Cretaceous Mammals of Southern Utah. I. Marsupials from the Kaiparowits Formation (Judithian)

Cretaceous Mammals of Southern Utah. I. Marsupials from the Kaiparowits Formation(Judithian)Author(s): Richard L. CifelliSource: Journal of Vertebrate Paleontology, Vol. 10, No. 3 (Sep. 20, 1990), pp. 295-319Published by: Taylor & Francis, Ltd. on behalf of The Society of Vertebrate PaleontologyStable URL: http://www.jstor.org/stable/4523327 .

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CIFELLI-MARSUPIALS OF THE KAIPARO WITS FORMATION 297

Distribution --Aquilan and Judithian (see below) Land Mammal ages, Campanian, western North America.

Horizons and Localities -The type and original hypodigm are from UALVP locality MR-6, Verdigris Coulee, 29 km east of Milk River, Alberta; upper mem- ber, Milk River Formation (fide Fox, 1987a). The specimens described herein were collected at OMNH localities V6 and V9, lower Kaiparowits Formation (Fig. 1), Kane County, Utah.

Revised Diagnosis -Small, generally primitive marsupial: upper molars anteroposteriorly short and transversely wide, with tall, uninflated principal cusps (protocone, metacone, paracone), sharp shearing crests, and well-developed B and D cusps. Paracone taller than metacone and closely appressed to it; both cusps tall, with concave labial faces. Differs from similar species, included in Protalphadon (below), in consistently lacking cusp in C position and in having narrower protoconal region. Lower molars with relatively taller trigonids and narrower talonids than in other Cretaceous marsupials.

Description and Discussion -Iqualadelphis lactea was briefly diagnosed and described by Fox (1987a); a revised diagnosis is given here to include newly- referred lower molars and to facilitate comparison with other relevant taxa. The upper molars (Fig. 2F, G) are notable for their transverse appearance and narrow protoconal region. These features generally vary ac- cording to tooth locus among marsupials; however, M2 of Iqualadelphis lactea exceeds even M3 of other known Cretaceous taxa in this respect. The posterior face of the protocone slopes somewhat, while the anterior face is vertical, so that the cusp is anteriorly recumbent. Protoconal cingula are lacking. The trigon cusps are tall, sharp, and uninflated. Both paraconule and metaconule appear as sharp cusps on the pre- and postpro- tocristae, respectively; their internal crests, which are rather weak, extend into the trigon basin in unworn specimens, terminating at the bases of paracone and metacone, respectively. The paracone and metacone are rather closely appressed; the paracone is noticeably taller than the metacone. The centrocrista is straight anteroposteriorly and follows a deep notch between paracone and metacone, in correlation with the great height of those cusps. The labial faces of paracone and metacone are slightly concave. The preparacrista is a salient, sharp crest with a V-shaped notch about half- way between paracone and stylocone (cusp B). The preparacrista is high, and the lowest point in its notch is at a height about half that of the paracone. The stylocone is sharp and prominent, although not nearly so tall as the paracone. A sharp crest descends the anterior face of cusp B and joins a similar, small crest descending from cusp A. At their junction a small car- nassial-like notch may be discerned in unworn teeth. Cusp A is well-developed, with a sharp ridge extending anteriorly and another lingually, confluent with the preprotocrista. There is no cusp in the C position; however, the margin of the stylar shelf anterior to the ectoflexus is developed as a faint ridge, connecting an-

teriorly to the labial base of cusp B. Small cuspules on this crest are present in the region of the ectoflexus of one specimen (OMNH 20160). As is usual for M2 of Cretaceous peradectids, the ectoflexus is not deep. The posterior part of the stylar shelf is broad. Cusp D, although smaller than the stylocone, is well-developed and bladelike, with a crest descending anteriorly to- ward the ectoflexus at the labial margin of the tooth. A small cusp E is present. The postmetacrista is developed as a tall, sharp crest that descends at a steep angle from the apex of the metacone.

Iqualadelphis lactea is the smallest marsupial species known from the lower Kaiparowits Formation and, in fact, is among the smallest Cretaceous members of the group. Isolated premolars are referred to the species on the basis of size. P2 (Fig. 2A-C) is somewhat smaller than, but generally comparable to, that of Alphadon wilsoni, as described and figured by Lillegraven (1969). Sharp crests descend anteriorly and posteriorly from the protoconid; a distinct heel is present posteriorly, but there is no anterobasal cuspule, as there is in A. wilsoni. P3 (Fig. 2D, E) is also similar to that of Al- phadon wilsoni, described by Lillegraven (1969), except for its smaller size. It is much taller than P2 and about equal to that tooth in length. The protoconid is tall, sharp, and uninflated; because it is less anteroposteriorly elongate than in P2, the tooth has a less bladelike appearance. Faint ridges descend anteriorly and posteriorly from the apex of the protoconid, and a very weak cingulum is present posterolingually. The heel is developed as a sharp cusp in a median position; from this cusp descend sharp lingual and labial crests.

The lower molars (Fig. 2H-M) are remarkable for the relatively great trigonid height, which is reminis- cent of the condition in various Early Cretaceous "metatherian-eutherian grade" mammals and certain Late Cretaceous eutherians. The trigonid cusps are slender and sharp; the protoconid is the tallest trigonid cusp, with paraconid being slightly lower than metaconid. The metaconid and paraconid are placed at the lingual side of the tooth, as is typical of lower molars of Cretaceous marsupials referred to Alphadon (e.g., Clemens, 1979). The paracristid and protocristid are sharp, deeply-notched crests. The lower molar talonids are narrower than the trigonids and are anteroposteriorly short, particularly on M4. The cristid obliqua meets the back of the trigonid below the notch between protoconid and metaconid, as in Alphadon (Clemens, 1966; Lillegraven, 1969) The talonid cusps are well- defined. The labial face of the hypoconid is sharply folded; the hypoconulid is somewhat lingually placed and "twinned" with the entoconid. The hypoconulid supports two small crests, which extend lingually and labially from its apex, respectively. Measurements are given in Table 1.

PROTALPHADON, gen. nov.

Type Species--Protalphadon lulli (Clemens, 1966). Included species - The type, Protalphadon creber

(Fox, 1971), and P. wahweapensis, sp. nov.






TABLE 1. Measurements of Iqualadelphis lactea Fox, 1987, from OMNH localities V6 and V9, lower Kaiparowits For- mation, Utah. Abbreviations: AP, anteroposterior length; ANW, anterior width; POW, posterior width.

Tooth Specimen no. AP ANW POW

M2 OMNH 20160 1.76 2.03 2.09 M2 OMNH 20120 1.63 2.01 2.02 P2 OMNH 20430 1.02 0.48 - P3 OMNH 20588 1.23 0.66 -

M3 OMNH 20531 1.46 0.92 0.84 M4 OMNH 20612 1.48 0.93 0.66

lulli from the Lance formation, based on relatively rare but distinctive upper molars generally lacking or, if not, with only a weakly developed stylar cusp in the C position. In this respect, the species differed from all other known, more "typical" species of Alphadon. "A." lulli has since been recognized from the "Mesa- verde" Formation, of Judithian age (Lillegraven and McKenna, 1986). Fox (1971) described "Alphadon" creber, which also generally lacks stylar cusp C, from the Aquilan upper Milk River Formation. Fox noted a possible relationship to "A." lulli, but based the diagnosis and comparisons mainly on the similar-sized, gracile Alphadon wilsoni from the Lancian. Recent evidence (e.g., Clemens, 1979; Fox, 1987a, b) suggests that the configuration of the stylar shelf seen in "A." lulli and "A." creber may be primitive for marsupials, although alternative models for a marsupial morphotype have been proposed (Clemens, 1966; Clemens and Lillegraven, 1986). The two species are similar in other respects, such as the possession of a rather narrow protoconal region on upper molars, which is also presumably primitive. Comprehensive revision cannot be attempted here, but there is a need for revised diag- noses of these two species in view of their similarities. The situation is complicated by the possibility that the hypodigm of "A." creber may actually include materials referable to two distinct but closely similar species (Fox, 1971).

A species from the lower Kaiparowits Formation is similar to both "A." lulli and "A." creber, but is not referable to either and is described as new below. These three species are herein referred to a new genus, Protal- phadon, thereby restricting Alphadon to include species that share morphology presumed to be advanced.

PROTALPHADON WAHWEAPENSIS, sp. nov.

(Fig. 3)

Type Specimen -OMNH 20115, left M3. Hypodigm-The type, and MNA V4572, OMNH

20121, and 20595 (M'); OMNH 20109, 20587 (M2); OMNH 20467 (M3); OMNH 20536, fragment of den- tary preserving M1-3; 20123 (M1); MNA V4516, V4574, OMNH 20599, 20125, and 20601 (M2or3); and OMNH 20597 (M2 or 3).

Horizon and Localities -OMNH localities V6 and

V9, lower Kaiparowits Formation (Fig. 1), Kane Coun- ty, Utah.

Diagnosis--Small marsupial closely resembling P. creber and P. lulli in having upper molars with relatively narrow protoconal region (although not as narrow as in Iqualadelphis) and in lacking or having very slight development of stylar cusp C. Upper molars similar to those of P. creber, differing from those of P. lulli, in being slightly smaller, in more frequently lacking stylar cusp C, in having stylocone more closely appressed to paracone, and in having narrower protoconal region. Lower molars with relatively lower trigonids and broader talonids than those attributed to P. creber, and closely resembling those attributed to P. lulli except for having paraconid more closely approximated to metaconid. Lower molars differ from those of P. lulli in that M1 is relatively smaller and in that the succeeding molars have paraconid and metaconid more closely approximated.

Etymology -Reference is to Wahweap Creek, which has its headwaters near the localities yielding specimens of this species.

Description and Discussion - Separation of small marsupial specimens from the lower Kaiparowits For- mation into distinct, recognizable taxa is not as clear- cut as could be desired. The smallest specimens are the morphologically most distinct; these have been referred above to Iqualadelphis lactea. A larger species, described here as Protalphadon wahweapensis, somewhat resembles Iqualadelphis lactea in presumably primitive features such as the (variable) absence of a stylar cusp C, but is much closer to the Aquilan P. creber and the Judithian through Lancian P. lulli in other respects. Upper molars of Protalphadon wahweapensis, although generally differing from those of P. creber in the features cited in the diagnosis, overlap the range of variation seen in that species. Upper molars are also very close to, although more recognizably different from, those of P. lulli. Lower molars have not been found in unquestioned association with upper molars of any of the taxa under consideration. How- ever, reasonably confident associations have been made for P. lulli by Clemens (1966) and for P. creber by Fox (1971). Lower molars are referred to Protalphadon wahweapensis on the basis of relative abundance, size, and morphological differences from those of the similarly sized Alphadon halleyi, which is also known from the lower Kaiparowits Formation and for which lower dentitions have been previously published (Sahni, 1972; Fox, 1979; Lillegraven and McKenna, 1986; Montel- lano, 1988). Upper molars attributed to Protalphadon wahweapensis are the most abundant of any small marsupial in the lower Kaiparowits Formation; the similarly sized Alphadon halleyi, described below, is relatively rare. A similarly rare and somewhat larger species, Alphadon sahnii, is also recognized from the lower Kaiparowits Formation. Upper and lower premolars of at least two and possibly all three species are present in the existing collection but, because of the difficulties in associating such isolated teeth, their assignment and






tightly appressed, although they are lower in height and not so closely approximated as in Iqualadelphis lactea. The centrocrista is linear; the labial surfaces of both paracone and metacone are flat to slightly concave. The conules are distinct in the one specimen in which they are preserved (MNA V4572) and bear sharp cristae. Stylar cusp A is small. Its lingual face is developed as a flat, lingually-dipping wear surface. A ridge descends the posterior surface of cusp A to a shallow notch between that cusp and the stylocone, so that the latter cusp is posteriorly recumbent. Cusp B is, by a slight margin, the largest of the stylar cusps (cusp D is nearly as large or equal to it in size) and is notably smaller than the paracone, to which it is closely approximated. The stylocone is slightly posterior to the paracone, so that the preparacrista turns posteriad as it runs from the paracone to the apex of the stylocone. The preparacrista dips between the apices of these cusps, but is not deeply notched. Stylar cusp B is anteroposteriorly elongate, and a sharp ridge descends from its apex to the shallow ectoflexus along the labial margin of the tooth. No stylar cusp C is present, although a slight irregularity in the crest descending from the stylocone is present in two specimens, and in the third (OMNH 20121) a faint cuspule is barely visible, just anterior to the ectoflexus. Cusp D is slightly smaller than or subequal to the stylocone in size. Like that cusp, it is developed anteroposteriorly rather than being conical, and bears a ridge along its axis. Anteriorly, this ridge is continuous with the low crest extending from the stylocone through the region of the ectoflexus. Posteriorly, a shallow dip separates cusp D from the posterolabial corner of the tooth, which is developed into a small cusp E. The postmetacrista is a sharp, high crest. M2 (Fig. 3E) is larger than M', and probably more tranverse as well, although this cannot be determined with certainty because the protocone is lacking on all M's currently available. The protocone of M2 is somewhat narrow compared to the condition in species such as Alphadon marshi, but is not so narrow as in Iqual- adelphis lactea. The posterior face of the protocone is obliquely sloping, while the anterior face is vertical, giving the protocone a somewhat recumbent appearance. The conules and their cristae are sharp and well- defined. The stylar shelf is as described for M', except that the ectoflexus is somewhat deeper, the stylocone more distinctly larger than stylar cusp D, and there is no development of a cusp in the E position. Cusp C as such is absent, but in one specimen (OMNH 20109) a small cuspule is present on the posterior flank of the stylocone, just anterior to the deepest reentrant of the ectoflexus. M3 (Fig. 3F) is larger and more transverse than M2, with a deeper ectoflexus, but otherwise resembles that tooth in morphology, including the development of cusps on the stylar shelf. No cusp or cuspule is present in the C position, although cusp D in one specimen (OMNH 20467) is expanded anteriorly almost to the ectoflexus. The two M3s available are somewhat divergent in form. One specimen (OMNH 20115) is considerably larger than the other,

and appears to have somewhat more robust principal cusps (paracone, metacone, stylocone). The other specimen (OMNH 20467) bears a very strongly developed, sharp ridge in the D position; this ridge is faintly expanded in two places, somewhat suggestive of being bifid, although the ridge is continuous. Upper molars of Protalphadon wahweapensis are unlike those of all other lower Kaiparowits marsupials (except Iqualadel- phis lactea, which are smaller and otherwise distinctive) in lacking a stylar cusp C in having anteroposteriorly elongate, trenchant B and D cusps. Although the possibility that the sample represents two closely similar species cannot be discounted, it appears more likely at present that the differences between the two available M3s are due to intraspecific variation.

Lower molars from the first three loci are known from OMNH 20536 (Fig. 3G-I) and from isolated teeth (Fig. 3J-L), although distinction of isolated M2 from M3 is unclear with the small sample available. M1, poorly preserved on available specimens, is considerably smaller than the succeeding molars, a point of contrast with P. lulli. The height differential between trigonid and talonid is less than on succeeding teeth, and the talonid is relatively short and broad compared to those molars. M2 and M3 are, successively, longer and broader. They are generally similar to lower molars ascribed to various species of Alphadon (e.g., Clemens, 1966; Lillegraven, 1969; Fox, 1979; Montellano, 1988), and detailed description is unnecessary. The cusps are relatively low and uninflated; the protoconid is the tallest trigonid cusp, and the paraconid is slightly lower than the metaconid. Lower molars referred to Protal- phadon wahweapensis differ from those ascribed to P. creber, a species similar in size and in upper molar morphology, in having relatively lower trigonids; from those ascribed to P. lulli, a slightly larger but similar species, in having relatively smaller M, and in the closer approximation of paraconid and metaconid on M2-3; and from Alphadon halleyi, a similarly sized species known from the same localities, in its relatively smaller M1 and somewhat higher tooth crowns. Mea- surements are given in Table 2.

TURGIDODON, gen. nov.

Type Species - Turgidodon praesagus (Russell, 1952).

Included Species--The type, and Turgidodon rhaister (Clemens, 1966), T. russelli (Fox, 1979), T. parapraesagus (Rigby and Wolberg, 1987), T. lillegraveni, sp. nov., and T. madseni, sp. nov.

Distribution - Judithian through Lancian Land Mammal ages, Late Cretaceous, western North Amer- ica.

Diagnosis--Large Cretaceous peradectids. Upper molars, lower molars, P3, and P3 with principal cusps moderately to greatly inflated, robust, and with strongly developed wear surfaces in mature individuals. P3, where known, large relative to P2 and M1, bulbous, and low-crowned relative to width; wear predominantly



302 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 10, NO. 3, 1990

horizontal and on the apex of the paracone, rather than oblique, on the faces of that cusp. Upper molars with stylar cusps A-D present and well-developed; cusp B large and inflated, producing swelling on labial side of tooth. P3, where known, with robust protoconid and relatively short talonid.

Etymology - Turgidus, L., inflated or swollen; odon- tos, Gr., tooth; in reference to the inflated, sometimes bulbous appearance of tooth cusps among species of the genus.

Discussion--Clemens (1966) described a large, distinctive marsupial from the Lance Formation, referring it to Alphadon as a then new species, A. rhaister, on the basis of general similarities of upper molar stylar shelf morphology to other species then placed in the genus. He noted, however, that the species differed more from other described species of the genus Al- phadon than they did from each other, and commented that knowledge of additional morphology ofA. rhaister could reveal differences sufficient to warrant its allo- cation to a new genus. This suggestion is adopted here, but for other reasons, developed below. The history and circumstances surrounding several of the other species herein referred to Turgidodon are somewhat confusing. Following a suggestion by Clemens (1966), Sahni (1972) referred to Alphadon a Judithian species originally described by Russell (1952) as Delphodon? praesagus, on the basis of a specimen from the Oldman Formation of Alberta. Fox (1979) described further, incomparably better materials from the Oldman For- mation, and provided the first useful diagnosis of the species. Fox (1979) recognized the close affinity of Ju- dithian "A." praesagus to Lancian "A." rhaister and to a then new additional species from the Oldman Formation, "A." russelli. This last-named species is clearly separable from Turgidodon praesagus based on the large, well-represented samples from the Oldman Formation but, because the species are closely similar in morphology and overlap in size, there is some question as to assignment of specimens from elsewhere. The type of Turgidodon praesagus, NMC 114, is a mandibular ramus with one tooth, M3. This tooth slightly exceeds the described size range for Turgidodon russelli, as given by Fox (1979). However, the situation for specimens referred to "A." praesagus by Sahni (1972) is less clear-cut. Of the Judith River sample, the upper molars (which are more diagnostic than lowers) all appear to be referable to Turgidodon russelli, differing from those of T. praesagus in being smaller and in having less inflated cusps; lower molars are appropriate for either species, but more closely fall within the size range of T. russelli (Sahni, 1972:table 1; Fox, 1979:tables 1, 2). It is possible, although not demonstrated, that Sahni's entire hypodigm belongs to T. russelli, and that T. praesagus is thus not known from the Judith River Formation, at least based on published reports.

There is some question as to the status of Turgidodon parapraesagus (Rigby and Wolberg, 1987). The species, based on a mandibular fragment with

M3_, was dis-

TABLE 2. Measurements of Protalphadon wahweapensis, gen. et sp. nov., from OMNH localities V6 and V9, lower Kaiparowits Formation, Utah. Abbreviations as in Table 1.


P3 OMNH 20202 1.42 0.92 M' OMNH 20121 1.80 - -

OMNH 20595 1.66 - - M2 OMNH 20109 1.76 2.06 2.03

OMNH 20587 1.90 2.01 2.16 M3 OMNH 20115 2.30 2.37 2.55 M, OMNH 20536 1.52 0.88 0.89

OMNH 20123 1.66 0.96 0.96 M2 OMNH 20536 1.88 1.14 1.22 M2or3 MNA V4516 1.96 1.14 1.14

MNA V4574 1.88 1.05 1.06 OMNH 20599 1.86 1.03 1.12 OMNH 20125 1.84 1.07 1.12 OMNH 20601 1.82 1.07 1.05

M3 OMNH 20536 2.13 1.28 1.32 M3 or 2 OMNH 20597 2.26 1.26 1.34

tinguished from T. praesagus as follows: "cristid obliqua meeting the post vallid low and labial to the notch between the protoconid and metaconid (meets on the protoconid); metaconid is not smaller than the paraconid in occlusal view; the hypoconulid is more twinned with the entoconid than posteriorly projecting; the trigonid is slightly shorter anteroposteriorly than in A. praesagus" (p. 62). Cretaceous marsupial lower molars with a labial attachment of the cristid obliqua to the trigonid have long been referred to the Pediomyidae, specifically Pediomys and Aquiladelphis, and this fea- ture in fact has been demonstrated to be characteristic of the family (Clemens, 1966, 1979; Lillegraven, 1969; Fox, 1971). This introduces the possibility that the specimen in question, and the species upon which it is based, could belong to a pediomyid, perhaps one of the larger described species such as Pediomys hatcheri (see Clemens, 1966). However, the illustration of the specimen in question (Rigby and Wolberg, 1987:pl. 4) does not appear to bear this out. Of the other features listed, the metaconid is not smaller than the paraconid on lower molars of T. praesagus; the remaining characters are variable in all Cretaceous marsupials, including T. praesagus. A broken upper molar referred to "A." parapraesagus by Rigby and Wolberg unques- tionably belongs to a marsupial within the genus Tur- gidodon as it is defined herein, but the tooth locus that it represents, and its pertinence to the species represented by the type, are problematic. If the tooth is M1, a possibility entertained but rejected by those authors, it could belong to Turgidodon rhaister or a species close to it. T. rhaister, a Lancian species, is the largest mem- ber of the genus and significantly exceeds T. praesagus in size. A species close to but distinct from T. rhaister was reported from the Hunter Wash local fauna in the San Juan Basin (Clemens, 1973a), which may be stratigraphically equivalent to the Fossil Forest fauna of Rigby and Wolberg (1987). Other materials belonging




o: i

FIGURE 4. Turgidodon lillegraveni, gen. et sp. nov. A, B, C, P2 (OMNH 20572) in labial, occlusal, and lingual views, respectively; D, M2-3 (OMNH 20540, type specimen) in occlusal view; E, M3 (OMNH 20118) in occlusal view; F, M4 (OMNH 20593) in occlusal view; G, H, I, P2 (MNA V4632) in labial, occlusal, and lingual views, respectively; J, K, L, P3 (OMNH 20437) in labial, occlusal, and lingual views, respectively. Jaw fragments and tooth roots have been eliminated from the figure where necessary; scale bar = 1 mm.

to T. rhaister, or one or more other species closely similar to it, have been reported from the St. Mary Formation (Lillegraven and McKenna, 1986), the Lance Formation (Clemens, 1966, 1973b), Hell Creek For- mation (Lillegraven and McKenna, 1986), and Scol- lard Formation (Lillegraven, 1969).

The above-mentioned species, and the following referred species, are grouped into a new genus to reflect their distinction from contemporaneous marsupials on the basis of shared, derived morphology. This distinction was previously recognized by Clemens (1966), on the basis of specializations of the most apomorphous species, T. rhaister, and by Fox (1979) on the basis of derived resemblances of the Judithian T. russelli and T. praesagus to the Lancian T. rhaister. The presence of additional taxa in the Kaiparowits Formation of southern Utah indicates that this group enjoyed a moderate radiation in North America during the Late Cre- taceous. A possible relative of Turgidodon is Bistius

bondi, described on the basis of an upper molar from the San Juan Basin (Clemens and Lillegraven, 1986). These authors noted that Bistius is most comparable to certain Late Cretaceous marsupials, notably "Al- phadon" rhaister and "A." cf. rhaister (see Clemens, 1966), but excluded it from the Marsupialia because of the presence of large pre- and postprotoconal cingula. Although protoconal cingula are more generally characteristic of eutherian than marsupial upper molars, they are variably present in some Cretaceous marsupial species and are most common among species of Turgidodon. It is worth noting also that the curious selene-like structure on the posterior face of the stylocone in Bistius is seen in large species of Turgidodon.

TURGIDODON LILLEGRA VENI, sp. nov.

(Fig. 4)

Type Specimen-OMNH 20540, fragment of right maxilla with M2 and labial half of M3.




Hypodigm-The type, and OMNH 20572, 20431, and 20194, isolated P2s; OMNH 20589, fragment of right maxilla with M3; 20118, left M3 lacking the posterior part of the stylar shelf; 20586, right M2or3 lacking the paracone and anterior part of the stylar shelf; 20593, left M4 lacking protocone; MNA 4632, right P2; and OMNH 20437, right P3.

Horizons and Localities - OMNH localities V6 and V9, lower Kaiparowits Formation (Fig. 1), Kane Coun- ty, Utah.

Diagnosis --Closely similar to but slightly smaller than Turgidodon praesagus. M2-3 stylar cusps D, C, and particularly B smaller and lower than in T. praesagus, with cusp B more tightly appressed to paracone than in that species; ectoflexus of M2 deeper than in T. praesagus. Known premolars (p2, P2, P3) less inflated and smaller than in that species.

Etymology--For J. A. Lillegraven, in recognition of his contributions to knowledge of Cretaceous marsupials.

Description - Premolars are provisionally assigned to T. lillegraveni on the basis of size and close similarity to those of T. praesagus, known by direct association (Fox, 1979). Additional premolars in the existing collection may be referable to the species, belonging to loci other than those mentioned in the hypodigm, but their assignment is problematic. The only upper premolar currently known is P2 (Fig. 4A-C), which is represented by three specimens. It greatly resembles the homologous tooth of T. praesagus, as represented by UALVP 14801, differing mainly in being slightly smaller and less inflated than in the Canadian species. P2 bears a robust paracone that is somewhat broader transversely relative to height than in some of the small species of Alphadon, such as A. wilsoni, as described by Lillegraven (1969). A crest descends the posterior face of the paracone in unworn specimens, terminating in a small heel at the posterolabial margin of the tooth. Faint cingula border the tooth labially and lingually. P2 evidently served an important role in mastication, as two of the three specimens show heavy wear, developed on the apex of the paracone and as a distinctive facet descending the posterolingual face of that cusp, onto and past the lingual cingulum.

The upper molars bear robust cusps, as they do in other species referred to the genus. M' is not yet known, unless an enigmatic specimen mentioned below represents this tooth. M2 (Fig. 4D) bears distinct stylar cusps A-D; a low ridge is present at the posterolabial comrner of the tooth, in the position of cusp E. A flat facet is present on the narrow shelf extending lingually from cusp A, as is common among Cretaceous peradectids. A labially-placed ridge joins cusp A with cusp B; so far as is known, there is no distinct notch in this ridge. Cusp B is large and bulbous, but is relatively smaller and placed closer to the paracone than the corresponding cusp in T. praesagus. As with that species and with T. rhaister, the preparacrista is poorly developed and is not a continuous, notched crest. Rather, a ridge descends labially from the paracone to a point

between cusps A and B; this is joined by a weaker, more posteriorly placed crest descending lingually from cusp B. Cusp C is smaller than cusp D and both are relatively smaller than the corresponding cusps in T. praesagus. They are longer than wide and bear anteroposteriorly oriented ridges on their flanks, but are distinct and unjoined. Cusp C is centrally placed, and occurs at the labial margin of the stylar shelf in the single M2 of the sample belonging to this species. The ectoflexus is deeper than is generally the case in M2 of T. praesagus. The paracone and metacone are approx- imately equal in height and robusticity, are well-separated, and are connected by a linear centrocrista. Api- cal wear is much more strongly developed on the paracone, which is also marked by a large wear facet on its anterolingual surface. Wear is also obliquely developed on the postmetacrista, from the apex of the metacone to the posterolabial angle of the tooth. The postmetacrista is rather low compared to the condition in Iqualadelphis. Internal cristae on the conules are faint. The protocone lacks pre- and postcingula. M3 (Fig. 4D, E) is anteroposteriorly shorter and transversely broader than M2, as is usual in Cretaceous peradectids. The stylocone is larger and more distant from the paracone than on M2, but less so than on M3 of T. praesagus. The preparacrista is low, but more obvious- ly continuous than on M2, in which it is developed more as anterior ridges on corresponding faces of the paracone and stylocone than as a distinct crest. The crest descending the anterior face of cusp B is weaker than on M2. A weak keel descends the posterior face of cusp B and extends along the labial margin of the stylar shelf anterior to the ectoflexus, which is deeper than that of T. praesagus. The remainder of the stylar shelf is as described for M2. The internal conule cristae are well-marked. Both M3s preserving the protocone (OMNH 20589, 20118) bear faint pre- and postcingula. M4 is represented by OMNH 20593 (Fig. 4F), which lacks the protoconal region. The preparacrista is relatively much longer than in the preceding molars, in correspondence with the great anterior development of the stylar shelf in marsupial ultimate upper molars. The labial margin of the stylar shelf is rimmed with low eminences, for which no cusp homologies are obvious. The stylar shelf terminates at the metacone, which is considerably smaller than the paracone.

P2, represented by MNA V4632 (Fig. 4G-I), is similar to that of Turgidodon praesagus, described by Fox (1979). It is elongate, premolariform, and somewhat compressed; sharp crests descend the anterior and posterior slopes of the protoconid. The heel bears a single cusp. A weak but continuous cingulum is present on the lingual side of the tooth.

Fox (1979) noted that P3 of the Oldman Formation species Turgidodon praesagus is not readily distin- guished from that of the somewhat smaller T. russelli, and that individual specimens fitting within the over- lapping part of the species size ranges might be con- fused. A similar situation is confronted among the large Kaiparowits marsupials. The current sample includes




Ln(P3 area)

2.0

T. praesagus O

1.5 -

. Twrnsselli

1.0 + OMNH 20533

OMNH20201--------- ----------OA.marshi A. halleyi O 0O

0.5

0.0 - A. wilsoni 0 T. lillegraveni

T. madseni

-0.5

-1.0 I I I I I I

1.4 1.6 1.8 2.0 2.2 2.4 2.6

Ln(M2 area) FIGURE 5. Plot of log-converted P3 area (ANW x AP) vs. M2 area (ANW x AP) for six species of Cretaceous Peradectidae, with hypothesized association of isolated P3s to Turgidodon madseni and T. lillegraveni, respectively. Solid line represents regression (Pearson correlation), with Ln(P3 area) being the dependent variable; vertical dashed lines, positions of T. madseni and T. lillegraveni (represented by OMNH 20538 and 20540, respectively); horizontal dashed lines, positions of isolated P3s (OMNH 20437, 20533, 20201). Data from the following sources: T. praesagus and T. russelli (sample means), Fox (1979); Alphadon halleyi (one P3 specimen; midpoint of M2 range used), Montellano (1988); A. sahnii (one P3 specimen; midpoint of M2 range used), Lillegraven and McKenna (1986); A. marshi and A. wilsoni (associated specimen and sample means, respectively), Lillegraven (1969).

three marsupial P3s that, because of their size and in- flatedness, are recognizable as belonging to species of Turgidodon. Of these, two are similar in size and morphology, and the third, OMNH 20437, is considerably larger. It thus seems likely that both species of Tur- gidodon recognized herein from the Kaiparowits For- mation are represented by P3, although this cannot be certainly ascertained until complete specimens and larger samples are available for study. Furthermore, as described below, an unusual variant represented by an upper molar may belong to another species, similar in size to T. lillegraveni, and the possibility that OMNH

TABLE 3. Measurements of Turgidodon lillegraveni, gen. et sp. nov., from OMNH localities V6 and V9, lower Kai- parowits Formation, Utah. Abbreviations as in Table 1.


P2 OMNH 20572 1.62 0.99 OMNH 20431 1.58 0.98 OMNH 20194 1.64 1.02

M2 OMNH 20540 2.79 3.00 3.24 M2 or 3 OMNH 20586 - - 3.52 M3 OMNH 20540 3.02 - -

OMNH 20589 3.34 3.73 3.68 OMNH 20118 - 3.85 -

M4 OMNH 20593 2.13 - - P2 MNA 4632 2.41 1.18 P3 OMNH 20437 2.29 1.37

20437 belongs to this taxon, if it is distinct, cannot be discounted.

OMNH 20437 (Fig. 4J-L) is a large marsupial P3 provisionally referred to T. lillegraveni. It is considerably smaller (AP = 2.29; ANW = 1.37) than those referred to T. praesagus (Fox, 1979), which on the basis of upper molar dimensions appears to be only a slightly larger species. However, there appears to be an allo- metric relationship between molar size and premolar size in Cretaceous marsupials, with larger species having relatively much larger premolars. As shown in Fig. 5, OMNH 20437 is of appropriate size for upper molars of T. lillegraveni, and is larger than would be expected for any other marsupial species from the lower Kaiparowits Formation. OMNH 20437 bears a tall protoconid that is somewhat inflated, but less so than in T. praesagus. Keels descend the anterior and posterior faces of the protoconid; the posterior keel is more pronounced than in T. praesagus. The anterior keel turns posteriorly and lingually at the base of the crown, to become a well-marked lingual cingulum. There is no anterior cuspule. The heel is broad and low, lacking distinct cusp development, and bears a dorsolabi- ally facing flat surface. Measurements are given in Ta- ble 3.

TURGIDODON sp. cf. T. LILLEGRAVENI

(Fig. 6) OMNH 20117 (from locality V6; Fig. 1) is a max-

illary fragment preserving the right M2. It is similar in








Lillegraven and McKenna (1986). The single specimen preserving the protocone (OMNH 20594; Fig. 7B) lacks protoconal cingula; the protocone itself is well-developed, being intermediate in height between the paracone and metacone, and is somewhat recumbent anteriorly. The protoconule is well-developed; an anterior crista extends from it to join the strongly developed protocrista running labiad to cusp A, and a posterior crista descends to the base of the paracone, where a slight keel is developed, so that a V-shaped notch is present between paracone and paraconule. The metaconule is tightly appressed to the lingual face of the metacone; between these cusps a notch is formed. Wear is strongly developed on the centrocrista, in the trigon basin, and on the median surfaces of the conules or their internal cristae; the notches just described apparently form "en echelon" shearing surfaces (Hiiemae and Kay, 1973) with the centrocrista. The paracone is the tallest cusp on the tooth, with the metacone being small by comparison. As is usual among primitive marsupials, the parastylar region of M4 is very strongly projecting. Stylar cusp A is present, and is as described for the preceding molars. Cusp B, slightly larger than cusp A, is connected to the paracone by a long preparacrista, in which a small notch is developed near the base of the stylocone. A large cusp, referred to here as cusp C (see Fix, 1979:98-99; Lillegraven and McKenna, 1986:29-30 for discussion), is present at the margin of the stylar shelf, somewhat posterior to the apex of the paracone. Cusp C is elongate; in one specimen (OMNH 20594) it bears two apices. In the type, minute cuspules are present on the margin of the stylar shelf between cusps B and C. No cusp D is present; the stylar shelf terminates abruptly at the posterior margin of cusp C.

Anterior premolars of Turgidodon madseni are probably present in the collection, but remain to be identified as such because of the difficulty in distinguishing the species from the slightly larger T. lillegraveni and the slightly smaller Alphadon sahnii without large samples and complete specimens. Two isolated P3s are tentatively referred to Turgidodon madseni, OMNH 20533 and 20201. These are clearly too small to belong to T. lillegraveni, are probably too large for other marsupial species from the lower Kaiparowits Formation, and are of appropriate size for upper molars of T. madseni (Fig. 5). P3 (Fig. 7C-E) is premolariform, with a protoconid that is moderate in height and in inflation of its walls. A slight keel descends the anterior face of the protoconid, turning lingually and then posteriorly at the base of the crown to become a weak lingual cingulum, which continues posteriorly to form a labial crest for the talonid. No cingulum is present labially. A keel also descends the posterior face of the protoconid, terminating at the notch anterior to the heel, which is developed as a sharp cusp. P3 of T. russelli generally has a relatively longer, narrower talonid with a somewhat taller heel than is seen in T. madseni. OMNH 20201 and 20533 are smaller and less inflated than P3 of T. russelli, described by Fox (1979), and are

similar in size to specimens from the Scollard For- mation referred to Alphadon marshi by Lillegraven (1969). Upper molars from the Scollard Formation referred to A. marshi are larger than those of T. madseni, which thus has a relatively larger P3, as do other species of Turgidodon (Fig. 5). P3 of T. madseni also differs from that of A. marshi (as represented by specimens from the Scollard Formation) in being more inflated, in having a less conical, lower protoconid, in lacking strong cingula, and in having a lower, blunter talonid cusp.

Lower molars of Turgidodon madseni are known for two loci, M, and M3. M, (Fig. 7F-H) has a low trigonid and a talonid that is broad and short, even for a tooth of that locus. The cusps are slightly inflated in comparison to gracile species such as Alphadon wilsoni, but not nearly so robust as in T. praesagus. The anterocingulid is variably developed but is generally weak. The protoconid is the tallest cusp on the tooth; the paraconid and metaconid are notable in being both low and subequal in size. The paraconid is anteriorly placed, as is typical on marsupial Mls, and the metaconid is well posterior to the protoconid. Small car- nassial-like notches are present on the paracristid and protocristid, but those crests are neither strongly developed nor deeply notched. The cristid obliqua at- taches to the back of the trigonid below the notch in the protocristid, as is typical of Cretaceous lower molars ofAlphadon-like construction (Clemens, 1966; Lil- legraven, 1969). The posterior face of the metaconid is developed as a ridge, which partially occludes the lingual opening of the talonid basin. The three talonid cusps are subequal in height, and the hypoconulid is lingually shifted and "twinned" with the entoconid. M, of Turgidodon madseni differs from that of T. russelli, the most closely similar species, in being smaller (as with the upper first molar), although it may reach the lower size range of that species. The principal size difference is tooth length; in T. russelli, the talonid is relatively longer, which may account for much of the difference in size. The paraconid and metaconid of T. madseni are relatively lower than in T. russelli, in which the cusps (especially the metaconid) are more inflated. M3 (Fig. 7I-K) is larger than M,, with a taller trigonid, stronger anterocingulid, and more inflated cusps. The paraconid is in a more posterior position than on M1; as a consequence, the paraconid and metaconid (the latter cusp broken on the single specimen available) are more closely appressed. In these and other morphological features, the tooth is highly similar to M3 of T. russelli, as described by Fox (1979) and, in fact, falls within the range of variation seen in specimens of that species from the Oldman Formation. Mea- surements are given in Table 4.

Turgidodon sp.

A large species of Turgidodon is represented by two fragmentary specimens (OMNH 20728, right Mx

lacking protoconid; OMNH 20918, posterolabial corner of




TABLE 4. Measurements of Turgidodon madseni, gen. et sp. nov., from OMNH localities V6 and V9, lower Kaipa- rowits Formation, Utah. Abbreviations as in Table 1.


M' OMNH 20538 - 2.08 - M2 OMNH 20538 2.53 2.52 2.72

OMNH 20591 2.33 - - M3 OMNH 20538 2.75 2.92 2.92

OMNH 20590 - - 3.11 M3 OMNH 20594 2.44 3.33 2.23 P3 OMNH 20533 2.11 1.21

OMNH 20201 1.95 1.16 M, OMNH 20600 2.26 1.41 1.18

OMNH 20124 2.09 1.04 1.09 OMNH 20596 2.17 1.08 1.20

M3 OMNH 20530 3.06 1.97 1.87

left Mx) from OMNH locality V14. This locality lies in the lower to middle Kaiparowits Formation (Fig. 1). The large size and bulbous cusps in both specimens indicate reference to Turgidodon; beyond this, iden- tification is problematic. The Kaiparowits taxon is similar in size (OMNH 20728 estimated AP = 3.63; ANW = 2.17; POW = 2.25) to the Lancian T. rhaister (Clemens, 1966), but differs from that species in having a small upper molar cusp D. Taxa comparable to T. rhaister have been reported from the Lance Formation (Clemens, 1966, 1973b) and the Fruitland/Kirtland formation(s) (Clemens, 1973a). Rigby and Wolberg (1987) suggested that one or both of these might be referable to T. parapraesagus. The Kaiparowits taxon lacks the well-developed stylar cusp D seen in the un- named Lance species (Clemens, 1966:fig. 12) and the apparently unusual condition of the cristid obliqua cited for T. parapraesagus by Rigby and Wolberg (1987).

ALPHADON Simpson, 1927 ALPHADON HALLEYI Sahni, 1972

Type Specimen-AMNH 77367, left M, (fide Lil- legraven and McKenna, 1986).

Newly-referred Specimens - OMNH 20119, left M1 lacking protocone; 20537, left MI lacking protocone and metacone; 20171, left M2?.

Horizons and Localities--The type specimen was collected at the Clambank Hollow locality, Judith Riv- er Formation, Montana (Sahni, 1972). Newly-referred specimens were collected at OMNH localities V6 and V9, lower Kaiparowits Formation (Fig. 1), Kane Coun- ty, Utah.

Discussion--Sahni (1972) based this species on the type and a referred upper molar from the Judith River Formation, believing it to be larger than "Alphadon" lulli. Fox (1979) referred an MI, an M3, and two Mls from the Oldman Formation to A. halleyi, which, at the time, was the only described Judithian marsupial smaller than Turgidodon russelli. Lillegraven and McKenna (1986) placed additional materials, including P3 and lower molars from all four loci, in the species.

They further noted that the type is significantly smaller than reported by Sahni, and restricted the definition of the species by referring two specimens figured by Fox (1979) and two undescribed specimens from the Judith River Formation to a then new species, Alpha- don sahnii, which was based primarily on specimens from the "Mesaverde" Formation. Welcome additions to knowledge of Alphadon halleyi have been published by Montellano (1988), who reported two relatively complete lower dentitions and numerous isolated upper and lower teeth. Montellano (1988) questioned the distinctness of A. sahnii from A. halleyi and suggested that they are synonymous; as discussed below, material from the Kaiparowits Formation support the view that the two species are distinct. Alphadon halleyi has been well-described in the references cited, and the fragmentary specimens referred to the species herein add no knowledge. Measurements are given in Table 5. The lower molar, OMNH 2017 1, is evidently from a smaller individual than that of the type M1, AMNH 77367. With the limited samples available, the significance of this size difference cannot be determined.

ALPHADON SAHNII Lillegraven and McKenna, 1986 (Fig. 8)

Type Specimen-UCMP 125337, right M'. Newly-referred Specimens - OMNH 20114, left

M2 or 3; 20116, left M2 or 3 lacking protocone; 20122 (broken); 20602 (MI); and 20598 (M2?).

Horizons and Localities--The type was collected at the Fales Rocks locality, "Mesaverde" Formation, Wyoming (Lillegraven and McKenna, 1986). Newly- referred specimens were collected at OMNH locality V6, lower Kaiparowits Formation (Fig. 1), Kane Coun- ty, Utah.

Discussion and Description - Lillegraven and McKenna (1986) diagnosed this species as being intermediate in size between the Lancian Alphadon wilsoni and A. marshi, and thus being marginally larger than the Judithian Alphadon halleyi, which is found in many of the same localities as A. sahnii. They based most of their discussion and diagnosis on comparison of A. sahnii with the Lancian species, with which they hypothesized a close relationship, rather than A. halleyi. Montellano (1988) questioned the distinctiveness of the two Judithian species and argued that A. sahnii should be considered a junior synonym of A. halleyi on the following grounds: 1, the main criterion diagnosing A. sahnii from A. halleyi is size; 2, a large sample of dental specimens from the Two Medicine Forma- tion, Montana, shows broad variation without bimodal distribution in measurements; and 3, comparison of measurements of the two species indicates overlap- ping ranges, and some individual teeth (lower molars) can with equal validity be placed in either species on the basis of size, especially if tooth locus is incorrectly assumed.

However, Lillegraven and McKenna's (1986:31-32)




diagnosis of Alphadon sahnii is based not on size but on the following morphological criteria: "molar cusps slightly inflated; P2-3 usually lacking anterolingual parts of basal cingulum; p2-3 with anterior border of main cusp unkeeled and with strong wear on posterior crest of main cusp." Thus, comparisons must be made among premolars before synonymy can be addressed. Fur- thermore, the lack of a bimodal distribution in measurements from the Two Medicine sample could simply indicate that Alphadon sahnii is not present in the local faunas known from that unit. A. halleyi, as represented by the Two Medicine sample, is notably smaller in most dental dimensions than A. sahnii from the "Mesaverde" Formation, with little overlap in range (Montellano, 1988:tables 2, 3). Because the original data set was not published, it is not possible to evaluate the statistical significance of these differences. The available sample of small marsupials from the Kai- parowits Formation is insufficient to resolve this issue, but it supports the distinctiveness of Alphadon sahnii from A. halleyi. Two morphs are clearly recognizable among the Kaiparowits upper molars; lowers also seem to fall into two categories, although the distinction is less clear. Both species in question are morphologically distinct from the other small marsupials known from the lower Kaiparowits Formation. An interesting but presently untestable speculation is that intraspecific variation and size overlap of the species are reduced where the species co-occur ("Mesaverde," Kaiparo- wits, and perhaps Judith River and Oldman formations) due to character displacement and reduced intraspecific variation, whereas increased size variation is seen when only one species is present (as seems to be the case in the Two Medicine local faunas).

Two upper molars referable to A. sahnii perhaps represent M2 (OMNH 20114; Fig. 8A) and M3 (20116; Fig. 8B), respectively, although this cannot be determined with certainty because of the small sample available, because of breakage in one specimen (20116), and because M3 of the species is incompletely known (see Lillegraven and McKenna, 1986:34). Both specimens are large in comparison to teeth referred to Al- phadon halleyi, above, and differ from molars referred to that species in having notably more robust and somewhat inflated cusps, as described by Lillegraven and McKenna (1986). The protoconal region is broad in comparison to that on molars of Iqualadelphis and Protalphadon species, being more comparable in this regard to the Lancian Alphadon marshi. Both pre- and postprotoconal cingula are present on the single specimen (20114) that preserves that part of the tooth. The conules are prominent cusps and bear strong cristae. The internal cristae are developed as curved shearing surfaces, extending to the median side of paracone and metacone, respectively, and sweeping upward somewhat from the bases of those cusps. The paracone and metacone are well-separated; the paracone is slightly larger than the metacone. The labial face of the paracone is gently convex, while that of the metacone is flat. The centrocrista is linear. The anterior part of the

gir,

FIGURE 8. Alphadon sahnii Lillegraven and McKenna, 1986. A, B, M2 or 3 (OMNH 20114, 20116, respectively) in occlusal views; C, D, E, M2? (OMNH 20598) in labial, occlusal, and lingual views, respectively. Tooth roots have been eliminated from the figure where necessary; scale bar = 1 mm.

stylar shelf in one specimen (OMNH 20114) projects labially somewhat more than it does in examples of A. sahnii from the "Mesaverde" Formation. Stylar cusp A is well-developed, but is rapidly transformed by wear into a flat, lingually sloping wear surface; this facet is continuous along the anterior margin of the preprotocrista. Stylar cusp B, the largest stylar cusp, is well- developed, and is somewhat bulbous, although it is not nearly so tall as the paracone. A ridge extends anteriorly from the apex of cusp B, descending to a shallow notch between it and cusp A. The preparacrista is dis- continuous, not forming an extensive shearing surface. It descends the anterior face of the paracone, terminating lingual to the notch formed between cusps A and B. About half way down, it is joined by a weak crest descending lingually from the stylocone. The ectoflexus is well-developed on both specimens, being somewhat deeper in OMNH 20114. A ridge, better




TABLE 5. Measurements of Alphadon halleyi Sahni, 1972 (from OMNH localities V6 and V9); A. sahnii Lillegraven and McKenna, 1986 (from OMNH locality V6) and A. sp. cf. A. sahnii (from OMNH locality V5), Kaiparowits For- mation, Utah. Abbreviations as in Table 1.


Alphadon halleyi MI OMNH 20119 1.72 - -

OMNH 20537 1.78 - - M2? OMNH 20171 1.68 1.01 1.08

Alphadon sahnii (lower Kaiparowits Formation) M2 or 3 OMNH 20114 2.04 2.24 2.32

OMNH 20116 2.42 - -

M, OMNH 20122 2.03 0.89 0.93 OMNH 20602 - 0.91 -

M2 OMNH 20598 2.18 1.31 1.42

Alphadon sp. cf. A. sahnii (upper Kaiparowits Formation) p2 OMNH 20186 1.44 0.83 P3 OMNH 20185 1.82 1.07 M2 or 3 OMNH 20150 - 2.54 -

M, OMNH 20144 1.92 0.97 0.95 M2 OMNH 20138 2.30 1.25 1.29 M3 OMNH 20139 2.23 1.31 1.20 M4 OMNH 20140 - 1.17 0.99

developed and bearing a minute cuspule in one specimen (20116), extends from the posterolabial base of the stylocone along the anterior margin of the ectoflexus. Cusp C, marginally placed at the center of the ectoflexus, is somewhat smaller than cusp D on 20116 and larger than that cusp on 20114, differences previously described as distinguishing M2 from M3 in Al- phadon sahnii (Lillegraven and McKenna, 1986). Both cusps are anteroposteriorly elongate in one specimen (20114) and slightly more conical on the other (20116). A notch separates cusps C and D; a faint crest descends the posterior face of the latter cusp at the labial margin of the stylar shelf. There is no development of a cusp E. The postmetacrista is unremarkable, except for a distinctive notch immediately labial to the metacone.

The lower molars (Fig. 8C-E) differ from those ascribed to Alphadon halleyi in being larger, higher crowned, and having more robust, slightly inflated cusps, as previously described on the basis of materials from elsewhere (Lillegraven and McKenna, 1986). The newly-referred specimens are somewhat smaller than comparable lower molars from the "Mesaverde" For- mation, but otherwise add no knowledge to morphology or variation within the species as already described, and elaboration here is unnecessary. Measurements are given in Table 5.

ALPHADON sp. cf. A. SAHNII Lillegraven and McKenna, 1986

(Fig. 9)

A number of specimens from locality V5, in the upper Kaiparowits Formation (Fig. 1), may be refer-

able to Alphadon sahnii. This site lies about 470 m stratigraphically above localities V6 and V9, from which the other materials referred to the species were collected. The mammalian assemblage from locality V5 remains poorly known, and there is a possibility that more than one species is represented by the specimens herein assigned to A. sp. cf. A. sahnii. Furthermore, because this species closely resembles A. halleyi in both size and morphology (see Montellano, 1988, and above) and because complete upper molars are not yet known from locality V5, reference to A. halleyi cannot be def- initely excluded.

P2 and P3 are represented by OMNH 20186 (Fig. 9A-C) and 20185 (Fig. 9D-F), respectively. OMNH 20186 is slightly smaller than either of the two P2s referred to the species by Lillegraven and McKenna (1986:table 7). It generally resembles those teeth, except that an anterior keel on the main cusp is altogether lacking. OMNH 20186 may also be somewhat shorter, although this is difficult to determine because the base of the crown is lacking. P3 is a robust, modestly inflated, short tooth compared to that ofAlphadon wilsoni. The posterior accessory cusp is longer and broader than in p2, and the basal cingulum is better developed. As noted in the description of A. sahnii (Lillegraven and McKenna, 1986), wear is strong on the posterior crest of the main cusp and is not otherwise present; there is a weak anterior keel on the principal cusp. OMNH 20185 is almost identical in length and width to UW 17082, the only previously-described P3 for which both measurements are known (Lillegraven and McKenna, 1986:table 7). The Utah specimen is somewhat more robust than AMNH 109445 (referred to A. sahnii by Lillegraven and McKenna, 1986), with a broader heel and a stronger labial cingulum. OMNH 20150 (Fig. 9G) is a left M2 or 3 lacking the posterior part of the stylar shelf. It is not distinguishable in observable morphology from the respective upper molars of A. sahnii, with which it agrees well in size. Of the four lower molars in the available sample, each is tentatively identified as belonging to a different locus: 20144 (Fig. 9H- J), M1; 20138 (Fig. 9K-M), M2; 20139 (Fig. 9N-P), M3; and 20140 (Fig. 9Q-S), M4. The teeth agree well in size and morphology with those referred above to A. sahnii from the lower Kaiparowits Formation, being generally larger than those of A. halleyi; however, they fit within the size range of that species as interpreted by Montellano (1988). Measurements are given in Ta- ble 5.

ALPHADON ATTARAGOS

Lillegraven and McKenna, 1986 (Fig. 10)

Type Specimen-UW 17079, left M1. Newly-referred Specimens-OMNH 20152, right M'

lacking metacone and posterior comrner of stylar shelf; 20147, left M2; 20143, right M,; 20142, right M2; 20146, left M2; 20141, right M3 lacking most of the enamel; and 20145, left M4 (or, less probably, M3).






ii~

FIGURE 10. Alphadon attaragos Lillegraven and McKenna, 1986. A, M' (OMNH 20152) in occlusal view; B, M2 (OMNH 20147) in occlusal view; C, D, E, M, (OMNH 20143) in oblique labial, occlusal, and oblique lingual views, respectively; F, G, H, M2 (OMNH 20146) in oblique labial, occlusal, and oblique lingual views, respectively; I, J, K, M4 (OMNH 20145) in labial, occlusal, and lingual views, respectively. Tooth roots have been eliminated from the figure where necessary; scale bar =1 mm.

an appearance probably accentuated as the tooth be- comes worn. As in the type, the hypoconulid is dam- aged, but what remains substantiates the suggestion of Lillegraven and McKenna (1986) that it was conical, not bladelike. As in Protalphadon lulli, M2 (Fig. 10F- H) is not appreciably longer than M,, nor does it differ greatly in several other respects commonly differen- tiating M, and M2 of Cretaceous marsupials. Primary among these are the configuration and relative development of the trigonid cusps. The paraconid is ante-

riorly placed, so that the trigonid has a relatively open appearance in M2 ofA. attaragos, although less so than in M . The paraconid is a low cusp, not much taller than it is in the first molar. The protoconid is the tallest cusp and is posteriorly recumbent. The metaconid is not so posteriorly placed as in M,, and the talonid is relatively longer than in that tooth. The anterocingulid is weak, and extends from a point below the notch in the paracristid to the anterior base of the protoconid. The height differential between trigonid and talonid is




not much greater than in M1. M3 and M4 are generally similar to those of Alphadon wilsoni, except for their smaller size and somewhat broader talonids. M3 is currently known by a single, poorly preserved specimen lacking most of the enamel. The trigonid is relatively taller and more anteroposteriorly compressed than in the preceding molars, with the paraconid being taller and less anteriorly projecting, and the metaconid with a more vertical posterior face. OMNH 20145 (Fig. 10I- K) is tentatively identified as M4 of A. attaragos, although it could be M3. The trigonid is tall compared to the talonid, which is narrower than the trigonid, as expected for a tooth of this locus. The paraconid is slightly lower than the metaconid, and is more closely appressed to that cusp than in the preceding molars. The hypoconulid projects somewhat from the posterior margin of the tooth.

MI (Fig. 10A), incompletely known, approximates an equilateral triangle in occlusal view. The tooth is narrower compared to length than in Iqualadelphis lactea, with the protoconal region more broadly developed. Protoconal cingula are lacking. Both paraconule and metaconule are distinct cusps; their internal cristae extend downward to notches, then upward to the median bases of paracone and metacone, respectively. The preprotocrista extends labially along the anterior margin of the tooth, terminating at stylar cusp A. The metacone is lacking in OMNH 20152, but the preserved part of the centrocrista indicates that this structure was linear, not extending labially at its trough. Stylar cusp A is trenchant and is separated from the stylocone by a well-marked notch, which is visible in both occlusal and labial aspects. The stylocone, relatively larger than in A. wilsoni, is nearly as tall as the paracone and is anteroposteriorly elongate and posteriorly recumbent. A strong keel descends its anterior face to the notch between cusps A and B. The preparacrista descends labially from the paracone to a sharp but shallow notch (less than half of the distance from the apex to base of the paracone). Cusp C, though smaller than the stylocone, is a distinctive, conical, marginally-placed cusp. An ectoflexus as such is lacking, although the appearance of the tooth is influenced by the fact that the posterior part of the stylar shelf is missing. M2 (Fig. 10B) is larger than MI, although (as with the lower molars) the difference in size is less than is the case in many other Cretaceous marsupial species. The paracone, metacone, and stylocone are subequal in height, the last-mentioned cusp being slightly shorter that the others. The labial faces of paracone and metacone are flat to somewhat concave. Cusp A is more anteriorly projecting, with a stronger anterior keel, than in M1. Cusp C is separated from the stylocone by a deep notch, and is located at the margin of the stylar shelf, adjacent to the reentrant formed by the shallow ectoflexus. Cusp D, larger than cusp C, is elongate and bladelike. Cusps C and D are closely approximated and are partially joined, although their apices are well separated. A ridge descends posteriorly from the apex of cusp D, along the margin of the stylar

TABLE 6. Measurements of Alphadon attaragos Lillegra- ven and McKenna, 1986, from OMNH locality V5, upper Kaiparowits Formation, Utah. Abbreviations as in Table 1.


M' OMNH 20152 1.56 1.65 - M2 OMNH 20147 1.83 1.86 1.90 M, OMNH 20143 1.72 0.83 0.90 M2 OMNH 20142 1.74 0.84 0.94

OMNH 20146 1.73 0.90 0.89 M3 OMNH 20141 1.41" 0.75* 0.83* M3 or 4 OMNH 20145 1.71 1.09 0.92

*Total tooth size under-represented by measurements owing to enamel loss on parts of this specimen.

shelf. This ridge terminates in a slight notch near the posterolabial corner of the tooth, which delineates a small cusp E. The postmetacrista is not strongly notched.

OMNH 20153, lacking the conules and protocone, may represent M3 of A. attaragos, but is not formally referred to the species. It is larger than OMNH 20152 and 20147, but is similar in most morphological de- tails. The paracone somewhat exceeds the metacone in height; both cusps have concave labial faces and are taller than in teeth of preceding loci referred to A. attaragos. The stylar cusps are developed as they are in the preceding molars, except that cusp E is not distinct. The stylocone is farther from the paracone and, owing to the great height of that cusp, is far lower than it, unlike preceding teeth. The preparacrista is high and is not deeply notched. This, coupled with the towering, labially concave surfaces of the paracone and metacone, the high postmetacrista, and the combination of cusps and ridges at the margin of the stylar shelf, gives the stylar region the appearance of an enclosed basin. Measurements are given in Table 6.

DISCUSSION Until recently, the morphology of the Late Creta-

ceous marsupial genus Alphadon was considered to approximate a morphotype for the group (Clemens, 1966), a view that was apparently substantiated by assignment to the Marsupialia of Holoclemensia texana, from the Albian of north Texas (Slaughter, 1968). However, because of the close similarity of Holoclem- ensia to other Trinity therians, such as Pappotherium, most workers have not followed this assignment, and instead simply consider Holoclemensia to be a metatherian-eutherian grade mammal of uncertain affinities (e.g., Turnbull, 1971; Kielan-Jaworowska et al., 1979; Kielan-Jaworowska, 1982). Because the species has recently been returned to the Marsupialia in a syn- thetic classification (Aplin and Archer, 1987), a brief review of the evidence is warranted. Slaughter's (1968, 1971) reference of Holoclemensia texana to the Mar- supialia was based on: 1) cusp C largest of stylar cusps; 2) metacone of upper molars larger with respect to the




paracone than in Pappotherium pattersoni, a presumed eutherian; and 3) hypoconulid of lower molars slightly shifted lingually and incipiently "twinned" with the entoconid. Recent evidence presented by Fox (1987a, b) suggests that marsupials may primitively have lacked a stylar cusp C; in any event, a cusp in that position evidently evolved several times among Cretaceous mammals (see discussions by Clemens, 1979; Clemens and Lillegraven, 1986). With regard to the relative sizes of paracone and metacone, I find the metacone on the holotype of Pappotherium pattersoni (SMP-SMU 61725) to be relatively larger than that on the holotype of Holoclemensia texana (SMP-SMU 61997). Regard- less, many Late Cretaceous Eutheria (such as Gypsonic- tops and Paranyctoides), like their marsupial contem- poraries, have metacones that appear enlarged when compared with those of various Trinity therians. Twin- ning of the hypoconulid with the entoconid has been recognized as a marsupial synapomorphy (Clemens, 1979; Clemens and Lillegraven, 1986). Referral of Trinity lower molars to taxa based on uppers is problematic (see, e.g., Turnbull, 1971). However, the hypoconulid of SMP-SMU 62131, referred by Slaughter (1971) to H. texana, appears to be no more twinned with the entoconid than is the case for other Trinity therians, for Deltatheridiidae, or for many Cretaceous Eutheria. In sum, the marsupial affinities of Holoclem- ensia remain to be adequately documented. The earliest undoubted marsupial is Pariadens kirklandi, from the Cenomanian Dakota Formation of southern Utah (Cifelli and Eaton, 1987). This species is referred to the Stagodontidae, which are generally regarded as somewhat derived with respect to a marsupial morphotype (see Clemens, 1979). A recent body of evidence suggests that cusp C was lacking in primitive marsupials (Clemens, 1979; Fox, 1987a, b; Fox and Naylor, 1986; Cifelli, 1990). Iqualadelphis lactea, described on the basis of upper molars from the Aquilan Milk River Formation of Alberta (Fox, 1987a) and now known by additional specimens from the Kai- parowits Formation (including lower premolars and molars), is primitive with respect to most other Cre- taceous taxa in this regard, as are Stagodontidae and various other Cretaceous taxa, as discussed by Fox (1987b). Using Trinity therians for outgroup comparison, Iqualadelphis lactea is more primitive than other described marsupials in several other respects, including the tall, closely appressed paracone and metacone, with the latter shorter than the former; the narrow protoconal region; and the relatively tall trigonids and low, narrow talonids of the lower molars.

Until recently, students of marsupial evolution uni- versally followed Simpson (1927) in referring Alpha- don and structurally similar Cretaceous taxa to the extant family Didelphidae (e.g., Clemens, 1966, 1979; Fox, 1971). Fox (1987a) advocated recognition of the Didelphidae on the basis of presence of stylar cusp C in included taxa (implying independent acquisition of that cusp within "Pediomyidae," or, if not, a poly- phyletic origin of that family), leaving Iqualadelphis

without familial designation. Three species herein placed in the new genus Protalphadon, including two previously referred to Alphadon, pose vexing problems in this respect, for a small cuspule in the C position is variably, albeit rarely, present in all three. It cannot be ascertained whether this is indicative of special relationship to more advanced taxa (the variable cuspule representing either a reduced cusp formerly present, or an intermediate character state between complete absence and consistent presence), or simply a minor, in- dependently acquired variant, perhaps inherited as a tendency from a non-exclusive ancestor. Reig et al. (1987), following a suggestion by Crochet (1980), restricted the Didelphidae, without diagnosing it, to Di- delphinae, Caluromyinae, and Herpetotheriinae, as those taxa are circumscribed by them. Remaining taxa, presumably primitive, were placed by these authors in the Peradectidae, an action which effectively replaced one former "wastebasket" taxon (Didelphidae) with another (Peradectidae). Marshall and de Muizon (1988) elaborated on this scheme by defining the Didelphidae on the basis of presumed synapomorphies of the upper molars, including metacone larger than paracone and centrocrista. V-shaped. (The term "dilambdodont" in reference to the configuration of the centrocrista is, strictly speaking, incorrect. The centrocrista includes crests descending internally from the apices of paracone and metacone, the postparacrista and premeta- crista, respectively. A V-shaped centrocrista, in combination with strongly developed and labially directed preparacrista and postmetacrista, results in an upper molar of dilambdodont appearance.) Although this course is followed here, it must be pointed out that it raises several issues that cannot be adequately addressed without thorough species-level treatment of many taxa. For instance, the type species of Alphadon, A. marshi Simpson, 1927, is well-represented by specimens from the Lancian Lance Formation, Wyoming (Clemens, 1966), the Scollard Formation, Alberta (Lil- legraven, 1969), and several other units (see Lillegra- ven and McKenna, 1986). The materials from the Scol- lard Formation are of great importance because they comprise a large sample with a number of relatively complete specimens, including UALVP 2846, associated upper and lower molar series, which established with certainty the identity of Alphadon lower molars (Lillegraven, 1969). However, the specimens from the Scollard Formation tend to be larger than those from the Lance Formation (Clemens, 1973b), and the significance of this difference remains to be determined. More importantly, upper molars from the Scollard Formation, including UALVP 2846, tend to have a distinctly V-shaped centrocrista and metacone larger than paracone (cf. Lillegraven, 1969:figs. 14, 15; I thank Dr. J. Case for pointing this out to me), characters which may or may not be similarly expressed in Lance upper molars (cf. Clemens, 1966:figs. 2-6). Thus, two taxa may be represented by the two samples or, if not, Alphadon marshi may share advanced dental morphology considered by Marshall and de Muizon (1988)




to be unique to the Didelphidae. These features are lacking in other species currently referred to Alphadon. If one species is represented by the two samples, if it can be shown that these characters are consistent in their expression for A. marshi, and if they are indeed synapomorphies with Didelphidae (as defined by Mar- shal and de Muizon, 1988) rather than convergent or parallel specializations, then a new generic name may be needed for the remaining species now placed in Alphadon. Suspicion that homoplasy could be in- volved is aroused by the apparent independent acquisition of these characters at least twice among marsupials of the Paleocene Itaborai local fauna, Brazil, and by their absence in the late Tertiary South Amer- ican ?didelphid, Hondadelphys fJieldsi (cf. Marshall, 1987).

Excluding Glasbius Clemens, 1966, Iqualadephis Fox, 1987 and Albertatherium Fox, 1971, all North Amer- ican Cretaceous marsupials lacking pediomyid or stagodontid specializations have hitherto been placed in the genus Alphadon. Three species, presumed primitive in lacking a stylar cusp C, are herein excluded from Alphadon on this basis, and are referred to the new genus Protalphadon. This taxonomic procedure is not wholly satisfactory in the sense that the genus is defined by relative primitiveness rather than synapomorphy, but it permits Alphadon to be recognized on the basis of derived morphology. Of the species of Protalphadon, the Aquilan species P. creber Fox, 197 1, would appear to be most primitive (relative to a morphotype represented by Iqualadelphis lactea), mainly in the proportions and respective heights of the lower molar trigonids and talonids. P. lulli Clemens, 1966, now known from Judithian as well as Lancian local faunas (Lillegraven and McKenna, 1986), differs in being slightly larger, in having a broader protoconal region on upper molars, and in having lower, relatively narrower lower molar trigonids with respect to talonids. P. wahweapensis, herein described from the Kai- parowits Formation, does not differ greatly from P. creber in upper molar morphology, but presents presumed advanced features of the lower molars seen in P. lulli, although this latter species remains distinct in the lesser size differential between M, and the remaining lower molars, and in the relatively open trigonids of M2-3. Although specific relationships of these taxa remain to be documented, they appear to represent constituents of a somewhat archaic lineage that per- sisted through the Campanian and Maastrichtian of North America.

The phylogeny of remaining species previously referred to Alphadon is likewise poorly understood, although relationships between several of the included species have been suggested and briefly discussed (e.g., Fox, 1971, 1979; Lillegraven and McKenna, 1986). Fox (1979) suggested a relationship of Judithian "Al- phadon" praesagus and "A." russelli to Lancian "A." rhaister. This relationship is herein formally recognized by the referral of these species to a new genus, Turgidodon. In this genus are also placed two species

from the Kaiparowits Formation, T. lillegraveni and T. madseni; as discussed above, several other taxa, including "Alphadon" sp. cf. "A." rhaister from the Lance Formation (Clemens, 1966, 1973b) and "Al- phadon" parapraesagus Rigby and Wolberg, 1987, are referable to the genus but are not yet well known. The species of Turgidodon share derived dental morphology indicating that they represent a monophyletic group. Most of these specializations are apparently adapta- tions for crushing (Clemens, 1966; Fox, 1979), and include inflation of cusps on all tooth crowns; enlarged, bulbous posterior premolars (P3 and P3) with a strong, distinctive wear pattern; and relatively small first molars. The species of Turgidodon are also large relative to other Cretaceous peradectids. The smallest species, T. madseni (from the lower Kaiparowits Formation), appears to be most primitive in features such as the relatively slight inflation of cusps, the slight enlarge- ment of the posterior premolars, and the short preparacrista on upper molars; T. russelli (known from the Oldman, Judith River, "Mesaverde," and Two Medicine formations) is closely similar. The large Lan- cian species T. rhaister, together with one or more similar but undescribed species of Lancian age (cf. Clemens, 1979) and, perhaps, Bistius bondi, are the most apomorphous and appear to represent terminal members of this specialized clade of Cretaceous Per- adectidae.

Of the marsupial species currently known from the lower Kaiparowits Formation, one (Iqualadelphis lactea) is shared with the Verdigris Coulee local fauna (from the lower Milk River Formation), the only well- known assemblage of Aquilan age. Alphadon halleyi and A. sahnii are found at several Judithian localities and are unique to that Land Mammal Age (Lillegraven and McKenna, 1986). The remaining species from the lower Kaiparowits Formation are not yet recognized from elsewhere. Of these, Turgidodon lillegraveni and T. madseni are closely similar to T. praesagus and T. russelli, respectively, which are uniquely Judithian species known from more northerly assemblages; Prot- alphadon wahweapensis is intermediate in morphology between the Aquilan P. creber and the Judithian to Lancian P. lulli. Closest affinity of the lower Kaipa- rowits marsupials is thus to those of the Judithian, although there is some indication that the assemblage may be somewhat older than typical Judithian local faunas. Marsupials of the upper Kaiparowits Forma- tion are not yet well enough known to merit more than passing comment. The specifically identifiable taxa, Alphadon attaragos and A. sp. cf. A. sahnii, are unique to the Judithian. Thus, deposition of the Kaiparowits Formation may correspond to a time roughly represented by slightly pre-Judithian through Judithian Land Mammal Age assemblages as they are known from elsewhere.

Fiorillo (1988) has shown that, for previously described Judithian faunas of the north-central Rocky Mountain region, variation in composition may reflect latitudinal zonation of North American terrestrial fau-




nas. Although the uniqueness of most lower Kaipa- rowits marsupials may be in part due to temporal differences between them and other known local faunas, it is likely that some of the differences reflect zoogeo- graphic differentiation among North American Late Cretaceous terrestrial faunas. Pediomyid and stagodontid marsupials constitute important (and, in the case of pediomyids, abundant) elements in most of the northerly Late Cretaceous assemblages from the Aqui- lan through the Lancian, but are rare or absent from the Kaiparowits fauna (Eaton and Cifelli, 1988). Al- though pediomyids have been recorded from as far south as Baja California (Lillegraven, 1972), they are rare elements of most known southern faunas, including those of the San Juan Basin, New Mexico (Clemens, 1973a; Rigby and Wolberg, 1987) and the "Mesa- verde" Formation of central Wyoming (Lillegraven and McKenna, 1986). Stagodontid marsupials are not known from either of these areas; it has been suggested that geographic distribution of stagodontids during the Late Cretaceous may have been influenced by marine incursions of the Pierre/Bearpaw sea in western North America (Fox and Naylor, 1986).

ACKNOWLEDGMENTS

I thank Drs. Malcolm C. McKenna, William A. Clemens, Jr., Richard C. Fox, and Jeffrey G. Eaton for various comments, advice, help, and information. Dr. Fox kindly permitted and facilitated my study of specimens at UALVP, and Dr. Louis L. Jacobs provided me with casts of SMP-SMU Trinity therians. I am grateful to Eaton and to Scott Madsen, Ken Thiessen, Winford Sterling, Beth Larson, Dave Schmidt, and Mary C. Cifelli for assistance in field and laboratory activities. The Department of Geology, Museum of Northern Arizona, provided some logistic support for field work, and I thank Dr. Mike Morales for his co- operation in this respect. Support for this project was provided by the Office of Research Administration and Department of Zoology, University of Oklahoma, and by grants from the National Geographic Society (no. 2881-84), National Science Foundation (BSR 8507598, 8796225, 8906992), and Petroleum Research Fund of the American Chemical Society (no. 20311-G8). Stu- dent participation in the project was made possible by an REU supplement to the NSF award. The SEM pho- tos were prepared by Eric Sherburn at the Samuel Rob- erts Noble Electron Microscopy Laboratory, Univer- sity of Oklahoma, access to which was kindly provided by Dr. Scott Russell, Director.

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Received 24 May 1989; accepted 27 October 1989.



Documents

Cretaceous Mammals of Southern Utah. I. Marsupials from the Kaiparowits Formation (Judithian)