asmall amount of contact is a synapomor-phy of Xenosaurus and an autapomor-phy of V. niloticus.
27. Nasal: Posterior tapered portion (inhorizontal plane) (0) mediolaterally wid-er at base than long along long axis ofnasal (Fig. 12C); (1) longer than wide(Fig. 12D).
Evolution. Under Analysis 1, thelonger-than-wide morphology is ances-tral, with wider-than-long a synapomor-phy of Xenosaurus + Anguidae and,within that clade, longer-than-wide asynapomorphy of the southern clade ofXenosaurus. Under Analysis 2, theancestral state for Anguimorpha isambiguous. If the ancestral state iswider-than-long, then the longer-than-wide morphology is a synapomorphy ofB. ammoskius + S. crocodilurus and thesouthern clade of Xenosaurus. If theancestral state is longer-than-wide, thenwider-than-long is a synapomorphy ofAnguidae. Furthermore, wider-than-long is either a synapomorphy of E.serratus + Xenosaurus and longer-than-wide a synapomorphy of the southernclade of Xenosaurus, or wider-than-longis an autapormophy of E. serratus and asynapomorphy of the northern clade ofXenosaurus.
28. Nasal: Osteoderms of lateral row poste-rior to enlarged anterolateral osteoderm(0) comparable in size to or smaller thanosteoderms of medial row (Fig. 3A); (1)larger and more prominent than osteo-derms of medial row; anterolateralosteoderm especially large (Fig. 12D).
Evolution. Under both analyses,greater size and prominence of thelateral row is a synapomorphy of thenorthern clade of Xenosaurus.
29. Nasal: Anterior portion of lateral edgecorresponding to underlying lateralbend of cartilaginous nasal capsule (0)with no change in angle or withdeflection in horizontal plane away fromthe midline of a few degrees relative tothe posterior portion of the lateral edge(Fig. 13A); (1) with slight deflectionfrom posterior portion of about 10u; (2)with notable bend, deflecting from theposterior portion by about 40u(Fig. 12D).
Evolution. Under both analyses, an-cestral character states are ambiguousbetween a change in angle of 10u and40u across most of the tree. UnderAnalysis 1, the only unambiguous syn-apomorphy is the lack of a change inangle uniting Varanus. Under Analysis2, the ambiguity along the stem ofVaranoidea shifts to no change inangle/slight change in angle.
Septomaxilla
Unfortunately, the septomaxilla is un-known in all of the extinct taxa. In general,this element is neglected in studies ofsquamate osteology. It received the mostattention in work dealing with the complexolfactory organs of lizards (Stebbins, 1948;Bellairs, 1949; Hallerman, 1994; Bernstein,1999). A few characters are used in currentphylogenetic works on Serpentes (Lee andScanlon, 2002). In the course of thisinvestigation, I was able to identify anumber of informative characters in theseptomaxilla. In part, this stems from theunusually complex septomaxilla of Xeno-saurus, in and upon which several canalsand ridges are formed that do not appearon the septomaxillae of most other squa-mates.
30. Septomaxilla: Posteromedial corner ofcupular portion (0) with a long para-
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septal process, several times as long asmediolaterally wide at base (Fig. 13B);(1) sending back moderate-length orshort process, about twice as long asmediolaterally wide at base; (2) processabsent or reduced to minor projection ofcorner, septomaxilla roughly an equilat-eral triangle in overall shape (Fig. 13C).
Variation. The process becomes lon-ger during postnatal ontogeny, but itsproportions are consistent with thescoring for most of ontogeny.
Evolution. Under both analyses,moderate length of the process isancestral and absence is a synapomor-phy of Xenosaurus. Under Analysis 1,
great length is a synapomorphy ofVaranidae. Great length is also eithera synapomorphy of Anguidae withmoderate length an autapomorphy ofC. enneagrammus, or great length is anautapomorphy of Helodermatidae andO. ventralis + E. multicarinata. UnderAnalysis 2, great length is a synapo-morphy of Anguidae + Varanoidea, andmoderate length is an autapomorphy ofC. enneagrammus.
31. Septomaxilla: Deflection of boneaway from rostral process of nasalseptum to form distinct anteromedialsurface (0) absent (Fig. 13B); (1) pres-ent (Fig. 13C).
Figure 13. A, Nasals of Heloderma suspectum TMM-M 9001, dorsal, anterior to the left. Illustrates character 29(0). B, Rightseptomaxilla of Elgaria multicarinata TMM-M 8958, dorsal, anterior to the left. Illustrates characters 30(0), 31(0), 34(0). C, Leftseptomaxilla of Xenosaurus newmanorum NAUQSP-JIM uncatalogued specimen, dorsal, anterior to the left. Illustrates characters30(2), 31(1), 34(1), 36(0), 38(0), 41(1). D, Right septomaxilla of Elgaria multicarinata TMM-M 8958, medial, anterior to the left.Illustrates character 32(0).
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Evolution. Under both analyses, thepresence of the anteromedial surface isa synapomorphy of Xenosaurus.
32. Septomaxilla: Medial ethmoidal nervesand vasculature (0) running in connec-tive tissue near surface of septomaxilla,not enclosed by bone (Fig. 13D); (1)enclosed by septomaxilla (Fig. 3.32B).
Evolution. Under Analysis 1, enclo-sure is a synapomorphy of Xenosaurus +Anguidae and an autapomorphy of L.borneensis. Under Analysis 2, enclosuremay be ancestral, in which case lack ofenclosure is an autapomorphy of P.torquatus and S. crocodilurus. If enclo-
sure is not ancestral, it is a synapomor-phy of Anguimorpha or a synapomorphyof Xenosaurus and of Anguidae +Varanoidea. Under any of these hypoth-eses of character evolution, lack ofenclosure is a synapomorphy of Vara-nus.
33. Septomaxilla: Lateral ethmoidal nervesand vasculature (0) running in connec-tive tissue near surface of septomaxilla,not enclosed by bone (Fig. 14C); (1)enclosed by septomaxilla (Fig. 14D).
Evolution. Under Analysis 1, lateralenclosure is either a synapomorphy ofAnguidae + Xenosaurus, with lack of
Figure 14. A, Left septomaxilla of Xenosaurus rackhami UTEP-OC ‘‘MALB’’ 388, lateral, anterior to the left. B, Left septomaxillaof Xenosaurus newmanorum NAUQSP-JIM uncatalogued specimen, medial, anterior to the right. Illustrates characters 32(1),40(1). C, Right septomaxilla of Elgaria multicarinata TMM-M 8958, lateral, anterior to the right. Illustrates characters 33(0), 37(0),39(0). D, Left septomaxilla of Xenosaurus newmanorum NAUQSP-JIM uncatalogued specimen, lateral, anterior to the left.Illustrates characters 33(1), 37(1), 39(1), 40(0).
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enclosure a synapomorphy of Angui-dae, or lateral enclosure is a synapo-morphy of Xenosaurus and an autapo-morphy of Helodermatidae. UnderAnalysis 2, only the latter hypothesisof character evolution is most parsimo-nious.
34. Septomaxilla: Dorsal ridges followinganterolateral and anteromedial edges(0) absent or low (Fig. 13B); (1) highand sharp (Fig. 13C).
Evolution. Under both analyses, ahigh, sharp morphology is a synapomor-phy of Xenosaurus.
35. Septomaxilla: Ventral surface posteriorto vomeronasal cupula (0) smooth
(Fig. 15A); (1) impressed into longitudi-nal grooves by vomeronasal nerve(Fig. 15B).
Variation. The sulci become moredeeply incised during ontogeny but arepresent in even the youngest individualsexamined.
Evolution. Under both analyses, thepresence of vomeronasal nerve im-pressions is a synapomorphy of Xeno-saurus.
36. Septomaxilla: Anteroposterior length offlattened dorsal region near anteriorapex, in front of capsular depression.Measured as proportion of total antero-posterior length of septomaxilla from
Figure 15. A, Right septomaxilla of Elgaria multicarinata TMM-M 8958, ventral, anterior to the left. Illustrates characters 35(0),42(0). B, Right septomaxilla of Elgaria multicarinata TMM-M 8958, lateral, anterior to the right. Illustrates characters 35(1), 42(1).C, Left septomaxilla of Xenosaurus grandis NAUQSP-JIM 1460, dorsal, anterior to the left. Illustrates characters 36(1), 38(1),41(0). D, Left septomaxilla of Xenosaurus grandis NAUQSP-JIM 1460, lateral, anterior to the left. Illustrates character 37(0).
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anterior apex back along anteroposterioraxis: (0) 0.35 or greater (Fig. 13C); (1)less than 0.35 (Fig. 15C).
Variation. The lamina of bone poste-rior to the cupular region of the septo-maxilla lengthens slightly during ontoge-ny, so the ratios above should be taken toapply to fairly mature individuals.
Evolution. Because no other squa-mate possesses the flattened region, theancestral state within Xenosaurus isambiguous.
37. Septomaxilla: Ratio of dorsoventralheight of anterolateral face at shortestlevel to anteroposterior length of face(0) less than 0.10 (Fig. 14C); (1) 0.10 to0.50 (Fig. 14D); (2) greater than 0.50(Fig. 15D).
Evolution. A dorsoventrally short an-terolateral face with a height-to-lengthratio of less than 0.10 is ancestral underboth analyses. Also under both analy-ses, a ratio of 0.10 to 0.50 is asynapomorphy of Xenosaurus and aratio greater than 0.50 is a synapomor-phy of the southern clade of Xeno-saurus.
38. Septomaxilla: Anterolateral dorsal ridgecontinuing from lateral wing (0) broadand rounded (Fig. 13C); (1) narrow andsharp (Fig. 15C).
Evolution. The ancestral state withinXenosaurus is ambiguous.
39. Septomaxilla: Ratio of anteroposteriorlength of lateral wing to anteropos-terior length of septomaxilla alonganteroposterior axis from level of ante-rior apex to level of back of lateral wing(0) greater than 0.55 (Fig. 14C); (1) 0.55or less (Fig. 14D).
Evolution. Under both analyses, aratio of 0.55 or less is a synapomorphyof the northern clade of Xenosaurus andan autapomorphy of Helodermatidae.
40. Septomaxilla: Anterolateral ethmoid ca-nal (0) open only at round terminal
foramina (Fig. 14D); (1) open alongmuch of anterolateral face as long fissure(Fig. 14A).
Evolution. Under both analyses,closure is the primitive state andthe existence of the fissure is a synap-omorphy of the southern clade ofXenosaurus.
41. Septomaxilla: Canal paralleling andrunning lateral to the medial edge ofthe septomaxilla or to the antero-medial dorsal ridge (when visible)(0) absent (Fig. 15C); (1) present(Fig. 13C).
Evolution. Under both analyses,presence of the canal is a synapo-morphy of the northern clade ofXenosaurus.
42. Septomaxilla: Ratio of mediolateralwidth of vomeronasal cupula at itswidest level to width of septomaxilla atthat level (0) 0.45 or greater (Fig. 15A);(1) less than 0.45 (Fig. 15B).
Evolution. Under both analyses, aratio of less than 0.45 is a synapomorphyof the northern clade of Xenosaurus.
Maxilla
The maxilla is only partially preserved inE. lancensis and M. ornatus.
43. Maxilla: Medial premaxillary process,portion projecting beyond dental gutter,(0) anteroposteriorly very short, abouttwice as tall at posterior end as long(Fig. 16A); (1) short, about as tall aslong; (2) intermediate length, abouttwo-thirds as tall as long (Fig. 16B); (3)long, about half as tall as long(Fig. 16C).
Variation. The medial premaxillaryprocess becomes slightly dorsoventrallytaller during ontogeny, but despite this,no variation that would affect scoring wasevident.
Evolution. Under both analyses, avery short process is ancestral for the
XENOSAUR PHYLOGENY N Bhullar 95
entire group and for Anguimorpha and along process is a synapomorphy of thenorthern clade of Xenosaurus. Theancestral states for Xenosaurus + E.serratus and Xenosaurus are ambiguousbetween short and intermediate. UnderAnalysis 1, the ancestral state for Angu-idae + Xenosauridae is ambiguousamong very short, short, and intermedi-ate, as is that for Xenosaurus + R.rugosus. The long morphology is asynapomorphy of Anguidae + Heloder-matidae, and intermediate length is anautapomorphy of E. multicarinata. Un-der Analysis 2, the ancestral states forAnguidae + Varanoidea and Varanoidea
are ambiguous among very short, short,and intermediate lengths. The long mor-phology is a synapomorphy of O. ventralis+ C. enneagrammus and an autapomor-phy of . Along the other branch ofAnguimorpha, the ancestral state forXenosauridae and for Xenosaurus + R.rugosus is the very short morphology.
44. Maxilla: Major anterior foramen forcontents of infraorbital canal (ethmoidalnerve and accompanying structures) (0)exiting onto lamina intercristalis, lateralto crista transversalis (Fig. 16D); (1)exiting posteromedial to crista transver-salis (Fig. 16A).
Figure 16. A, Left maxilla of Shinisaurus crocodilurus UF 72805, medial, anterior to the right. Illustrates characters 43(0), 44(1),46(2), 63(1). B, Left maxilla of Exostinus serratus, CT scan of USNM v16565, medial, anterior to the right. Illustrates characters43(2), 45(0), 46(1), 60(1), 63(0). C, Left maxilla of Xenosaurus platyceps UF 45622, medial, anterior to the right. Illustratescharacters 43(3), 45(1), 55 (n for numerator, d for denominator), 56 (n for numerator, d for denominator), 60(0). D, Left maxilla ofElgaria multicarinata TMM-M 8958, anterior. Illustrates character 44(0).
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Evolution. Under both analyses, theancestral state of the character isambiguous. However, the medial fora-men is not widespread outside ofAnguimorpha, and I tentatively suggestthat the ancestral state is for the exit tobe in the upper region of the laminaintercristalis. Under Analysis 1, a medialexit is then a synapomorphy of Angui-morpha and a lateral exit is a synapo-morphy of Anguidae. Under Analysis 2,the ancestral state for Anguimorpha isambiguous.
45. Maxilla: Anterior end of lacrimal recess(0) relatively posterior, greater than onequarter of the way to the posterior endof the facial process (Fig. 16B); (1)relatively anterior, one quarter of theway back or less (Fig. 16C).
Evolution. Under both analyses, therelatively anterior morphology is ances-tral for the total group and the relativelyposterior morphology is ancestral forXenosaurus + R. rugosus, with therelatively anterior morphology a synap-omorphy of Xenosaurus. Under Analysis1, the ancestral state for Anguidae +Xenosaurus and for the clades withinAnguidae is ambiguous. Under Analysis2, the relatively posterior morphology isa synapomorphy of O. ventralis + C.enneagrammus.
46. Maxilla: Anterior portion of dorsalmargin of lacrimal recess—posterodor-sal rise in plane of facial process (0)shallow, 30u or less (Fig. 17A); (1)moderate, between 30u and 35u(Fig. 16B); (2) steep, 35u and greater(Fig. 16A).
Evolution. Under both analyses, ashallow angle of 30u or less is ancestral.In the absence of data for B. ammoskius,a steep angle of 35u or greater is anautapomorphy of S. crocodilurus. Anangle between 30u and 35u is a synap-omorphy of Xenosaurus, and an angle of35u or greater is a synapomorphy of X.agrenon + X. rectocollaris.
47. Maxilla: Articular facet posterior tofacial process (0) mediolaterally narrow,hardly differentiated from sharp dorsaledge of maxilla (Fig. 17B); (1) medio-laterally wide, with a distinct dorsallyfacing table (Fig. 17C).
Evolution. Under Analysis 1, the widemorphology is a synapomorphy of E.serratus + Xenosaurus and of S. crocodi-lurus + B. ammoskius. Under Analysis 2,the ancestral state for Xenosauridae isambiguous.
48. Maxilla: Mediolaterally expanded facetposterior to facial process: (0) forlacrimal; (1) for jugal.
Evolution. Because of widespreadmissing data, the ancestral state for thecharacter is ambiguous at all levels.
49. Maxilla: Width of palatal shelf at widestlevel (measured in horizontal planeperpendicular to axis of toothrow) (0)less than one-fifth length of maxillarytoothrow (Fig. 17D); (1) one-fifth lengthof maxillary toothrow or greater(Fig. 18A).
Evolution. Under both analyses, awide palatal shelf is an autapomorphyof E. serratus.
50. Maxilla: Posterior end of tooth row (0)relatively straight, collinear with moreanterior portion (Fig. 17D); (1) mediallydeflected (Fig. 18A).
Evolution. Under both analyses, me-dial deflection is an autapomorphy of E.serratus.
51. Maxilla: Infraorbital canal (0) round forentire length, confined to medial, steepportion of palatal shelf (see E. multi-carinata, The Deep Scaly Project[2007], coronal slices 35–124); (1) me-diolaterally expanded and oval for por-tion of length, extending above flat-tened, horizontal lateral portion ofpalatal shelf (Fig. 18B).
Evolution. Under both analyses, anexpanded canal is a synapomorphy of
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Xenosaurus + R. rugosus and of Var-anus, and an autapomorphy of C.enneagrammus.
52. Maxilla: Supradental thickening (0) ab-sent (Fig. 18C); (1) weak, low ridgeabove teeth (Fig. 18D); (2) strong,rounded ridge above teeth, differentiat-ed dorsally by groove (Fig. 19A).
Variation. The ridge becomes stron-ger with increasing age.
Evolution. Under both analyses, weakdevelopment is an autapomorphy of E.serratus. Under Analysis 1, the ancestralstate for the entire group is ambiguousbetween absence of the thickening andthe weakly developed morphology, as are
the ancestral states for Anguimorpha andAnguidae + Helodermatidae. Strong de-velopment is a synapomorphy of Xeno-saurus + R. rugosus and of S. crocodilurus+ M. ornatus. Under Analysis 2, absenceis the ancestral state for the entire groupand for Anguimorpha and Anguidae +Varanoidea. Within Varanoidea, weakdevelopment is an autapomorphy ofHelodermatidae. Strong development isa synapomorphy of Xenosauridae.
53. Maxilla: Major labial foramina: (0) pos-teriormost one or more foraminaabruptly larger than others (Fig. 19B);(1) nearly the same size, with only asubtle and gradual trend of posteriorenlargement (Fig. 19A).
Figure 17. A, Left maxilla of Restes rugosus, CT scan of YPM PU 14640, medial, anterior to the right. Illustrates character 46(0).B, Left maxilla of Elgaria multicarinata TMM-M 8958, dorsal, anterior to the left. Illustrates character 47(0). C, Left maxilla ofXenosaurus grandis NAUQSP-JIM 1460, dorsal, anterior to the left. Illustrates character 47(1). D, Skull of Xenosaurusnewmanorum, CT scan of UMMZ 126056, ventral, anterior to the left. Illustrates characters 49(0), 50(0), 93(1).
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Evolution. Under both analyses,rough equivalence in size along theentire row is a synapomorphy of Xeno-saurus + R. rugosus.
54. Maxilla: Foramina (0) concentrated insingle row of labial foramina (Fig. 18C);(1) present in two rows—ventral labialforamina and dorsal row upon lowerportion of facial process (Fig. 18D).
Evolution. Under both analyses, theancestral state for Xenosaurus + E.serratus and for the southern clade ofXenosaurus is ambiguous, such thatpresence of the dorsal row could eitherbe an autapomorphy of E. serratus and asynapomorphy of the southern cladeof Xenosaurus or a synapomorphy of
Xenosaurus + E. serratus, with lack of adorsal row a synapomorphy of thenorthern clade of Xenosaurus.
55. Maxilla: Ratio of length of facialprocess along base (at dorsoventrallevel of inflection toward horizontalbetween rami of lacrimal) to totallength of maxilla from anterior edgeof facial process at that dorsoventrallevel to posterior end of maxilla(Fig. 16C) (0) 0.20 to less than 0.30;(1) 0.30 to less than 0.40; (2) 0.40 toless than 0.50; (3) 0.50 to less than0.60; (4) 0.60 to less than 0.70; (5) 0.70to less than 0.80.
Variation. As the orbit becomesproportionally smaller during growth,
Figure 18. A, Left maxilla of Exostinus serratus, CT scan of USNM v16565, ventral, anterior to the left. Illustrates characters49(1), 50(1). B, Cutaway near posterior end of infraorbital canal of rostrum of Exostinus serratus, CT scan of USNM v16565,anterior. Illustrates character 51(1). C, Left maxilla of Elgaria multicarinata TMM-M 8993, lateral, anterior to the left. Illustratescharacters 52(0), 54(0), 59(0), 61(0), 62(1). D, Left maxilla of Exostinus serratus, CT scan of USNM v16565 lateral, anterior to theleft. Illustrates characters 52(1), 54(1), 57(0), 58(0), 59(1), 61(3), 62(4).
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the posterior suborbital portion of themaxilla shortens relative to the remain-der of the bone. However, this transfor-mation occurs largely during early onto-genetic stages, and I scored thischaracter on relatively large individuals.
Evolution. Under both analyses, state1 is autapomorphic for X. agrenon, X.grandis, and B. ammoskius, state 4 isautapomorphic for O. ventralis, andstate 5 is autapomorphic for L. bor-neensis. Under Analysis 1, the ancestralstate for the entire group is ambiguousamong state 0, state 1, state 2, and state3. The ancestral state for Anguimorphais ambiguous between state 2 and state3, as is that for S. crocodilurus + Vara-nidae, Varanidae, Varanus, Xenosaurus
+ Anguidae, and Xenosaurus + R.rugosus. The ancestral state for S.crocodilurus + B. ammoskius is state 2,as is that for E. serratus + Xenosaurusand all nodes therein. Finally, theancestral state for Anguidae is state 3,making state 2 an autapomorphy of E.multicarinata. Under Analysis 2, theancestral state for the entire group isambiguous among state 0, state 1, andstate 2. The ancestral state for Xeno-sauridae and all nodes therein is state 2,and state 3 is autapomorphic for R.rugosus. The ancestral state for Angui-dae + Varanoidea and for Anguidae isambiguous between state 2 and state 3.The ancestral state for O. ventralis + C.enneagrammus is state 3, as is that for
Figure 19. A, Left maxilla of Xenosaurus platyceps UF 45622, lateral, anterior to the left. Illustrates characters 52(2), 53(1),57(1), 61(2). B, Left maxilla of Elgaria multicarinata TMM-M 8958, lateral, anterior to the left. Illustrates character 53(0). C, Leftmaxilla of Xenosaurus rackhami UTEP-OC ‘‘MALB’’ 388, lateral, anterior to the left. Illustrates character 58(2). D, Left maxilla ofXenosaurus grandis NAUQSP-JIM 1460, lateral, anterior to the left. Illustrates character 58(3).
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Varanoidea, making state 2 autapo-morphic for V. exanthematicus.
56. Maxilla: Ratio of length of facial processalong base (at dorsoventral level ofposterior inflection toward horizontal)to greatest height posterior to nasal facet(Fig. 16C) (0) 0.50 to less than 0.75; (1)0.75 to less than 1.00; (2) 1.00 to lessthan 1.25; (3) 1.25 to less than 1.50; (4)1.50 to less than 1.75; (5) 1.75 to lessthan 2.00; (6) 2.00 to less than 2.25.
Evolution. Under both analyses, state0 is a synapomorphy of Varanus andstate 6 is an autapomorphy of L.borneensis and of O. ventralis. State 2is an autapomorphy of C. enneagram-mus and a synapomorphy of S. crocodi-lurus + B. ammoskius. Furthermore, theancestral state for Xenosaurus is ambig-uous between state 3 and state 4. WithinXenosaurus, state 5 is autapomorphic forX. newmanorum, and state 2 is synapo-morphic for X. agrenon + X. rectocol-laris, with state 1 an autapomorphy of X.agrenon. Under Analysis 1, the ancestralstate for the entire group is ambiguousamong state 1, state 2, and state 3. Theancestral state for Anguimorpha is state2. State 4 is a synapomorphy of Xeno-saurus + Anguidae. Under Analysis 2,the ancestral state for the entire group isambiguous among state 0, state 1, state2, state 3, and state 4. The ancestralstates for Anguimorpha and Xenosaur-idae are ambiguous among the last threeof those states. That for Anguidae +Varanoidea is state 4. The ancestral statefor Xenosaurus + R. rugosus is ambigu-ous between state 3 and state 4.
57. Maxilla: Narial margin of facial process(0) dorsoventrally tall, horizontal portionabout as extensive as or less extensivethan vertical portion (Fig. 18D); (1)dorsoventrally short, horizontal marginmore extensive than vertical portion(Fig. 19A).
Evolution. Under both analyses, aproportionally short vertical margin is a
synapomorphy of Xenosaurus. UnderAnalysis 1, a short vertical margin is asynapomorphy of Varanidae and anautapomorphy of Helodermatidae. Un-der Analysis 2, a short vertical margin isa synapomorphy of Varanoidea.
58. Maxilla: Vertical portion of narial marginof facial process (0) failing to tiltanterodorsally beyond the vertical bymore than a few degrees (Fig. 18D); (1)tilting slightly beyond the vertical toform a dorsal overhang of the naris bythe facial process with a slight anterioreminence (Fig. 19A); (2) tilting beyondthe vertical to form a dorsal overhangwith a pronounced but rounded anterioreminence (Fig. 19C); (3) tilting beyondthe vertical to form a marked dorsaloverhang with a pronounced and sharplypointed anterior eminence (Fig. 19D).
Variation. Smaller individuals ofX. rackhami do not show as muchanterior projection of the overhang aslarge adults, which were scored.
Evolution. Under both analyses, aslight overhang is a synapomorphy ofXenosaurus, a moderately pronouncedoverhang is a synapomorphy of X.rackhami + X. grandis, and a verypronounced overhang is an autapomor-phy of X. grandis.
59. Maxilla: Posterior portion of nasal facetupon facial process (0) curving smoothlyin transverse plane, following generalcurvature of facial process (Fig. 18C);(1) distinctly folded toward the verticalrelative to remainder of facial process,forming an upturned posterior tab of thenasal facet (Fig. 18D).
Evolution. Under Analysis 1, theupturned tab is a synapomorphy ofXenosaurus + R. rugosus and of S.crocodilurus + B. ammoskius. UnderAnalysis 2, the upturned tab is asynapomorphy of Xenosauridae.
60. Maxilla: Highest point of facial process:(0) prominent, posterior corner between
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prefrontal facet and orbital (posterior)edge (Fig. 16C); (1) dorsal edge of facialprocess nearly horizontal (Fig. 17A); (2)upturned tab of nasal facet (Fig. 16B).
Evolution. Under both analyses, theancestral state for the entire group is forthe highest point to be the cornerbetween the prefrontal facet and orbitaledge. The ancestral state for Xenosaurus+ R. rugosus is a horizontal dorsal edgeof the facial process, with the upturnedtab of the nasal facet the highest pointautapomorphically in E. serratus and X.rectocollaris. The corner between theprefrontal facet and orbital edge thehighest point synapomorphically in thenorthern clade of Xenosaurus. Under
Analysis 1, the ancestral state for Angu-idae + Xenosaurus is ambiguous be-tween the prefrontal facet/orbital edgecorner and a horizontal dorsal edge, as isthe ancestral state for Anguidae +Helodermatidae. A horizontal dorsaledge is an autapomorphy of L. borneen-sis. Under Analysis 2, a horizontal dorsaledge is a synapomorphy of Xenosaurus +R. rugosus, and the ancestral state forVaranoidea is ambiguous between theprefrontal facet/orbital edge corner anda horizontal dorsal edge.
61. Maxilla: Canthal crest (0) absent(Fig. 18C); (1) minimally developed:abrupt medial fold of facial process,but no projecting ridge (Fig. 20A); (2)
Figure 20. A, Left maxilla of Heloderma suspectum TMM-M 9001, lateral, anterior to the left. Illustrates character 61(1). B, Leftmaxilla of Shinisaurus crocodilurus MVZ 204291, lateral, anterior to the left. Illustrates characters 62(0), 118(1). C, Left maxilla ofRestes rugosus YPM PU 14640, lateral, anterior to the left. Illustrates character 62(2). D, Fragmentary left maxilla of Exostinuslancensis AMNH 8498, lateral, anterior to the left. Illustrates character 62(3).
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projecting as a low ridge (Fig. 19A); (3)projecting as an extensive, strong ridge(Fig. 18D).
Variation. The crest, when present,becomes somewhat stronger with age,and the scoring here represents thecondition in relatively large individuals.
Evolution. Under both analyses, theancestral state for the entire group isambiguous between slight and moderatedevelopment of the crest. The ancestralstate for Anguimorpha is moderatedevelopment. Also under both analyses,lack of a crest is a synapomorphy ofAnguidae, a moderately developed crestis an autapomorphy of X. platyceps, andan extensive crest is an autapomorphy ofE. serratus. Under Analysis 1, theancestral state for S. crocodilurus +Varanidae is ambiguous between lackof a crest and slight development. UnderAnalysis 2, lack of a crest is a synapo-morphy of S. crocodilurus + M. ornatusand of Varanus.
62. Maxilla: Osteoderms upon facial process(0) absent (Fig. 20B); (1) present asnearly continuous sculptured plate or asmall number of rectangular plates(Fig. 18C); (2) present as sculpturedplate with sculpture concentrated intolow mounds (Fig. 20C); (3) present asseveral low, polygonal (generally moreedges than rectangles) tesserae(Fig. 20D); (4) present as pronouncedmounds (Fig. 18D). This character wasdescribed and scored as ‘‘rugosity absentor present’’ by Conrad (2005, 2008).
Variation. Fusion of osteoderms todermal elements proceeds during post-natal ontogeny, and mound-shaped os-teoderms develop from flat lattices ofbone (personal observation). Thus, rel-atively large individuals were scored.
Evolution. Under both analyses, theancestral state for the entire group andfor Anguimorpha is no osteodermalfusion. The ancestral state for Xeno-saurus + R. rugosus is a sculptured
plate concentrated into scattered lowmounds. The low, polygonal, tesselatedmorphology is a synapomorphy of E.lancensis + Xenosaurus, and the pro-nounced mound-shaped morphology is asynapomorphy of E. serratus + Xeno-saurus and an autapomorphy of Helo-dermatidae. The latter result is consis-tent with the presence of low, polygonaltesserae instead of pronounced moundsin primitive helodermatids (Hoffstetter,1957). Under Analysis 1, the ancestralstate for Anguidae + Xenosaurus isambiguous among all four states. Theancestral state for Anguidae is ambigu-ous between state 0 and state 1. UnderAnalysis 2, the ancestral state for Xeno-sauridae is the absence of fused osteo-derms; presence of a few large sculp-tured plates is an autapomorphy of E.multicarinata. Note, however, that theapparently primitive (Conrad, 2005,2008) glyptosaurid anguids generallyhave large sculptured plate-like osteo-derms fused to the facial process (Mes-zoely, 1970; personal observation).
63. Maxilla: Tooth height (0) short, less thanhalf of tooth extending beyond margin ofbone (Fig. 16B); (1) tall, half or more oftooth extending beyond margin of bone(Fig. 16A).
Evolution. Under both analyses, theancestral state is ambiguous at all nodeswhose branches have mixed states.However, this is largely a result ofincomplete taxon sampling, as few non-anguimorph squamates have tall teeth.
64. Maxilla: Tooth count (average, roundedto nearest integer) (0) 7; (1) 8; (2) 9; (3)10; (4) 11; (5) 12; (6) 13; (7) 14; (8) 15;(9) 16; (A) 17; (B) 18.
Variation. As noted, average valueswere scored. Ontogenetic increase intooth number was previously document-ed for some squamates (Edmund, 1969;Ananjeva et al., 2003), but it was notin abundant evidence for the taxa Iexamined.
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Evolution. Under both analyses, acount of seven is an autapomorphy ofHelodermatidae, nine is an autapomor-phy of V. exanthematicus, 12 is anautapomorphy of E. serratus and S.crocodilurus, and 17 is an autapomorphyof E. multicarinata. Additionally, a countof 16 is a synapomorphy of Xenosaurusand a count of 18 is a synapomorphy ofthe northern clade of Xenosaurus, aswell as an autapomorphy of X. rectocol-laris. Under Analysis 1, the ancestralstate for the entire group is ambiguousfrom 13 to 16, and that for Anguimorphais ambiguous between 13 and 14. Theancestral state for S. crocodilurus +Varanidae is ambiguous from 12 to 14,and a count of 15 is an autapomorphy ofB. ammoskius. A count of 11 is a
synapomorphy of Varanidae. Along theother major anguimorph lineage, acount of 16 is a synapomorphy of E.multicarinata + O. ventralis. UnderAnalysis 2, the primitive state for theentire group is ambiguous from 14 to16. A count of 11 is a synapomorphy ofVaranoidea.
Prefrontal
The prefrontal is unknown for E. lancen-sis and M. ornatus.
65. Prefrontal: Frontal process (0) relativelyshort and broad-based at divergencefrom main body of prefrontal, abouttwice as long along long axis as wideat base perpendicular to long axis(Fig. 21A); (1) relatively long and nar-
Figure 21. A, Left prefrontal of Exostinus serratus, CT scan of USNM v16565 lateral, anterior to the left. Illustrates characters 65(0),68(2), 69(2), 70(1), 71(1). B, Left prefrontal of Xenosaurus grandis NAUQSP-JIM 1460, lateral, anterior to the left. Illustrates characters65(1), 68(0). C, Left prefrontal of Elgaria multicarinata TMM-M 8958, lateral, anterior to the left. Illustrates characters 66(0), 69(0), 70(0),71(0), 72(0). D, Left prefrontal of Restes rugosus YPM PU 14640, lateral, anterior to the left. Illustrates characters 66(1), 69(1).
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row-based, about two-and-a-half timesas long as wide (Fig. 21B).
Variation. The frontal process be-comes relatively shorter and more stoutwith age, and this character was scoredon relatively large individuals. Largeadults were available for all taxa scoredas having long frontal processes.
Evolution. Under both analyses, along frontal process is an autapomorphyof O. ventralis and of X. newmanorumand a synapomorphy of X. grandis + X.rackhami.
66. Prefrontal: Row of osteoderms alonglateral edge of dermal surface (0) absent(Fig. 21C); (1) present (Fig. 21D).
Variation. Osteoderms fuse to theprefrontal postnatally.
Evolution. Under Analysis 1, presenceof a lateral row of osteoderms is asynapomorphy of S. crocodilurus + B.ammoskius and of Xenosaurus + R.rugosus. Under Analysis 2, presence ofthe lateral row is a synapomorphy ofXenosauridae.
67. Prefrontal: Distinct osteodermal patternof two small osteoderms adjacent to nasalfacet and longer, lateral row of four withanteriormost laterally displaced, (0) ab-sent (Fig. 12B); (1) present (Fig. 22A).
Variation. Osteoderms fuse to theprefrontal postnatally.
Figure 22. A, Left prefrontal of Restes rugosus YPM PU 14640, dorsal, anterior to the left. Illustrates characters 67(1), 68(1). B,Left prefrontal of Xenosaurus newmanorum NAUQSP-JIM uncatalogued specimen, dorsolateral, anterior to the left. Illustratescharacter 68(3). C, Left prefrontal of Xenosaurus newmanorum NAUQSP-JIM uncatalogued specimen, lateral, anterior to the left.Illustrates character 72(1). D, Left vomer of Xenosaurus grandis NAUQSP-JIM 1460, dorsolateral, anterior to the left. E, Leftvomer of Xenosaurus newmanorum NAUQSP-JIM uncatalogued specimen, same view. D and E illustrate characters 73(0), 73(1),74(1), 74(2), 75(1), 76(2).
XENOSAUR PHYLOGENY N Bhullar 105
Evolution. Under both analyses, the‘‘two and four’’ pattern is a synapomor-phy of Xenosaurus + R. rugosus.
68. Prefrontal: Osteoderms (0) low, barelyd o m e d , w i t h f l a t a p p e a r a n c e(Fig. 21B); (1) moderately pronounced,with some doming (Fig. 22A); (2)pronounced with domes and low keels(Fig. 21A); (3) pronounced with highdomes and sharp keels (Fig. 22B).
Variation. Osteoderms become moredomed during postnatal ontogeny, butas mentioned in the description forcharacter 13, the keel forms early.
Evolution. Under both analyses, themoderately pronounced morphology isancestral. The low, barely domedmorphology is a synapomorphy of S.crocodilurus + B. ammoskius. Theancestral states for Xenosaurus + E.serratus and for Xenosaurus are am-biguous between the moderately pro-nounced morphology and the domedand moderately keeled morphology.The low morphology is a synapomor-phy of the southern clade of Xeno-saurus and the highly domed andhighly keeled morphology a synapo-morphy of the northern clade.
69. Prefrontal: Canthal crest (0) absent(Fig. 21C); (1) present as distinct ridge(Fig. 21D); (2) present as sharp, pro-nounced ridge (Fig. 21A).
Evolution. Under both analyses, asharp, pronounced morphology is anautapomorphy of E. serratus. UnderAnalysis 1, a distinct crest is a synapo-morphy of S. crocodilurus + B. ammos-kius and of Xenosaurus + R. rugosus.Under Analysis 2, it is a synapomorphyof Xenosauridae.
70. Prefrontal: Emargination or straightedge in maxillary flange (0) dorsoven-trally extensive, representing over half ofentire edge length of flange (Fig. 21C);(1) dorsoventrally restricted, less thanhalf of entire edge length (Fig. 21A).
Variation. The maxillary flange isextremely thin early in postnatal on-togeny, and in young individuals, itmay be damaged or only partiallyossified. This character is best scoredon relatively large individuals.
Evolution. Under both analyses, therestricted morphology is an autapomor-phy of E. serratus and of Helodermatidae.
71. Prefrontal: Lacrimal foramen (0) rela-tively unconstricted, margins remaindivergent (Fig. 21C); (1) relativelyconstricted, margins become nearlyparallel (Fig. 21A).
Evolution. Under both analyses, theparallel morphology is an autapomorphyof E. serratus.
72. Prefrontal: Lacrimal facets (0) relativelysmooth (Fig. 21C); (1) adorned withcomplex ridges and bumps (Fig. 22C).
Variation. When the complexadorned morphology is present, it tendsto be more pronounced in older indi-viduals.
Evolution. Under both analyses, theadorned morphology is a synapomorphyof Xenosaurus + R. rugosus.
Vomer
The vomer is unknown in E. serratus, E.lancensis, R. rugosus, and M. ornatus. It isnot visible in the single known specimen ofB. ammoskius (Conrad, 2006).
73. Vomer: Anterior facet for medial pre-maxillary process of maxilla (0) less thanthree times as long along its long axis asta l l perpendicular to long axis(Fig. 22D); (1) three or more times aslong as tall (Fig. 22E).
Evolution. Under both analyses, theelongated morphology is a synapomor-phy of the northern clade of Xenosaurus.
74. Vomer: Anterior facet for medial pre-maxillary process of maxilla (0) abruptlydiverging ascending portion of ventraledge absent (Fig. 23A); (1) abruptly
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diverging ascending portion of ventraledge relatively short, beginning overhalfway to medial limit of facet(Fig. 22E); (2) ascending portion rela-tively long, beginning less than halfwayto medial limit of facet (Fig. 22D).
Evolution. Under both analyses, theancestral states for the entire groupand for Anguimorpha are ambiguousbetween absence and the short mor-phology. The ancestral state for thesouthern clade of Xenosaurus is am-biguous between the short and longmorphologies, and the long morpholo-gy is an autapomorphy of E. multi-carinata. Under Analysis 1, the ances-tral state for S. crocodilurus +
Varanidae is ambiguous between ab-sence and the short morphology. Theancestral state for Varanidae is ab-sence. Along the other major branch ofAnguimorpha, the ancestral state forXenosaurus + Anguidae is ambiguousbetween absence and the short mor-phology, but the short morphology isthe ancestral state for Xenosaurus andfor Anguidae.
75. Vomer: Anterior process from antero-medial corner (0) absent (Fig. 23A); (1)present, short—about as long along longaxis as wide perpendicular to it(Fig. 22D); (2) present, long—longeralong long axis than wide perpendicularto long axis (Fig. 22E).
Figure 23. A, Left vomer of Varanus exanthematicus TMM-M 8956, dorsolateral, anterior to the left. Illustrates characters 74(0),75(0). B, Rostrum of Pristidactylus torquatus CAS 85234, ventral, anterior to the left. Illustrates characters 76(0), 78(0), 87(0). C,Left vomer of Xenosaurus rackhami UTEP-OC ‘‘MALB’’ 388, ventromedial, anterior to the left. D, Left vomer of Xenosaurusplatyceps UF 45622, same view. C and D illustrate characters 76(1), 77(0), 78(1), 78(2), 79(0), 81(0), 81(1), 82(0), 82(1), 83(0),83(1). E, Left vomer of Xenosaurus newmanorum NAUQSP-JIM uncatalogued specimen, same view. F, Left vomer ofXenosaurus platyceps UF 45622, same view. E and F illustrate characters 76(2), 79(1), 80(0), 80(1).
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Evolution. Under both analyses, pres-ence of a short process is a synapomor-phy of Xenosaurus, and a long process isa synapomorphy of the northern clade ofXenosaurus.
76. Vomer: Lateral parasagittal crest onventral surface (0) short, extends abouta third of the way to the back of thevomer (Fig. 23B); (1) intermediatelength, extends about half of the wayto the back of the vomer (Fig. 23C); (2)long, extends about two-thirds of theway to the back of the vomer (Fig. 23F).
Evolution. Under both analyses, theancestral state for the entire group isambiguous between short and interme-diate length. The ancestral state forXenosaurus is the intermediate mor-phology, with the short morphology anautapomorphy of X. agrenon and thelong morphology a synapomorphy of thenorthern clade. Under Analysis 1, theancestral state for Anguimorpha isambiguous between short and interme-diate length. The ancestral state forXenosaurus + Anguidae is intermediatelength, that for Anguidae is ambiguousbetween intermediate length and thelong morphology, and that for Varanidaeis the short morphology. Under Analysis2, intermediate length is ancestral forAnguimorpha. The long morphology is asynapomorphy of O. ventralis + C.enneagrammus, and the short morphol-ogy is a synapomorphy of Varanidae.
77. Vomer: Lateral parasagittal crest (0)extends largely dorsoventrally (Fig.23C); (1) folds medially as a tall flange,underhanging much of the vomer (Fig.24A).
Evolution. Under both analyses, themedial folding is an autapomorphy of X.agrenon.
78. Vomer: Mediolateral width of lateralflange bordered medially by lateralparasagittal crest at widest anteroposte-rior level (0) narrow, less than half that of
remainder of vomer (Fig. 23B); (1) inter-mediate, one half of that of remainder ofvomer to just under equal to that ofremainder of vomer (Fig. 23D); (2) wide,equal to or wider than that of remainderof vomer (Fig. 23C).
Evolution. Under both analyses, thenarrow morphology is ancestral for theentire group and for Anguimorpha. Theintermediate morphology is ancestral forXenosaurus and the wide morphology isa synapomorphy of the southern clade ofXenosaurus. Under Analysis 1, theancestral state for Xenosaurus + Angu-idae is ambiguous between narrow andintermediate, and the ancestral state forAnguidae is ambiguous between inter-mediate and wide. Under Analysis 2, theancestral state for Anguidae + Varanoideaand for Xenosauridae is narrow, makingthe intermediate morphology a synapo-morphy of Anguidae and the wide asynapomorphy of O. ventralis + C.enneagrammus.
79. Vomer: Medial parasagittal crest (0)ends posterior to vomerine foramen(Fig. 23C); (1) ends at level of, or ante-rior to, vomerine foramen (Fig. 23F).
Evolution. Under both analyses, ter-mination at or anterior to the vomerineforamen is a synapomorphy of thenorthern clade of Xenosaurus.
80. Vomer: Medial parasagittal crest extend-ing to or past level of vomerine foramen(0) passes lateral to foramen (Fig. 23E);(1) passes medial to foramen (Fig. 23F).
Evolution. Given the restricted distribution of the character states, it isimpossible to infer the ancestral stateof this character.
81. Vomer: Vomerine foramen (0) small,mediolateral width less than one-eighthmediolateral width of vomer at samelevel (Fig. 23D); (1) large, mediolateralwidth one-eighth mediolateral width ofvomer at same level or greater(Fig. 23C).
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Evolution. Under both analyses, alarge foramen is an autapomorphy ofX. rackhami.
82. Vomer: Posterior end of palatine process(0) nearly straight in horizontal plane(Fig. 23D); (1) bowed laterally (Fig. 23C).
Evolution. Under both analyses, lat-eral bowing is a synapomorphy of X.grandis + X. rackhami.
83. Vomer: Palatine process, width mea-sured by ratio of mediolateral width towidest mediolateral width of vomer, (0)mediolaterally wide, ratio 0.44 or greater(Fig. 23D); (1) mediolaterally narrow,ratio less than 0.44 (Fig. 23C).
Evolution. Under both analyses, theancestral state for the entire group is
the wide morphology, as is that forAnguimorpha. The ancestral state forthe southern clade of Xenosaurus isambiguous, with the narrow morphol-ogy either a synapomorphy of theentire clade and the wide morphologyan autapomorphy of X. rectocollaris orthe narrow morphology an autapomor-phy of X. agrenon and a synapomorphyof X. grandis + X. rackhami. UnderAnalysis 1, the narrow morphology isan autapomorphy of S. crocodilurus.Under Analysis 2, the ancestral statefor Xenosauridae is ambiguous.
Palatine
The palatine is unknown in E. serratus, E.lancensis, R. rugosus, and M. ornatus. It is
Figure 24. A, Rostrum of Xenosaurus agrenon UTACV r45008, ventral, anterior to the left. Illustrates character 77(1). B, Leftpalatine of Xenosaurus newmanorum NAUQSP-JIM uncatalogued specimen, dorsal, anterior to the top. C, Left palatine ofXenosaurus grandis NAUQSP-JIM 1460, same view. D, Left palatine of Elgaria multicarinata TMM-M 8958, same view. B throughD illustrate characters 84(0), 84(1), 85(0), 85(1), 85(2), 86(0), 86(1), 88 (n for numerator, d for denominator), 89(0).
XENOSAUR PHYLOGENY N Bhullar 109
not visible in the single known specimen ofB. ammoskius (Conrad, 2006).
84. Palatine: Choanal margin (0) straight orconvex anteriorly in horizontal plane(Fig. 24D); (1) concave anteriorly inhorizontal plane (Fig. 24C).
Evolution. Under both analyses, ante-rior concavity is a synapomorphy of thenorthern clade of Xenosaurus and anautapomorphy of X. grandis. UnderAnalysis 1, anterior concavity is anautapomorphy of Helodermatidae andof L. borneensis. Under Analysis 2, theancestral states for Varanoidea and Var-anidae are ambiguous, with anteriorconcavity either a synapomorphy ofVaranoidea and convexity or linearity asynapomorphy of Varanus or anteriorconcavity an autapomorphy of Heloder-matidae and L. borneensis.
85. Palatine: Eminence in choanal margin(0) absent (Fig. 24D); (1) small andlocated medial to the mediolateralmidpoint of the margin (Fig. 24C); (2)large, broadly curved, and locatedaround the mediolateral midpoint ofthe margin (Fig. 24B).
Evolution. Under both analyses, ab-sence of the eminence is ancestral forthe entire group and the small, medialmorphology is a synapomorphy of Xe-nosaurus. The large, broad morphologyis a synapomorphy of the northern cladeof Xenosaurus.
86. Palatine: Maxillary process (0) about asanteroposteriorly long as mediolaterallywide (Fig. 24D); (1) distinctly anteropos-teriorly longer than mediolaterally wide(Fig. 24C).
Evolution. Under both analyses, thelonger-than-wide morphology is a syn-apomorphy of Xenosaurus.
87. Palatine: Pterygoid process ventral surface(0) bearing teeth (Fig. 23B); (1) bearingmidline ridge or groove (Fig. 5B); (2)smooth (Fig. 25A). Presence or absence
of palatine teeth was character 82 of Esteset al. (1988).
Variation. I did not have ontogeneticseries for taxa that possess palatineteeth, but the palatal teeth upon thepterygoid of E. multicarinata increase innumber during postnatal ontogeny.
Evolution. Under both analyses, theancestral state for the entire group isambiguous among the three states, butthe ancestral state for Anguimorpha isabsence of teeth and ridges. Thepresence of ridges in X. rectocollaris,and of teeth in O. ventralis and L.borneensis, is autapomorphic for eachof these taxa.
88. Palatine: Pterygoid process, ratio oflength along long axis beginning atposterior end of base of vomerineprocess to width perpendicular to longaxis at constriction behind base ofvomerine process (Fig. 24C) (0) 1.1 orless; (1) greater than 1.1 to 1.2; (2)greater than 1.2 to 1.3; (3) greater than1.3 to 1.4; (4) greater than 1.4 to 1.5; (5)greater than 1.5.
Variation. The pterygoid process insome but not all taxa becomes rela-tively wider with age, and all scoringswere performed on relatively largeindividuals.
Evolution. Under both analyses, theancestral state for Xenosaurus is ambig-uous between state 1 and state 2. State 0is a synapomorphy of X. agrenon + X.rectocollaris, and state 4 is an autapo-morphy of X. rackhami. Under Analysis1, the ancestral state for the entire groupis ambiguous among all states, as is thatfor Anguimorpha and Xenosaurus +Anguidae, as well as Shinisaurus +Varanidae. State 0 is a synapomorphyof Varanidae and an autapomorphy ofHelodermatidae. Under Analysis 2, state5 is ancestral for the entire group,Anguidae + Varanoidea, and Xenosaur-idae. State 0 is a synapomorphy ofVaranoidea.
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89. Palatine: Dorsomedial tongue for ptery-goid articulation (0) anteroposteriorlylonger than mediolaterally wide at base(Fig. 24B); (1) mediolaterally wider atbase than long (Fig. 25C).
Evolution. Under both analyses, thewider-than-long morphology is anauta-pomorphy of X. platyceps. Under Anal-ysis 1, the wider-than-long morphologyis a synapomorphy of Varanidae and anautapomorphy of Helodermatidae. Un-der Analysis 2, it is a synapomorphy ofVaranoidea.
90. Palatine: Anterior to mediolateral di-vergence of dorsomedial and ventrolat-eral tongues for pterygoid articulation,medial edge of dorsoventrally diverging
ventrolateral tongue (0) raised intosharp, underhanging ridge (Fig. 25B);(1) raised into low ridge with little ifany underhang (Fig. 25A).
Evolution. Under both analyses, thelow, rounded morphology is a synapo-morphy of the southern clade of Xeno-saurus.
Frontal
91. Frontal: Frontals (0) remain unfusedthroughout ontogeny (Estes et al., 1988,Fig. 13B); (1) fuse at some point duringontogeny (Fig. 25D).
Variation. Frontal fusion occurs dur-ing ontogeny; in the taxa (specified inMaterials and Methods) for which very
Figure 25. A, Left palatine of Xenosaurus rackhami UTEP-OC ‘‘MALB’’ 388, ventral, anterior to the left. B, Left palatine ofXenosaurus newmanorum NAUQSP-JIM uncatalogued specimen, same view as A. A and B illustrate characters 87(2), 90(0),90(1). C, Left palatine of Xenosaurus platyceps UF 45622, dorsal, anterior to the left. Illustrates character 89(1). D, Frontal ofElgaria multicarinata TMM-M 8958, dorsal, anterior to the left. Illustrates characters 91(0), 94(0), 97(0), 104(1), 108(0). E, Anteriortip of frontal of Exostinus serratus, CT scan of USNM v16565, ventral, anterior to the left. Illustrates character 93(0).
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young postnatal specimens were avail-able, a seam and sometimes a split at theanterior end still remained.
Evolution. Under both analyses, thefused morphology is ancestral for theentire group. Under Analysis 1, pairingis a synapomorphy of Varanidae and ofAnguidae + Helodermatidae, with thefused morphology an autapomorphy ofE. multicarinata. Under Analysis 2, theancestral state for Anguidae + Varanoi-dea is ambiguous; either the pairedmorphology is a synapomorphy of thatclade, and fused morphology is anautapomorphy of E. multicarinata, orthe paired morphology is a synapomor-phy of O. ventralis + C. enneagrammusand of Varanoidea.
92. Frontal: Frontals in taxa where fusionoccurs (0) remain separate for someperiod of time postnatally; (1) fuseprenatally.
Variation. This character dependsupon the recognition of ontogeneticvariation. It is possible that unrecog-nized individual variation occurs regard-ing when and whether fusion occurs, inparticular among the extinct taxa.
Evolution. Under both analyses, theancestral state for the entire group isprenatal fusion. Postnatal fusion is anautapomorphy of E. lancensis and of M.ornatus.
93. Frontal: In taxa with fused frontals,frontals fuse and raised seam at line offusion vanishes (0) only at most ad-vanced ontogenetic stages (Fig. 25E);(1) by attainment of approximately two-thirds of ‘‘adult’’ size of frontals(Fig. 17D).
Variation. As noted, this character isscored based on the nature of inferredontogenetic variation.
Evolution. Under both analyses, theancestral state for the entire group andfor Anguimorpha is early disappear-ance of the seam. Under Analysis 1,
the ancestral state for E. lancensis +Xenosaurus and for E. serratus + Xeno-saurus is ambiguous, and late disappear-ance is an autapomorphy of M. ornatus.Under Analysis 2, the ancestral state forXenosauridae is ambiguous.
94. Frontal: Constriction (0) weak, ratio ofwidest mediolateral width of frontaltable anterior to level of greatest con-striction to width at greatest constrictionless than 1.15 (Fig. 25D); (1) moderate,ratio 1.15 to 1.7; (2) strong, ratio greaterthan 1.7 (Fig. 26A).
Variation. In many taxa, includingS. crocodilurus, the frontals in youngerindividuals are considerably more con-stricted than in older individuals, con-comitant with the relatively larger size ofthe eyes. Individuals scored here wererelatively large adults.
Evolution. Under both analyses, theancestral state for the entire group andfor Anguimorpha is moderate constric-tion, and weak constriction is an auta-pomorphy of S. crocodilurus. UnderAnalysis 1, weak constriction is a synap-omorphy of Varanidae and of Anguidae+ Helodermatidae, and strong constric-tion is a synapomorphy of E. serratus +Xenosaurus and an autapomorphy of M.ornatus. Under Analysis 2, weak con-striction is a synapomorphy of Anguidae+ Varanoidea, and the ancestral state forXenosauridae is ambiguous betweenweak and strong constriction.
95. Frontal: Osteoderms (0) lacking keels orwith weak keels (Fig. 26A); (1) stronglykeeled, at least in part (Fig. 26B).
Variation. Osteoderms fuse to thefrontal postnatally in most taxa, but thekeel may be the first part of eachosteoderm to form.
Evolution. Under both analyses, thekeeled morphology is a synapomorphyof the northern clade of Xenosaurus.
96. Frontal: Orbital rows of osteodermsalong lateral edges (0) flat and rectan-
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gular (Fig. 26C); (1) small and domed(Fig. 26B).
Variation. Osteoderms fuse to thefrontal postnatally in most taxa.
Evolution. Under both analyses, theancestral state for the entire group isambiguous and the ancestral state forAnguimorpha is flat and rectangular. Thedomed morphology is a synapomorphy ofE. lancensis + Xenosaurus, and the flat,rectangular morphology is an autapomor-phy of X. rectocollaris.
97. Frontal: Osteoderms in center of expand-ed posterior portion of frontal (0) all flatand plate-like (Fig. 25D); (1) some flat andplate-like, others broad and domed (Klem-bara, 2008); (2) some flat and plate-like,
others small and domed (Fig. 26C); (3) allsmall and domed (Fig. 26B).
Variation. Osteoderms become fusedto the frontal and become more domedduring ontogeny.
Evolution. Under both analyses, theancestral state for the entire group isambiguous among all three states, andthat for Anguimorpha is ambiguous be-tween state 1 and state 2. State 2 isancestral for R. rugosus + Xenosaurus, andstate 3 is a synapomorphy of E. lancensis +Xenosaurus and an autapomorphy of B.ammoskius. Under Analysis 1, the ances-tral states for S. crocodilurus + Varanidaeand for Xenosaurus + Anguidae areambiguous like Anguimorpha. State 0 is
Figure 26. A, Frontal of Xenosaurus grandis NAUQSP-JIM 1460, dorsal, anterior to the left. Illustrates characters 94(2), 95(0),102(1), 103(1). B, Frontal of Xenosaurus newmanorum NAUQSP-JIM uncatalogued specimen, dorsal, anterior to the left.Illustrates characters 95(1), 96(1), 97(3), 98(1), 99(1), 100(0), 102(0), 103(0), 108(1). C, Frontal of Restes rugosus YPM PU14640, dorsal, anterior to the left. Illustrates characters 96(0), 97(2), 98(0), 99(0). D, Frontal of Exostinus serratus, CT scan ofAMNH 1608, dorsal, anterior to the left. Illustrates characters 98(2), 100(1), 108(2).
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ancestral for Anguidae + the heloderma-tid lineage. Under Analysis 2, the ances-tral state for Xenosauridae is ambiguouslike Anguimorpha, and the ancestral statefor Anguidae + Varanoidea is state 0.
98. Frontal: Region of strong developmentof orbital rows of osteoderms alonglateral edges (0) restricted, extendinganteriorly only up to greatest constric-tion of frontal table or ending posteriorto it (Fig. 26C); (1) intermediate, ex-tending anteriorly past greatest con-striction of frontal table and for lessthan a third of the length of theprefrontal facet (Fig. 26B); (2) exten-sive, extending anteriorly past greatestconstriction of frontal table and forabout a third of the length of theprefrontal facet (Fig. 26D).
Variation. Osteoderms fuse to thefrontal during postnatal ontogeny.
Evolution. Under both analyses, theancestral state for the entire group is arestricted extent. The intermediatemorphology is a synapomorphy of S.crocodilurus + B. ammoskius and of E.serratus + Xenosaurus, and the exten-sive morphology is an autapomorphy ofE. serratus.
99. Frontal: Transverse rows of osteodermsin posterior expanded portion (0) two tothree (Fig. 26C); (1) four or more(Fig. 26B).
Evolution. Under both analyses, theancestral state for the entire group isambiguous, and four or more rows is asynapomorphy of E. serratus + Xenosaurus.
100. Frontal: Posteriormost transverse rowof osteoderms in posterior expandedportion (0) similar in prominence tomore anterior rows (Fig. 26B); (1) lessprominent than more anterior rows(Fig. 26D).
Variation. No variation affecting scor-ing was evident, save, most likely, theontogenetic variation already noted inosteoderm characters.
Evolution. Under both analyses, thereduced prominence of the posterior-most row is either a synapomorphy ofE. lancensis + Xenosaurus, with similarprominence a synapomorphy of Xeno-saurus, or it is an autapomorphy of E.lancensis and of E. serratus.
101. Frontal: Distance from posterior end ofprefrontal facet to posterior end offrontal (0) relatively great, 2.25 or moretimes length of posterior sharply taper-ing portion of prefrontal facet(Fig. 27A); (1) relatively small, fewerthan 2.25 times length of posteriorportion of facet (Fig. 27B).
Evolution. Under both analyses, arelatively small distance is an autapo-morphy of E. serratus. Under Analysis1, that character state is also anautapomorphy of Helodermatidae anda synapomorphy of Varanidae. UnderAnalysis 2, it is a synapomorphy ofVaranoidea.
102. Frontal: Anterior mediolaterally ta-pered tip of frontal (0) mediolaterallywider at base than anteroposteriorlylong (Fig. 26B); (1) longer than wide(Fig. 26A).
Evolution. Under both analyses, lon-ger than wide is a synapomorphy of thesouthern clade of Xenosaurus.
103. Frontal: Internasal spine (0) closelyapproaching anterior tip of frontal(Fig. 26B); (1) halting posterior toanterior tip with frontal extendingbeyond it for half or more of the lengthof the spine, forming an extensiveanterior lamina (Fig. 26A).
Evolution. Under both analyses, aposterior termination of the spine is a syn-apomorphy of X. rackhami + X. grandis.
104. Frontal: Posteriorly, medial and lateraledges of nasal facets converge (0) at arelatively wide angle of 70u or greater(Fig. 27C); (1) at a relatively narrowangle of less than 70u (Fig. 25D).
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Evolution. Under Analysis 1, theancestral states for all clades with mixedcharacter distribution are ambiguous.Under Analysis 2, the ancestral state forthe entire group is a relatively narrowangle, as is that for Anguimorpha. Theancestral state for Xenosauridae isambiguous. On the other branch ofAnguimorpha, the ancestral state forAnguidae + Varanoidea is a relativelynarrow angle, with the wider morphol-ogy a synapomorphy of C. enneagram-mus + O. ventralis and an autapomorphyof Lanthonotus borneensis.
105. Frontal: Ventral edges of cristae cranii,at closest approach in a horizontalplane, separated by (0) greater than
one-third of the mediolateral width ofthe frontal at that anteroposterior level(Fig. 27D); (1) one-third or less of themediolateral width of the frontal(Fig. 28A).
Evolution. Under both analyses, wideseparation is the primitive state for theentire group and for Anguimorpha.Under Analysis 1, close approach is asynapomorphy of S. crocodilurus +Varanidae and of E. lancensis + Xeno-saurus. Under Analysis 2, close ap-proach is a synapomorphy of Varani-dae, and the ancestral state forXenosauridae is ambiguous.
106. Frontal: Cristae cranii deepen anteriorto expanded portion of frontal to (0)
Figure 27. A, Frontal of Xenosaurus newmanorum NAUQSP-JIM uncatalogued specimen, left lateral, anterior to the left.Illustrates characters 101(0), 106(0), 107(0). B, Frontal of Exostinus serratus, CT scan of AMNH 1608, left lateral, anterior to theleft. Illustrates characters 101(1), 106(1), 107(1). C, Anterior tip of frontal of Exostinus serratus, CT scan of USNM v16565, dorsal,anterior to the left. Illustrates character 104(0). D, Frontal of Restes rugosus, CT scan of YPM PU 14640, ventral, anterior to theleft. Illustrates character 105(0).
XENOSAUR PHYLOGENY N Bhullar 115
less than twice their dorsoventralheight along the expanded portion(Fig. 27A); (1) equal to or greater thantwice their dorsoventral height alongthe expanded portion (Fig. 27B).
Evolution. Under both analyses, shallow cristae cranii are ancestral for theentire group and for Anguimorpha, andthe deep morphology is an autapomor-phy of E. lancensis. Under Analysis 1,the deep morphology is a synapomor-phy of Varanidae and of Anguidae +Helodermatidae. Under Analysis 2, thedeep morphology is a synapomorphy ofAnguidae + Varanoidea.
107. Frontal: Angle of posterior descent ofcristae cranii just behind horizontal
portion of ventral edges (0) less than 40u(Fig. 27A); (1) 40u or greater (Fig. 27B).
Evolution. Under both analyses, asteep slope is an autapomorphy of E.serratus. Under Analysis 1, a steepslope is a synapomorphy of Varanidaeand an autapomorphy of Helodermati-dae. Under Analysis 2, it is a synapo-morphy of Varanoidea.
108. Frontal: Cristae cranii project laterallybeyond dermal table of frontal (0) notat all (Fig. 25D); (1) only in region ofgreatest constriction (Fig. 26A); (2)extensively beginning in region ofgreatest constriction and extendingnearly to anterior tip of frontal(Fig. 26D).
Figure 28. A, Frontal of Exostinus serratus, CT scan of AMNH 1608, ventral, anterior to the left. Illustrates character 105(1). Leftpalpebrals, dorsal, anterior to the top: B, Elgaria multicarinata TMM-M 8958; C, Xenosaurus newmanorum NAUQSP-JIMuncatalogued specimen; D, Xenosaurus agrenon UTACV r45008; E, Xenosaurus grandis NAUQSP-JIM 1460. B through Dillustrate characters 109(0), 109(1), 110(0), 110(1), 111(0), 111(1), 112(0), 112(1), 113(0), 113(1). F, Rostrum of Elgariamulticarinata CAS 85234, left lateral, anterior to the left. Illustrates character 114(0).
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Evolution. Under both analyses, noprojection is the ancestral state for theentire group and for Anguimorpha.Moderate projection is a synapomorphyof E. serratus + Xenosaurus, and exten-sive projection is an autapomorphy of E.serratus and a synapomorphy of Varanus.Under Analysis 1, moderate projection isa synapomorphy of Varanidae and anautapomorphy of Helodermatidae. Un-der Analysis 2, moderate projection is asynapomorphy of Varanoidea.
Palpebral
The palpebral is unknown for M. ornatus, B.ammoskius, E. lancensis, and E. serratus. It isabsent in P. torquatus and Helodermatidaeand is so reduced in L. borneensis that its mor-phology in relation to the characters describedhere is unscorable (Maisano et al., 2002).
109. Palpebral: Overall shape: (0) mediolat-erally elongate triangle with lateralconstriction caused by step in posteriormargin (Fig. 28B); (1) mediolaterallyshorter triangle without lateral constric-tion caused by step in posterior margin(Fig. 28C).
Evolution. Under both analyses, themediolaterally elongate morphology is asynapomorphy of Anguimorpha, and themore equilateral morphology is a syn-apomorphy of R. rugosus + Xenosaurusand an autapomorphy of O. ventralis.
110. Palpebral: Posterior edge (0) withrelatively straight or smoothly curvingmargin (Fig. 28E); (1) with wavy mar-gin (Fig. 28D); (2) with ragged margin(Fig. 28C).
Evolution. Under both analyses, thewavy morphology is an autapomorphyof X. agrenon, and the ragged morphol-ogy is a synapomorphy of the northernclade of Xenosaurus.
111. Palpebral: Fused osteoderms (0) absent(Fig. 28B); (1) present as slight dorsalrugosities (Fig. 28E); (2) present acrossmost of dorsal surface; less coverage
upon anterior two-thirds and alonganterior edge (Fig. 28D); (3) strongacross dorsal surface, including anteriorportion, with distinct, tall row alonganterior edge (Fig. 28C).
Variation. Osteodermal fusion todermal elements, including the palpe-bral, occurs postnatally, although rela-tively small specimens of X. platycepsalready show some dorsal rugosity.
Evolution. Under both analyses, aslight dorsal rugosity is a synapomorphyof R. rugosus + Xenosaurus, a moder-ately strong covering of osteoderms is asynapomorphy of Xenosaurus, and astrong covering is a synapomorphy ofthe northern clade of Xenosaurus.
112. Palpebral: Foramen near anterior edge,just lateral to mediolateral level of apex ofslight concavity in posterior margin (0)absent (Fig. 28C); (1) present (Fig. 28E).
Evolution. Under both analyses,presence of the foramen is a synapo-morphy of X. rackhami + X. grandis.
113. Palpebral: Strong s-curve to medial edgein horizontal plane, with anterior emargi-nation and posterior bulge accompaniedby dorsoventral deepening (0) absent(Fig. 28B); (1) present (Fig. 28D).
Variation. In some large adultE. multicarinata, the medial edge of thepalpebral displays a slight s-curve, butnot to the extent of the taxa scored as (1).
Evolution. Under both analyses, theancestral state for the entire group isambiguous, as is that for Anguimorpha.Under Analysis 1, the ancestral state forR. rugosus + Xenosaurus is presence ofthe s-curve, with all mixed nodesambiguous. Under Analysis 2, theancestral state for Xenosauridae ispresence of an s-curve, and that forAnguidae + Varanoidea is absence.
Lacrimal
The lacrimal is unknown for all of theextinct taxa save B. ammoskius, but some of
XENOSAUR PHYLOGENY N Bhullar 117
its basic dimensions can be inferred fromthe morphology of the maxilla and prefron-tal. This is the method by which character114 is scored for all taxa.
114. Lacrimal: Size relative to maxilla (0) small,around one-quarter length of maxilla orsmaller (Fig. 28F); (1) large, around one-third length of maxilla (Fig. 1C).
Evolution. Under both analyses, arelatively large lacrimal is a synapomor-phy of R. rugosus + Xenosaurus.
115. Lacrimal: Angle between antorbital andsuborbital rami measured along lowermargin (0) high, greater than 135u(Fig. 29A); (1) low, less than 135u(Fig. 29C).
Evolution. Under both analyses, anangle of less than 135u is a synapomor-phy of X. rackhami + X. grandis.
116. Lacrimal: Fused osteoderms (0) absent(Fig. 29A); (1) present as slight rugos-ities (Fig. 29C); (2) present as lowmounds (Fig. 29B); (3) present as tallmounds, some of which bear keels(Fig. 29D).
Variation. Osteoderms become fusedto dermal elements postnatally.
Evolution. Under both analyses, thepresence of fused osteoderms as slightrugosities is a synapomorphy of Xeno-saurus, low mounds is an autapomorphyof X. grandis, and tall, sometimes keeled
Figure 29. Left lacrimals, lateral, anterior to the left: A, Elgaria multicarinata TMM-M 8958; B, Xenosaurus newmanorumNAUQSP-JIM uncatalogued specimen; C, Xenosaurus agrenon UTACV r45008; D, Xenosaurus grandis NAUQSP-JIM 1460. Athrough D illustrate characters 115(0), 115(1), 116(0), 116(1), 116(2), 116(3), 117(0), 117(1), 120(0), 120(1), 121(0), 121(1),122(0), 122(1). Left lacrimals, medial, anterior to the right: E, Xenosaurus platyceps UF 45622; F, Xenosaurus grandis NAQSP-JIM 1460; E and F illustrate characters 119(0), 119(1), 122(0), 122(1).
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mounds is a synapomorphy of the north-ern clade of Xenosaurus.
117. Lacrimal: Subpalpebral fossa (0) absent(Fig. 29A); (1) present (Fig. 29B).
Evolution. Under Analysis 1, thefossa is a synapomorphy of Xenosaurusand of S. crocodilurus + B. ammoskius.Under Analysis 2, it is a synapomorphyof Xenosauridae.
118. Lacrimal: Subpalpebral fossa (0) con-tained entirely in lacrimal (Fig. 1C); (1)extending onto adjacent elements(Fig. 20B).
Evolution. Under both analyses,most nodes optimize ambiguously.The ancestral state for the southernclade of Xenosaurus is containmentwithin the lacrimal.
119. Lacrimal: Lacrimal foramen (0) large,expanse at greatest extent is half or moreof length of antorbital ramus of lacrimal(Fig. 29F); (1) small, less than half asextensive as antorbital ramus (Fig. 29E).
Evolution. Under both analyses, thesmall, constricted morphology is anautapomorphy of X. platyceps.
120. Lacrimal: Dorsal and ventral prefrontalprocesses (0) project as prominentwedges beyond main body of lacrimalin sagittal plane (Fig. 29A); (1) barelyproject if at all beyond body of lacrimal insagittal plane (Fig. 29B).
Evolution. Under both analyses, lackof projection or minor projection isancestral for the entire group, andprojection is an autapomorphy of X.newmanorum, E. multicarinata, and X.grandis. Under Analysis 1, projection isan autapomorphy of Helodermatidaeand a synapomorphy of Varanidae.Under Analysis 2, it is a synapomorphyof Varanoidea.
121. Lacrimal: Lacrimal canal (0) deeplyincised into medial surface of lacri-mal, with strong overhanging and/orunderhanging ridges, the latter formed
by flange of ventral prefrontal process(Fig. 29A); (1) shallowly incised, withmarginal ridges only in anteriormostportion (Fig. 29B).
Evolution. Under both analyses, theancestral state for the entire group isambiguous. Under Analysis 1, shallowincision is ancestral for Anguimorpha,and deep incision is a synapomorphy ofAnguidae. Under Analysis 2, the ances-tral state for Anguimorpha is ambigu-ous, as are those for Anguidae +Varanoidea and Varanoidea.
122. Lacrimal: Posteriorly, ventral prefrontalprocess (0) diminishes mediolaterally(Fig. 29D); (1) expands mediolaterally(Fig. 29B).
Evolution. Under both analyses, mediolateral expansion along a posteriorcline is a synapomorphy of the northernclade of Xenosaurus.
Jugal
The jugal is unknown for M. ornatus.
123. Jugal: Postorbital ramus (0) long axisrelatively straight (Fig. 3C); (1) longaxis broadly curved in sagittal plane(Fig. 5C).
Evolution. Under both analyses, sag-ittal curvature is an autapomorphy of X.rectocollaris.
124. Jugal: Fused osteoderms or osteoder-mal sculpturing (0) absent (Fig. 30A);(1) present on ventral two-thirds ofpostorbital ramus (Fig. 30B); (2) pres-ent on all of postorbital ramus(Fig. 30C). This character was scoredas presence or absence of sculpturingby Estes et al. (1988).
Variation. Osteoderms fuse to thejugal during early postnatal ontogeny.
Evolution. Under both analyses, theancestral state for the entire group andfor Anguimorpha is a lack of sculptur-ing or fused osteoderms and that for R.rugosus + Xenosaurus is partial cover-
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age. Having osteoderms upon theentire dermal surface is a synapomor-phy of E. serratus + Xenosaurus. UnderAnalysis 1, partial coverage is anautapomorphy of S. crocodilurus. Theancestral state for Xenosaurus + Angu-idae and for Anguidae + Helodermati-dae is ambiguous between absence andpartial coverage. Under Analysis 2,partial coverage is an autapomorphy ofHelodermatidae; the ancestral state forXenosauridae and for S. crocodilurus +M. ornatus is ambiguous between ab-sence and partial coverage.
125. Jugal: Fused osteoderms (0) relativelyunconsolidated, vermiculate plate witha few mounds (Fig. 30B); (1) mostly
consolidated into discrete osteoderms(Fig. 30C).
Variation. Osteoderms fuse tothe jugal during early postnataldevelopment.
Evolution. Under both analyses, allmixed internal nodes are ambiguousregarding ancestral states.
126. Jugal: Ridge between orbital and ad-ductor surfaces (0) at or posterior tomidline of postorbital ramus of jugal(perpendicular to its long axis), orbitalsurface relatively sagittally oriented(Fig. 30D); (1) anterior to midline,orbital surface relatively transverselyoriented (Fig. 31A).
Figure 30. A, Left jugal of Elgaria multicarinata TMM-M 8958, lateral, anterior to the left. Illustrates character 124(0). B, Rightjugal of Restes rugosus YPM PU 14640, lateral, anterior to the right. Illustrates characters 124(1), 125(0), 132(2), 133(0). C, Leftjugal of Exostinus serratus, CT scan of AMNH 1608, lateral, anterior to the left. Illustrates characters 124(2), 125(1), 132(1). D,Left jugal of Xenosaurus newmanorum NAUQSP-JIM uncatalogued specimen, medial, anterior to the right. Illustrates characters126(0), 128(1).
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Evolution. Under both analyses, theancestral state for the entire group is alocation at or posterior to the midline.The ancestral states for the southernclade of Xenosaurus and for S. croco-dilurus + M. ornatus are ambiguousand a location anterior to the midline isan autapomorphy of Helodermatidae.
127. Jugal: Base of postorbital ramus (0) lessextensive perpendicular to its long axisthan base of suborbital ramus orapproximately as extensive (Fig. 31A);(1) more extensive than base of subor-bital ramus (Fig. 31B).
Evolution. Under both analyses, themore extensive morphology is an autapo-morphy of X. platyceps and of X. grandis.
128. Jugal: Adductor surface (0) expandsventrally (Fig. 31C); (1) diminishesventrally, resulting in a longer quadra-tojugal process (Fig. 30D).
Evolution. Under both analyses, ven-tral diminishment is a synapomorphy ofXenosaurus.
129. Jugal: Foramen piercing table at junc-tion of maxillary, orbital, and adductorsurfaces (0) absent (Fig. 31D); (1)present (Fig. 31C).
Evolution. Under both analyses, theancestral states for the entire group andfor Anguimorpha are absence of theforamen. Under Analysis 1, the ancestralstate for S. crocodilurus + Varanidae is
Figure 31. A, Left jugal of Xenosaurus agrenon UTACV r45008, medial, anterior to the right. Illustrates characters 126(1),127(0). B, Left jugal of Xenosaurus platyceps UF 45622, medial, anterior to the right. Illustrates characters 127(1), 130(1), 131(1).C, Left jugal of Exostinus serratus, CT scan of AMNH 1608, medial, anterior to the right. Illustrates characters 126(0), 128(0),129(1), 131(0). D, Left jugal of Shinisaurus crocodilurus UF 72805, medial, anterior to the right. Illustrates characters129(0), 130(0).
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absence of the foramen; that forAnguidae + Xenosaurus is ambiguous,as is that for Helodermatidae + Angu-idae and all nodes therein. UnderAnalysis 2, presence of the foramen isa synapomorphy of E. serratus +Xenosaurus and of C. enneagrammus+ O. ventralis.
130. Jugal: Foramen piercing adductor sur-face just posterior to table at junction ofmaxillary, orbital, and adductor surfac-es (0) absent (Fig. 31D); (1) present(Fig. 31B).
Evolution. Under both analyses, theancestral states for the entire group andfor Anguimorpha are ambiguous. Un-der Analysis 1, the ancestral state for S.crocodilurus + Varanidae and for An-guidae + Helodermatidae is absence ofthe foramen. Under Analysis 2, theancestral state for Anguidae + Varanoi-dea is absence, and that for Xenosaur-idae is ambiguous.
131. Jugal: Anterior expansion at meeting ofanterior and dorsal edges of postorbitalramus (0) absent (Fig. 31C); (1) pres-ent (Fig. 31B).
Evolution. Under both analyses, theancestral states for R. rugosus + Xeno-saurus and E. lancensis + Xenosauruswere ambiguous. The ancestral state forXenosaurus is expansion. Lack of ex-pansion is an autapomorphy of X.rectocollaris.
132. Jugal: Tip of postorbital ramus (0)without strong change in sagittal angleat level of postorbital facet (Estes et al.,1988, Fig. 13B); (1) moderately project-ed posteriorly at beginning of level ofpostorbital facet by less than 20u to longaxis of majority of postorbital ramus(Fig. 30C); (2) strongly projected poste-riorly beginning at level of postorbitalfacet by 20u or more to long axis ofmajority of postorbital ramus (Fig. 30B).
Evolution. Under both analyses, theancestral state for the entire group and
for Anguimorpha is moderate posteriorprojection, as is that for shinisaurs. Theancestral state for Varanidae is lack ofprojection, and that for R. rugosus +Xenosaurus is ambiguous betweenmoderate and strong projection. UnderAnalysis 1, the ancestral state for S.crocodilurus + Varanidae is moderateprojection, as is that for Xenosaurus +Anguidae. The ancestral state for An-guidae + Helodermatidae and forAnguidae is ambiguous between noand moderate projection. Under Anal-ysis 2, the ancestral state for Angui-morpha, Anguidae + Varanoidea, andXenosauridae is moderate projection. Alack of projection is an autapomorphyof C. enneagrammus and a synapomor-phy of Varanoidea.
133. Jugal: Posterior edge of postorbitalramus (0) straight or smoothly curved(Fig. 30B); (1) abruptly angled towardthe vertical at level of postorbital facet(Fig. 3C).
Evolution. Under both analyses,abrupt vertical angulation is a synapo-morphy of X. rackhami + X. grandis.
Postorbital/Postfrontal
The postorbital and postfrontal are un-known in M. ornatus, E. serratus, and E.lancensis. The postorbital is unknown in B.ammoskius. Only the postfrontal ossifies inHelodermatidae and L. borneensis.
134. Postorbital/Postfrontal: Postorbital andpostfrontal (0) remain separate wellafter hatching/birth or throughout on-togeny (Fig. 32A); (1) fuse in lateprenatal or early postnatal ontogeny(Fig. 32B) (see character 14 of Esteset al., 1988).
Variation. As noted, this characterinvolves the assessment of the ontoge-netic stage of a specimen. Justificationsfor age assessments of the fossils weregiven in Materials and Methods.
Evolution. Under both analyses, theancestral state for the entire group
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and for Anguimorpha is lack of fusion,and early fusion is a synapomorphy ofthe southern clade of Xenosaurus.Under Analysis 1, the ancestral statefor S. crocodilurus + Varanoidea isambiguous. Under Analysis 2, earlyfusion is a synapomorphy of Varanusand an autapomorphy of S. crocodilurus.
135. Postorbital/Postfrontal: Angle of post-frontal ‘‘clasp’’ of frontoparietal suture(taken between long axes of anteriorand posterior processes of postfrontal)(0) less than 80u (Fig. 5A); (1) 80u to85u inclusive (Fig. 4A); (2) greater than85u (Fig. 3A).
Evolution. Under both analyses, state2 is ancestral for the entire group. Theancestral state for Xenosaurus is am-biguous between state 2 and state 1.
State 0 is a synapomorphy of X.agrenon + X. rectocollaris and anautapomorphy of X. platyceps.
136. Postorbital/Postfrontal: Dorsal ridgeadjacent to lateral edge of postorbital(0) absent (Fig. 33A); (1) present(Fig. 32B).
Evolution. Under both analyses, ab-sence of a ridge is the ancestral state forthe entire group and for Anguimorpha.Under Analysis 1, presence of a ridge isa synapomorphy of Xenosaurus and anautapomorphy of S. crocodilurus. Un-der Analysis 2, the ancestral state forXenosauridae is ambiguous.
137. Postorbital/Postfrontal: Postorbital (0)relatively flat, lying largely in horizontalplane (Fig. 33A); (1) bearing deep
Figure 32. Skulls, dorsal, anterior to the left: A, Xenosaurus newmanorum, CT scan of UMMZ 126056; B, Xenosaurus rackhami,CT scan of UTEP 4555. A and B illustrate characters 134(0), 134(1), 136(1), 138(0), 139(1), 139(2), 140(0), 140(1), 141(0),141(1), 142(1), 165(1), 165(3), 166(0), 166(1).
XENOSAUR PHYLOGENY N Bhullar 123
flange descending from lateral edge,creating a surface in the sagittal plane,perpendicular to the main body of thebone (Fig. 33B).
Evolution. Under both analyses, theflat morphology is ancestral for theentire group and for Anguimorpha.Under Analysis 1, presence of a flangeis a synapomorphy of Xenosaurus andan autapomorphy of S. crocodilurus.Under Analysis 2, the ancestral state forXenosauridae is ambiguous.
138. Postorbital/Postfrontal: Tip of postor-bital process of postfrontal (0) pointed,formed by meeting of smoothly curv-ing medial and lateral edges (Fig. 32A);(1) squared-off because of posterior
inflection of medial edge in horizontalplane (Fig. 32B).
Evolution. Under both analyses, theancestral state for the entire group andfor Anguimorpha is pointed, and thesquared-off morphology is a synapo-morphy of the southern clade ofXenosaurus and an autapomorphy ofS. crocodilurus. Under Analysis 1, thesquared-off morphology is a synapo-morphy of Varanus and an autapomor-phy of Helodermatidae. Under Analysis2, the ancestral state for Varanoidea isambiguous.
139. Postorbital/Postfrontal: Narrowness ofpostorbital measured by ratio of antero-posterior length to mediolateral width
Figure 33. A, Temporal region of Elgaria multicarinata CAS 85234, dorsolateral, anterior to the left. Illustrates characters 136(0),137(0), 139(0), 142(0). B, Left postorbital of Xenosaurus newmanorum NAUQSP-JIM uncatalogued specimen, dorsolateral,anterior to the left. Illustrates character 137(1). C, Left pterygoid of Shinisaurus crocodilurus UF 72805, ventral, anterior to the left.Illustrates characters 143(0), 145(0). D, Left pterygoid of Xenosaurus newmanorum NAUQSP-JIM uncatalogued specimen,ventral, anterior to the left. Illustrates characters 143(1), 145(2).
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just posterior to divergence of posteriorprocess of postfrontal (0) 4.0 or greater(Fig. 33A); (1) between 2.5 and 4.0(Fig. 32A); (2) 2.5 or less (Fig. 32B).
Evolution. Under both analyses, theancestral state of the entire group andof Anguimorpha is the narrow mor-phology, and the wide morphology is asynapomorphy of X. rackhami + X.grandis. Under Analysis 1, intermediatewidth is a synapomorphy of Xenosaurusand an autapomorphy of S. crocodi-lurus. Under Analysis 2, the ancestralstate for Xenosauridae is ambiguousbetween the narrow and intermediatemorphologies.
140. Postorbital/Postfrontal: Posterior end ofsquamosal process of postorbital (0)pointed (Fig. 32A); (1) rounded(Fig. 32B).
Evolution. Under both analyses, therounded morphology is an autapomor-phy of X. rackhami.
141. Postorbital/Postfrontal: Posterior end ofsquamosal process of postorbital (0)gently curved medially in horizontalp lane or not curved media l ly(Fig. 32A); (1) strongly curved mediallyin horizontal plane, resulting in sharpchange in angle of medial edge(Fig. 32B).
Evolution. Under both analyses,strong curvature is a synapomorphy ofX. rackhami + X. grandis.
142. Postorbital/Postfrontal: Lateral edge ofpostorbital (0) straight or nearly straightin horizontal plane (Fig. 33A); (1)broadly curved in horizontal plane(Fig. 32B).
Evolution. Under both analyses,the ancestral state for Xenosaurus isambiguous.
Pterygoid
The pterygoid is unknown in E. lancensisand E. serratus and is not substantiallyvisible in B. ammoskius.
143. Pterygoid: Margin of pterygoid border-ing infraorbital fenestra (0) smoothlycurved (Fig. 33C); (1) bearing smalleminence just medial of posterior apex(Fig. 33D).
Evolution. Under both analyses,presence of an eminence is a synapo-morphy of the northern clade ofXenosaurus and an autapomorphy ofHelodermatidae.
144. Pterygoid: Medial and lateral edges ofvomerine process posterior to obliqueanterior edge (0) weakly divergent (by20u or less) in horizontal plane(Fig. 34A); (1) strongly divergent (bygreater than 20u) in horizontal plane(Fig. 34B).
Evolution. Under both analyses,strong divergence is an autapomorphyof R. rugosus and of C. enneagrammus.
145. Pterygoid: Bears (0) large row or patchof teeth (Fig. 33C); (1) one or two smallteeth, sometimes bilaterally asymmetri-cal (Fig. 34B); (2) no teeth (Fig. 33D).Presence or absence of pterygoid teethwas character 83 of Estes et al. (1988).
Variation. Pterygoid teeth oftenincrease in number with age (personalobservation), and observations on thischaracter were made using relativelylarge individuals. Additionally, whenteeth are highly reduced, their presencecan vary from side to side in anindividual or from individual to individ-ual in a species (e.g., C. enneagrammus).
Evolution. Under both analyses, re-duction of pterygoid dentition is asynapomorphy of Xenosaurus + R.rugosus and an autapomorphy of C.enneagrammus. Absence of pterygoiddentition is a synapomorphy of Xeno-saurus and of Varanus.
Ectopterygoid
The ectopterygoid is unknown for allextinct taxa in the study (not sufficientlyexposed in B. ammoskius).
XENOSAUR PHYLOGENY N Bhullar 125
146. Ectopterygoid: Prominent descendingprojection of maxillary process (0)absent (Fig. 34C); (1) present (Fig. 34D).
Evolution. Under both analyses,presence of a descending projection isa synapomorphy of Xenosaurus.
Parietal
The parietal is unknown in R. rugosus andE. serratus.
147. Parietal: Ratio of anteroposterior lengthalong midline (to apex of meeting ofsupratemporal processes) to mediolat-eral width at frontoparietal suture(Fig. 34E) (0) less than 0.70; (1) 0.70to less than 0.75; (2) 0.75 to less than
0.80; (3) 0.80 to less than 0.85; (4) 0.85to less than 0.90; (5) 0.90 to less than0.95; (6) 0.95 to less than 1.00; (7) 1.00to less than 1.05; (8) 1.05 to less than1.10; (9) 1.10 to less than 1.15; (A) 1.15to less than 1.20; (B) 1.20 to less than1.25; (C) 1.25 or greater.
Variation. The length-to-width ratioof the parietal body increases withgrowth, especially in the earlier partsof ontogeny (personal observation).Thus, care must be taken to userelatively large adult individuals inscoring this character.
Evolution. Under both analyses, theancestral state for the entire group isambiguous among state 1, state 2, state
Figure 34. Right pterygoids, ventral, anterior to the left: A, Xenosaurus newmanorum NAUQSP-JIM uncatalogued specimen.Illustrates character 144(0). B, Restes rugosus, CT scan of YPM PU 14640. Illustrates characters 144(1), 145(1). Leftectopterygoids, maxillary articulation surfaces, anterior to the left: C, Elgaria multicarinata TMM-M 8958; D, Xenosaurusnewmanorum NAUQSP-JIM uncatalogued specimen. C and D illustrate characters 146(0), 146(1). E, Parietal of Xenosaurusrackhami UTEP-OC ‘‘MALB’’ 388, dorsal, anterior to the left. Illustrates characters 147 (n for numerator, d for denominator),150(0), 151(1), 153(1), 154(1), 156(1).
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3, and state 4. The ancestral state forAnguimorpha is ambiguous betweenstate 3 and state 4. Additionally, theancestral state for S. crocodilurus + M.ornatus is state 5. State 6 is a synapo-morphy of S. crocodilurus + B. ammos-kius, and state 9 is an autapomorphy ofS. crocodilurus. The ancestral state forAnguidae is ambiguous between state 3and state 4. State 7 is an autapomorphyof O. ventralis. State C is an autapo-morphy of E. lancensis. The ancestralstate for Xenosaurus is ambiguousbetween state 3 and state 4. A reducedratio is a synapomorphy of the southernclade of Xenosaurus, whose ancestralstate is ambiguous between state 1 andstate 2. State 0 is a synapomorphy of X.agrenon + X. rectocollaris. State 8 is anautapomorphy of L. borneensis, andstate 0 is an autapomorphy of V.exanthematicus. Under Analysis 1, theancestral state for S. crocodilurus +Varanidae is ambiguous between state4 and state 5, and that for Varanus isstate 4. The ancestral state for Xeno-saurus + Anguidae and for Anguidae +Helodermatidae is ambiguous betweenstate 3 and state 4. Under Analysis 2,the ancestral state for Anguidae +Varanoidea is ambiguous between state3 and state 4, as is that for Varanoideaand all nodes therein. The ancestralstate for Xenosauridae is ambiguousamong state 3, state 4, and state 5, as isthat for Xenosaurus + E. lancensis.
148. Parietal: Ratio of anteroposterior lengthof supratemporal processes beginningat apex of their meeting to mediolateralwidth at widest separation of processes(Fig. 35A) (0) less than 0.20; (1) 0.20 toless than 0.25; (2) 0.25 to less than 0.30;(3) 0.30 to less than 0.35; (4) 0.35 to lessthan 0.40; (5) 0.40 to less than 0.45; (6)0.45 to less than 0.50; (7) 0.50 orgreater.
Variation. The posterior portion ofthe parietal becomes relatively moreelongate with growth, especially in
early ontogeny (personal observation),so it is important to score this characteron relatively large adults.
Evolution. Under both analyses, theancestral state for Varanidae is state 5,and state 7 is an autapomorphy of L.borneensis. State 7 is a synapomorphyof Anguidae. The ancestral state for S.crocodilurus + M. ornatus is state 4,and state 3 is an autapomorphy of S.crocodilurus. Finally, the ancestralstate for Xenosaurus is ambiguousbetween state 2 and state 3. Theancestral state for the northern cladeof Xenosaurus is state 2, and state 0 isan autapomorphy of X. newmanorum.In the southern clade, state 1 is anautapomorphy of X. grandis. UnderAnalysis 1, the ancestral state for theentire group, Anguimorpha, S. croco-dilurus + Varanidae, and Xenosaurus +Anguidae is ambiguous between state 4and state 5. Under Analysis 2, theancestral state for the entire group,Anguimorpha, Anguidae + Varanoidea,and Varanoidea is state 5. State 4 is anautapomorphy of Helodermatidae. Onthe other branch of Anguimorpha, state4 is a synapomorphy of Xenosauridae.
149. Parietal: Attachment areas for adductormusculature (0) dorsolateral or lateral,without extensive overhanging flange;(1) ventral, roofed over by flange ofparietal table (Fig. 35B) (see character54 of Estes et al., 1988).
Variation. Although the overhangingflange in those taxa with ventral originoften becomes relatively more exten-sive with age, I did not observeintraspecies variation that would alterthe scoring of the character.
Evolution. Under both analyses, theancestral state for Xenosaurus + E.lancensis is ventral origin. Under Anal-ysis 1, the ancestral state for the entiregroup and for Anguimorpha is dorsalorigin, and ventral origin is a synapo-morphy of Xenosaurus + Anguidae.
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Note that this is dependent upon theuse of an iguanian as the immediateanguimorph outgroup. Most sclero-glossans show ventral origin (Esteset al., 1988). Under Analysis 2, theancestral state for all mixed nodes isambiguous.
150. Parietal: Lateral edges forming marginsof supratemporal fenestrae (0) stronglycurved in a horizontal plane (Fig. 34E);(1) weakly curved, especially anterior toapex of temporal emargination(Fig. 35A).
Variation. In the taxa showing lateralor dorsolateral origin of the adductormusculature (character 149-0), the
degree of emargination increases withage as the braincase becomes relativelysmaller and the adductor chamberrelatively larger.
Evolution. Under both analyses, rel-atively weak curvature is an autapo-morphy of X. agrenon.
151. Parietal: Number of osteoderms oneach side lateral to midline osteodermjust posterior to parietal foramen (0)three (Fig. 1A); (1) two (Fig. 34E); (2)one (Conrad, 2006, fig. 2A).
Evolution. Under both analyses, theancestral state for the entire group isambiguous between three osteodermsand two osteoderms. The ancestral
Figure 35. A, Parietal of Xenosaurus agrenon UTACV r45008, dorsal, anterior to the left. Illustrates characters 148 (n fornumerator, d for denominator), 150(1), 152(1), 153(0), 155(2), 156(0). B, Parietal of Elgaria multicarinata TMM-M 8958, ventral,anterior to the left. Illustrates characters 149(1), 152(0), 155(0), 157(0). C, Parietal of Xenosaurus platyceps UF 45622, ventral,anterior to the left. Illustrates characters 154(2), 155(1), 157(1). D, Parietal of Xenosaurus newmanorum NAUQSP-JIMuncatalogued specimen, ventral, anterior to the left. Illustrates characters 154(3), 158(1).
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state for shinisaurs is two osteodermsand one osteoderm is an autapomorphyof M. ornatus.
152. Parietal: Parietal foramen (0) set farback from frontoparietal suture, con-siderably posterior to anterolateral ex-tensions of parietal bearing postfrontalfacets (Fig. 35B); (1) set close tofrontoparietal suture, at anteroposteriorlevel of anterolateral extensions bearingpostfrontal facets (Fig. 35A).
Variation. State 0 reportedly occursin some S. crocodilurus (J. L. Conrad,personal communication), although notin the specimens examined.
Evolution. Under both analyses, theancestral state for the entire group andfor Anguimorpha is ambiguous. UnderAnalysis 1, the ancestral state forXenosaurus + Anguidae and for Helo-dermatidae + Anguidae is ambiguous.The ancestral state for E. multicarinata+ O. ventralis is relatively posteriorplacement. Under Analysis 2, the an-cestral state for S. crocodilurus +Varanoidea is the relatively posteriorplacement, with placement close to thefrontoparietal suture an autapomorphyof S. crocodilurus. The ancestral statefor Anguidae + Helodermatidae isambiguous. Under Analysis 2, theancestral state for Anguidae + Varanoi-dea is relatively posterior placement.
153. Parietal: Parietal foramen (0) relativelylarge (Fig. 35A); (1) small, barely largerthan tiny nutrient foramina (Fig. 34E).
Evolution. Under both analyses, thesmall morphology is an autapomorphyof X. rackhami.
154. Parietal: Anterior edge in horizontalplane (0) convex (Conrad, 2006, fig.2A); (1) relatively straight (Fig. 34E);(2) slightly concave (Fig. 35C); (3)strongly concave (Fig. 35D).
Evolution. Under both analyses, theancestral state for the entire groupis ambiguous among straight, slightly
concave, and strongly concave. The an-cestral state for shinisaurs is relativelystraight and a convex morphology is anautapomorphy of B. ammoskius. Theancestral state for Anguidae and xenosaursis also straight, with convex an autapo-morphy of E. lancensis, slightly concave asynapomorphy of the northern cladeof Xenosaurus, and strongly concavean autapomorphy of X. newmanorum.Strongly concave is an autapomorphy ofL. borneensis. Under Analysis 1, therelatively straight morphology is ancestralfor Anguimorpha, and slightly concave isan autapomorphy of Helodermatidae.Under Analysis 2, the ancestral state forAnguimorpha is ambiguous between rel-atively straight and slightly concave.
155. Parietal: Notch in posterior edge ofparietal at meeting of medial edges ofsupratemporal processes (0) absent(Fig. 35B); (1) weak, more than fourtimes as mediolaterally wide as antero-posteriorly long (Fig. 35C); (2) strong,four times or less as mediolaterally wideas anteroposteriorly long (Fig. 35A).
Evolution. Under both analyses,the ancestral state for the entiregroup and for Anguimorpha is ambig-uous between weakly notched andstrongly notched, as are the ancestralstates for Varanidae and Anguidae.The absence of a notch is a synapo-morphy of shinisaurs and an autapo-morphy of E. multicarinata, Heloder-matidae, and V. exanthematicus. Theancestral state for E. lancensis +Xenosaurus is weakly notched. Thestrongly notched morphology is asynapomorphy of X. agrenon + X.rectocollaris, and absence of a notchis a synapomorphy of X. rackhami + X.grandis. Under Analysis 1, the ances-tral state for shinisaurs + Varanidae isambiguous between weakly andstrongly notched, as is that for Xeno-saurus + Anguidae. Under Analysis 2,the ancestral state for Xenosauridae isweakly notched.
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156. Parietal: Dorsal fossae for m. articulo-parietalis attachment (0) shallow, onlyslightly stepped down from parietaltable (Fig. 35A); (1) deep, divided fromparietal table by sharp ridge along atleast part of fossa (Fig. 34E).
Variation. The relative depth of thefossae increases somewhat with age,most prominently in the early stages ofpostnatal ontogeny.
Evolution. Under both analyses, theancestral condition for the entire group isambiguous, and the deep morphology isa synapomorphy of X. rackhami + X.grandis and an autapomorphy of C.enneagrammus. Under Analysis 1, theancestral state for Anguimorpha is am-biguous, and the ancestral state for
Xenosaurus + Anguidae is the shallowmorphology. Under Analysis 2, theancestral state for Anguimorpha is theshallow morphology, and the deep mor-phology is a synapomorphy of Varanidae.
157. Parietal: Ventral excavations on supra-temporal processes for transversospina-lis group muscles (0) widely separatedby sulcus processi ascendentis (Fig.35B); (1) moderately separated;bridged by flange of parietal extendingposteriorly past sulcus processi ascen-dentis but do not approach each otherclosely, leaving between them a broadtriangular wedge of cerebral table(Fig. 35C); (2) approach each otherclosely, leaving between them only athin ridge of cerebral table (Fig. 36A).
Figure 36. Parietals, ventral, anterior to the left: A, Heloderma suspectum TMM-M 9001. Illustrates character 157(2). B,Xenosaurus grandis NAUQSP-JIM 1460. Illustrates character 158(0). Left supratemporals, lateral, anterior to the left: C,Xenosaurus newmanorum NAUQSP-JIM uncatalogued specimen; D, Xenosaurus grandis NAUQSP-JIM 1460. E, Xenosaurusagrenon UTACV r45008. C through E illustrate characters 159(0), 159(1), 160(0), 160(1), 161(1), 162(1), 163(0), 163(1), 163(2).
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Evolution. Under both analyses,widely separated is the ancestral statefor the entire group and for Anguimor-pha. The ancestral state for E. lancensis+ Xenosaurus is moderately separated,and that for the southern clade ofXenosaurus is ambiguous betweenmoderately separated and closely ap-proaching. Closely approaching is anautapomorphy of Helodermatidae. Un-der Analysis 1, the ancestral state forXenosaurus + Anguidae is ambiguousbetween closely approaching and mod-erately separated. Under Analysis 2, theancestral state for Xenosauridae iswidely separated, and moderately sep-arated is a synapomorphy of Xeno-saurus + E. lancensis.
158. Parietal: Ventral ridges contacting tae-niae marginales (0) also bound adductorattachment surface medially for entirelength (Fig. 35D); (1) diverge just pos-terior to level of prefrontal facet fromridge delineating medial margin ofadductor attachment surface (Fig. 36B).
Evolution. Under both analyses, divergence is a synapomorphy of thenorthern clade of Xenosaurus.
Supratemporal
The supratemporal is unknown for allextinct taxa save B. ammoskius, in which anegligible amount of its morphology is visible.
159. Supratemporal: Anterior edge (0) dor-soventrally short, less than half greatestheight of supratemporal (Fig. 36D); (1)dorsoventrally tall, more than halfgreatest dorsoventral height of supra-temporal (Fig. 36C).
Evolution. Under both analyses, theancestral state for the entire group andfor Anguimorpha is the short morphol-ogy. Under Analysis 1, the ancestralstate for Xenosaurus is ambiguous, andthe tall morphology is an autapomorphyof S. crocodilurus. Under Analysis 2,the tall morphology is a synapomorphyof Xenosauridae and the short mor-
phology is a synapomorphy of X.rackhami + X. grandis.
160. Supratemporal: Foramen piercing lat-eral surface near ridge dividing squa-mosal facet and adductor attachmentsurface about two-thirds of the way toposterior end of supratemporal (0) pre-sent (Fig. 36E); (1) absent (Fig. 36D).
Evolution. Under both analyses, theancestral state for the entire group isambiguous, and absence of the foramenis a synapomorphy of X. rackhami + X.grandis. Under Analysis 1, the ancestralstate for Anguimorpha is ambiguous,and the ancestral state for Xenosaurus+ Anguidae is presence of the foramen.Under Analysis 2, the ancestral state forAnguimorpha is presence of the fora-men, and absence is a synapomorphy ofVaranidae and of X. rackhami + X.grandis.
161. Supratemporal: Foramen piercing lat-eral surface (0) above (Fig. 37A); (1)below ridge dividing squamosal facetand adductor attachment surface(Fig. 36E).
Evolution. Under both analyses, aventral position is a synapomorphy ofXenosaurus.
162. Supratemporal: Ventral flange wrap-ping under supratemporal process ofparietal (0) smoothly curved alongventromedial edge (Fig. 37A); (1) pro-duced into wedge (Fig. 36C).
Evolution. Under both analyses, theancestral state for the entire groupand Anguimorpha is smoothly curved.Under Analysis 1, production into awedge is an autapomorphy of S.crocodilurus and a synapomorphy ofXenosaurus. Under Analysis 2, produc-tion into a wedge is a synapomorphy ofXenosauridae.
163. Supratemporal: Wedge-shaped ventralflange wrapping under supratemporalprocess of parietal (0) small and nub-like (Fig. 36E); (1) squat, obtuse wedge
XENOSAUR PHYLOGENY N Bhullar 131
(Fig. 36C); (2) sharp, more acutewedge (Fig. 36D).
Evolution. Under both analyses, theancestral state is squat and obtuse. Thesmall, nub-like morphology is a synapo-morphy of X. agrenon + X. rectocollaris,and the sharp, acute morphology is a syn-apomorphy of X. rackhami + X. grandis.
Squamosal
The squamosal is unknown for all of theextinct taxa.
164. Squamosal: Posterior portion (0) unex-panded mediolaterally (Fig. 37B); (1)mediolaterally expanded (Fig. 37C).The presence or absence of a canthal
crest in the temporal region was men-tioned as a possible synapomorphy ofXenosauridae by Estes et al. (1988).
Evolution. Under both analyses, expansion is the ancestral state for theentire group and for Anguimorpha.Under Analysis 1, narrowness is asynapomorphy of Varanidae and ofAnguidae + Helodermatidae. UnderAnalysis 2, narrowness is a synapomor-phy of Anguidae + Varanoidea.
165. Squamosal: Dorsal ridge adjacent tolateral edge (0) absent (Fig. 37D); (1)relatively low (Fig. 32A); (2) interme-diate height (Fig. 5A); (3) pronounced(Fig. 32B).
Figure 37. A, Left supratemporal of Elgaria multicarinata TMM-M 8958, lateral, anterior to the left. Illustrates characters 161(0),162(0). Left squamosals, ventral, anterior to the left: B, Elgaria multicarinata TMM-M 8958. Illustrates character 164(0). C,Xenosaurus newmanorum NAUQSP-JIM uncatalogued specimen. Illustrates characters 164(1), 167, 169(3). Left squamosals,lateral, anterior to the left: D, TMM-M 8956. Illustrates characters 165(0), 168(0), 169(0). E, Xenosaurus newmanorum NAUQSP-JIM uncatalogued specimen; F, Xenosaurus grandis NAUQSP-JIM 1460. E illustrates 168(1) and F illustrates 168(2).
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Evolution. Under both analyses,presence of a low ridge is a synapomor-phy of Xenosaurus, presence of a ridgeof intermediate height is a synapomor-phy of the southern clade of Xenosaurus,and presence of a sharp ridge is anautapomorphy of X. rackhami.
166. Squamosal: Dorsal ridge adjacent tolateral edge (0) most prominent poste-riorly (Fig. 32A); (1) most prominentanteriorly (Fig. 32B).
Evolution. Under both analyses, an-terior prominence is an autapomorphyof X. agrenon and of X. rackhami.
167. Squamosal: Width, assessed by ratio ofmediolateral width at anteroposteriorlevel of closure of supratemporal fe-nestra to anteroposterior length ofsquamosal (Fig. 37C) (0) 0.15 or less;(1) 0.15 to 0.30; (2) 0.30 to 0.40; (3)0.40 or above.
Evolution. Under both analyses, theancestral state for the entire group andfor Anguimorpha is ambiguous be-tween state 1 and state 2. The ancestralstate for Xenosaurus is state 2, and state3 is a synapomorphy of X. rackhami +X. grandis. Under Analysis 1, theancestral state for Shinisaurus + Var-anidae is state 1, and state 0 is asynapomorphy of Varanidae. UnderAnalysis 2, state 0 is a synapomorphyof Anguidae + Varanoidea.
168. Squamosal: Suspensorial end curvaturein a sagittal plane (0) without abruptterminal hook (Fig. 37D); (1) terminalhook present and reaches the verticalor only slightly beyond the vertical(Fig. 37E); (2) terminal hook progress-es well beyond the vertical, foldingunder the remainder of the squamosaland extending anteriorly for a shortdistance (Fig. 37F).
Evolution. Under both analyses, cur-vature of the hook to near the vertical is asynapomorphy of Xenosaurus, and curva-ture well beyond the vertical is a synap-omorphy of X. rackhami + X. grandis.
169. Squamosal: Ventral ridge dividing at-tachment surface for m. anguli oris 1aand m. adductor mandibularis externussuperficialis 1b from that for m. adduc-tor mandibularis externus medialis andm. adductor mandibularis externusprofundus (0) absent (Fig. 37D); (1)uniformly weak (Fig. 38A); (2) sharponly in posterior portion of squamosal(Fig. 38B); (3) sharp and well-definedfor most of length of squamosal(Fig. 37C).
Evolution. Under both analyses, ab-sence of a ridge is ancestral for theentire group and for Anguimorpha. Asharp ridge is an autapomorphy of E.multicarinata, and a ridge of mixedprominence is ancestral for X. rack-hami + X. grandis, whereas a weakridge is an autapomorphy of X. rack-hami. Under Analysis 1, a sharp ridgeis an autapomorphy of S. crocodilurus.The ancestral state for Xenosaurus isambiguous between a ridge of mixedprominence and a sharp ridge, as isthat for the southern clade of Xeno-saurus. Under Analysis 2, a sharp ridgeis a synapomorphy of Xenosauridae,and a ridge of mixed prominence is asynapomorphy of X. rackhami + X.grandis.
Quadrate
The quadrate is unknown in the fossilxenosaurs and in M. ornatus.
170. Quadrate: Two-thirds or more of theway down its dorsoventral height,lateral edge of tympanic crest (0)abruptly angles medially in plane ofthe crest, possibly associated withattachment of lateral collateral ligamentand other connective tissue (Fig. 38C);(1) curves smoothly without abruptmedial angulation (Fig. 38E).
Evolution. Under both analyses, lackof a medial deflection is a synapomor-phy of Varanidae and of X. agrenon + X.
XENOSAUR PHYLOGENY N Bhullar 133
rectocollaris. Under Analysis 1, theancestral state for Anguidae is ambig-uous. Under Analysis 2, lack of adeflection is a synapomorphy of C.enneagrammus + O. ventralis.
171. Quadrate: Anteromedial emarginationof dorsal surface of cephalic condyle (0)relatively deep, enclosing angle of 35uor more (Fig. 39A); (1) relatively shal-low, enclosing angle of less than 35u(Fig. 39C).
Evolution. Under both analyses, theshallow morphology is a synapomorphyof X. agrenon + X. rectocollaris.
172. Quadrate: Posterior eminence fromlateralmost portion of dorsal surface ofcephalic condyle (0) small, rounded
bump (Fig. 39A); (1) pronouncedwedge (Fig. 39B).
Evolution. Under both analyses, theancestral state for the entire group isambiguous; that for Anguimorpha isthe small, bump-like morphology; andthe wedge morphology is a synap-omorphy of X. rackhami + X. grandis.
173. Quadrate: Depression for tympaniccavity (0) strong, deeply concave pos-teriorly in horizontal plane (Fig. 38C);(1) weak, weakly concave posteriorly inhorizontal plane (Fig. 38D).
Variation. The depression for thetympanic cavity deepens with age, butrelative differences can still be ob-served in early postnatal individuals.
Figure 38. Left squamosals, ventral, anterior to the left: A, Xenosaurus rackhami UTEP-OC ‘‘MALB’’ 388. Illustrates character169(1). B, Xenosaurus grandis NAUQSP-JIM 1460. Illustrates character 169(2). Left quadrates, posterior: C, Elgaria multicarinataTMM-M 8958; D, Xenosaurus newmanorum NAUQSP-JIM uncatalogued specimen. C and D illustrate characters 170(0), 173(0),173(1). E, Xenosaurus agrenon UTACV r45008. Illustrates character 170(1).
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Evolution. Under both analyses, theshallow morphology is a synapomorphyof Xenosaurus and of Varanidae.
Braincase
The braincase is unknown for all extincttaxa save B. ammoskius, in which it is largelyobscured.
174. Braincase: Ratio of greatest mediolat-eral width to anteroposterior lengthfrom posterior end of paroccipitalprocess anteriorly to level of anteriorend of alar process (Fig. 39C) (0) 1.20or less; (1) between 1.20 and 1.50; (2)1.50 or greater.
Variation. The proportions of thebraincase vary significantly during
ontogeny (Barahona and Barbadillo,1998; Bever et al., 2005). In particular,the paroccipital processes become rel-atively longer with the relative expan-sion of the adductor chamber relativeto the brain, and the alar processes ofthe prootic lengthen. This charactermust be evaluated on relatively large,adult individuals with fused braincases.
Evolution. Under both analyses, aratio of 1.20 or less is an autapomorphyof X. newmanorum. Under Analysis 1,the ancestral state for the entire groupand for Anguimorpha is 1.50 or greater.A ratio of 1.20 to 1.50 is an autapomor-phy of S. crocodilurus, a synapomorphyof Anguidae, and a synapomorphy of X.rackhami + X. grandis. A ratio of 1.20 or
Figure 39. Left quadrates, dorsal, anterior to the top: A, Xenosaurus newmanorum NAUQSP-JIM uncatalogued specimen; B,Xenosaurus grandis NAUQSP-JIM 1460. A and B illustrate characters 171(0), 172(0), 172(1). C, Xenosaurus agrenon UTACVr45008. Illustrates character 171(1). D, Braincase of Xenosaurus newmanorum NAUQSP-JIM uncatalogued specimen, dorsal,anterior to the top. Illustrates characters 174, 181(0).
XENOSAUR PHYLOGENY N Bhullar 135
less is a synapomorphy of E. multi-carinata + O. ventralis. Under Analysis2, the ancestral state for the entire groupand Anguimorpha is ambiguous be-tween 1.20 to 1.50 and 1.50 or greater.The ancestral state for Anguidae isambiguous between 1.20 or less and1.20 to 1.50.
175. Braincase: Carotid fossa and retractor pits(0) shallow, barely excavated (Fig. 40A);(1) deeply excavated (Fig. 40B).
Variation. The carotid fossa andretractor pits deepen somewhat withage, and only relatively large adultswere scored.
Evolution. Under both analyses, theshallow morphology is the ancestralstate for the entire group and for
Anguimorpha and the ancestral statefor Xenosaurus is ambiguous. UnderAnalysis 1, the ancestral state for Xeno-saurus + Anguidae and all mixed nodestherein is ambiguous. Under Analysis 2,the ancestral state for Xenosauridae andfor Anguidae + Varanoidea is theshallow morphology. The deep mor-phology is an autapomorphy of O.ventralis and of Helodermatidae.
176. Braincase: Domed portion of ventralsurface spanning sphenoid/basioccipitalsuture (0) divided into bilateral swell-ings with median groove (Fig. 40C); (1)projected into a single swelling withoutmidline groove, bearing small tubercleslightly posterior to apex of dome inbasioccipital region (Fig. 40D).
Figure 40. A, Braincase of Xenosaurus agrenon UTACV r45008, anterior. Illustrates character 175(0). B, Braincase ofXenosaurus platyceps UF 45622, anterior. Illustrates character 175(1). C, Braincase of Xenosaurus grandis NAUQSP-JIM 1460,ventral, anterior to the left. Illustrates character 176(0). D, Braincase of Xenosaurus agrenon UTACV r45008, ventral, anterior tothe left. Illustrates character 176(1).
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Evolution. Under both analyses,the undivided morphology is anautapomorphy of C. enneagrammusand a synapomorphy of X. agrenon +X. rectocollaris. Under Analysis 1,the ancestral state for the entiregroup and for Anguimorpha is am-biguous. The ancestral state for Xe-nosaurus + Anguidae is the dividedmorphology. Under Analysis 2, theancestral state for the entire group,Anguimorpha, Xenosauridae, and An-guidae + Varanoidea is the dividedmorphology.
177. Braincase: Sphenooccipital tubercles(0) rounded and blunt (Fig. 41A); (1)acutely pointed (Fig. 41B).
Variation. The sphenooccipital tubercles become more prominent withage, and their terminal shape forms in thelater stages of postnatal ontogeny; thischaracter should be scored on relativelylarge adults with fused braincases.
Evolution. Under both analyses, thepointed morphology is an autapomor-phy of O. ventralis and of X. rackhami.
178. Braincase: Recessus vena jugularis (0)ends anteriorly behind anterior tip ofalar process of sphenoid (Fig. 41C); (1)extends along entirety of lateral surfaceof alar process (Fig. 41D).
Variation. The recessus vena jugu-laris and the alar process of the sphenoid
Figure 41. A, Braincase of Xenosaurus newmanorum NAUQSP-JIM uncatalogued specimen, left lateral, anterior to the left.Illustrates character 170(0). B, Braincase of Xenosaurus rackhami UTEP-OC ‘‘MALB’’ 388, left lateral, anterior to the left.Illustrates character 177(1). C, Braincase of Xenosaurus grandis NAUQSP-JIM 1460, left ventrolateral, anterior to the left.Illustrates character 178(0). D, Braincase of Xenosaurus newmanorum NAUQSP-JIM uncatalogued specimen, left ventrolateral,anterior to the left. Illustrates character 178(1).
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both develop largely after hatching. Thischaracter should be scored on relativelylarge adults.
Evolution. Under Analysis 1, exten-sion to the anterior end of the alarprocess is an autapomorphy of S.crocodilurus and a synapomorphy ofthe northern clade of Xenosaurus.Under Analysis 2, the ancestral statefor Xenosauridae is ambiguous and theancestral state for the southern clade ofXenosaurus is ending posterior to thetip of the alar process.
179. Braincase: Constriction of odontoidrecess (notochordal groove) in dorsalmargin of occipital condyle, measuredby angle through highest points ofnotch and deepest point (0) greater
than 120u (Fig. 42A); (1) 120u or less(Fig. 42B).
Variation. The recess becomessomewhat more constricted with ageand should be scored on relatively largeadults.
Evolution. Under both analyses, anangle of 120u or less is an autapomor-phy of O. ventralis and a synapomorphyof X. rackhami + X. grandis.
180. Braincase: Cava capsulares withinbraincase (0) leave relatively wide spacebetween them—mediolateral separa-tion at closest approach greater thanone-quarter mediolateral width of fo-ramen magnum at that dorsoventrallevel (Fig. 42A); (1) approach closely—mediolateral separation at closest ap-
Figure 42. A, Braincase of Xenosaurus newmanorum NAUQSP-JIM uncatalogued specimen, posterior. Illustrates characters179(0), 180(0). B, Braincase of Xenosaurus grandis NAUQSP-JIM 1460, posterior. Illustrates characters 179(1), 180(1). C,Braincase of Xenosaurus rackhami UTEP-OC ‘‘MALB’’ 388, dorsal, anterior to the top. Illustrates character 181(1). D, Braincaseof Xenosaurus newmanorum NAUQSP-JIM uncatalogued specimen, posterior. Illustrates characters 182(0), 183(1).
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proach one-quarter or less mediolateralwidth of foramen magnum at thatdorsoventral level (Fig. 42B).
Variation. The approach of the cavacapsulares increases somewhat with ageand should be scored in relatively largeadults.
Evolution. Under both analyses,close approach is an autapomorphy ofO. ventralis and of X. grandis.
181. Braincase: Paroccipital processes (0)distinctly posterolaterally directed(Fig. 39D); (1) only slightly posterolat-erally directed, nearly oriented medio-laterally (Fig. 42C).
Variation. The posterior direction ofthe paroccipital processes tends to
increase with age and should be scoredin relatively large adults.
Evolution. Under Analysis 1, theancestral state for the entire groupand Anguimorpha, as well as all internalmixed nodes, is ambiguous. UnderAnalysis 2, the ancestral state for theentire group and for Anguimorpha islateral extension. Posterolateral exten-sion is a synapomorphy of C. ennea-grammus + O. ventralis and an autapo-morphy of L. borneensis. The ancestralstate for Xenosauridae is ambiguous.
182. Braincase: Expanded tips of paroccipi-tal processes—ventral projections (0)absent (Fig. 42D); (1) present, squaredoff or blunt (Fig. 43A); (2) present,long and pointed (Fig. 43B).
Figure 43. A, Braincase of Xenosaurus agrenon UTACV r45008, posterior. Illustrates characters 182(1), 183(0). B, Braincase ofXenosaurus grandis NAUQSP-JIM 1460, posterior. Illustrates character 182(2). C, Left dentary of Xenosaurus rackhami UTEP-OC ‘‘MALB’’ 388, medial, anterior to the right. Illustrates characters 185(0), 197(1). D, Right dentary of Exostinus serratus, CTscan of AMNH 1608, lateral, anterior to the right. Illustrates characters 185(1), 186(1), 195(1), 196(1).
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Variation. The projections becomemore prominent during early postnatalontogeny and should be scored inrelatively large adults.
Evolution. Under both analyses, ab-sence of projections is an autapomorphyof S. crocodilurus and of X. newma-norum. Under Analysis 1, the ancestralstate for the entire group and forAnguimorpha is ambiguous betweensquared off and long and pointed, as isthat for S. crocodilurus + Varanidae,Xenosaurus + Anguidae, and Xeno-saurus. Under Analysis 2, the ancestralstate for the entire group and forAnguimorpha is long and pointed. Bluntor squared-off is an autapomorphy ofHelodermatidae and a synapomorphy ofXenosauridae. Within Xenosauridae, thelong and pointed state is a synapomor-phy of X. rackhami + X. grandis.
183. Braincase: Expanded tips of paroccipi-tal processes—dorsal projections (0)present as blunt or squared off tab(Fig. 43A); (1) low, barely divergent(Fig. 42D).
Variation. Dorsal projections tend tobecome more prominent during post-natal ontogeny and should be scored inrelatively large adults.
Evolution. Under Analysis 1, theancestral state for the entire groupand all mixed nodes therein is ambig-uous. Under Analysis 2, the ancestralstate for the entire group and forAnguimorpha is presence of relativelyextensive projections. The low androunded morphology is a synapomor-phy of Varanoidea and the northernclade of Xenosaurus and an autapo-morphy of C. enneagrammus.
Dentary
184. Dentary: Anterior tip of dentary (0)relatively pointed in sagittal plane(Fig. 1A); (1) blunt, truncated, withsteeply rising ‘‘chin’’ (genioglossus at-tachment area).
Evolution. Under both analyses, theancestral state for the entire group andfor Anguimorpha is the relatively point-ed morphology. The ancestral state forE. lancensis + Xenosaurus is ambiguous,and the ancestral state for Xenosaurus ispointed.
185. Dentary: Posterior, rising section ofdorsal edge of dentary extends for (0)more than six tooth positions (Fig.43C); (1) six or fewer tooth positions(Fig. 43D).
Evolution. Under Analysis 1, theancestral state for the entire group isambiguous, and the ancestral state forAnguimorpha is six or fewer toothpositions. More than six tooth posi-tions is a synapomorphy of O. ventralis+ E. multicarinata and an autapomor-phy of M. ornatus. The ancestral statefor Xenosaurus + E. lancensis isambiguous, as is that of Xenosaurus +E. serratus. Under Analysis 2, theancestral state for the entire groupand for Anguimorpha is more than sixtooth positions. Six or fewer toothpositions is a synapomorphy of Var-anoidea and S. crocodilurus + B.ammoskius and an autapomorphy ofC. enneagrammus, R. rugosus, and E.serratus.
186. Dentary: Groove anterior to coronoidfacet on lateral surface of dentary (0)shallow and short, not approachingposteriormost mental foramen (Fig.44A); (1) deep and long, approachingor running to posteriormost mentalforamen (Fig. 43D).
Evolution. Under both analyses, theancestral state for the entire group andfor Anguimorpha is the shallow, shortmorphology. Under Analysis 1, thedeep, long morphology is a synapo-morphy of Xenosaurus + R. rugosus andan autapomorphy of S. crocodilurus.Under Analysis 2, the deep, longmorphology is a synapomorphy ofXenosauridae.
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187. Dentary: Lateral coronoid facet (0)shallowly impressed, surrounded dor-sally and anteriorly by low ridge(Fig. 44B); (1) deeply impressed, sur-rounded by sharp ridge (Fig. 44C).
Evolution. Under both analyses,deep impression with a sharp ridge isa synapomorphy of the northern cladeof Xenosaurus and an autapomorphy ofC. enneagrammus.
188. Dentary: Coronoid process (0) extend-ing posteriorly beyond surangular pro-cess (Fig. 44A); (1) ending anterior totip of surangular process (Fig. 44D).
Evolution. Under both analyses, theancestral state for the entire group isambiguous, and that for Anguimorphais extension beyond the surangular
process. Ending anterior to the suran-gular process is a synapomorphy of X.agrenon + X. rectocollaris and anautapomorphy of S. crocodilurus andof Helodermatidae.
189. Dentary: Surangular notch betweensurangular and angular process (0)absent (Estes et al., 1988, fig. 11B);(1) present (Fig. 44D). Presence orabsence of a surangular notch wascharacter 63 of Estes et al. (1988).
Evolution. Under both analyses, theancestral state of the entire group isambiguous.
190. Dentary: Tip of angular process (0)pointed (Fig. 44B); (1) blunt andslightly bifurcated (Fig. 44D).
Figure 44. A, Left dentary of Elgaria multicarinata TMM-M 8958, lateral, anterior to the left. Illustrates characters 186(0), 188(0). B,Left dentary of Xenosaurus grandis NAUQSP-JIM 1460, lateral, anterior to the left. Illustrates characters 187(0), 190(0). C, Leftdentary of Xenosaurus newmanorum NAUQSP-JIM uncatalogued specimen, lateral, anterior to the left. Illustrates character 187(1).D, Left dentary of Xenosaurus agrenon UTACV r45008, lateral, anterior to the left. Illustrates characters 188(1), 189(1), 190(1).
XENOSAUR PHYLOGENY N Bhullar 141
Evolution. Under both analyses, ablunt, slightly bifurcated angular pro-cess is a synapomorphy of X. agrenon +X. rectocollaris.
191. Dentary: Suprameckelian lip (0) be-comes dorsoventrally taller anteriorly,but Meckel’s groove remains fairlywidely open (Fig. 45A); (1) becomesdorsoventrally tall anteriorly, restrictingMeckel’s groove to thin slit (Fig. 45B).
Evolution. Under both analyses, theancestral state for Xenosaurus + R.rugosus and Xenosaurus + E. lancensiswas ambiguous.
192. Dentary: Wedge-shaped process extend-ing posteriorly from suprameckelian lip
near posterior end of dental gutter (0)absent (Fig. 45C); (1) present (Fig. 45D).
Evolution. Under both analyses, thepresence of a wedge-shaped process isan autapomorphy of E. serratus.
193. Dentary: Apex of posterior u-shapedemargination in intramandibular septum(Fig. 45A) at level of (0) third or fewertooth position from back of dentary; (1)fourth tooth position from back; (2) fifthtooth position from back; (3) sixth ormore tooth position from back.
Evolution. Under both analyses, theancestral state for Xenosaurus + R.rugosus is at the level of the fourthtooth position from the back, and the
Figure 45. A, Left dentary of Shinisaurus crocodilurus UF 72805, medial, anterior to the right. Illustrates characters 191(0), 193,195(2). B, Left and right dentaries of Restes rugosus YPM PU 14640, lateral and medial, respectively, anterior to the left.Illustrates character 191(1). C, Left dentary of Xenosaurus rectocollaris, CT scan of UF 51443, dorsal, anterior to the left.Illustrates characters 192(0), 194(0). D, Right dentary of Exostinus serratus, CT scan of AMNH 1608, dorsal, anterior to the left.Illustrates characters 192(1), 194(1).
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state for Xenosaurus + E. lancensis andXenosaurus + E. serratus is ambiguousbetween the fourth and fifth toothposition from the back. The ancestralstate for Xenosaurus is the fifth toothposition from the back. A position at thelevel of the fourth tooth position from theback is an autapomorphy of X. grandis,and one at the level of the sixth from theback is an autapomorphy of X. new-manorum. Finally, a position at the levelof the sixth from the back is anautapomorphy of E. multicarinata. Un-der Analysis 1, the ancestral state for theentire group, for Anguimorpha, S. croco-dilurus + Varanidae, Xenosaurus + An-guidae, and Anguidae + Helodermatidae,is the third or fewer tooth position fromthe back. A position at the level of thefourth tooth position from the back is asynapomorphy of Xenosaurus + R. rugo-sus, of E. multicarinata + O. ventralis andof S. crocodilurus + M. ornatus. UnderAnalysis 2, the ancestral state for theentire group and for Anguimorpha isambiguous between the third and fourthtooth positions from the back. That forXenosauridae is the fourth tooth positionfrom the back, and that for Varanoidea isthe third from the back.
194. Dentary: Posterior end of tooth row inhorizontal plane (0) relatively straight orwith slight medial inflection (Fig. 45C); (1)with marked medial inflection (Fig. 45D).
Evolution. Under both analyses, me-dial inflection is an autapomorphy of E.serratus.
195. Dentary: Tooth height (0) short, withone-third or less of most teeth extend-ing above dorsal margin of dentary(Fig. 45A); (1) intermediate height,between one-third and half of mostteeth extending above dorsal margin ofdentary (Fig. 46A); (2) tall, with half ormore of most teeth extending abovedorsal margin of dentary (Fig. 46B).
Evolution. Under both analyses, theancestral state for the entire group is
ambiguous between tall and interme-diate height, and the ancestral state forAnguimorpha is intermediate height.The ancestral state for Xenosaurus + R.rugosus is intermediate height, and theshort morphology is a synapomorphy ofXenosaurus. Under Analysis 1, theancestral state for Xenosaurus + Angu-idae is intermediate height. The tallmorphology is a synapomorphy of S.crocodilurus + Varanidae and an auta-pomorphy of Helodermatidae. UnderAnalysis 2, the ancestral state forAnguidae + Varanoidea and for Xeno-sauridae is intermediate height. The tallmorphology is a synapomorphy ofshinisaurs and of Varanoidea.
196. Dentary: Tooth height (0) declines dras-tically posteriorly, with two or three teethanterior to most posterior tooth abouthalf to two-thirds the height of tallestdentary teeth (Fig. 46A); (1) declinesless, with teeth just anterior to mostposterior tooth nearly the same height astallest dentary teeth (Fig. 43D).
Evolution. Under both analyses, aprecipitous decline is the ancestral statefor the entire group and for Anguimor-pha. Lack of a decline is ancestral forXenosaurus + R. rugosus and forshinisaurs. A precipitous decline is asynapomorphy of Xenosaurus. UnderAnalysis 1, lack of a decline is asynapomorphy of Xenosaurus + R.rugosus and of shinisaurs. Under Anal-ysis 2, lack of a decline is a synapomor-phy of Xenosauridae.
197. Dentary: Shafts of teeth (0) do notchange drastically in diameter posteri-orly, save at anterior tip in premaxil-lary–maxillary occlusal transition(Fig. 46A); (1) increase markedly indiameter posteriorly (Fig. 43C).
Variation. The differentiation ofshaft widths becomes more pro-nounced with age.
Evolution. Under both analyses, amarked posterior increase in diameter
XENOSAUR PHYLOGENY N Bhullar 143
is a synapomorphy of X. rackhami + X.grandis.
Coronoid
The coronoid is unknown for E. lancensisand M. ornatus.
198. Coronoid: Anterolateral process (0)anteroposteriorly longer than dorsoven-trally tall at base (Fig. 46C); (1) tallerthan long (Fig. 46D).
Evolution. Under both analyses, tallerthan long is an autapomorphy of X. new-manorum, of X. agrenon, and of X. grandis.
199. Coronoid: Posterolateral process: (0)ventral margin directed posterodor-sally, resulting in taper for entire length
(Fig. 47A); (1) ventral margin directedstraight posteriorly for most of length,resulting in a dorsoventrally extensiveprocess (Fig. 46C).
Evolution. Under both analyses, astraight ventral margin and tall pos-terolateral process is a synapomorphyof Xenosaurus.
200. Coronoid: Posteromedial process (0)trending posteroventrally withoutstrong bend toward the vertical(Fig. 46B); (1) becoming nearly verticalat tip, resulting in highly bowed ap-pearance of coronoid arch (Fig. 47B).
Evolution. Under Analysis 1, theancestral state for the entire group and
Figure 46. A, Right mandible of Xenosaurus platyceps UF 45622, medial, anterior to the left. Illustrates characters 195(0),196(0), 197(0), 200(1), 201(1), 202(1), 203(0), 204(0). B, Left mandible of Elgaria multicarinata CAS 54241, medial, anterior to theright. Illustrates characters 195(1), 200(0), 201(0). C, Right mandible of Xenosaurus platyceps UF 45622, lateral, anterior to theright. Illustrates characters 198(0), 199(1), 205(2), 206(1), 208(1). D, Right mandible of Xenosaurus newmanorum NAUQSP-JIMuncatalogued specimen, lateral, anterior to the right. Illustrates characters 198(1), 206(0), 207(1).
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for Anguimorpha is ambiguous. Theancestral state for Anguidae + Heloder-matidae is the relatively straight mor-phology. Under Analysis 2, the ancestralstate for the entire group and forAnguimorpha is the bowed morphology.The straight morphology is a synapo-morphy of Anguidae + Varanoidea andan autapomorphy of R. rugosus.
201. Coronoid: Anteromedial process (0)with abrupt constriction of dorsal andventral margins about a third of the waytoward anterior tip followed by contin-ued taper (Fig. 46B); (1) graduallytapering without abrupt constrictionor with slight step in dorsal, but notventral, margin (Fig. 47B).
Evolution. Under both analyses, agradual taper is a synapomorphy ofXenosaurus and of Varanus.
202. Coronoid: Anteromedial process (0)more than twice as long along long axisas tall perpendicular to long axis atwidest level (Fig. 47B); (1) twice aslong as tall or less, with thickenedprocess restricting exposed portionanteriorly (Fig. 46A).
Evolution. Under both analyses,twice as long as tall or shorter is asynapomorphy of the northern clade ofXenosaurus. Under Analysis 1, twice aslong as tall or shorter is a synapomor-phy of Varanus and an autapomorphyof Helodermatidae. Under Analysis 2,
Figure 47. A, Left mandible of Elgaria multicarinata CAS 54241, dorsolateral, anterior to the left. Illustrates characters 199(0),205(0), 207(0), 208(0). B, Left coronoid of Xenosaurus agrenon UTACV r45008, medial, anterior to the right. Illustrates characters200(1), 201(1), 202(0), 203(1). C, Right mandible of Restes rugosus, CT scan of YPM PU 14640, medial, anterior to the left.Illustrates character 204(1). D, Right mandible of Xenosaurus rackhami UTEP-OC ‘‘MALB’’ 388, lateral, anterior to the right.Illustrates character 205(1).
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twice as long as tall or shorter is asynapomorphy of Varanoidea.
203. Coronoid: Medially facing flange ex-tending posteriorly from posteromedi-al process for attachment of bodena-poneurosis; ratio of greatest widthperpendicular to long axis to lengthalong long axis (0) 0.25 or less(Fig. 46A); (1) greater than 0.25(Fig. 47B).
Evolution. Under both analyses, anextensive flange is a synapomorphy ofX. agrenon + X. rectocollaris.
204. Coronoid: Posterior end of posterome-dial process (0) extends for shortdistance along prearticular (ventrome-dial) rim of adductor fossa (Fig. 46A);(1) ends anterior to adductor fossa(Fig. 47C).
Evolution. Under both analyses, ter-mination anterior to the adductor fossa isa synapomorphy of the southern clade ofXenosaurus and an autapomorphy of R.rugosus.
205. Coronoid: Anterior surangular foramen(0) not overlapped by coronoid(Fig. 47A); (1) partially overlapped bycoronoid, forming emargination in ven-tral margin of bone (Fig. 47D); (2) fullyoverlapped by coronoid, piercingthrough the bone (Fig. 46C).
Evolution. Under both analyses, par-tial overlap is an autapomorphy of L.borneensis. Complete overlap is asynapomorphy of Xenosaurus, and par-tial overlap is an autapomorphy of X.rackhami.
206. Coronoid: Anterior surangular foramenin coronoid (0) single (Fig. 46D); (1)double (Fig. 46C).
Evolution. Under both analyses, thepaired morphology is an autapomorphyof X. platyceps.
Surangular/Prearticular/Articular
The surangular/prearticular/articular com-plex is unknown in E. lancensis and M. ornatus.
207. Surangular/prearticular/articular: Strongdorsal crest on surangular lateral to m.adductor externus medialis attachmenttable (0) absent (Fig. 47A); (1) present(Fig. 46D).
Variation. The crest becomes moreprominent with age, and only relativelylarge adults should be scored.
Evolution. Under both analyses,presence of a crest is a synapomorphyof Xenosaurus and an autapomorphy ofHelodermatidae.
208. Surangular/prearticular/articular: Pos-terior surangular foramen (0) anteriorto articular (Fig. 47A); (1) at antero-posterior level of anterior edge ofarticular (Fig. 46C).
Evolution. Under both analyses, aposition at the anterior edge of thearticular is a synapomorphy of Xenosaurus.
209. Surangular/prearticular/articular: Fossaventral to arc of medial coronoid facet(subcoronoid fossa) (0) shallow, onlyslightly impressed (Fig. 48A); (1) deep,forming a strongly impressed bowl-shaped cavity (Fig. 48B).
Evolution. Under both analyses, adeep subcoronoid fossa is a synapo-morphy of Xenosaurus + E. serratus.
210. Surangular/prearticular/articular: Sub-coronoid fossa (0) with no medialoverhang at posterior end or only slightridge developed there (Fig. 48A); (1)posteriorly continuing into bone as ablind pocket, sometimes pierced by aforamen, such that a portion of themedial wall of the surangular bearingthe facet for the posteromedial processof the coronoid overhangs it (Fig. 48B).
Evolution. Under both analyses, lackof overhang is the ancestral state for theentire group and for Anguimorpha, andpresence of an overhang is the ancestralstate for Xenosaurus + R. rugosus. UnderAnalysis 1, the ancestral state for Xeno-saurus + Anguidae and for Anguidae +Helodermatidae is ambiguous, and over-
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hang is an autapomorphy of L. borneen-sis. Under Analysis 2, overhang is asynapomorphy of Xenosaurus + R. rugo-sus, and the ancestral state for Varanoi-dea and Varanidae is ambiguous.
211. Surangular/prearticular/articular: Subcoro-noid fossa (0) without foramina; (1) piercedby one or more small foramina; (2) piercedby one large posterior foramen serving asexit for canal from adductor fossa.
Evolution. Under both analyses, theancestral state for the entire group isambiguous, and that for Anguimorphais one or more small foramina. A singlelarge posterior foramen is a synapo-morphy of Xenosaurus.
Cervical Skeleton
Most or all of the cervical skeleton islacking in all fossils save B. ammoskius.
212. Cervical skeleton: Intercentra threeand four (0) dorsoventrally taller thananteroposteriorly long (Fig. 48C); (1)anteroposteriorly longer than dorsoven-trally tall (Fig. 48D).
Evolution. Under both analyses,the ancestral state for the entire groupand for Anguimorpha is taller thanlong. Under Analysis 1, the ances-tral state for Xenosaurus + Anguidaeand for Anguidae + Helodermatidaeis ambiguous. Under Analysis 2, long-er than tall is a synapomorphy of
Figure 48. A, Left postdentary elements of Elgaria multicarinata TMM-M 8958, medial, anterior to the right. Illustrates characters209(0), 210(0). B, Left postdentary elements of Xenosaurus grandis NAUQSP-JIM 1460, medial, anterior to the right. Illustratescharacters 209(1), 210(1). C, Cervical vertebrae of Shinisaurus crocodilurus MVZ 204291, left lateral, anterior to the left.Illustrates characters 212(0), 213(1). D, Cervical vertebrae of Heloderma suspectum CAS 513, right ventrolateral, anterior to theright. Illustrates characters 212(1), 213(0).
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Xenosaurus and an autapomorphy ofHelodermatidae.
213. Cervical skeleton: Intercentra threeand four (0) lateral surfaces gentlycontoured (Fig. 48D); (1) lateral sur-faces bearing small transverse process-es (Fig. 48C) (see Estes, 1983).
Evolution. Under both analyses, ab-sence of transverse processes is theancestral state for the entire group andfor Anguimorpha. Under Analysis 1,presence of transverse processes is asynapomorphy of Xenosaurus and anautapomorphy of S. crocodilurus. Un-der Analysis 2, longer presence oftransverse processes is a synapomorphyof Xenosauridae.
Trunk Skeleton
The trunk skeleton is unknown for allfossil taxa save B. ammoskius and R.rugosus. In the latter, only a few disarticu-lated vertebrae are preserved.
214. Trunk skeleton: Thoracic vertebralcolumn, neural spines (0) tall, anterioredges sloping at about 45u to centrum;(1) spines in posterior third of thoraciccolumn bearing long ribs low, anterioredges sloping at well under 45u(Fig. 49A); (2) all thoracic neural spineslow, sloping at under 45u (Fig. 49B).
Variation. Neural spines heightenwith age, especially during early post-natal ontogeny. This character shouldbe scored on relatively large adults.
Figure 49. Trunk skeletons, left lateral, anterior to the left: A, Xenosaurus newmanorum, CT scan of UMMZ 126057; B,Xenosaurus platyceps, CT scan of UF 25005; C, Xenosaurus rectocollaris, CT scan of UF 51443. A illustrates 214(1), 215(1), and216(0). B illustrates 214(2), 215(2), and 216(0). C illustrates 214(2), 215(0), and 216(1).
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Evolution. Under both analyses, thelow morphology in the posterior por-tion of the dorsal column is a synapo-morphy of Xenosaurus + R. rugosus.The uniformly low morphology in thethoracic dorsal column is an autapo-morphy of X. platyceps and of X.rectocollaris.
215. Trunk skeleton: Neural spines, pos-terodorsal projection formed by ante-roventral slope of posterior edges (0)absent on most vertebrae, posterioredges of neural spines vertical orsloping posteroventrally (Fig. 49C);(1) well-developed, tip of neural spineblunt or rectangular (Fig. 49A); (2)well-developed, tip of neural spineproduced into narrow finger-like pro-cess (Fig. 49B).
Variation. Neural spines grow substantially during early postnatal ontog-eny and so this character should not bescored on individuals less than abouthalf of adult size.
Evolution. Under both analyses, theancestral state for the entire group andfor Anguimorpha is the well-developed,blunt morphology. Absence is an auta-pomorphy of X. rectocollaris, and long,narrow production is an autapomorphyof X. platyceps.
216. Trunk skeleton: Lumbar neural spines(0) posteriorly sloped, anterior andposterior edges sloped with an ante-roventral/posterodorsal orientation(Fig. 49A); (1) low, flat rectangles withweak, if any, slope (Fig. 49C).
Evolution. Under both analyses, thelow, rectangular morphology is a syn-apomorphy of X. agrenon + X. recto-collaris.
Caudal Skeleton
The caudal skeleton is unknown for allfossils save B. ammoskius.
217. Caudal skeleton: Caudal vertebral count(average, rounded to nearest integer) (0)
35 to 39; (1) 40 to 44; (2) 45 to 49; (3) 50to 54; (4) 55 to 59; (5) 60 to 64; (6) 65 to69; (7) 70 to 74; (8) 75 to 79; (9) 80 to 84;(A) 85 to 89; (B) 90 to 94.
Variation. As noted, the valuesscored above are averages. A smallamount of variation in caudal vertebralcounts occurs. Furthermore, intact tailsare present in a small fraction ofspecimens from modern skeletal col-lections and a smaller fraction still offossils.
Evolution. Under both analyses, theancestral state for Xenosaurus is 40 to44 and that for the southern clade ofXenosaurus is ambiguous between 35to 39 and 40 to 44. A count of 60 to64 is a synapomorphy of Varanidae,and a count of 90 to 94 a synapomor-phy of Varanus or an autapomorphyof V. exanthematicus. A count of 65 to69 is an autapomorphy of O. ventralis,and 35 to 39 is an autapomorphy ofHelodermatidae. Under Analysis 1,the ancestral state for the entire groupand for Anguimorpha is ambiguousbetween 40 to 44 and 45 to 49, as isthat for Xenosaurus + Anguidae andAnguidae + Helodermatidae. A countof 50 to 54 is a synapomorphy of E.multicarinata + O. ventralis. Theancestral state for S. crocodilurus +Varanidae is 45 to 49. Under Analysis2, the ancestral state for the entiregroup and for Anguidae is ambiguousbetween 45 to 49 and 50 to 54, as isthat for Anguidae + Varanoidea andfor Varanoidea. The ancestral state forAnguidae is 50 to 54. The ancestralstate for Xenosauridae is 45 to 49, and40 to 44 is a synapomorphy ofXenosaurus.
218. Caudal skeleton: Caudal autotomyplanes (0) present (Fig. 50A); (1) ab-sent (Fig. 164). (See character 103 ofEstes et al., 1988).
Variation. Autotomy planes areformed in most taxa by the time ofhatching.
XENOSAUR PHYLOGENY N Bhullar 149
Evolution. Under Analysis 1, theancestral state for the entire groupand for Anguimorpha is ambiguous.Under Analysis 2, the ancestral state forthe entire group and for Anguimorphais presence of autotomy planes, andtheir absence is a synapomorphy ofXenosaurus and of Varanoidea.
Pectoral Girdle
The pectoral girdle is unknown for allextinct taxa save B. ammoskius.
219. Pectoral girdle: Scapulocoracoidemargination: (0) dorsal and ventralmargins strongly diverging for most oflength (Fig. 51A); (1) dorsal andventral margins weakly diverging or
nearly parallel for most of length(Fig. 51B).
Evolution. Under both analyses,weak or no divergence is a synapomor-phy of the northern clade of Xeno-saurus and of Varanus, as well as anautapomorphy of C. enneagrammus.
220. Pectoral girdle: Scapulocoracoid emar-gination; ratio of greatest height per-pendicular to long axis to length alonglong axis (0) 0.70 or greater (Fig. 51C);(1) less than 0.70 (Fig. 51D).
Evolution. Under both analyses, theancestral state for Anguidae is ambigu-ous, and a ratio of less than 0.70 is asynapomorphy of the northern clade ofXenosaurus.
Figure 50. A, Caudal vertebrae of Shinisaurus crocodilurus MVZ 204291, left lateral, anterior to the left. Illustrates character218(0). Caudal vertebrae, dorsal, anterior to the left: B, Xenosaurus newmanorum, CT scan of UMMZ 126057; C, Xenosaurusplatyceps, CT scan of UF 25005. B and C illustrate characters 218(1), 268(0), 268(1).
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221. Pectoral girdle: Sharp hook-like over-hang of scapulocoracoid emarginationby scapula (0) absent (Fig. 51B); (1)present (Fig. 51C).
Evolution. Under both analyses,presence of an overhang is a synapo-morphy of X. rackhami + X. grandis.
222. Pectoral girdle: Length of anteriorcoracoid emargination along long axisfrom apex of emargination to anteriorend of dorsal margin (0) equal to orgreater than length of remainder ofscapulocoracoid along line of axis con-tinued posteriorly from apex (Fig. 51A);(1) less than length of remainder ofscapulocoracoid (Fig. 51C).
Evolution. Under Analysis 1, theancestral state for the entire groupand for Anguimorpha is ambiguous, asis that for all mixed internal nodes.Under Analysis 2, the ancestral state forthe entire group and Anguimorpha is aslong or longer than the remainder ofthe scapulocoracoid. Shorter than theremainder is a synapomorphy of Xeno-saurus and of Varanoidea.
223. Pectoral girdle: Anterior coracoidemargination; ratio of greatest heightperpendicular to long axis to lengthalong long axis (Fig. 51B) (0) 0.50 orless; (1) between 0.50 and 0.85; (2) 0.85or greater.
Figure 51. A, Left scapulocoracoid of Elgaria multicarinata TMM-M 8993, lateral, anterior to the left. Illustrates characters 219(0),222(0), 223. B, Left scapulocoracoid of Xenosaurus newmanorum NAUQSP-JIM uncatalogued specimen, lateral, anterior to theleft. Illustrates characters 219(1), 221(0), 224(1). C, Left scapulocoracoid of Xenosaurus rackhami UTEP-OC ‘‘MALB’’ 388, lateral,anterior to the left. Illustrates characters 220(0), 221(1), 222(1), 225(0). D, Left scapulocoracoid of Xenosaurus platyceps UF45622, lateral, anterior to the left. Illustrates characters 220(1), 224(0), 225(1).
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Evolution. Under both analyses, theancestral state for the entire group andfor Anguimorpha is between 0.50 and0.85. The state 0.50 or less is anautapomorphy of X. newmanorum,whereas 0.85 or greater is an autapo-morphy of X. platyceps and of L.borneensis. Under Analysis 1, the an-cestral state for Anguidae + Heloderma-tidae and for Anguidae is ambiguousbetween 0.50 or less and between 0.50and 0.85. The state 0.50 or less is asynapomorphy of Varanus. Under Anal-ysis 2, the ancestral state for Anguidae +Varanoidea is ambiguous between states0.50 or less and between 0.50 and 0.85.
224. Pectoral girdle: Posterior coracoidemargination (0) absent, ventral marginof coracoid curves smoothly (Fig. 51D);(1) present at least as abrupt anteriorchange in angle of ventral margin ofcoracoid toward the horizontal andstraightening of curve (Fig. 51B) (seecharacter 112 of Estes et al., 1988).
Evolution. Under both analyses, theancestral state for the entire group isambiguous, and that for Anguimorphais absence of the emargination. Pres-ence of the emargination is an autapo-morphy of X. newmanorum, of C.enneagrammus, and of L. borneensis.
225. Pectoral girdle: Posterior end of cora-coid (0) terminating in a point(Fig. 51C); (1) squared-off or blunt,attenuate (Fig. 51D).
Evolution. Under both analyses, thesquared-off or blunt morphology is asynapomorphy of the northern clade ofXenosaurus.
226. Pectoral girdle: Clavicle, flattened tipof sternal ramus (0) in plane parallel oroblique to that of flattened portion ofscapular ramus; (1) in plane nearlyperpendicular to that of flattenedportion of scapular ramus.
Evolution. Under both analyses, thenearly perpendicular morphology is a
synapomorphy of the northern clade ofXenosaurus.
227. Pectoral girdle: Clavicle, corner be-tween rami (0) projected into long,narrow process (Fig. 52A); (1) pro-duced into distinct, moderately longeminence (Fig. 52B); (2) producedonly slightly into small thickening orbump (Fig. 52C).
Evolution. Under both analyses, theancestral state for the entire group andfor Anguimorpha is ambiguous be-tween production into a moderatelylong eminence and slight production.The long morphology is an autapomor-phy of S. crocodilurus and of E. multi-carinata. Under Analysis 1, the ances-tral state for S. crocodilurus +Varanidae is ambiguous in the sameway as Anguimorpha. The ancestralstate for Xenosaurus + Anguidae isslight production, and moderate pro-duction is a synapomorphy of X.rackhami + X. grandis.
228. Pectoral girdle: Interclavicle, lateralprocesses (0) without proximal changein angle (Fig. 52A); (1) extendingperpendicular to longitudinal body ofinterclavicle for short proximal stretchbefore abruptly angling backward(Fig. 52B).
Evolution. Under both analyses, themorphology involving a proximal trans-verse stretch and a posterior inflectionis a synapomorphy of Xenosaurus.
229. Pectoral girdle: Interclavicle, angle ofdistal portion of lateral process to longi-tudinal body (0) 65u or less (Fig. 52B);(1) greater than 65u (Fig. 52C).
Evolution. Under both analyses, anangle greater than 65u is a synapomor-phy of the northern clade of Xeno-saurus and an autapomorphy of X.rectocollaris and of L. borneensis.
230. Pectoral girdle: Interclavicle, ratio oflength of lateral process to length ofposterior process (including section
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between lateral processes) (Fig. 52D)(0) 0.55 or greater; (1) less than 0.55.
Evolution. Under both analyses, theancestral state for the entire groupand for Anguimorpha is less than0.55, and 0.55 or greater is anautapomorphy of S. crocodilurus.Under Analysis 1, the ancestral statefor Anguidae + Helodermatidae andfor Anguidae is ambiguous. UnderAnalysis 2, a ratio of 0.55 or greateris an autapomorphy of E. multicar-inata and of Helodermatidae.
231. Pectoral girdle: Interclavicle, anteriorprocess (0) prominent, several times aslong as wide (Fig. 52A); (1) present assmall eminence or absent (Fig. 52C)
(see character 120 of Estes et al.,1988).
Evolution. Under both analyses, theancestral state for the entire group andfor Anguimorpha is small size orabsence. Prominence is a synapomor-phy of Anguidae and an autapomorphyof S. crocodilurus.
Forelimb
The forelimb is unknown for all fossils butB. ammoskius.
232. Forelimb: Ulna, ratio of width perpen-dicular to long axis at narrowest part ofshaft to length along long axis (0) 0.07or less (Fig. 53A); (1) greater than 0.07(Fig. 53B).
Figure 52. A, Interclavicle and right clavicle of Shinisaurus crocodilurus MVZ 204291, ventral, anterior to the top. Illustratescharacters 227(0), 228(0), 231(0). B, Interclavicle and right clavicle of Xenosaurus rackhami UTEP-OC ‘‘MALB’’ 388, ventral,anterior to the top. Illustrates characters 227(1), 229(0), 228(1). C, Interclavicle and right clavicle of Xenosaurus newmanorumNAUQSP-JIM uncatalogued specimen, ventral, anterior to the top. Illustrates characters 227(2), 229(1), 231(1). D, Interclavicle ofShinisaurus crocodilurus MVZ 204291, ventral, anterior to the left. Illustrates character 230 (n for numerator, d for denominator).
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Evolution. Under both analyses,relative width with a ratio greaterthan 0.07 is an autapomorphy of X.platyceps.
Pelvic Girdle
The pelvic girdle is unknown for E.serratus, E. lancensis, and M. ornatus. Onlythe ilium is preserved in R. rugosus; thetaxon cannot be scored for the otherelements. Ophisaurus ventralis has a vesti-gial pelvic girdle and could not be scored forthese characters.
233. Pelvic girdle: Narrowing at tip of ilium(0) primarily resulting from change inangle in ventral margin of ilium(Fig. 53C); (1) primarily resulting from
change in angle in dorsal margin(Fig. 53D).
Evolution. Under both analyses, taper-ing resulting from a dorsal change inangle is a synapomorphy of S. crocodi-lurus + B. ammoskius.
234. Pelvic girdle: Thyroid fenestra, ratio inplane of fenestra of longest antero-posterior length parallel to symphysisto widest mediolateral width perpen-dicular to symphysis (Fig. 54A) (0)less than 0.95; (1) from 0.95 to lessthan 1.20; (2) 1.20 or greater.
Evolution. Under both analyses,the ancestral state for the entire groupand for Anguimorpha is between 0.95and 1.20. A ratio of less than 0.95 is an
Figure 53. Left ulnae, anterior, distal to the left: A, Xenosaurus newmanorum NAUQSP-JIM uncatalogued specimen; B,Xenosaurus platyceps UF 45622. A and B illustrate characters 232(0), 232(1). Right ilia, lateral, anterior to the right: C,Xenosaurus newmanorum NAUQSP-JIM uncatalogued specimen. Illustrates character 233(0). D, Shinisaurus crocodilurus MVZ204291. Illustrates character 233(1).
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autapomorphy of X. newmanorum, ofX. rectocollaris, and of C. enneagram-mus. A ratio of 1.20 or greater is anautapomorphy of X. platyceps.
235. Pelvic girdle: Pubis, ratio of widthperpendicular to long axis just medialto pectineal tubercle to length alonglong axis from tubercle to symphysis (0)greater than 0.38 (Fig. 54B); (1) 0.38 orless (Fig. 54A).
Evolution. Under both analyses, aratio of 0.38 or less is an autapomorphyof X. newmanorum and of C. ennea-grammus.
236. Pelvic girdle: Ischium (0) flat, broadlyplate-like with constriction near medio-lateral midpoint (Fig. 54A); (1) narrow,tapering medially with constriction
absent or weakly present far medially(Fig. 54B).
Evolution. Under both analyses, thenarrow, tapering, unconstricted mor-phology is an autapomorphy of X.rectocollaris.
Hind Limb
The hind limb is unknown for all extincttaxa save B. ammoskius.
237. Hind limb: Femur, femoral neck inplane of knee flexion (0) wider perpen-dicular to long axis than long(Fig. 55A); (1) longer along long axisthan wide (Fig. 55B).
Evolution. Under both analyses,longer-than-wide is an autapomorphyof X. platyceps.
Figure 54. Pelvic girdles and posterior axial skeletons, ventral, anterior to the left: A, Xenosaurus newmanorum, CT scan ofUMMZ 126057; B, Xenosaurus rectocollaris, CT scan of UF 51443. A illustrates 234 (n for numerator, d for denominator), 235(1),236(0), and 267(1). B illustrates 235(0), 236(1), and 267(2).
XENOSAUR PHYLOGENY N Bhullar 155
238. Hind limb: Tibia, width measured byratio of anteroposterior length acrossextensor surface at proximal end, justdistal to epiphysis, to proximodistal length(0) wide, 0.25 or greater (Fig. 55C); (1)narrow, less than 0.25 (Fig. 55D).
Evolution. Under both analyses, theancestral state for the entire group andfor Anguimorpha is ambiguous. UnderAnalysis 1, the ancestral state for S.crocodilurus + Varanidae and for An-guidae + Helodermatidae is 0.25 orgreater. The ancestral state for Xeno-saurus + Anguidae is ambiguous. Un-der Analysis 2, the ancestral state forAnguidae + Varanoidea is 0.25 orgreater and that for Xenosauridae isambiguous.
239. Hind limb: Tibia, anterior crest mar-gin (0) straight or slightly convex(Fig. 55C); (1) concave in plane of crest(Fig. 55D).
Evolution. Under both analyses, theconcave morphology is a synapomorphyof the northern clade of Xenosaurusand an autapomorphy of X. agrenon.
240. Hind limb: Tibia, anterior crest occu-pies (0) about one-quarter of shaft oftibia (Fig. 55C); (1) about one-fifth ofshaft of tibia; (2) minimal portion ofshaft, crest reduced to small distaleminence (Fig. 56A).
Evolution. Under both analyses, theancestral state for the entire group isambiguous among all three states. That
Figure 55. Left femora, anterior, distal to the left: A, Xenosaurus grandis NAUQSP-JIM 1460; B, Xenosaurus platyceps UF45622. A and B illustrate characters 237(0), 237(1). Left tibiae, flexor view, distal to the right: C, Xenosaurus newmanorumNAUQSP-JIM uncatalogued specimen; D, Elgaria multicarinata TMM-M 8958. C and D illustrate characters 238(0), 238(1),239(0), 239(1), 240(0), 241(0), 241(1).
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for Anguimorpha is occupation of one-quarter of the shaft. Occupation of one-fifth of the shaft is an autapomorphy ofX. platyceps and of B. ammoskius.Occupation of a minimal portion ofthe shaft as a small nub or eminence isan autapomorphy of X. rackhami.
241. Hind limb: Tibia, proximal sulci onflexor surface for attachment of m.semimembranosus and m. tibialis pos-terior among other muscles (0) formingdistinct, shallow grooves (Fig. 55C); (1)barely incised, represented only by aflattening of tibial surface (Fig. 55D).
Evolution. Under both analyses, thesimple, flattened morphology is ancestral
for the entire group and for Anguimor-pha. Under Analysis 1, deep incision is asynapomorphy of Varanus or Varanidaeand of Anguidae. Under Analysis 2, theancestral state for Anguidae + Varanoi-dea is ambiguous.
242. Hind limb: Calcaneum, length of cal-caneal heel measured by ratio ofanteroposterior length to proximodistalwidth (0) long, 0.50 or greater(Fig. 56B); (1) short, less than 0.50(Fig. 56C).
Evolution. Under both analyses, theancestral state for the entire group isambiguous, and that for Anguimorphais the long morphology. The short
Figure 56. A, Right lower hind limb of Xenosaurus rackhami MCZ 54317, flexor view, distal to the left. Illustrates character240(2). B, Left astragalocalcaneum of Xenosaurus newmanorum NAUQSP-JIM uncatalogued specimen, flexor view, distal towardthe bottom. Illustrates character 242(0). C, Left astragalocalcaneum of Xenosaurus grandis MVZ 128947, flexor view, distaltoward the bottom. Illustrates character 242(1). Fifth metatarsals, extensor view, distal toward the bottom: D, left, Xenosaurusnewmanorum NAUQSP-JIM uncatalogued specimen; E, right, Elgaria multicarinata TMM-M 8958.
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morphology is a synapomorphy of thesouthern clade of Xenosaurus and anautapomorphy of L. borneensis.
243. Hind limb: Fifth metatarsal, flexo-ex-tensor bending such that metatarsal isconcave in the extensor direction (0)strongly arched, in part because of heavydevelopment of expanded proximal end(Fig. 56E); (1) weak, creating a gentle,nearly horizontal arc (Fig. 56D).
Evolution. Under both analyses, aweak flexo-extensor arch is a synapo-morphy of Xenosaurus.
244. Hind limb: Fifth metatarsal, anteropos-terior expansion of head measured byratio of anteroposterior length at longestproximodistal level to proximodistallength of metatarsal (0) relatively great,0.65 or greater (Fig. 56E); (1) relativelyslight, less than 0.65 (Fig. 56D).
Evolution. Under both analyses, theancestral state for the entire group andfor Anguimorpha is slight expansion.Under Analysis 1, relative expansion isa synapomorphy of Anguidae + Helo-dermatidae and of Varanus. UnderAnalysis 2, it is a synapomorphy ofAnguidae + Varanoidea, and slightexpansion is an autapomorphy of L.borneensis within that clade.
245. Hind limb: Fifth metatarsal, lateralplantar tubercle (0) nearly perpendicu-lar to medial plantar tubercle in planeperpendicular to long axis of metatar-sal; (1) at an acute angle to medialplantar tubercle.
Evolution. Under both analyses, anacute angle is a synapomorphy of thesouthern clade of Xenosaurus and ofVaranidae.
Osteoderms, General
These notes apply to all osteoderm char-acter categories. Osteoderms could only bevisualized on species of Xenosaurus, save X.agrenon, S. crocodilurus, L. borneensis frompublished x-rays (McDowell and Bogert,
1954) and CT scans (Maisano et al., 2002),Anguidae, and Helodermatidae, as well asthe postcranium of B. ammoskius. When thesouthern clade of Xenosaurus is mentionedas having a character state in the osteodermsection, it should be understood that thestate for X. agrenon is inferred. Varanus hasosteoderms (McDowell and Bogert, 1954),but they are too small to visualize reliablywith CT scanning, and alternative prepara-tions were unavailable. Osteoderms areunknown for the remaining fossil angui-morphs, save some isolated osteodermsassociated with M. ornatus (Klembara,2008). Pristidactylus torquatus does not havesignificant free osteoderms as an adult; thecondition in juveniles is unknown.
Regarding osteodermal variation, it isobvious that osteoderm patterns vary slightlywith scalation patterns. Additionally, osteo-derms develop postnatally for the most part;thus, it is important to score osteodermcharacters on relatively large adult individuals.
246. Osteoderms: Domed osteoderms (0)absent; (1) largely circular; (2) somecircular, but largely oval or obovate (seeConrad, 2005, 2008).
Evolution. Under both analyses, theancestral state for Xenosaurus + R.rugosus is domed and circular. Domedand circular plus oval is an autapomor-phy of E. lancensis. Under Analysis 1, theancestral state for the entire group andfor Anguimorpha is domed and circular.Lack of domed osteoderms is a synapo-morphy of S. crocodilurus + Varanidaeand of Anguidae. Under Analysis 2, theancestral state for the entire group andfor Anguimorpha is ambiguous betweenabsent and largely circular.
Cranial Osteoderms
247. Cranial osteoderms: Fused cranial os-teoderms (0) absent; (1) present(Fig. 1A).
Evolution. Under both analyses, ab-sence of fused cranial osteoderms is asynapomorphy of Varanidae.
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248. Cranial osteoderms: Supraorbital osteo-derm longitudinal rows (0) five(Fig. 2A); (1) four (Fig. 1A); (2) three(Fig. 5A); (3) two (Fig. 4A).
Evolution. Under both analyses, tworows is ancestral for Anguimorpha.Three rows is an autapomorphy of C.enneagrammus. The ancestral state forXenosaurus is ambiguous betweenthree and two rows. Four rows is asynapomorphy of the northern clade ofXenosaurus, and five rows is an auta-pomorphy of X. platyceps.
249. Cranial osteoderms: Full supraorbitalosteoderms in longitudinal row bearinglargest osteoderms (0) eight (Fig. 1A);(1) seven; (2) six; (3) five (Fig. 5A); (4)four; (5) three; (6) two (Fig. 3A).
Evolution. Under both analyses, acount of eight is a synapomorphy of thenorthern clade of Xenosaurus. Two is anautapomorphy of X. rackhami and of L.borneensis. Four is an autapomorphy ofE. multicarinata, and three is an autapo-morphy of Helodermatidae. Six is anautapomorphy of S. crocodilurus. UnderAnalysis 1, the ancestral state for Angu-imorpha is five, as is that for S. crocodi-lurus + Varanidae, Xenosaurus + Angu-idae, and Anguidae + Helodermatidae.Under Analysis 2, the ancestral state forAnguimorpha is ambiguous among six,five, and four. The ancestral state forXenosauridae is ambiguous between sixand five. The ancestral state for Anguidae+ Varanoidea is ambiguous between fiveand four, as is that for Anguidae. Three isa synapomorphy of Varanoidea
250. Cranial osteoderms: Supraorbital osteo-derms in longitudinal row bearinglargest osteoderms—largest osteo-derms (0) less than twice as extensivealong long axis as perpendicular to longaxis (Fig. 2A); (1) twice as extensive ormore along long axis as perpendicularto long axis (Fig. 4A).
Evolution. Under Analysis 1, theancestral state for the entire group
and for Anguimorpha is less than twiceas long as wide. Twice as long as wideor more is a synapomorphy of thesouthern clade of Xenosaurus and anautapomorphy of S. crocodilurus. Un-der Analysis 2, the ancestral state forthe entire group and for Anguimorphais ambiguous. The ancestral state forAnguidae + Varanoidea is less thantwice as long as wide.
251. Cranial osteoderms: Dorsal temporalosteoderms, peripheral rims (0) present(Fig. 1A); (1) absent (Fig. 4A).
Evolution. Under both analyses,presence of rims is a synapomorphy ofthe northern clade of Xenosaurus andan autapomorphy of Helodermatidae.
252. Cranial osteoderms: Dorsal temporalosteoderms (0) overlie entirety of dorsaltemporal fenestra and dorsal surfaces ofupper temporal arch bones (Fig. 1A);(1) overlie entirety of dorsal temporalfenestra and partially overlie dorsalsurfaces of upper arch bones, butposterodorsal tip of jugal, lateral edgeof postorbitofrontal, and anterolateralportion of squamosal lateral to medio-lateral level of external edge of post-orbitofrontal are exposed (Fig. 5A); (2)overlie dorsal temporal fenestra butleave exposed elements described instate 1 plus postfrontal portion ofpostorbitofrontal and most of squamosal(Fig. 4A); (3) only few and isolated,overlying dorsal temporal fenestra andposterior, median portion of postorbito-frontal (Fig. 3A); (4) absent.
Evolution. Under both analyses, theancestral state for the entire group isambiguous among all four states. Theancestral state for Anguimorpha is 0. State4 is a synapomorphy of Varanus, state 1 isa synapomorphy of the southern clade ofXenosaurus, and state 2 is a synapomor-phy of X. rackhami + X. grandis.
253. Cranial osteoderms: Transverse rows ofosteoderms behind posterior edge of
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parietal (0) spanning most of width ofparietal (Fig. 2A); (1) restricted tomediolateral area spanned by notch atmeeting of supratemporal processes(Fig. 5A); (2) absent (Fig. 4A).
Evolution. Under both analyses,absence is a synapomorphy of X. rac-khami + X. grandis. Under Analysis 1, aspan of most of the width of the parietalis ancestral for Anguimorpha, and arestricted span is a synapomorphy of thesouthern clade of Xenosaurus. Absenceis an autapomorphy of S. crocodilurus.Under Analysis 2, the ancestral state forAnguimorpha and for Xenosauridae isambiguous between a wide and arestricted span. The ancestral state forAnguidae + Varanoidea is a wide span.
254. Cranial osteoderms: Number of trans-verse rows of osteoderms behind pos-terior edge of parietal (0) two (Fig. 5A);(1) three (Fig. 2A).
Evolution. Under both analyses,three rows is an autapomorphy of X.platyceps. Under Analysis 1, three rowsis an autapomorphy of Helodermatidaeand of L. borneensis. Under Analysis 2,three rows is a synapomorphy ofVaranoidea.
255. Cranial osteoderms: Lateral temporalosteoderms, peripheral rims (0) absent(Fig. 5C); (1) present (Fig. 1C).
Evolution. Under both analyses, thepresence of rims is a synapomorphy ofXenosaurus. It is also an autapomorphyof X. grandis and of Helodermatidae.
256. Cranial osteoderms: Lateral temporalosteoderms, spacing—(0) closelypacked (Fig. 1C); (1) separated bysmall gaps (Fig. 5C); (2) separated bygaps of one scale or more (Fig. 4C); (3)present only as small slivers of ossifica-tion (Fig. 3C); (4) absent.
Evolution. Under both analyses, theancestral state for the entire group isambiguous among the last four states.That for Anguimorpha is ambiguous
between separation by small and largegaps. Presence as only small slivers ofossification is autapomorphic for X.rackhami. Under Analysis 1, the ances-tral state for S. crocodilurus + Varanidaeis ambiguous between separation bysmall and large gaps. The ancestral statefor Xenosaurus + Anguidae is ambigu-ous between close packing and separa-tion by small gaps. Close packing is theancestral state for Anguidae + Heloder-matidae. Separation by small gaps isancestral for the southern clade ofXenosaurus, and separation by largegaps is a synapomorphy of X. rackhami+ X. grandis. Under Analysis 2, theancestral state for Anguidae + Varanoi-dea is ambiguous between closelypacked and separated by small gaps.
257. Cranial osteoderms: Lateral temporalosteoderms, coverage of quadratojugalregion posterior to quadratojugal pro-cess of jugal (0) present (Fig. 1C); (1)absent (Fig. 5C).
Evolution. Under both analyses,noncoverage of the quadratojugal re-gion is a synapomorphy of the southernclade of Xenosaurus.
258. Cranial osteoderms: Mandibular osteo-derms (0) absent; (1) most of dentaryexposed; only portions of postdentarybones extensively covered; (2) coveringpart of lateral face of mandible, includ-ing dentary and postdentary bones, butleaving large areas of dentary andpostdentary bones exposed (Fig. 5B,C); (3) covering most of lateral face ofmandible save for retroarticular processand pterygoideus insertion on surangu-lar, present in three major longitudinalrows (Figs. 1B, C); (4) as with state 3but with four major longitudinal rows(Figs. 2B, C).
Evolution. Under both analyses, theancestral state for Anguimorpha isambiguous between state 1 and state2. The ancestral state for Xenosaurusis 2, and state 3 is a synapomorphy of
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the northern clade of Xenosaurus, withstate 4 an autapomorphy of X. platy-ceps. State 3 is also a synapomorphyof Anguidae. The ancestral stateof most other nodes under bothanalyses is ambiguous between state1 and state 2.
259. Cranial osteoderms: Mandibular osteo-derms (0) with strong, sharp keels(Fig. 1B, C); (1) unkeeled or subtlykeeled (Fig. 5B, C).
Evolution. Under both analyses,strong keeling of the mandibular osteo-derms is a synapomorphy of the north-ern clade of Xenosaurus.
260. Cranial osteoderms: Intermandibularosteoderms (0) present, well-developed(Fig. 1B); (1) present as multiple smallossifications (Fig. 2B); (2) present asone or two small ossifications (Fig. 5B);(3) absent (Fig. 4B).
Evolution. Under both analyses, thewell-developed morphology is an auta-pomorphy of X. newmanorum, andabsence is a synapomorphy of X.rackhami + X. grandis. Under Analysis1, the ancestral state for the entiregroup is ambiguous among multiplesmall ossifications, one or two smallossifications, and absence, and that forAnguimorpha is ambiguous betweenmultiple and one or two small ossifica-tions. The well-developed morphologyis a synapomorphy of Anguidae +Helodermatidae and an autapomorphyof L. borneensis. Under Analysis 2, theancestral state for the entire group isambiguous between one or two smallossifications and absence. That forAnguimorpha is one or two smallossifications. The well-developed mor-phology is a synapomorphy of Anguidae+ Varanoidea, and presence as multiplesmall ossifications is a synapomorphy ofthe northern clade of Xenosaurus.
261. Cranial osteoderms: Intermandibularosteoderms, well-developed portion
(0) in posterior half of mandible; (1)in anterior half of mandible (Fig. 1A).
Evolution. Under Analysis 1, poste-rior development is ancestral, anddevelopment in the anterior half ofthe mandible is a synapomorphy of thenorthern clade of Xenosaurus or of allxenosaurs. Under Analysis 2, the an-cestral state is ambiguous across mostof the tree, but the ancestral state ofVaranoidea is posterior development.
262. Cranial osteoderms: Intermandibularosteoderms, lateral rows (0) presentalong entirety of tooth-bearing regionof dentaries (Fig. 1B); (1) present onlyalong anterior portion (Fig. 2B).
Evolution. The ancestral state of thecharacter is entirely ambiguous.
263. Cranial osteoderms: Intermandibularosteoderms (0) spanning mandibularrami for large portion of anteroposteri-or extent (Fig. 1B); (1) developed onlylaterally for most of extent (Fig. 2B).
Evolution. Under both analyses, theancestral state for Anguimorpha isambiguous. Under Analysis 1, mostinternal nodes are ambiguous, save thatthe ancestral state for Anguidae +Helodermatidae is extensive develop-ment. Under Analysis 2, the ancestralstate for Anguidae + Varanoidea isextensive development, and that forXenosauridae is lateral development,making the extensive development in X.newmanorum an autapomorphy of thattaxon.
Cervical Osteoderms
264. Cervical osteoderms: Cervical osteo-derms (0) present dorsally in each scale(The Deep Scaly Project, 2007); (1)present dorsally in regularly spacedpattern, but not in each scale; (2)present dorsally as small ossificationsconcentrated anteriorly with occasionallarger osteoderms interspersed(Fig. 1A); (3) present dorsally as small
XENOSAUR PHYLOGENY N Bhullar 161
ossifications (Fig. 3A); (4) absent(Fig. 5A).
Evolution. Under both analyses, theancestral state for the entire group isambiguous among the last four states,and that for Anguimorpha is ambiguousbetween 1 and 2. The ancestral state forXenosaurus is 2, and state 3 is asynapomorphy of the southern cladeof Xenosaurus. State 4 is an autapo-morphy of X. rectocollaris. UnderAnalysis 1, the ancestral state for S.crocodilurus + Varanidae is 2, and thatfor Anguidae + Helodermatidae is 0.Under Analysis 2, the ancestral state forAnguidae + Varanoidea is ambiguousbetween 0 and 1, and that for Xeno-sauridae is ambiguous between 1 and 2.
Pectoral Osteoderms
265. Pectoral osteoderms: Osteoderms onpectoral limb (0) present on mostof extensor surfaces of stylopod andzeugopod and more lightly distributedon flexor surface (Fig. 57B); (1) presenton central two-thirds or more ofextensor surfaces, but only marginallyon flexor surfaces (Fig. 57A); (2) pres-ent only as narrow central band (aboutcentral one-third) of extensor surfaces,save for a few scattered ossificationsover elbow (Fig. 57C); (3) absent.
Evolution. Under both analyses, theancestral state for the northern clade ofXenosaurus is 1, and state 0 is anautapomorphy of X. platyceps. Theancestral state for the southern clade
Figure 57. Left pectoral limbs, extensor view, anterior to the left: A, Xenosaurus newmanorum, CT scan of UMMZ 126057; B,Xenosaurus platyceps, CT scan of UF 25005; C, Xenosaurus rectocollaris, CT scan of UF 51443. A illustrates 265(1) and 266(1).B illustrates 265(0) and 266(1). C illustrates 265(0) and 266(2).
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of Xenosaurus is 2, and state 3 is asynapomorphy of X. rackhami + X.grandis. Under Analysis 1, the ancestralstate for the entire group is ambiguousamong 1, 2, and 3. That for Anguimor-pha is ambiguous between 1 and 2. Theancestral state for Anguidae + Heloder-matidae is 0. Under Analysis 2, theancestral state for the entire group isambiguous between 2 and 3, and that forAnguimorpha is 2. State 0 is a synapo-morphy of Anguidae + Varanoidea, andstate 1 is a synapomorphy of thenorthern clade of Xenosaurus.
266. Pectoral osteoderms: Osteoderms onpectoral limb (0) present as small nubsof ossification; (1) present as largerounded ossifications (Fig. 57A); (2)present as large rounded ossificationsand in places as cone-shaped spicules(Fig. 57B).
Evolution. Under both analyses, theancestral state for the entire group ispresence as large rounded ossifications.Presence as small nubs of ossification isan autapomorphy of S. crocodilurus,and presence as large rounded ossifi-cations plus cone-shaped ossifications isan autapomorphy of X. platyceps.
Pelvic Osteoderms
267. Pelvic osteoderms: Osteoderms on pel-vic limb (0) present on extensor surfaceof stylopod and scattered on flexorsurface (McDowell and Bogert, 1954,plate 4); (1) present only on extensorsurface of stylopod (Fig. 54A); (2)absent.
Evolution. Under both analyses, theancestral state for the northern clade ofXenosaurus is extensor presence only,and presence on the extensor andflexor surfaces is an autapomorphy ofX. platyceps. Under Analysis 1, theancestral state for the entire group andfor Anguimorpha is ambiguous be-tween presence on the extensor surfaceand absence. Presence on the flexor
and extensor surfaces is a synapomor-phy of Anguidae + Helodermatidae andan autapomorphy of L. borneensis.Under Analysis 2, the ancestral statefor the entire group and for Anguimor-pha is absence, and presence on theextensor and flexor surfaces is asynapomorphy of Anguidae + Varanoi-dea. Presence on the extensor surfaceis a synapomorphy of the northernclade of Xenosaurus.
Caudal Osteoderms
268. Caudal osteoderms: Caudal osteoderms(0) in complete or nearly completerings around anterior portion of tail andscattered over more posterior portion(Fig. 50B); (1) scattered in anteriorportion of tail, sparse in more posteriorportion (Fig. 50C); (2) absent.
Evolution. Under both analyses, theancestral state for the entire group isambiguous between scattered and ab-sent. That for Anguimorpha is scat-tered, as is that for Xenosaurus. Ab-sence of cadual osteoderms is asynapomorphy of the southern cladeof Xenosaurus, and complete ringsthereof is an autapomorphy of X. new-manorum. Under Analysis 1, completerings is a synapomorphy of Anguidae +Helodermatidae and an autapomorphyof L. borneensis. Under Analysis 2,complete rings is a synapomorphy ofAnguidae + Varanoidea.
Scalation
Scalation is not informatively preservedon any of the extinct taxa.
269. Scalation: Canthus temporalis (0) scalesno larger or more prominent thanlateral and dorsal temporal scales, orbarely so (Fig. 58A); (1) scales mark-edly larger and more prominent, can-thus well-developed (Fig. 58B).
Evolution. Under both analyses, theancestral state for the entire groupand for Anguimorpha is a lack of
XENOSAUR PHYLOGENY N Bhullar 163
prominence. Under Analysis 1, theancestral state for S. crocodilurus +Varanidae is ambiguous, and promi-nence of the canthus is a synapomor-phy of the southern clade of Xeno-saurus. Under Analysis 2, theancestral state for Xenosauridae isambiguous, and prominence is anautapomorphy of L. borneensis.
270. Scalation: Tympanum (0) unscaled; (1)covered with thin scales, becomingthinner toward middle of tympanum(Fig. 58A); (2) covered with thick scalesbut still differentiated from surround-ing skin (Fig. 58B); (3) covered withthick scales and undifferentiated fromsurrounding skin (McDowell and Bo-gert, 1954, plate 1).
Variation. In S. crocodilurus, smalljuveniles have a tympanum that ap-pears naked to the eye (Sprackland,1993; Magdefrau, 1997; Bever et al.,2005). It is possible that a thin layer ofscales covers it, as in juvenile X.grandis. Relatively large adults shouldbe scored for this character.
Evolution. Under both analyses, thenondifferentiated covering of thickscales in L. borneensis is an autapo-morphy of that taxon. Under Analysis 1,the ancestral state for the entire groupand for Anguimorpha is ambiguousbetween unscaled and covered withthin scales. A thick scaly covering is anautapomorphy of S. crocodilurus. Theancestral state for Anguidae + Helo-
Figure 58. Temporal and tympanic regions, left lateral, anterior to the left: A, Xenosaurus newmanorum UF 25006. Illustratescharacters 269(0), 270(1). B, Xenosaurus rackhami UTEP 4555. Illustrates characters 269(1), 270(2). Necks, dorsal, anterior tothe left: C, Xenosaurus newmanorum UF 25006. Illustrates character 271(0). D, Xenosaurus rectocollaris UF 51443. Illustratescharacter 271(1).
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dermatidae is unscaled, and the ances-tral state for Xenosaurus is thinlyscaled, with thickly scaled but differ-entiated a synapomorphy of the south-ern clade of Xenosaurus. Under Anal-ysis 2, the ancestral state for the entiregroup and for Anguimorpha is un-scaled, and increased scalation is asynapomorphy of Xenosauridae, whoseancestral state is ambiguous betweenlightly scaled and heavily scaled butdifferentiated.
271. Scalation: Skin around neck (0) con-forms relatively tightly to underlyingmuscular structure (Fig. 58C); (1) puffsout considerably, such that neck ap-pears wide and little differentiatedfrom back of head (Fig. 58D).
Evolution. Under both analyses, theloose collar-like morphology is anautapomorphy of X. rectocollaris.
272. Scalation: Lateral fold (0) absent; (1)present, relatively weakly developed,discontinuous; (2) present, well-devel-oped, continuous along body. (Scoredas lateral fold absent or present in Esteset al., 1988).
Evolution. Under both analyses, lackof a fold is the ancestral state for theentire group and for Anguimorpha.Presence of a weak fold is a synapo-morphy of Xenosaurus, and a strongfold is a synapomorphy of the southernclade of Xenosaurus. Under Analysis 1,a well-developed fold is a synapomor-phy of E. multicarinata + O. ventralis.Under Analysis 2, the ancestral statefor Anguidae is ambiguous amongabsent, weakly developed, and stronglydeveloped.
273. Scalation: Dark markings on venter (0)absent; (1) present peripherally; (2)present across most of venter.
Evolution. Under both analyses, lackof markings is the ancestral state forthe entire group and for Anguimorpha.Under Analysis 1, peripheral markings
are an autapomorphy of S. crocodi-lurus and the ancestral state for thesouthern clade of Xenosaurus is am-biguous among absence, peripheralpresence, and extensive presence, asis the state for X. agrenon + X.rectocollaris.
274. Scalation: Epidermal ridge microstruc-ture (0) polygonal; (1) not arranged inregular polygons.
Evolution. This character was scoredfrom the work of Harvey (1991, 1993).Under both analyses, the ancestral statefor the entire group and for Anguimor-pha is polygonal microstructure. UnderAnalysis 1, a lack of polygonal arrange-ment is a synapomorphy of Anguidae +Helodermatidae. Under Analysis 2, theancestral state for Anguidae + Varanoi-dea is ambiguous.
RESULTS
Ingroup Topology and Effects of Ordering
Analysis 1 and Analysis 2 yielded thesame fully resolved topology for Xenosaurusand its extinct relatives (Figs. 6, 7). In thesingle recovered topology, R. rugosus issister to all other xenosaurs, and E. lancensisis sister to E. serratus + Xenosaurus. WithinXenosaurus, the northern clade of X. new-manorum + X. platyceps is sister to thesouthern clade, which is divided into twoadditional clades: X. agrenon + X. rectocol-laris and X. rackhami + X. grandis. Boot-strap values greater than 50% are given atthe internal nodes. For both trees, allinternal nodes for the ingroup had bootstrapvalues greater than 50%.
Analysis 1 yielded a single most parsimo-nious tree with a length of 924 steps(Fig. 6). Of the 274 characters used in theanalysis, 253 were parsimony-informativeand 21 were parsimony-uninformative. Thetree consistency index was 0.4708 (0.3147rescaled and 0.4573 excluding uninforma-tive characters), the homoplasy index was0.5292 (0.5427 excluding uninformativecharacters), and the retention index was
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0.6685. The parametric bootstrap test re-sulted in values of greater than 50% for allingroup nodes and for the nodes within theshinisaur clade. The other nodes wereconstrained.
Analysis 2 yielded a single most parsimo-nious tree with a length of 875 steps(Fig. 7). Of the 274 characters used in theanalysis, 253 were parsimony-informativeand 21 were parsimony-uninformative. Thetree consistency index was 0.4971 (0.3488rescaled and 0.4836 excluding uninforma-tive characters), the homoplasy index was0.5029 (0.5164 excluding uninformativecharacters), and the retention index was0.7017. The parametric bootstrap test re-sulted in values of greater than 50% for allingroup nodes, for Xenosauridae, for Angui-dae + Varanoidea, and for Varanoidea andall nodes therein.
A comparison of the Analysis 1 andAnalysis 2 trees using a Templeton test withthe Analysis 2 tree as the best or uncon-strained instance (see Materials and Meth-ods) demonstrated that the toplogies weresignificantly different (P , 0.0001, Wil-coxon signed-rank statistic 556.0, N 5 70, Z5 24.3500). As expected, the tree length ofthe unconstrained tree (Analysis 2) was lessthan that of the constrained tree (Analysis1), and the consistency and retentionindices were higher in the unconstrainedtree, which also had a lower homoplasyindex. The number of parsimony-informa-tive and parsimony-uninformative charac-ters was consistent between the two analy-ses, despite the differing outgrouptopologies. Finally, in both analyses, boot-strap values for the ingroup nodes were allgreater than 50%, with the lowest support(the only values less than 80%) being for theXenosaurus + E. serratus node and theXenosaurus + E. lancensis node. Theinternode bounded by these nodes was theonly branch to collapse when characterswere run unordered, as described below.Ingroup topologies were identical betweenthe two trees.
When the matrix was run with allcharacters unordered, the internode be-
tween E. serratus + Xenosaurus and E.lancensis + Xenosaurus collapsed. Thissomewhat unexpected result emphasizesthat the position of R. rugosus as sister toall other xenosaurs here included is fairlyrobust, and that E. lancensis is known fromspecimens representing a relative paucity ofphylogenetic information. At a glance, theloss of resolution of E. serratus + Xeno-saurus seems absurd; E. serratus is nearlyidentical to Xenosaurus in several uniquefeatures. Notable among these is the highlydomed form of the maxillary osteoderms, asopposed to the primitively flat osteodermsof E. lancensis. That distinction is repre-sented in the scorings of character 62, amultistate character representing a morpho-cline from a flat plate-like morphology to abroken-up domed morphology. The natureof the problem lies in the status of E.lancensis as a ‘‘transitional form,’’ uniquelydisplaying a broken-up but undomed mor-phology. In an unordered scheme, thetransitional nature of this morphology isnot recognized, and it instead becomessimply an autapomorphy. Indeed, a simpli-fication of the character scoring to twostates (not domed and Xenosaurus-like, ordomed and Xenosaurus-like) results in amajority-rule consensus identical to theingroup tree produced by the ordered data.Two other multistate characters, 46 (thesteepness of the slanted dorsal margin of thelacrimal recess) and 108 (the lateral projec-tion of the cristae cranii), likewise havestates that are unambiguous synapomor-phies of E. serratus + Xenosaurus, whereasE. lancensis has an intermediate state.
Outgroup Topology
The alliance of S. crocodilurus and thefossil B. ammoskius was established byConrad (2005, 2006) and Conrad et al.(2011). My study also agrees with Conrad etal. (2011) in placing M. ornatus Klembara2008 as sister to a Shinisaurus + Bahndwi-vici clade in a phylogenetic analysis. Allother relationships were set using a con-straint tree to generate Analysis 1 (see
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Materials and Methods). However, Analysis2 was generated by specifying only P.torquatus as an outgroup for the analysisand therefore generated a hypothesis ofanguimorph relationships (Fig. 7). UnderAnalysis 2, the initial split of Anguimorpha isbetween the traditional Xenosauridae, in-cluding the Xenosaurus clade and theshinisaurs, and an Anguidae + Varanoideaclade. Anguidae consists of an Anguinae +Diploglossinae clade to the exclusion ofGerrhonotinae, and Varanoidea has itstraditional topology of Helodermatidae +Varanidae, with Varanidae consisting of L.borneensis and Varanus.
Character States Supporting Clades andTerminal Taxa
Following are lists of character statessupporting the focal clades in this study(synapomorphies) and terminal taxa (auta-pomorphies) under each hypothesis. Starredstates (*) are unambiguous. Clade number-ing is arbitrary, but clades common to bothhypotheses (clades 1 to 22) have the samenumber under both listings. Characterstates unique to one hypothesis are denotedwith a capital ‘‘U’’ (not marked as such whenstate being transitioned from is different),and states that differ between analyses inambiguity are denoted with a lowercase ‘‘u.’’
When dealing with scores of ?, acceleratedtransformation (ACCTRAN) optimization isassumed. My character descriptions areworded with neither accelerated transitionnor delayed transformation (DELTRAN)optimization in mind, and they are thusmore complete guides to character distribu-tion than the following lists. One exceptionobtains in the case of the character descrip-tions and in the lists below—when data aretruly missing, instead of a character beinginapplicable to the taxon (see Strong andLipscomb, 1999), I use a DELTRAN-typeassumption, placing ambiguous synapomor-phies at more exclusive nodes instead ofassuming early transformation. Those trans-formations are listed in brackets followingthe other transformations optimized at the
nodes in question. Specifically, those nodesare all of those for which one branch iscompletely extinct and therefore representedby incomplete fossils: Xenosaurus + R.rugosus, Xenosaurus + E. lancensis, Xeno-saurus + E. serratus, S. crocodilurus + M.ornatus, and S. crocodilurus + B. ammoskius.Additionally, I use the same approach for theosteodermal characters of X. agrenon at theX. agrenon + X. rectocollaris node becausedata were unavailable regarding the osteo-derms of X. agrenon.
Analysis 1
1. Xenosaurus + Restes rugosus: 1 0-2*; 510-1*; 52 1-2 U*; 53 0-1*; 59 0-1 U*; 646-7 U; 66 0-1 U*; 67 0-1*; 69 0-1 U*; 720-1*; 97 1-2; 109 0-1*; 111 0-1*; 113 0-1U; 114 0-1*; 131 0-1; 132 1-2; 145 0-1*;184 0-1; 186 0-1 U*; 191 0-1; 193 0-1U*; 196 0-1 U*; 214 0-1*;
2. Restes rugosus: 43 2-0 U; 125 1-0 U; 1440-1*; 204 0-1*
3. Xenosaurus + Exostinus lancensis: 62 2-3*; 93 1-0; 96 0-1*; 97 2-3*; 100 0-1; 1050-1 U*; 185 1-0 U; 193 1-2 [152 0-1];
4. Exostinus lancensis: 1 2-1; 92 1-0*; 1474-C*; 154 1-0*; 246 1-2*
5. Xenosaurus + Exostinus serratus: 46 0-1*; 54 0-1; 62 3-4*; 93 1-0; 98 0-1*; 99 0-1*; 108 0-1*; 191 1-0 [7 1-2; 8 0-3; 9 0-1;11 0-1; 19 0-1; 22 0-1 U; 47 0-1 U; 55 3-2 U; 63 1-0; 130 0-1; 68 1-2; 94 1-2 U;111 1-2; 124 1-2; 200 0-1 U; 209 0-1]
6. Exostinus serratus: 49 0-1*; 50 0-1*; 522-1*; 60 1-2*; 61 1-3*; 64 7-5*; 69 1-2*;70 0-1*; 71 0-1*; 98 1-2*; 101 0-1*; 1060-1*; 107 0-1*; 108 1-2*; 131 1-0; 1322-1; 185 0-1 U; 192 0-1*; 193 2-0*; 1940-1*
7. Xenosaurus: 2 0-1*; 8 3-4*; 9 1-2*; 10 0-1; 17 0-1*; 21 2-3*; 23 0-1*; 26 0-1*; 450-1*; 56 4-3; 57 0-1*; 58 0-1*; 64 7-9*;93 0-1*; 100 1-0; 104 0-1; 128 0-1*; 1841-0; 195 1-0*; 196 1-0*; 201 0-1* [30 1-2; 31 0-1; 34 0-1; 35 0-1; 37 0-1; 75 0-1;85 0-1; 86 0-1; 116 0-1; 117 0-1 U; 1352-1; 136 0-1; 137 0-1 U; 139 0-1 U; 1420-1; 145 1-2; 146 0-1; 147 4-3; 148 4-2;
XENOSAUR PHYLOGENY N Bhullar 167
159 0-1 U; 161 0-1; 162 0-1 U; 165 0-1;167 1-2; 168 0-1; 169 0-3 U; 173 0-1;199 0-1; 205 0-2; 207 0-1; 208 0-1; 2111-2; 213 0-1 U; 228 0-1; 238 0-1; 243 0-1; 248 3-2; 260 0-1 U; 261 0-1 U; 263 0-1 U; 264 1-2; 265 0-1 U; 268 0-1 U; 2720-1]
8. Northern clade of Xenosaurus: 13 0-1*;16 0-1*; 18 0-1; 20 1-0*; 21 3-4*; 22 1-2*; 28 0-1*; 29 1-2; 39 0-1*; 41 0-1*;42 0-1*; 43 2-3*; 54 1-0; 60 1-0*; 649-B*; 68 2-3*; 73 0-1*; 75 1-2*; 76 1-2*; 79 0-1*; 84 0-1*; 85 1-2*; 95 0-1*;110 0-2*; 111 2-3*; 116 1-3*; 122 0-1*; 143 0-1*; 154 1-2*; 158 0-1*; 1780-1 U*; 187 0-1*; 202 0-1*; 219 0-1*;220 0-1*; 225 0-1*; 226 0-1*; 229 0-1*; 239 0-1*; 248 2-1*; 249 3-0*; 2510-1*; 255 0-1*; 258 2-3*; 259 1-0*;267 2-1*
9. Xenosaurus newmanorum: 56 3-5*; 650-1*; 88 1-2; 135 1-2; 147 3-4; 148 2-0*;154 2-3*; 174 2-0*; 181 1-0; 182 1-0*;198 0-1*; 223 1-0*; 224 0-1*; 234 1-0*;235 0-1*; 237 0-1*; 260 1-0*; 263 1-0 u;268 1-0 u
10. Xenosaurus platyceps: 61 1-2*; 80 0-1;89 0-1*; 118 0-1; 119 0-1*; 120 0-1*; 1270-1*; 135 1-0*; 193 2-3*; 206 0-1*; 2141-2*; 215 1-2*; 223 1-2*; 232 0-1*; 2341-2*; 240 0-1*; 248 1-0*; 254 0-1*; 2583-4*; 262 0-1; 265 1-0 u; 266 1-2*; 2671-0*
11. Southern clade of Xenosaurus: 11 1-2*;12 0-1*; 27 0-1 u*; 36 0-1; 37 1-2*; 38 0-1; 40 0-1*; 43 2-1; 68 2-0*; 74 1-2; 78 1-2*; 83 0-1 U; 90 0-1*; 102 0-1*; 126 0-1;134 0-1*; 138 0-1*; 147 3-1*; 151 0-1;157 1-2; 165 1-2*; 183 1-0 U; 204 0-1*;217 1-0; 242 0-1*; 245 0-1*; 250 0-1 U*;252 0-1*; 253 0-1 U*; 256 0-1 U*; 257 0-1*; 260 1-2 U*; 264 2-3*; 265 1-2 U*;268 1-2*; 269 0-1 U*; 270 1-2 U*; 2721-2*; 273 0-2
12. Xenosaurus agrenon + Xenosaurus rec-tocollaris: 46 1-2*; 56 3-2*; 88 1-0*; 1351-0*; 142 1-0; 147 1-0*; 155 1-2*; 1631-0*; 170 0-1*; 171 0-1*; 175 1-0; 1760-1*; 188 0-1*; 190 0-1*; 203 0-1*; 2160-1*;
13. Xenosaurus agrenon: 55 2-1*; 56 2-1*;74 2-1; 76 1-0*; 77 0-1*; 110 0-1*; 148 2-3; 150 0-1*; 166 0-1*; 181 1-0; 198 0-1*;217 0-1; 239 0-1*
14. Xenosaurus rectocollaris: 8 4-0*; 16 0-1*; 60 1-2*; 64 9-B*; 83 1-0; 87 2-1*; 961-0*; 123 0-1*; 131 1-0*; 148 2-1*; 2141-2*; 215 1-0*; 229 0-1*; 234 1-0*; 2360-1*; 271 0-1*; 273 2-0 [264 3-4]
15. Xenosaurus grandis + Xenosaurus rack-hami: 5 0-1*; 15 0-1*; 58 1-2*; 65 0-1*;82 0-1*; 103 0-1*; 112 0-1*; 115 0-1*;133 0-1*; 139 1-2*; 141 0-1*; 151 1-2*;155 1-0*; 156 0-1*; 159 1-0 u; 160 0-1*;163 1-2*; 167 2-3*; 168 1-2*; 169 3-2 u;172 0-1*; 174 2-1 U*; 179 0-1*; 182 1-2u; 197 0-1*; 221 0-1*; 227 2-1 u*; 2482-3; 252 1-2*; 253 1-2*; 256 1-2*; 2602-3*; 265 2-3*
16. Xenosaurus rackhami: 56 3-4; 81 0-1*;88 1-4*; 126 1-0; 135 1-2; 140 0-1*; 1482-3; 153 0-1*; 165 2-3*; 166 0-1*; 1692-1*; 177 0-1*; 205 2-1*; 240 0-2*; 2493-6*; 252 2-3*; 256 2-3*
17. Xenosaurus grandis: 55 2-1*; 58 2-3*; 840-1*; 116 1-2*; 120 0-1*; 127 0-1*; 1471-2; 157 2-1; 180 0-1*; 181 1-0; 1932-1*; 198 0-1*; 255 0-1*
18. Shinisaurus crocodilurus + Merkuro-saurus ornatus: 20 1-2*; 22 0-1 U; 252-0; 52 1-2 U*; 155 1-0*; 193 0-1 U*;196 0-1 U*
19. Shinisaurus crocodilurus + Bahndwiviciammoskius: 47 0-1 U*; 98 0-1*; 147 5-6*[29 1-2; 55 3-2 U; 59 0-1 U; 66 0-1 U; 690-1 U; 117 0-1 U; 200 0-1 U; 218 1-0 U;233 0-1]
20. Merkurosaurus ornatus: 7 1-0; 23 0-1*;92 1-0*; 94 1-2 U*; 185 1-0 U*
21. Bahndwivici ammoskius: 22 1-0 U; 552-1*; 64 5-8* U; 97 1-3*; 134 1-0 U; 1512-3*; 154 1-0*; 240 0-1*
22. Shinisaurus crocodilurus: 5 0-1*; 94 1-0*; 124 0-1 U*; 138 0-1*; 147 6-9*; 1484-3*; 152 0-1 u* [14 1-0 U; 46 0-2; 83 0-1 U; 88 1-5 U; 93 0-1; 113 0-1 U; 126 0-1; 136 0-1 U; 137 0-1 U; 139 0-1 U; 1590-1 U; 169 0-3 U; 174 2-1 U; 178 0-1 U;182 1-0; 183 1-0 U; 186 0-1 U; 188 0-1;213 0-1 U; 222 1-0 U; 227 2-0; 230 1-0;
168 Bulletin of the Museum of Comparative Zoology, Vol. 160, No. 3
231 1-0; 249 3-2 U; 250 0-1 U; 253 0-2;256 1-2; 258 2-1; 260 0-2 U; 263 0-1 U;265 0-2 U; 266 1-0; 268 0-1 U; 273 0-1 U]
23. Xenosaurus + Anguidae: 27 1-0*; 32 0-1*; 33 0-1; 43 0-2; 45 1-0; 56 2-4*; 60 0-1; 62 0-2; 78 0-1; 124 0-1; 125 0-1; 1290-1; 149 0-1*; 157 0-1; 175 0-1; 210 0-1;212 0-1
Analysis 2
1. Xenosaurus + Restes rugosus: 1 0-2*; 451-0 U*; 51 0-1*; 53 0-1*; 60 0-1 U*; 620-2 U*; 67 0-1*; 72 0-1*; 97 1-2; 109 0-1*; 111 0-1*; 114 0-1*; 131 0-1; 132 1-2;145 0-1*; 191 0-1; 210 0-1 U*; 214 0-1*
2. Restes rugosus: 55 2-3 U*; 105 1-0 U;136 1-0 U; 137 1-0 U; 139 1-0 U; 144 0-1*; 185 0-1 U*; 200 1-0 U*; 204 0-1*
3. Xenosaurus + Exostinus lancensis: 62 2-3*; 93 1-0; 96 0-1*; 97 2-3*; 100 0-1; 1111-2; 125 0-1 U; 193 1-2 [152 0-1; 157 0-1 U; 184 0-1]
4. Exostinus lancensis: 1 2-1; 92 1-0*; 1475-C*; 154 1-0*; 246 1-2*
5. Xenosaurus + Exostinus serratus: 46 0-1*;54 0-1; 62 3-4*; 93 1-0; 98 0-1*; 99 0-1*;108 0-1*; 191 1-0 [7 1-2; 8 0-3; 9 0-1; 110-1; 14 0-1 U; 19 0-1; 43 0-2 U; 63 1-0; 681-2; 124 1-2; 129 0-1 U; 130 0-1; 209 0-1]
6. Exostinus serratus: 49 0-1*; 50 0-1*; 522-1*; 60 1-2*; 61 1-3*; 64 7-5*; 69 1-2*;70 0-1*; 71 0-1*; 98 1-2*; 101 0-1*; 1060-1*; 107 0-1*; 108 1-2*; 131 1-0; 1322-1; 185 0-1 u*; 192 0-1*; 193 2-0*; 1940-1*
7. Xenosaurus: 2 0-1*; 8 3-4*; 9 1-2*; 10 0-1; 17 0-1*; 21 2-3*; 23 0-1*; 26 0-1*; 450-1*; 56 4-3; 57 0-1*; 58 0-1*; 64 7-9*;93 0-1*; 100 1-0; 104 0-1; 128 0-1*; 1841-0; 195 1-0*; 196 1-0*; 201 0-1* [30 1-2; 31 0-1; 33 0-1 U; 34 0-1; 35 0-1; 37 0-1; 75 0-1; 78 0-1 U; 85 0-1; 86 0-1; 88 5-1 U; 116 0-1; 135 2-1; 142 0-1; 145 1-2;146 0-1; 147 5-3; 148 4-2; 161 0-1; 1650-1; 167 1-2; 168 0-1; 173 0-1; 175 0-1U; 199 0-1; 205 0-2; 207 0-1; 208 0-1;211 1-2; 212 0-1 U; 217 2-1 U; 218 0-1U; 222 0-1 U; 228 0-1; 238 0-1; 243 0-1;248 3-2; 264 1-2; 272 0-1]
8. Northern clade of Xenosaurus: 13 0-1*;16 0-1*; 18 0-1; 20 1-0*; 21 3-4*; 22 1-2*; 28 0-1*; 29 1-2; 39 0-1*; 41 0-1*; 420-1*; 43 2-3*; 54 1-0; 60 1-0*; 64 9-B*;68 2-3*; 73 0-1*; 75 1-2*; 76 1-2*; 79 0-1*; 83 1-0 U; 84 0-1*; 85 1-2*; 95 0-1*;110 0-2*; 111 2-3*; 116 1-3*; 122 0-1*;143 0-1*; 154 1-2*; 158 0-1*; 183 0-1U*; 187 0-1*; 202 0-1*; 219 0-1*; 220 0-1*; 225 0-1*; 226 0-1*; 229 0-1*; 239 0-1*; 248 2-1*; 249 2-0*; 250 1-0 U; 2510-1*; 253 1-0 U; 255 0-1*; 256 1-0 U;258 2-3*; 259 1-0*; 260 2-1 U; 265 2-1U; 267 2-1*; 269 1-0 U; 270 2-1 U; 2731-0 U
9. Xenosaurus newmanorum: 56 3-5*; 650-1*; 88 1-2; 135 1-2; 147 3-4; 148 2-0*;154 2-3*; 174 1-0*; 181 1-0; 182 1-0*;198 0-1*; 223 1-0*; 224 0-1*; 234 1-0*;235 0-1*; 237 0-1*; 260 1-0*; 263 1-0 u*;268 1-0 u*
10. Xenosaurus platyceps: 61 1-2*; 80 0-1;89 0-1*; 118 0-1; 119 0-1*; 120 0-1*; 1270-1*; 135 1-0*; 174 1-2 U; 193 2-3*; 2060-1*; 214 1-2*; 215 1-2*; 223 1-2*; 2320-1*; 234 1-2*; 240 0-1*; 248 1-0*; 2540-1*; 258 3-4*; 262 0-1; 265 1-0 u*; 2661-2*; 267 1-0*
11. Southern clade of Xenosaurus: 11 1-2*;12 0-1*; 27 0-1 u; 36 0-1; 37 1-2*; 38 0-1; 40 0-1*; 43 2-1; 68 2-0*; 74 1-2; 78 1-2*; 90 0-1*; 102 0-1*; 126 0-1; 134 0-1*;138 0-1*; 147 3-1*; 151 0-1; 157 1-2; 1651-2*; 178 1-0 U; 204 0-1*; 217 1-0; 2420-1*; 245 0-1*; 249 2-3 U; 252 0-1*; 2570-1*; 264 2-3*; 268 1-2*; 272 1-2*; 2731-2
12. Xenosaurus agrenon + Xenosaurus rec-tocollaris: 46 1-2*; 56 3-2*; 88 1-0*; 1351-0*; 142 1-0; 147 1-0*; 155 1-2*; 163 1-0*; 170 0-1*; 171 0-1*; 174 1-2 U; 175 1-0; 176 0-1*; 188 0-1*; 190 0-1*; 203 0-1*; 216 0-1*
13. Xenosaurus agrenon: 55 2-1*; 56 2-1*;74 2-1; 76 1-0*; 77 0-1*; 110 0-1*; 148 2-3; 150 0-1*; 166 0-1*; 181 1-0; 198 0-1*;217 0-1; 239 0-1*
14. Xenosaurus rectocollaris: 2-0*; 16 0-1*;60 1-2*; 64 9-B*; 83 1-0; 87 2-1*; 96 1-0*; 123 0-1*; 131 1-0*; 148 2-1*; 214
XENOSAUR PHYLOGENY N Bhullar 169
1-2*; 215 1-0*; 229 0-1*; 234 1-0*; 2360-1*; 271 0-1*; 273 2-0 [264 3-4]
15. Xenosaurus grandis + Xenosaurus rack-hami: 5 0-1*; 15 0-1*; 58 1-2*; 65 0-1*;82 0-1*; 103 0-1*; 112 0-1*; 115 0-1*;133 0-1*; 139 1-2*; 141 0-1*; 151 1-2*;155 1-0*; 156 0-1*; 159 1-0 u*; 160 0-1*;163 1-2*; 167 2-3*; 168 1-2*; 169 3-2 u*;172 0-1*; 179 0-1*; 182 1-2 u*; 197 0-1*;221 0-1*; 227 2-1 u; 248 2-3; 252 1-2*;253 1-2*; 256 1-2*; 260 2-3*; 265 2-3*
16. Xenosaurus rackhami: 56 3-4; 81 0-1*;88 1-4*; 126 1-0; 135 1-2; 140 0-1*; 1482-3; 153 0-1*; 165 2-3*; 166 0-1*; 169 2-1*; 177 0-1*; 205 2-1*; 240 0-2*; 249 3-6*; 252 2-3*; 256 2-3*
17. Xenosaurus grandis: 55 2-1*; 58 2-3*; 840-1*; 116 1-2*; 120 0-1*; 127 0-1*; 1471-2; 157 2-1; 180 0-1*; 181 1-0; 193 2-1*; 198 0-1*; 255 0-1*
18. Shinisaurus crocodilurus + Merkuro-saurus ornatus: 20 1-2*; 25 2-0; 61 1-0U*; 149 1-0 U; 151 0-2 U; 155 1-0*; 1951-2*
19. Shinisaurus crocodilurus + Bahndwiviciammoskius: 94 2-1 U; 98 0-1*; 147 5-6*;185 0-1 U*; [27 0-1 U; 29 1-2; 48 0-1 U;56 4-2 U; 68 1-0 U; 118 0-1 U; 126 0-1;233 0-1]
20. Merkurosaurus ornatus: 7 1-0; 23 0-1*;47 1-0 U; 92 1-0*
21. Bahndwivici ammoskius: 22 1-0 U*; 552-1*; 64 5-8 U; 97 1-3*; 124 1-0 U; 1512-3*; 154 1-0*; 240 0-1*
22. Shinisaurus crocodilurus: 5 0-1*; 64 7-5U*; 94 1-0*; 134 0-1 U*; 138 0-1*; 1476-9*; 148 4-3*; 152 0-1 U [32 1-0 U; 460-2; 93 0-1; 182 1-0; 188 0-1; 227 2-0;230 1-0; 231 1-0; 253 1-2; 256 1-2; 2582-1; 266 1-0]
23. Xenosauridae: 3 0-1*; 6 0-1*; 7 0-1; 220-1*; 24 0-1*; 47 0-1; 52 0-2*; 59 0-1*;66 0-1*; 69 0-1*; 83 0-1; 93 1-0; 94 1-2;104 1-0; 105 0-1; 113 0-1; 117 0-1*; 1240-1; 136 0-1; 137 0-1; 139 0-1; 147 4-5;148 5-4*; 159 0-1*; 162 0-1*; 169 0-3*;178 0-1; 181 0-1; 182 2-1*; 186 0-1*; 1960-1*; 213 0-1*; 250 0-1; 253 0-1; 256 0-1; 260 0-2; 261 0-1; 263 0-1; 265 0-2;268 0-1; 269 0-1; 270 0-2*; 273 0-1
DISCUSSION
Relation to Previous Studies andTaxonomic Issues Raised
Under both starting hypotheses, xeno-saurs formed a clade within Anguimorphawhen allowed to vary across the entire tree,supporting the monophyly of the ingroup ofsix extant species of Xenosaurus and threeextinct taxa relative to the other includedtaxa. The relationship of the extinct taxa toXenosaurus is thus consistent with historicaldescriptions of the fossils suggesting xeno-saur affinities. Of the two prior studiespresenting explicitly phylogenetic hypothe-ses of relationships among extinct and extantxenosaurs, the position of R. rugosus outsideof a clade including Xenosaurus and E.serratus is consistent with those of bothGauthier (1982) and Conrad (2005, 2008).Restes rugosus as sister to all other xeno-saurs is specifically consistent with Conrad(2005, 2008). However, E. serratus as theimmediate sister to Xenosaurus was sug-gested by Gauthier (1982) but not Conrad(2005, 2008), who recovered a monophyleticExostinus. Note that the relationships ofxenosaurs were a primary focus of Gau-thier’s but not Conrad’s work (J. Conrad,2008; personal communication).
A single recent study suggests an allianceof the Mongolian Cretaceous taxon C.intermedia with xenosaurs (Conrad, 2008).A full analysis using the characters identi-fied in the present work will have toproceed after examination of fossil material,and in particular CT scans, of C. intermedia.More recent work has indicated that C.intermedia might not be an anguimorph (J.A. Gauthier, personal communication);thus, a broader spread of scleroglossancharacters and taxa than used in this studymight be required to establish its phyloge-netic position.
As predicted by previous studies (Gau-thier, 1982; Estes, 1983; Conrad, 2008), Irecovered Exostinus as a paraphyletic groupconsisting of two successive sister taxa toXenosaurus. Notwithstanding concernsabout the assignment of specimens to E.
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lancensis, that taxon would then require anew genus name, and Exostinus wouldbecome monotypic, including only E. serra-tus. I propose to resurrect the nameHarpagosaurus, applied by Gilmore (1928)to a maxilla now referred to E. lancensis(Estes, 1964, 1983). A more formal defini-tion will require further study of knownmaterial of E. lancensis, which may repre-sent several taxa (Gao and Fox, 1996).
As already discussed, the recovery of amonophyletic Xenosauridae in generatingAnalysis 2 is consistent with most morpho-logical phylogenetic hypotheses, but notwith studies based on molecular structureor with hypotheses proposed by Conrad(2005, 2008). Aside from this result, theclose relationship of B. ammoskius to S.crocodilurus was again confirmed (Conrad,2006). Moreover, M. ornatus, B. ammoskius+ Shinisaurus as recovered by Conrad et al.(2011). That result provides support for theshinisaur affinities of the taxon (Klembara,2008).
Temporal Implications
Exostinus serratus, sister to Xenosaurus,is nearly identical to the crown clade in mostaspects of its known anatomy. Many of thecharacter states appearing in the crownclade had thus arisen by the age of theOrellan sediments from which E. serratuswas collected (Swisher and Prothero, 1990).Thus far, no extinct taxa that fall within thecrown clade Xenosaurus have been identi-fied. This ‘‘genus’’ may be very ancientindeed, like some anguid ‘‘genera’’ (Estes,1983; personal observation). Exostinus lan-censis, from the Late Cretaceous, is theoldest extinct taxon on the stem of Xeno-saurus according to this study. The knownfossil record of Anguidae and Helodermati-dae, the putative sister groups to thexenosaur lineage in Analysis 1, are consis-tent with a Mesozoic split. Odaxosauruspiger is a primitive glyptosaur from theCretaceous (Meszoely, 1970; Gauthier,1982; Estes, 1983), and the primitivehelodermatids G. pulchra and P. nessovi
are from the Upper Cretaceous of Mongoliaand the Albian-Cenomanian of Utah, re-spectively. (If P. nessovi is indeed ahelodermatid, its presence in the EarlyCretaceous would suggest significant ghostlineages for xenosaurs and anguids.) Thefossil record of shinisaurs extends back tothe late Paleocene/early Eocene (Smith,2006b), leaving a longer ghost lineage forthe shinisaur branch of the Xenosauridae inAnalysis 2. However, a number of NorthAmerican Cretaceous ‘‘platynotan’’ taxaknown from fragmentary remains have yetto be fully examined in a phylogeneticcontext, and among these might be foundpart of the missing shinisaur lineage (Estes,1983; K. T. Smith, personal communication;personal observation).
Some notable stratigraphic incongruitiesare present in the phylogenetic hypothesesrecovered here. The Paleocene R. rugosus issister to all remaining xenosaurs, includingthe Cretaceous E. lancensis. The R. rugosuslineage has yet to be recovered from theMesozoic. However, R. rugosus itself ap-pears to be exceedingly rare in Paleogenefaunas (Smith, 2006b; K. T. Smith, personalcommunication), and this may apply to itspredecessors, as well. The second incongru-ity is the closer relationship of B. ammoskiusfrom the North American Eocene to theextant Asian S. crocodilurus than Merkur-osaurus ornatus from the European Mio-cene (Conrad, 2006; Klembara, 2008). Thismight suggest an early Paleogene transat-lantic dispersal of the Merkurosaurus line-age, much like that which has beensuggested to have resulted in the appear-ance of the primitive helodermatid E.gallicum in the Eocene of France (Hoff-stetter, 1957) and the iguanian Geiseltaliel-lus in the Eocene of Germany (K. T. Smith,personal communication). One would thenexpect to find the Merkurosaurus lineage inearlier European deposits and in EarlyPaleogene or Mesozoic North Americandeposits. The former has not yet beenreported, but the latter expectation may befulfilled by the host of shinisaur-related taxabeing identified from screenwashed early
XENOSAUR PHYLOGENY N Bhullar 171
Eocene and late Paleocene North Americanmicrofaunas (Smith, 2006b). Alternatively,in the case of both shinisaurs and heloder-matids, the North American and Europeanrepresentatives could have been derivedfrom an unknown Asian stock. Primitivehelodermatids were present in present-dayMongolia during the Late Cretaceous (Gaoand Norell, 2000).
Finally, taxa farther down the stem ofXenosaurus than R. rugosus are notablylacking. As noted already, relatively primitivehelodermatids and shinisaurs have beenfound, but another frustrating absence existsalong the stem of Anguidae. The highlyderived glyptosaurs are the only putative stemanguids known, and even that placement isnot strongly supported, for they alreadypossess most of the derived features of anguids(Conrad, 2005, 2008; Conrad et al., 2011; J. A.Gauthier, personal communication).
Biogeography of Xenosaurs
There is a striking difference in latitudebetween the locations of collections of thestem xenosaurs in this study, all of whichwere found in Colorado, Wyoming, andfarther north still, and the present distribu-tion of Xenosaurus in central and southernMexico. That pattern obtains for othersquamate taxa, as well—notably diploglos-sine anguids (Gauthier, 1982; Smith, 2006b;personal observation) and polychrotineiguanians (Smith, 2006a, 2006b). The ap-parent contraction of the ranges of parts ofclades has been convincingly attributed tothe contraction of megathermal climatezones during the global cooling followingthe Paleocene/Eocene thermal maximum bySmith (2006b).
Xenosaurus are, with few exceptions,crevice-dwelling lizards and are distributedalong the great north–south-extendingmountain ranges of Mexico. The initial splitwithin Xenosaurus is a division between anorthern clade, consisting of X. newma-norum and X. platyceps in the Sierra MadreOriental, and a southern clade, consisting ofthe remaining taxa (King and Thompson,
1968; Canseco Marquez, 2005), of whichthe X. agrenon + X. rectocollaris clade ismore to the west and the X. grandis + X.rackhami clade is more to the east, extend-ing into Central America. Xenosaurus rack-hami has a particularly wide distribution,and I observed more intraspecies variationin that species of Xenosaurus than in theothers for which I had sample sizes largerthan one or two. Further details of thebiogeography of Xenosaurus were providedby Canseco Marquez (2005).
Comments on Ingroup Clades
Xenosauridae. Analysis 2, the uncon-strained analysis, strongly recovered amonophyletic Xenosauridae in the classicalsense, as also suggested, but not cladisticallytested, by Smith (2006b). Many of thecharacters supporting the clade were notused by Conrad (2005, 2008). Two charac-ters, the subpalpebral fossa and the medio-laterally expanded facet on the maxilla, arepresent in association with slightly differentelements in the two taxa, but this does notinvalidate their potential homology accord-ing to the tree. Several other characters,including the upfolded tab of the facialprocess of the maxilla, are unique withinSquamata. Part of the difficulty of resolvingthe degree of relatedness between xeno-saurs and shinisaurs is the poor fossil recordalong the stem of Anguimorpha. It is quitepossible that the character states that seemso peculiar to the classical Xenosauridae arein fact ancestral for Anguimorpha as awhole.
Xenosaurus + Restes rugosus. The mostinclusive clade of the xenosaur lineagealready has the characteristic dentition ofthe group. Among the bones surroundingthe nasal capsule, the maxilla shows acombination of plesiomorphic and derivedfeatures, notably a primitively platey, con-tinuous osteodermal covering. The palpe-bral and prefrontal already display typicalxenosaur morphologies. Likewise, the fron-tal and jugal bear several synapomorphieswith the other xenosaurs, but they are
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primitive in various respects, as well. Whatis preserved of the palate is intermediatebetween Xenosaurus and the remainder ofAnguimorpha, in particular the persistenceof remnants of the pterygoid dentition.Restes rugosus is the only fossil xenosaurto preserve any of the palate. The primi-tively long, narrow postorbital suggests thatthe supratemporal arch was not expandedand heavily ornamented as in Xenosaurus. Itis thus likely that the general flattening ofthe head and possibly the body evident inthe crown clade was not as developed in theancestor of this more inclusive clade.
Differences in synapomorphies support-ing the clade between Analysis 1 andAnalysis 2 have largely to do with the issueof xenosaurid monophyly. In Analysis 1,several features shared by xenosaurs andshinisaurs optimize as convergent and areadded to the apomorphy list for Xenosaurus+ R. rugosus.
Restes rugosus. Restes rugosus displays ahost of plesiomorphic characters for xeno-saurs, exhibiting few obvious autapomor-phies in its known anatomy. The mostobvious of its autapomorphies is the unusu-ally large angle of divergence of the medialand lateral edges of the palatine process ofthe pterygoid. It is unclear whether thatmorphology indicates a similarly peculiarmorphology for the remainder of the palate,which is not preserved. In Xenosaurus,despite the widening of the head, thepalatine process of the pterygoid is notparticularly expanded.
Xenosaurus + Exostinus lancensis. Exo-stinus lancensis is not a well-known taxon,and this clade is supported largely by themore broken-up osteoderms on the maxillaand the Xenosaurus-like domed osteodermsof the frontal. The frontal is still uncon-stricted interorbitally compared with E.serratus and Xenosaurus, but the cristaecranii approach each other more closelythan in R. rugosus. Exostinus lancensis is theonly fossil xenosaur, unfortunately, to pre-serve the parietal. The supratemporal pro-cesses are broken and so could not be
scored, but they appear to have been shortas in Xenosaurus.
Exostinus lancensis. This is a difficulttaxon for reasons already stated, relating toincompleteness and difficulty in the assign-ment of specimens. Its recovered positioncloser to the crown clade than R. rugosusrequires a reversal in tooth form fromslightly bicuspid to unicuspid. However,despite the assertion of the most recentdescription that all teeth in E. lancensis areunicuspid (Gao and Fox, 1996), someAMNH specimens I examined for this studyshow an apical, longitudinal groove like thatwhich extends basally from the divisionbetween the smaller mesial and the largerdistal cusps in those xenosaurs that have abicuspid morphology (e.g., AMNH 15366).The apices of the teeth of all of thesespecimens are damaged. Furthermore, al-though the skull roof osteoderms of E.lancensis are domed like those of E. serratusand Xenosaurus, their form is unusual. Theyare oval or obovate and on the parietal showa concentric distribution unique to E.lancensis.
Xenosaurus + Exostinus serratus. Thesetwo taxa are nearly identical in many aspectsof their osteology, although only the rostralportions of the skull are known for E.serratus, and these incompletely. The os-teoderms in general are of the characteristicXenosaurus form and distribution. Thedentition also has the form seen in primitiveparts of the crown clade. However, thenares are primitively large and elongate;concomitantly, the nasal process of thepremaxilla, although expanded, is not soexpanded as in Xenosaurus, and the slope ofthe narial margin of the maxilla is gentlerand longer. Unfortunately, premaxillae areunknown from other fossil xenosaurs.
Exostinus serratus. This is essentially ashort-faced xenosaur, its rostrum autapo-morphically short, reflected in features suchits reduced tooth count. Additionally, theunusually wide palatal shelf of the maxillasuggests a particularly wide skull with themaxillae diverging from each other at a highangle. The lack of a posterior expansion of
XENOSAUR PHYLOGENY N Bhullar 173
the jugal is another strange autapomorphy.The various unique features of this taxonraise the question of whether xenosaurswere relatively diversified earlier than thecrown radiation. In turn, it is unclear whereless autapomorphic lineages more similar tothe crown might be found.
Xenosaurus. Xenosaurus, in part becauseconstituents are extant and thus much morecompletely known, is supported by a largenumber of synapomorphies. Notable are themediolateral expansions of the nasal processof the premaxilla and the squamosal and therelative mediolateral widening of the parie-tal. Several bones, such as the septomaxillaand coronoid, are expanded and enclosemore nerves and vasculature than theprimitive state. The body is flattened andthe neural spines relatively low; various otheraxial and appendicular synapomorphies alsoexist, such that the postcranium of Xeno-saurus is fairly distinct among anguimorphs.
Northern clade of Xenosaurus. The north-ern clade of Xenosaurus, widely separatedgeographically from the remaining species,retains a number of ancestral characters thatthe southern clade has lost, notably theproportions of the skull roof bones. How-ever, the taxa within the northern clade areunited by a consistent suite of synapomor-phies—more than the southern taxa. Amongthese synapomorphies are several featuresof the anterior maxilla and premaxilla.Furthermore, the heavy osteodermal armorof the northern clade optimizes as primitiveif the heavily armored helodermatids andanguids are the immediate sister taxon toxenosaurs. However, it optimizes as derivedor ambiguous if the more lightly armoredshinisaurs are used.
Xenosaurus newmanorum. This is a large-bodied species (King and Thompson, 1968).Other than its large size, it is in general theless autapomorphic of the two examinedspecies from the northern clade. It has aparticularly tall head for Xenosaurus, possi-bly a primitive feature (Herrel et al., 2001).As the less autapomorphic part of thenorthern clade, which itself retains a num-ber of ancestral characters, X. newmanorum
might be a better taxon to include inphylogenetic analyses than the commonlyused X. grandis and X. platyceps (e.g.,Conrad, 2008, who noted the shortcomingsof scoring a composite ‘‘Xenosaurus’’ fromX. grandis and X. platyceps—although thesetwo taxa do bracket the clade).
Xenosaurus platyceps. This is the flattestspecies of Xenosaurus, in head and body.Several autapomorphies of the maxilla andskull roof relate to the particularly flat, widehead of the taxon, and unusual morpholo-gies of the axial and appendicular skeletonsmight also relate to this marked dorsoven-tral compression.
Southern clade of Xenosaurus. The south-ern clade of Xenosaurus is united by a largenumber of synapomorphies, most of themrelatively subtle, such as the proportions ofosteodermal sculpturing and proportions ofarticular parts of the dermal cranial roof andsidewall. The ranges of some of the taxawithin are considerably greater than those ofthe species within the northern clade (i.e., X.rackhami; King and Thompson, 1968), andthe individual species as a whole are moremorphologically divergent than the relativelysimilar X. newmanorum and X. platyceps.
Xenosaurus agrenon + Xenosaurus recto-collaris. This clade, consisting of two little-known taxa for which I had but onespecimen each, is supported by the fewestsynapomorphies of the clades within Xeno-saurus. Nevertheless, some of these syn-apomorphies (e.g., the unusual notch in theposterior region of the parietal, the mor-phology of the central region of thebasisphenoid, and the bizarre flattenedneural spines of the lumbar region) arestriking and unique, and the clade appearsrobust. In general, this clade shares severalancestral character states with the northernclade that are no longer present in the well-supported X. rackhami + X. grandis clade.In contrast to the meager osteodermalarmor of the latter clade, the X. agrenon +X. rectocollaris clade shares relatively heavyarmor with the northern clade.
Xenosaurus agrenon. This species isparticularly little known, appearing exter-
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nally very similar to X. grandis, but inter-nally sharing a number of synapomorphieswith X. rectocollaris. A distinct form of thesupratemporal arch is one of the fewautapomorphies distinguishing it from itscommon ancestor with that taxon.
Xenosaurus rectocollaris. This is the mostunusual of the species of Xenosaurus at firstglance. Its head is particularly short andstout, although the shortening appears toinvolve the postorbital dermal bones of theadductor/otic region, instead of the bonessurrounding the nasal capsule as in E.serratus. Externally, the taxon is distin-guished by a bold dark-on-light colorpattern different from the light-on-darkpatterns of the other species of Xenosaurus,and it bears a strange cuff of puffy tissuearound its neck. It would be interesting toinvestigate possible ecological correlationsof the singular anatomy of this animal.
Xenosaurus rackhami + Xenosaurusgrandis. These two species share a numberof synapomorphies, most strikingly a dra-matic reduction of cranial osteoderms (post-cranial osteoderms are absent). Certainother features distinct to Xenosaurus, suchas the anteroposterior expansion of the tipof the jugal and the mediolateral expansionof the supratemporal arch, are at their mostextreme in these two taxa, which are alsoperhaps the best represented in U.S.museum collections.
Xenosaurus rackhami. This species isslender of head and body compared withother Xenosaurus, and some individualshave particularly flat heads. In X. rackhami,the reduction of osteoderms is the extremeamong examined Xenosaurus, and severalpeculiar autapomorphies of the skull roofand supratemporal bar, as well as thedentition, also obtain.
Xenosaurus grandis. This is a relativelyunusual species of Xenosaurus, stout androbust where its sister taxon is slim andslight. The reduction of osteoderms is lessextreme in X. grandis, and some of theautapomorphies of the taxon relate to itsgenerally stout form. Xenosaurus grandis isthe most common species of Xenosaurus in
U.S. collections, and the most heavilyfigured and described (notably by Barrowsand Smith, 1947). It is generally used as theexemplar for Xenosaurus, and sometimesfor the classical Xenosauridae as a whole(Wever, 1978; Estes et al., 1988). Consid-ering the large number of apomorphiesbetween X. grandis and the Xenosaurusancestor, it is not the ideal choice. Only onerecent study (Conrad, 2008; extended inConrad et al., 2011) included a prudentcombination of X. grandis and X. platyceps,bracketing Xenosaurus.
Morphological Characters in PhylogeneticAnalysis and Specific Issues ofCharacter Evolution
My analysis includes an unusual numberof characters for such a restricted group oflizards (compared with, e.g., Rieppel andZaher [2002] for uropeltid snakes, a group ofsimilar size and high specialization). Thesurfeit of characters owes in part to mydiscovery of a number of informative fea-tures in previously unappreciated elements,such as the septomaxilla and the palpebral—these discoveries in turn owing to theavailability of disarticulated skeletal material.Characters such as small foramina in thesediminutive bones were remarkably invariantwithin taxa, and the fact that this seemscounterintuitive suggests that a large numberof characters dealing with subtle differencesin anatomy are arbitrarily neglected in grossanatomical phylogenetics. Further work, inparticular, on subtle features of disarticulat-ed bones, could be immensely profitable inincreasing the number of gross-scale charac-ters to achieve greater parity with the size ofmolecular-scale datasets (Chippindale andWiens, 1994). Already, work on subtle andtiny foramina dotting the dermatocranialelements of certain mammals has shown thatthe clustering of these foramina are consis-tent within taxa and appear to be phyloge-netically informative (Wible, 2003; Kearneyet al., 2005).
In addition to hypotheses of relationships,phylogenetic analyses provide a thorough
XENOSAUR PHYLOGENY N Bhullar 175
catalogue of anatomical changes in thestructures utilized, whether at the gross,histological, or molecular scale—they are insome ways ‘‘shorthand’’ descriptions ofanatomy. Several characters or charactersystems here examined stand out as poten-tially fruitful for additional study. Theenclosure of the ethmoid nerves within thepremaxilla (character 6) is unusual withinSquamata. It is interesting that xenosaursshow both this character and very heavyosteodermal sculpturing—as do very oldindividuals of E. multicarinata. The appear-ance of xenosaur-like features in very latestage E. multicarinata might suggest aheterochronic relationship, wherein somecharacters of xenosaurs are peramorphicwith respect to those of anguids and perhapsother anguimorphs.
The increased number of foramina in thepremaxilla (characters 7 and 8) and maxilla(characters 53 and 54) in xenosaurs mightsuggest an increased acuity of integumen-tary sensation, perhaps related to thedecreased utility of sight in the darkenvironments frequented at least by indi-viduals of Xenosaurus. Increased numbersof foramina on the face have been suggestedto imply great tactile acuity in amphisbae-nians, as well (Kearney et al., 2005). Theincreased diameter of the infraorbital canalwithin xenosaurs (character 51) indicates anincrease in the size of the containedneurovascular bundle, which includes theV2 division of the trigeminal nerve. Anenlarged canal for V3 is associated with theenormously elaborated sensory capabilitiesof the platypus snout (Rowe et al., 2008).
The various septomaxillary charactersidentified herein are remarkably phyloge-netically useful and consistent with regardto variation, considering the general neglectof this skeletal element in the non-snakesquamate literature. Clearly the septomax-illa is complex and evolutionarily labile, andI predict that it will prove a rich source ofcharacters for other clades, as well. Themorphology in Xenosaurus, with its fullyenclosed medial and lateral canals, isespecially remarkable, and one wonders at
the possible soft tissue and sensory corre-lates. The complete enclosure of the lateralcanal in Xenosaurus and Heloderma recallsthe sister taxon relationship between thosetaxa suggested by some analyses in molec-ular-scale studies (Townsend et al., 2004).
Several transformations in the temporalregion, notably the lateral and ventralexpansion of the postorbital and squamosaland the anteroposterior expansion of thejugal, occur along the stem of Xenosaurus.Seemingly accompanying these changes arethe strong surangular crest and the subcor-onoid fossa. Possibly these features arevariously related to the enormously elabo-rated adductor musculature of Xenosaurus(Haas, 1960). If they are so related, theymay together represent a complex ofcharacters that are not fully independentfrom each other.
Finally, Xenosaurus shows a lack ofdepression in the posterior end of thequadrate for the tympanic cavity (character173). Varanidae also display this character,but the quadrates of those taxa are heavilymodified. Possibly the lack of depression isrelated to a reduction of the tympanic cavityalso associated with the scaling over (andthus apparent functional impedance) of thetympanum (character 270). However, thedepression remains in Shinisaurus, whosetympanum is also scaled over in adulthood.
Character nonindependence is a recur-ring problem in phylogenetic analysis(Martins and Garland, 1991; Schaffer etal., 1991; Huelsenbeck and Nielsen, 1999;McCracken et al., 1999). Given the level ofintegration among the parts of a multicel-lular (or unicellular) organism, it is unlikelythat characters can ever be fully indepen-dent. Nevertheless, studies such as minecould profit from careful analysis ofcharacter correlation, taking into accountontogeny and the soft tissue relations ofbones. The character list I provided isarranged by sensory capsule, for example,because most dermatocranial elements areinvolved in sheathing one of the threecapsular regions (with the otic region beingmore complicated because of the additional
176 Bulletin of the Museum of Comparative Zoology, Vol. 160, No. 3
presence of the adductor chamber). Signif-icant changes in the basic structure of oneof the sensory capsules surely wouldproduce complementary changes in multi-ple sheathing bones. Considering theingroup of this study, a few other potentialsources of nonindependence arise. Thehead of Xenosaurus is unusually wide,and this general change may be related tothe mediolateral expansion of several der-matocranial elements and even the captureof previously external vascular and nervousstructures by the septomaxilla. In E.serratus, the shortness and width of thesnout could be related to several autapo-morphies of the taxon. Osteodermal devel-opment obviously shows general trends,with most regions of osteoderms reduced,for example, in X. grandis + X. rackhami.However, these trends are not alwaysuniform, preventing the scoring of a singlecombined character for the various poten-tially related transformations. For instance,cranial osteoderms are best developed in X.newmanorum and X. platyceps, especiallyin the former. Limb osteoderms, however,are more prominent and numerous in X.platyceps, whereas caudal osteoderms aremore developed in X. newmanorum. Thus,neither taxon can been scored overall ashaving the most ‘‘highly developed’’ osteo-derms, even if cranial and postcranialcategories are established.
Finally, an initial foray into studies of theintraspecies variation of characters is madeherein, although the attempt is basicallylimited to an effort to justify characterselection and scoring. A great deal ofadditional work needs to be done onintraspecies variation in all vertebrates,for this variation is the raw material ofevolution (Darwin, 1859; Bever, 2006 andreferences therein). In particular, com-pared with the attempts made here, furtherstudies must incorporate larger samplesizes, greater ontogenetic spreads, andcareful control of localities/populationsand the temporal aspect of collection.Xenosaurus provides an interesting casestudy for population studies because pop-
ulations of the species are spatially restrict-ed, often occupying a single rock cliff(Ballinger et al., 2000). That spatial restric-tion may account for the relatively largenumber of species of Xenosaurus, and it isnot clear whether significant gene flowoccurs among isolated populations (Lemos-Espinal et al., 2004). On a larger scale,aspects of variation can provide additionalcharacters for phylogenetic analysis. Inshort, morphological characters for phylo-genetic analysis are by no means exhaust-ed, even in the most heavily studied clades.A push for careful, thorough anatomicalanalysis of as much of the body as possible,ranging from the microscopic scale toaspects of variation and behavior, will yielda vast number of additional characters. Thelimited exercise provided by this workdemonstrates that even a thorough, bone-by-bone analysis of the skeleton alone canyield hundreds of novel characters andproduce a fully resolved phylogeny withhigh support values. In this case, congru-ence with DNA-based analyses allowsfurther confidence in the results, butconsidering the number of the charactersand the high support for the morphologicaltree, incongruence would necessitate care-ful reconsideration not only of the mor-phological but also of the molecular dataand analyses.
ACKNOWLEDGMENTS
This work is dedicated to my first advisorand colleague, my AP Biology teacher EricKessler, faculty of science, Blue ValleyNorth High School, Overland Park, Kansas.Also to my mother, Amarjit K. Bhullar, forshowing me the way, in the words ofHarvard’s alma mater, ‘‘for Right everbravely to live.’’
For financial support, I am grateful tothe Jackson School of Geosciences at TheUniversity of Texas at Austin, the DonaldD. Harrington Foundation, National Sci-ence Foundation (Graduate Research Fel-lowship), and Harvard University (JamesMills Peirce Graduate Fellowship). For
XENOSAUR PHYLOGENY N Bhullar 177
smaller grants, I thank Yale University, theJackson School of Geosciences, Sigma Xi,the Society of Systematic Biologists, theAmerican Society of Ichthyologists andHerpetologists, and the American Museumof Natural History Roosevelt Fund.
For allowing me to borrow unusualamounts of material pertaining to my thesisand to other projects, I thank Drs. MattCarrano (USNM); Mark Norell and CarlMehling (AMNH-VP); Kenney Krysko (UF);Jens Vindum (CAS); Jim Hanken, JonathanLosos, and Jose Rosado (MCZ); TravisLaDuc and Dave Cannatella (TNHC); JimMead (NAUQSP-JIM); Jimmy McGuire(MVZ); Greg Schneider (UMMZ); MaureenKearney and Alan Resetar (FMNH); JacquesGauthier (YPM-VZ and YPM-VP); GregWatkins-Colwell (YPM-VZ); Walter Joyce(YPM-VP); Jon Campbell and Carl Franklin(UTA); Carl Lieb and Bob Webb (UTEP);Gregg Gunnell and Jeffrey Wilson (UMMP);Amy Henrici (CM); and Darryl Frost(AMNH-H). I would also like to thankJacques Gauthier, Jessie Maisano, MaureenKearney, and Olivier Rieppel for allowing meto use their CT scans of the heads of X.grandis and X. platyceps.
For help in specimen preparation andscanning, I thank Jessie Maisano, MattColbert, Rich Ketcham, Marilyn Fox, andthe late Bob Rainey. In addition, I thank thefollowing fellow students for discussion andsupport: Krister Smith, Gabe Bever, RachelDunn, Tyler Lyson, Taka Tsuihiji, WalterJoyce, Jason Downs, Brian Andres, JohnVandenBrooks, Matt Benoit, Alana Kawa-kami, Ted Macrini, Murat Maga, HeatherAhrens, Alicia Kennedy, Agustın Scanferla,Jack Conrad, and Yi Hongyn.
My colleagues in Mexico, Luis CansecoMarquez, Julio Lemos-Espinal, and AdrianNieto Montes de Oca discussed xenosaurphylogeny and ecology with me extensively.
The master’s thesis of which this work isthe majority was enabled by a series ofexcellent advisors. The first of these wasEric Kessler, my high school biology teach-er, who fostered my interest in organismicbiology and herpetology. Second came
Jacques Gauthier at Yale, who trained mein vertebrate anatomy and squamate sys-tematics, as well as phylogenetic methodol-ogy. Tim Rowe at The University of Texas atAustin further assisted in my developmentas an anatomist and a phylogenetic thinker.My primary advisor, Chris Bell, supportedme in numerous ways, not least by offeringthe use of his extensive collection ofsquamate skeletons. Finally, Arhat Abzha-nov is my current advisor at Harvard. Hisflexibility and patience have allowed me tobegin work in a new field without sacrificingthe old.
Jack Conrad and Keqin Gao providedenormously helpful reviews of this work, forwhich they have my thanks and my sympa-thy.
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