Therian Mammals from the Cenomanian (Upper Cretaceous) Dakota Formation, Southwestern Utah

Therian Mammals from the Cenomanian (Upper Cretaceous) Dakota Formation, SouthwesternUtahAuthor(s): Jeffrey G. EatonSource: Journal of Vertebrate Paleontology, Vol. 13, No. 1 (Mar. 18, 1993), pp. 105-124Published by: Taylor & Francis, Ltd. on behalf of The Society of Vertebrate PaleontologyStable URL: http://www.jstor.org/stable/4523489 .

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106 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 13, NO. 1, 1993

S4LT LAKE O 100km

SALT LAKE

CITY/- -

Uinta P Basin

C) "

olley CITY .. ,GREEN'

.'

HANNOCK T errace- 2

*KaN4B FIGURE 1. Distribution of surficial Cretaceous sediments in Utah (stippled, after Hintze, 1974) and areas of known fossil mammal localities in the Dakota Formation. Area 1 is the first known locality, in the San Rafael Swell, and area 2 is the locality from which the holotype of Pariadens kirklandi was recovered. The specimens discussed in this report were recovered from areas 3 and 4.

Cenomanian. Detailed locality data may be obtained from the Museum of Northern Arizona.

Methods

More than 2,700 kg of matrix were removed from localities that yielded mammals as a result of test screen- washing. Most of the matrix is from the most fossil- iferous locality, MNA locality 1067 (Fig. 1, area 3). The matrix was wet-screened through two screen sizes, standard window screen and a fine mesh (0.3 mm, 0.012 in.). All resultant concentrate was picked under a microscope.

Measurements

A trigonid angle is included in some discussions of specimens. This is the angle between the lines drawn (using a camera lucida) from the apex of the protoconid to that of the paraconid and the metaconid. Such a measurement can be made consistently only on little- worn or unworn specimens.

All measurements are oriented as shown in Lille- graven (1969:fig. 5) and are given in millimeters. Mea-

surements were made by superimposing the specimen image (using the camera lucida) onto 10 x 10 to the inch graph paper, calibrated with each square equal to 0.1 mm. All new specimens described here are Mu- seum of Northern Arizona (MNA) specimens.

Abbreviations

FMNH Field Museum of Natural History UAVP University of Alberta, Edmonton, Canada UCM University of Colorado Museum, Boulder

SE -O

S-90 M Member m

0) L10

upler member

" 0 -80 I-

L

-I-

Wr• Z

IJ. vertebrate (

o -

U localities

( Z-

S10

(m)-0

i--

w"_ _ _ _ _

FIGURE 2. Age and stratigraphic relationships of the Da- kota Formation east of the Paunsaugunt Plateau (area 3 of Fig. 1) and stratigraphic position of vertebrate localities. L = lower, M = middle, U = upper.



EA TON- CENOMANIAN THERIANS FROM UTAH 107

AWD B

1 mm

FIGURE 3. Theria. A-G, order, family, genus, and species undetermined. A, V6245, Rdp3, occlusal view (stereopair); B, same, lingual view; C, V6017, LMx, occlusal view (stereopair); D, same, labial view (stereopair); E, V6246, LMx (partial), occlusal view (stereopair); F, V6464, LMx, occlusal view (stereopair); G, same, lingual view (stereopair).

UCMP University of California Museum of Pa- leontology, Berkeley

AP anteroposterior dimension LB lingual-buccal dimension

TRIW width of trigonid TALW width of talonid

* indicates damage to specimen (measurement not estimated)

x indicates tooth position unknown, e.g., LMx

SYSTEMATIC PALEONTOLOGY

Class MAMMALIA Subclass THERIA

Order and Family Undetermined Genus and Species Undetermined

Figures 3A, B

Referred Specimen -Loc. 1067: V6245, Rdp3.

Description--V6245 (Figs. 3A, B) is most similar to

dp3s of marsupials (e.g., Clemens, 1966:fig. 76; Mon- tellano, 1986:fig. 22b) in having a broadly open, buccolingually compressed trigonid. The specimen is close in size (AP = 1.72; LB = 0.76) to V6051 (Fig. 5E), a

dp3 described below as Alphadon clemensi sp. nov.; however, there are substantial morphological differences. The trigonid of V6245 is broadly open lingually (trigonid angle of 1350) and its paraconid and metaconid are subequal, whereas in V6051 the paraconid is much smaller than the metaconid. The cristid obliqua of V6245 originates lingually, climbing the posterior wall of the metaconid, and in V6051 it originates behind the protoconid. On V6245 the cristid obliqua terminates halfway across the talonid basin at the large, worn hypoconid. The entocristid of V6245 is straight and terminates at an entoconid that is well-separated from the hypoconulid, whereas on V6051 the entoconid and hypoconulid are close together. There is no cusp in the position of the hypocolid. The postcristid descends ventrolabially from the entoconid rather than from the hypoconulid.

While a postcristid is present on all known Creta- ceous marsupials, it is also present on some eutherians and Trinity therians, so it cannot be considered uniquely derived for marsupials. The lack of twinning between the entoconid and hypoconulid is distinctly unmar- supial-like. As is the absence of a hypoconid; therefore, this specimen can be assigned with certainty only to subclass.




)C

vvvv

V L

smmIJ

Kd

1mm,0

FIGURE 4. Dakotadens, gen. nov. A-M, D. morrowi, sp. nov. A, V5827, RM 1, occlusal view (stereopair); B, V5825, holotype, RMx, occlusal view (stereopair); C, same, labial oblique view (stereopair); D, V5824, RMx, occlusal view (stereopair). E, V5828, LMx, occlusal view (stereopair); F, V6037, RMx, occlusal view (stereopair); G, V6318, RMx, occlusal view (stereopair); H, V6023, Rmx, occlusal view (stereopair); I, same, lingual view; J, V6042, Rmx, occlusal view (stereopair); K, same, lingual view; L, V5378, Rmx, occlusal view (stereopair); M, same, lingual view. Dakotadens sp. N, V5345, LMx, occlusal view (stereopair); 0, V6025, LMx, occlusal view (stereopair).



EATON-CENOMANIAN THERIANS FROM UTAH 109

Genus and Species Undetermined Figures 3C-E

Referred Specimens-Loc. 939, V6017, LMx. Loc. 1067: V6136, RMx; V6246, LMx (labial half).

Description--V6017 (Figs. 3C, D) is a small (AP =

1.6"; LB = 1.52) upper molar missing the parastylar region. The stylar shelf narrows anteriorly and is absent labial to the paracone. Cusps are present in the C and D positions as part of a continuous crest at the labial margin of the stylar shelf. The paracone has a broad circular base and is the largest and tallest cusp of the tooth. The metacone is positioned more lingually than the paracone causing the centrocrista to align obliquely to the anteroposterior axis of the tooth. The centrocrista is V-shaped in side view and the trigon basin is deep. The paraconule is well-developed and winged, the metaconule is smaller and is unwinged (no postcris- ta). The protocone is low and broad and, relative to the width of the tooth, is close to the paracone and metacone.

V6136, a RMx, is small (AP = *; LB = 1.42) and similar to V6017 in having a series of small cuspules along a continuous ridge at the labial margin of the stylar shelf. The paracone is tall and slender; the metacone is broken. The metaconule is higher on the postprotocrista than it is on V6017. The protoconular area is broad relative to the anteroposterior dimension of the tooth.

V6246 (Fig. 3E) is the labial half of a small (AP =

1.93; LB = *) upper molar with a labially shifted paracone that is much taller than, and closely approximated to, the metacone. Stylar cusp A is present (the tip of the cusp is broken), cusp B is absent, the C(?) cusp is large and expanded labially; there is no distinct cusp D or E. The paraconule is not connected to the paracone and no preparacrista is present.

Discussion - These upper molars are similar to those of pediomyids in that no stylar cusp B is present, the stylar shelf narrows anteriorly, and there is no preparacrista connecting the paracone to stylar cusp B. In overall shape and small size, these specimens are similar to teeth of the smallest pediomyid recovered from the Lance Formation, Pediomys krejcii. These specimens are not assigned to the Pediomyidae because of the large size of the paracone relative to the metacone and the weakly developed metaconule. As V6017 and V6246 are similar to the dp3 illustrated by Clemens (1966:fig. 30) as ?Pediomys sp., it is possible that these upper molars represent deciduous teeth. No lower molars having pediomyid characteristics were located in the sample and no dp3s of Alphadon-like taxa have been illustrated, further limiting assignment of these teeth.

Cifelli (1990a) described several fragmentary specimens (from the Turonian) of undetermined affinities that are similar to the Dakota specimens described here. Similarities include narrowing of the stylar shelf anteriorly, lack of metaconular cristae, and presence of stylar cusps in or near the C and D positions. They

TABLE 1. Measurements (in mm) ofDakotadens morrowi, gen. et sp. nov.

MNA no. Upper teeth AP LB

V5824 RMx 2.77 2.59 V5825 RMx 2.68 2.70 V5827 RMI? 2.82 2.48 V5828 LMx 2.51 2.89 V6318 RMx 1.70* 2.38*

MNA no. Lower teeth AP TRIW TALW

V5354 Rmx 2.7* 1.65 1.55 V5374 Lmx 2.42 1.40 1.48 V5378 Rmx 2.50 1.39 1.32 V5386 Lmx 2.5* 1.3* 1.7* V5394 Lmx 2.58 1.60 1.6* V6023 Rmx 2.82 1.85 1.90 V6028 Rmx 2.33 1.22 1.32 V6032 Rmx 2.95 1.52 1.85 V6038 Lmx 2.60 1.50 1.70 V6042 Rmx 2.41 1.58 1.52 V6096 Rmx 2.58 1.31 1.51

differ in that the specimens recovered from the Dakota Formation are much smaller, have more weakly developed stylar cusps C and D, and lack the narrowed protoconal region inferred to be present by Cifelli (1990a) on the Turonian specimens.

Genus and Species Undetermined Figures 3F, G

Referred Specimen-Loc. 1067: V6467, LMx.

Description--V6467 (Figs. 3F, G) similar to but much smaller (AP = 1.09; LB = 0.90) than the molars described above as genus and species undetermined. V6467 clearly has three roots. The stylar shelf on this specimen is absent labial to the paracone, no distinct stylar cusps are present, and there is an anterior projection on the labial wall of the tooth. There is no indication that conules were present.

Discussion -As with the larger pediomyid-like molars described above this tooth has some pediomyid characteristics but may well represent a deciduous tooth.

DAKOTADENS, gen. nov.

Type Species--Dakotadens morrowi.

Etymology--Named after the Dakota Formation, from which the type and all referred specimens were recovered, and dens, Latin for tooth.

Diagnosis--Same as for the species.

DAKOTADENS MORROWI, sp. nov. Figures 4A-M, Table I

Holotype-MNA V5825, RMx, Loc. 1067. Etymology -Named for Jared Morrow, who discov-

ered the type locality, and helped haul, screen-wash and sort the sediments from the Dakota Formation.




Distribution -Late(?) Cenomanian, Dakota Forma- tion, southwestern Utah, MNA localities 1064, 1067, 1071.

Diagnosis--Upper molars with broad stylar shelf and low cuspules along labial margin of tooth. Ectoflexus weakly developed. Stylar cusp "A" present, cusp "B" largest or subequal with cusp "D," cusp "C" variable in size and position, presence of cusp "E" variable. Metacrista cuspate, preparacrista oriented towards cusp "A", except Ml on which the preparacrista connects to stylar cusp "B." Paracone largest cusp or subequal with metacone. Centrocrista broad and U-shaped in side view. Paraconule weakly "winged" and better developed than unwinged metaconule. Protocone broad, low, and positioned anteriorly. Lower molars with protocone taller than subequal paraconid and metaconid. Cristid obliqua originating behind protoconid forming a broadly open talonid basin. Entoconid and hypoconulid closely positioned, entoconid tallest cusp on talonid, hypoconulid next tallest, hypoconid lowest. No postcristid present.

Referred Specimens -Loc. 1067: V5354, Rmx; V5374, Lmx; V5378, Rmx; V5824, RMx; V5827, RMI?; V5828, LMx; V6023, Rmx; V6028, Rmx; V6032, Rmx; V6037, RMx; V6038, Lmx; V6042, Rmx; V6096, Rmx; V6318, RMx. Loc. 1071: V5394, Lmx. Loc. 1064: V5386, Lmx.

Description--V5827 (Fig. 4A) is considered to be

an M1 due to the anterior narrowing of the stylar shelf. All stylar cusps lie along the labial margin of the stylar shelf and are buccolingually compressed. Stylar cusp A (the use of stylar cusp terminology here is not meant to imply homology with the stylar cusps of marsupials, but to describe a topographic position similar to the series described for marsupials) is situated at the terminus of the anterolabial cingulum. Cusp B is the largest stylar cusp; a small cuspule is present posterior to B. A well-developed C(?) cusp, smaller than cusp B, is present. The D(?) cusp is low and small. Alternatively, the cuspule posterior to cusp B could be considered a small C cusp, with the next posterior cusp a large D cusp, and the posteriormost cuspule undesignated. There is a small cuspule in the E position. The postmetacrista bears several cusps. The base of the paracone merges with cusp B, due to the anterior narrowing of the stylar shelf. A weakly developed paracrista, unlike that on any of the more posterior molars, connects the paracone to stylar cusp B. The paracone and metacone are slightly worn, but appear to be subequal in size and height. The paracone and metacone are broadly separated and the centrocrista is U-shaped in side view. There is a distinct paraconule, but the metaconule is poorly developed, consisting of a bump on the postprotocrista.

V5825 is a RMx (Figs. 4B, C), the holotype, and has a broad stylar shelf and all stylar cusps are buccolingually compressed along the labial margin of the tooth. The ectoflexus is not well-developed. A distinct stylar cusp A is present. B is the largest stylar cusp, and a small C(?) cusp is present posterior to B. The D cusp

is slightly smaller than B, and cusp E is small and low. The metastyle does not project posteriorly. The postmetacrista is cuspate; the preparacrista leads to the notch between stylar cusps A and B. The metacone and paracone are subequal in size and height, and are separated by a broad valley, U-shaped in side view. The paraconule is unwinged, and the metaconule is miniscule. The talon basin is deep. The protocone is broad and low. Another upper molar, V5824 (Fig. 4D), is similar to the holotype, but differs in that the anterior face of stylar cusp B is concave. V5828 (Fig. 4E) is similar to the other molars described above, but is proportionally larger in the buccolingual dimension and lacks stylar cusps C and E (possibly as a result of abrasion).

V6037 (Fig. 4F) has a distinct stylar cusp A on the terminus of a sharp ridge that is developed on the anterior margin of the anterolabial cingulum. Cusp B is the largest and tallest of the stylar cusps and is only slightly lower than the paracone. No cusp C is present, and cusp D is smaller than cusp B. Several cuspules are present on the posterolabial part of the stylar shelf, including three cusps on the postmetacrista, but no distinct cusp E is seen. The ectoflexus is weakly developed. The metacone is larger and slightly taller than the paracone and has a deep notch on its labial side. The trigon basin is broad and open; the unwinged paraconule is better developed than the metaconule.

V6318 (Fig. 4G) is an ultimate upper molar, but as the dental formula of Dakotadens is unknown, it is not certain if the ultimate tooth position is a third or fourth molar. Although the tooth is incomplete, it is clear that there was a strong anterolabial lobe. The stylar shelf has one large, centrally placed stylar cusp (C?), and a smaller cusp posterior to it. The paracone is taller than the metacone. The paraconule is well-developed and is connected to the paracone by a crest that continues up the lingual face of the paracone. A large metaconule is present. The protocone is badly damaged.

No method for distinguishing tooth position of lower molars was determined. MNA V6023 (Figs. 4H, I) is typical of lower molars. It has a broad anterior cingulum that culminates in a cusp-like projection below the paracristid notch. In one specimen, V6042 (Figs. 4J, K), the anterior cingulum terminates in a doubled cuspule. The cusps of the trigonid form approximately a 450 angle, and the metaconid and paraconid are subequal in height and size. The cristid obliqua originates labially on the posterior wall of the trigonid and is convex labially. On some specimens a distinct line can be traced ventrolabially from the protocristid notch to the cristid obliqua. The talonid is broad and is open posteriorly between the hypoconid and hypoconulid, the point from which an anteroposteriorly oriented valley divides the talonid. The hypoconulid and entoconid are twinned. The entoconid is the tallest cusp of the talonid, and the hypoconulid can be taller than or subequal with the hypoconid. No postcristid is present. One specimen (V5394) has a distinct cuspule in the center of the talonid basin.



EA TON- CENOMANIAN THERIANS FROM UTAH 1 1 1

Several teeth in the sample, such as V5378 (Figs. 4L, M), may represent the ultimate lower molar. They have a medially positioned hypoconulid.

Discussion - The lower molars were allocated to the same taxon as the upper molars because the broad protocones of the upper molars fit the wide talonids basins of the lower molars.

Classification of this genus is difficult. The characteristics of the molar morphology, when taken together, fall outside of what has generally been considered typical for Cretaceous marsupials, including the relatively low and bulbous cusps, the weak ectoflexus, the unwinged and poorly developed metaconule, the broadly U-shaped centrocrista (in side view), the lack of a postcingulid, and the weakly developed notch between the metaconid and entocristid.

Relative to the Deltatheroida, considered a sister group of the Marsupialia by Kielan-Jaworowska and Nessov (1990), Dakotadens is similar only in having no postcristid but in most other regards, such as the broad protocone, wide talonid basins, closely approximated hypoconulid and entoconid, is derived. It could be argued that Dakotadens, which is considerably more marsupial-like than deltatheroidans, should at least be included in the Metatheria, but on the basis of being derived relative to the Deltatheroida so could many other tribotheres. Without knowledge of either the dental formula or the structure of the basicranial region, I consider it most appropriate at this time not to assign Dakotadens to an order.

Molars of Dakotadens have some features that are considered characteristic of marsupials such as a broad, cuspate stylar shelf (Clemens and Lillegraven, 1986) and overall shape of the teeth (LB:AP ratio). On lower molars, the paraconid and metaconid are subequal and the entoconid and hypoconulid are twinned. Other morphologic characters are a mosaic of those present in different marsupial families. Dakotadens shares with Alphadon-like marsupials (but not stagodontids) a subequal to larger and taller paracone than metacone, an entoconid taller than the hypoconulid, and the hypoconid being the lowest cusp of the talonid. By contrast, Dakotadens shares with Pariadens (but not Alphadon- like marsupials) a relatively low trigonid to talonid height differential, unwinged metaconule, and broad, low cusps. Furthermore, it shares with most pediomyids (and not stagodonts or Alphadon-like marsupials) a preparacrista oriented toward the parastylar region. Dakotadens shares with unequivocal stagodontids (Eodelphis and Didelphodon) and pediomyids a labial origin for the cristid obliqua.

The combination of characters found in Dakotadens is unlike that of any known Cretaceous eutherian. Of tribotheres, the taxon is most similar to Potamotelses aquilensis, described by Fox (1972), in that the molars have a broad stylar shelf, well-separated paracone and metacone, larger paracone than metacone, lack of pre- or postprotoconular cingulae, subequal size of paraconid and metaconid, distinct notch separating the hypoconulid from the hypoconid, and lack of a post-

cristid. Dakotadens differs from Potamotelses in having distinct para- and metaconules, a paracrista oriented toward the parastylar region rather than toward stylar cusp B, a more lingually placed metacone, a much broader protocone, lower molars not as anteroposteriorly elongate, no cuspule between the entoconid and hypoconulid, and a more labial origin for the cristid obliqua.

The mosaic of characters found in Dakotadens does not allow for assignment beyond subclass. With knowledge of the dental formula, inclusion of the taxon within the Metatheria (as the Deltatheroida has a marsupial dental formula) and probably the Marsupialia is likely. Dakotadens may be part of an early diversification of the order and did not leave later descendants.

DAKOTADENS Sp. Figures 4N, O

Referred Specimens -Loc. 1067: V5345, LMx; V6025, LMx.

Description-Mx. V5345 (Fig. 4N) is small (AP = 2.08*; LB = 2.55*) upper molar with the anterolabial corner missing. The stylar shelf is broad, with cusps along the labial margin of the stylar shelf. Cusp A is missing due to breakage, as is the stylocone, but the preparacrista appears to have attached to the latter. A small cusp C(?) is present on the anterior side of the weakly developed ectoflexus. A broad cusp, as tall of the metacone, is present in the D position. A small, low cusp is present in the area of E. The paracone is taller and larger than the metacone. The metacone is closer to the protocone than is the paracone. Neither the paraconule or metaconule are winged. The protocone lacks anterior or posterior cingula.

V6025 (Fig. 40), a badly worn specimen, is a small (AP = 1.60; LB = 2.08) ultimate upper molar. The preparacrista is oriented toward stylar cusp A. Cusp B was probably the largest stylar cusp; there is no hint of a C cusp, and the D cusp is smaller than cusp B. The posterior part of the stylar shelf is narrow and is close to the labial margin of the metacone, leaving no space for a stylar cusp E. The metacone is severely worn but appears to have been subequal to the paracone prior to wear. Wear on the preprotocrista oblit- erates any evidence of a paraconule; a small metaconule appears to have been present.

Discussion--These two teeth are morphologically very much like Dakotadens morrowi but are substan- tially smaller than the teeth attributed to that species (compare to Table 1). The range of size variation in D. morrowi is unknown, but the apparent size range suggests that a second species may be present. Some of the lower molars assigned to D. morrowi(e.g., V6028) may also represent this smaller species, but as there is no certain way to determine the tooth position of the lower molars it is possible that ml or some other lower molar of D. morrowi may be diminutive.




Order MARSUPIALIA

ALPHADONTIDAE, fam. nov.

Type Genus-Alphadon Simpson, 1927. Diagnosis - Upper molars with broad stylar shelves,

stylar cusps A, B, D well-developed, presence and size of stylar cusps in the C position variable. Meta- and paraconules distinct, paraconule and usually metaconule "winged." Preparacrista connects paracone to stylar cusp B on M 1-2, and usually on M3. Paracone and metacone well separated and approximately same size and height on M 1-3. Centrocrista and tips of paracone and metacone form a straight line (not V-shaped) in occlusal view. Lower molars have metaconid-paraconid subequal or paraconid slightly lower. Cristid obliqua originates medially at the protocristid notch.

Referred Genera--Alphadon, Albertatherium, Tur- gidodon, Anchistodelphys, Protalphadon.

Discussion -Alphadon was included in the Didel- phidae of Gray (182 1) when it was named by Simpson in 1927 and resided there until recently. Crochet (1979) noted that Alphadon did not have a V-shaped centrocrista (in occlusal view) which he considered to be characteristic of didelphids, and he allied Alphadon with the Tertiary taxon Peradectes (within the Pera- dectini). Reig et al. (1987) have followed suit, placing the Cretaceous genera Alphadon and Albertatherium in the Family Peradectidae. Aplin and Archer (1987) were less certain about the status of the Peradectidae and indicated that significant revisions at the family level are required. Krishtalka and Stucky (1983) suggested that the Family Peradectidae should not include the Cretaceous genera Alphadon and Albertatherium because, unlike peradectids, the cristid obliqua of these taxa originates medially (at the protocristid notch) and the talonid is not shortened relative to the trigonid. Montellano (1986) objected to the inclusion of Alpha- don in the Peradectidae because of the medial origin of the cristid obliqua on Alphadon and the relatively weakly developed conules and stylar cusps of Pera- dectes. I concur with Krishtalka and Stucky (1983) and Montellano (1986) that Alphadon and morphologically similar Cretaceous marsupials should not be included in the Peradectidae. The Peradectidae and Didelphidae are derived relative to alphadontids in sharing a labial origin for the cristid obliqua, as in pediomyids. As defined here, the Peradectidae should be reserved for marsupials with molars having a reduced entoconid and a weak or vestigal entoconid notch, shortened talonids relative to trigonids, and small or absent conules and stylar cusp C. The Didelphidae are herein recognized as marsupials with lower molars having ento- conids much taller than hypoconids or hypoconulids; the posterior wall of the trigonid essentially perpen- dicular to the anteroposterior axis of the tooth, and upper molars with moderate to strong conules and stylar cusp C, V-shaped centrocrista in occlusal view ("dilambdodont"), and lower and smaller paracone than metacone.

The alphadontids share primitive characters with

both the didelphids and peradectids: didelphids -strong entoconid with deep entoconid notch, strong conules and stylar cusp C; peradectids- dorsally projecting hypoconulid, protoconule area unexpanded posterolin- gually, centrocrista not V-shaped in occlusal view, and paracone and metacone of similar size.

Specimens described below from the Dakota For- mation and from younger strata in the same area (Ci- felli, 1990a, b, c) indicates that a diverse group of Alphadon-like taxa persisted through the Late Creta- ceous. These marsupial are derived relative to any old- er taxon considered by other workers to have metatherian affinities. They are well-advanced over the Trinity therians in having the paracone only slightly larger than the metacone, enlarged protocone, the paraconid subequal to the metaconid in height and size, a medial origin for the cristid obliqua, and less compressed trigonids. Alphadontids are also derived relative to Del- tatheroida in having distinct stylar cusps posterior of the stylocone, enlarged protoconular area, longer and broader talonid basins, and approximated hypoconulid and entoconid.

The family is morphologically distinct from the Sta- godontidae in not having enlarged paraconids, reduced paracones, and posteriorly enlarged molars. It is distinct from the Pediomyidae (or pediomyid-like taxa) in not having an anteriorly reduced stylar shelf or labial origin for the cristid obliqua. The Alphadontidae, as defined here, leaves some Cretaceous taxa without fa- milial affinities. Fox (1987b) left the Iqualadelphis in- certae sedis, and this assignment is followed here. Ci- felli (1990c) included Iqualadelphis in the Peradecti- dae, but its narrow stylar shelf suggests that placement is incorrect. Iugomortiferum Cifelli, 1990b is excluded because it has a relatively narrow stylar shelf, conules are weak or absent, and cusps are inflated. Glasbius is clearly outside the definition presented here of the Al- phadontidae.

ALPHADON CLEMENSI, sp. nov. Figures 5A-J, Table 2

Holotype-MNA V6338, LM2, Loc. 1067. Etymology--In recognition of Dr. William A. Clem-

en's contribution to our understanding of Mesozoic mammals.

Distribution -Late(?) Cenomanian, Dakota For- mation, southwestern Utah, MNA localities 1064, 1067.

Diagnosis - Stylar cusps B and D consistently large, cusp or cusps between B and D variable in size and placement, but present. Paracone with broader base and taller than metacone. Lower molars narrower relative to length than any known species of Alphadon, paraconid consistently smaller than metaconid. Most similar to A. sahnii, differing from that species in that stylar cusp C less consistently developed and metacone with smaller base.

Referred Specimens-Loc. 1064: V5387, RM2. Loc. 1067: V5352, LM3?; V5829, Lml (in mandible frag-




A

B

G

I

4b 1 mm

J FIGURE 5. Alphadon clemensi, sp. nov. A, V6338, holotype, LM2, occlusal view (stereopair); B, same, labial oblique view (stereopair); C, V5387, RM2, occlusal view (stereopair); D, V5352, LM3, occlusal view (stereopair); E, V6051, Rdp3, occlusal view (stereopair); F, same, lingual view; G, V5830, Rp3-m2, occlusal view (stereopair); H, same, lingual view; I, V5831, Lm3- 4, occlusal view (stereopair); J, same, lingual view.

ment with partial p3); V5830, Rp3-m2; V5831, Lm3- 4; V5855, LM3?; V6034, Rm3?; V6039, Lm2 or 3; V6051, Rdp3; V6097, Rm3?; V6244, Rm4; V6316, Lml?; V6321, LM3 (labial half); V6325, Rmx; V6463, Lmx; V6791, Lm3?; V6792, Lm2?; V6878, Rm4; V6879, Rml; V6881, Rmx (talonid); V6883, Rm4.

Description--V6338, the holotype (Figs. 5A, B), is

considered to represent an M2, based on the well-developed parastylar-anterolabial cingulum area, moderately developed ectoflexus, and the anterior position of the protocone. All stylar cusps are along the labial margin of the tooth. Stylar cusp A is worn but present;




TABLE 2. Measurements (in mm) of Alphadon clemensi, sp. nov.


V5352 LM3? 1.91 2.15 V5387 RM2 2.20 2.12 V6321 LM3 1.91 * V6338 LM2 2.25 2.28


V5829 Lml 1.62 0.95 0.95 V5830 Rp3 1.35 0.70

Rml 1.65 0.88 0.90 Rm2 2.10 1.10 1.15

V5831 Lm3 2.05 1.10 1.10 Lm4 1.95 1.08 0.97

V6034 Rm3? 2.10 1.20 1.25 V6039 Lmx 1.97 1.05 1.05 V6051 Rdp3 1.98 0.98 1.00 V6097 Rm3? 1.76 1.00 0.93 V6244 Rm4 1.75 0.93 0.90 V6316 Lml 1.62 0.82 0.80 V6325 Lmx 1.91 1.00 0.98 V6791 Lm3? 1.89 1.05 1.10 V6792 Lm2? 1.99 1.98 0.95 V6878 Rm4 1.78 0.99 0.82 V6879 Rml 1.72 * * V6883 Rm4 1.72 0.98 0.90

cusps B and D are about the same size. Cusp C is lower than B or D, is centrally placed, and has a single, broad base which divides into two cuspules. There is no stylar cusp E. The paracone and metacone have bases of the same size but the paracone is slightly taller. The preparacrista attaches to the anterior side of the stylocone. The conules are well developed and winged. The talon basin is deep. On V5387 (Fig. 5C), stylar cusp B is the largest and best developed; cusp C is approximately the same size as cusp D and is much smaller than cusp B. Cusp C is positioned just posterior to a moderately developed ectoflexus. No distinct cusp E is present. The paracone is the tallest cusp of the tooth and is positioned labially relative to the metacone. The paraconule is winged and connects both to the paracone and the anterolabial cingulum. The metaconule is also winged, connecting posteriorly to a short postcingulum at the base of the metacone. The metaconule is more poorly developed on V5378 than on V6338.

V5352 (Fig. 5D), an M3, has distinct stylar cusps A, B, C, and D along the labial margin. Cusps B and D are subequal in size, elongate, and buccolingually compressed. Cusp D is adjacent to the ectoflexus and is labial to the centrocrista notch. Two cuspules occur on the anterior side of the ectoflexus, just behind cusp B. Para- and metaconules are well developed and ar- ranged as in M2. The paracone is slightly larger than the metacone. A deep basin is developed labial to the metacone. V6321, the labial half of an M3, has the same stylar cusp configuration.

V6051 (Figs. 5E, F), a dp3 has a talonid morphologically identical to the ml described below and is of

appropriate size to be considered A. clemensi (AP = 1.98; TRIW = 0.98; TALW = 1.00). The trigonid is narrow, broadly open (trigonid angle is 1250), and elongate, with the paraconid developed as a small cuspule on the anteriorly-projecting crest of the protoconid. The metaconid is low and small. The cristid obliqua originates medially at the base of the posterior wall of the trigonid. The entoconid and hypoconid are subequal in height; the hypoconulid is lower and is weakly twinned with the entoconid.

The p3 (MNA V5830, Figs. 5G, H) has no cingulids. A single tall, anterior cusp dominates the tooth. A posteriorly directed crest descends from the anterior cusp apex into a small posterior basin. At the posterior margin of the tooth is a single, erect cusp.

The ml (MNA V5830, Figs. 5G, H) tapers anteriorly and has a more open trigonid (610) than those of m2- 4. The paraconid is smaller than, but about the same height as, the metaconid. There is no distinct trace of the cristid obliqua on the posterior wall of the trigonid, though its origin appears to be in a median position. The entoconid is slightly taller than the hypoconid and, unlike the condition seen on other lower molars, the hypoconulid is the lowest cusp of the talonid. The hypoconulid and entoconid are twinned but distinct. The ml of MNA V5830 (mandible with p3-m2, Figs. 5G, H) underwent considerably more wear than the m2. Another possible ml, V6316, has a much smaller paraconid than metaconid and is proportionally narrower relative to length than V5830.

An m2 (MNA V5830, Figs. 5I, J) is essentially identical to the m3, described below, but is slightly larger and the crests on either side of paracristid notch form a nearly straight line (1700 compared to 1200 on m3).

On m3 (MNA V5831, Figs. 5I, J), the anterior cingulid reaches a cusp-like apex just lingual to the paracristid notch. The metaconid is larger and taller than the paraconid, and the protoconid dominates the trigonid. The anterior wall of the paraconid is slightly concave, and the anteriormost edge of the paraconid forms a sharp ridge. The crests of the paracristid meet at an angle of 1200; those of the protocristid at 1480. The metaconid projects lingually more than does the paraconid. The cristid obliqua originates medially on the posterior wall of the trigonid.

On another m3, V6034, a small cuspule is present on the cristid obliqua near its point of origin, and the broad hypoconid is the lowest cusp of the talonid. The postcristid is distinctly cusp-like where it originates labial to the medially positioned hypoconulid, and descends ventrolabially on the posterior wall of the hypoconid. The hypoconulid is taller than the hypoconid and is twinned with, but not as tall as, the entoconid.

The m4 (MNA V5831, Figs. SI, J) is similar to m3, but smaller. The crests of the paracristid meet at the notch at a slightly broader angle (1300) and the metaconid projects lingually more strongly than on m3. The hypoconulid is tall, about the same height as the paraconid. The entoconid is broken on MNA V5831, but on another specimen, MNA V6244, the entoconid is relatively taller than on any of the other lower molars.




Discussion--The occurrence of a species of Alpha- don in the Cenomanian without another report of the genus until the Campanian is problematic, but may only reflect the poorly known faunas of the Turonian, Coniacian, and Santonian. The presence of Alphadon in the Cenomanian extends the temporal duration of Alphadon to about 25 ma. This is unusually long for a mammalian genus; nonetheless, detailed comparison to the type species (A. marshi) revealed insufficient differences to warrant establishment of a new genus.

These specimens also fit the definition of Alphadon sensu stricto provided by Marshall et al. (1990) in that the paracone and metacone are well-separated (not appressed as in their "Alphadon" spp.) with distinct and crested (=winged) meta- and paraconules. The Ceno- manian taxon differs from the definition provided by Marshall et al. (1990) for Alphadon only in its lack of a consistently large stylar cusp C.

Stylar cusp C is variable, both in terms of size and position, within this species. If size or position of stylar cusp C along were here considered a significant morphologic trait, then a new genus would have to be established and each upper molar in this sample might be interpreted to represent a different species.

ALPHADON LILLEGRA VENI, sp. nov.

Figures 6A-H, Table 3

Holotype-MNA V5835, RM2?, Loc. 1067. Etymology--In recognition of Dr. Jason A. Lille-

graven's contribution to our knowledge of Mesozoic mammals.

Distribution -Late(?) Cenomanian, Dakota For- mation, southwestern Utah, MNA localities 939, 1067.

Diagnosis - Extra stylar cusp present between cusps B and D on known upper molars; stylar cusps slender, subequal in size, uninflated. Paracone slightly taller than metacone. Larger than A. clemensi, also differs in having subequal metaconid and paraconid, metaconid not projecting lingually, and hypoconid taller than hypoconulid-entoconid. Larger than A. wilsoni, A. sahnii, A. halleyi, and A. attaragos. Closest to A. marshi and A. russelli, from which it differs in having lower, more slender, less inflated, subequal, stylar cusps, and more weakly twinned hypoconulid-entoconid. Stylar cusps better developed than in Protalphadon.

Referred Specimens -Loc. 1067: V5364, Lmx; V5370, LM4; V5372, Lmx; V5375, Lm4; V5833, Lmx; V5835, RM2?; V6052, LMx (partial); V6317, Rmx; V6393, LMx; V6394, LMx; V6882, Lmx. Loc. 939: V5826, RM 1?; V6099, RM2?.

Description - The M 1 described here (MNA V5826) was too damaged in preparation for photography to be figured. Stylar cusp A is present, cusps B and D are subequal in height, and cusp B is closely appressed against the paracone. Two small cusps are present in the C position and there is no ectoflexus. The stylar shelf broadens posteriorly and no E cusp is present. The paracone is the tallest cusp.

On the holotype M2 or M3 (V5835, Figs. 6A, B), stylar cusp A is moderately developed; cusps B, C, and

TABLE 3. Measurements (in mm) ofAlphadon lillegraveni, sp. nov.


V5370 LM4 2.2* 2.9* V5826 RMI? 2.7* 2.6* V5835 RM2? 2.45 2.68 V6052 LMx * 2.72 V6099 RM2? 2.68 3.05 V6393 LMx 2.32 2.48 V6394 LMx 2.50 *


V5364 Lmx 2.49 1.23 1.28 V5372 Lmx 2.48 1.22 1.20 V5375 Lm4 2.22 1.02 1.06 V5833 Lmx 2.22 1.18 1.15 V6317 Rmx 2.64 1.23 1.32 V6882 Lmx 2.28 1.10 1.19

D are subequal in size. Stylar cusp B is connected to the paracone by two crests. A small cuspule is present in the ectoflexus just posterior to cusp B. The paracone is taller and buccolingually broader than the metacone. The centrocrista is V-shaped in side view. The paraconule is strong and winged. The metaconule is damaged but appears to have been broader but lower than the paraconule. On V6099, stylar cusp D is slightly larger than cusp C and a cuspule is present between cusps B and C. V6393 (Fig. 6C) has subequal stylar cusps C and D, and a cuspule posterior to the B cusp. Stylar cusp A projects more anteriorly than on V5835 (possibly indicating that this is an M2 and V5835 is an M3). The conules are well developed and winged. The talon basin is deep. On all of these molars, no cusp E is present, metaconules and paraconules are well-developed, and the paracone is slightly taller than the metacone.

V5370 (Fig. 6D) lacks the anterior part of the stylar shelf, but probably represents M4. No A or B cusp is preserved. A strong preparacrista is located along the anterior border of the parastyle. The C cusp is well- developed on the anterior side of the slight ectoflexus but is smaller than cusp D. No E cusp is present. The paracone is much larger and taller than the metacone. The paraconule and metaconule are subequal in size, but the paraconule is unwinged, lacking a connection to the paracone.

In ml-3, the trigonid approximates an equilateral triangle (range 560-600) and the metaconid is equal to (V5364, Figs. 6E, F) or slightly taller (V5372, Figs. 6G, H) than the paraconid. The anterior cingulid is cusp- like at its upper terminus. A faint crest originating at the protocristid notch connects the cristid obliqua to the posterior wall of the trigonid. The entoconid and hypoconulid are close together, equal in size, and distinctly smaller and lower than the hypoconid. A postcristid is present.

An m4 (V5375) is worn but is tentatively assigned to this species on the basis of size. This molar has a



1 16 JOURNAL OF VERTEBRATE PALEONTOLOGY. VOL. 13. NO. 1. 1993

A CV

- p

D

tE G

F H

1mm

69K L

FIGURE 6. Alphadon lillegraveni, sp. nov. A, V5835, holotype, RM2?, occlusal view (stereopair); B, same, labial oblique view (stereopair); C, V6393, LMx, occlusal view (stereopair); D, V5370, LM4, occlusal view (stereopair); E, V5364, Lmx, occlusal view (stereopair); F, same, lingual view; G, V5372, Lmx, occlusal view (stereopair); H, same, lingual view. Alphadon sp. I, V6029, LMx, occlusal view (stereopair); J, V6790, RMx, occlusal view (stereopair); K, V6376, Lm3, occlusal view (stereopair); L, same, lingual view.

weak precristid; the metaconid and paraconid are low and subequal. The posteriorly elongated hypoconulid is centrally located at the back of the talonid and is the tallest cusp of the talonid.

Discussion -Alphadon clemensi and A. lillegraveni

both have larger paracones than metacones, but A. clemensi is regarded as being more primitive than A. lillegraveni because its paracone is larger and taller relative to the metacone. A larger paracone than metacone is considered to be primitive for tribosphenic




therians (Clemens and Lillegraven, 1986). In this regard, A. lillegraveni is closer to the type species, A. marshi, and to all other species of Alphadon, than is A. clemensi.

ALPHADON sp. Figures 6I-L, Table 4

Referred Specimens -Loc. 1067: V6029, LMx; V6239, LMx (partial); V6376, Lm3; V6492, Rmx (talonid); V6790, RMx. Loc. 939: V5634, Lmx (talonid); V6876, RMx.

Discussion--The seven teeth listed above indicate the possible presence of a species of Alphadon smaller than A. clemensi. V6029 (Fig. 61), an upper molar (possibly an MI due to the relatively long anteroposterior dimension relative to the buccolingual dimension, and the anterior narrowness of the stylar shelf) is smaller (Table 4) than any upper molar included in A. clemensi (Table 3). The stylar shelf is narrow anteriorly and broad posteriorly. Stylar cusps B and D are subequal in height, but cusp D has a much broader base. The stylar shelf is damaged between cusps B and D so that the relative size of cusp C cannot be determined. The specimen is morphologically similar to molars assigned above to A. clemensi. V6790 (Fig. 6J), a RMx (possibly an M3), is small (Table 4) and is missing the anterolabial portion of the tooth including stylar cusp A and most of cusp B. A cuspule is present at the ectoflexus posterior to cusp B. Stylar cusp C is present posterior to the ectoflexus and is subequal in height to cusp D, but has a broader base. The paracone is larger and taller than the metacone and the conules are equal- ly developed. Another small (Table 4) upper molar, V6876, has stylar cusps along the labial margin of the tooth. Cusps B and D are subequal in size, cusp C is smaller. V6239 is the posterior half of a small (Table 4) upper molar with a small cusp D, a cuspule on either side of the ectoflexus, and a cusp E.

V6376 (Figs. 6K, L) is smaller than m3s assigned to A. clemensi (compare Tables 3 and 4), but is considered to be an m3, as the trigonid is anteroposteriorly compressed and wider than the talonid. The cristid obliqua originates medially on the posterior wall of the trigonid and a cusp occurs on the cristid near its point of origin.

At least one species of Alphadon smaller than A. clemensi is present in the sample, but differences in the configuration of upper molar stylar cusps and the small sample size makes it impossible to determine whether more than one small species is present. A larger sample is necessary before one or more species can be diagnosed.

PROTALPHADON Cifelli 1990a PROTALPHADON, unnamed species

Figures 7A-C

Referred Specimens-Loc. 1067: V5855, LM2?; V6299, LM3?; V6387, RM4 (labial part).

Description-V5855 (Fig. 7A), a LM2? (AP = 2.08;

TABLE 4. Measurements (in mm) of Alphadon sp.


V6029 LMx 1.74 1.82 V6239 LMx * 1.90 V6790 RMx 1.4* 1.92 V6876 RMx * 1.55


V5634 Lmx * * 0.78 V6376 Lm3 1.58 0.97 0.80 V6492 Rmx * * 0.78

LB = 2.15), has a damaged stylar cusp area, but several cuspules are apparent in the area of stylar cusps B and D (the area of stylar cusp C is missing). The ectoflexus is well-developed. The paracone is slightly taller than the metacone and both cusps are concave labially. The metacone is shifted linguad relative to the paracone. The paraconule is strongly developed and connects to a broad and deep anterolabial cingulum. The metaconule is weakly developed. The protoconule area is narrow.

V6299 (Fig. 7B), a LM3?, is small (AP = 1.74; LB = 1.98) and moderately compressed anteroposteriorly. The stylar shelf is broad and all the stylar cusps are small but distinct. There is a stylar cusp A; stylar cusp B is the tallest and largest stylar cusp and is anteroposteriorly compressed and with the preparacrista forms a buccolingually oriented crest. Posterior of stylar cusp B there is a small, more labial cusp, followed by stylar cusp C at the ectoflexus, and posterior of C is another cuspule followed by a D stylar cusp. The paracone is tall and cone-shaped. The metacone is broken. The paraconule is prominent and closer to the protocone than the paracone. A deep, wide valley is formed between the paraconule and paracone posteriorly along the anterolabial cingulum. A strong crest on the posterior wall of the trigon basin connects the paraconule to the paracone. The metaconule is a weakly developed cusp on the postprotocrista and is not attached to the metacone by a crest (unwinged).

V6387 (Fig. 7C), the labial part of a RM4 (AP = 1.72; LB = *), has a well-developed and expanded anterolabial lobe. The tooth has a weakly developed ectoflexus with a small stylar cusp C. Two stylar cusps are present posterior to the ectoflexus. Anterior to the ectoflexus are at least two stylar cusps that precede stylar cusp A. The preparacrista is directed anterolabially, connecting to stylar cusp A. The paracone is taller and has a broader base than the metacone. The metaconule is a small cusp on a tall, wall-like postprotocrista.

Discussion - Cifelli (1 990a) erected the genus Protal- phadon to include two species formerly placed in Al- phadon, A. lulli and A. creber, as well as a new species, P. wahweapensis. The genus was diagnosed as having upper molars distinct from Iqualadelphis in being relatively longer and less transverse and in variably pos-




1 rmD 1 mm FIGURE 7. Protalphadon sp. A, V5855, LM2?, occlusal view (stereopair); B, V6299, LM3?, occlusal view (stereopair); C, V6387, RM4 (labial part), occlusal view (stereopair). D, genus and species undetermined, V6312, RMx, occlusal view (stereopair).

sessing a small stylar cusp in the C position. Upper molars of the species described here have anteroposterior/transverse proportions like Protalphadon and a small but distinct stylar cusp C. The upper molars are smaller and have a more cuspate stylar shelf margin than any other species of Protalphadon. The M3? of this species of Protalphadon bears some striking similarities to the M3 of P. lulli (particularly UCMP 47475, Clemens, 1966:fig. 8) in having an anteroposteriorly compressed stylar cusp B and a complexly cuspate stylar shelf, but differs in having a weakly developed metaconule.

V6299 is similar to the holotype of Iqualadelphis lactea (UAVP 28232) in size, the presence of a tall paraconule, and the deep valley formed by the anterolabial cingulum but in most other regards is different. The MNA specimen is closer to upper molars referred to I. lactea by Cifelli (1990c) which have a broader stylar shelf than the holotype. Upper molars of the species of Protalphadon differ from those of Iquala- delphis in not being as anteroposteriorly compressed, in having a more cuspate stylar shelf, and a more weakly developed metaconule. More material will be required to adequately diagnose this new species of Prot- alphadon.

V6299, the RM4, is included with this unnamed species because of its tall, slender paracone, size, and complexly cuspate labial margin of the stylar shelf. On M4s of Cretaceous marsupials, the preparacrista is directed anterolabially and connects to stylar cusp A (e.g., Lillegraven and McKenna, 1986:fig. 13D). No M4s of Protalphadon have been previously described and as this specimen also bears a strong similarity to M4s of Pediomys cooki (Clemens, 1966:fig. 25) it may not be appropriately included here.

Genus and Species Undetermined Figure 7D

Referred Specimen-Loc. 1067: V6312, RMx.

Description - The molar position of V6312 (Fig. 7D) is uncertain. This worn upper molar is small (AP =

1.48; LB = 1.57) and only stylar cusps B and D are clearly present on the stylar shelf. Stylar cusp D has a lingually directed crest that connects to the base of the metacone. The ectoflexus is distinct and no cusp C is present at its apex. The metacrista forms a sharp angle with the labial wall of the molar. The paracone is taller than the metacone and the protoconule area is very narrow relative to the labial part of the tooth. Both conules are winged.

Discussion--The tooth is placed within the Alpha- dontidae because of its relatively broad stylar shelf and winged conules. The specimen is most similar to molars of Protalphadon wahweapensis Cifelli, 1990a, except the MNA specimen is smaller, the stylar cusps and conules are more weakly developed, and the protoconal area is proportionally narrower.

Family ?STAGODONTIDAE Marsh, 1889

PARIADENS KIRKLANDI Cifelli and Eaton, 1987 Figures 8A-I, Table 5

Holotype-UCM 54155, Lm2-4, UCM Loc. 85358. Distribution - Late(?) Cenomanian, Dakota Forma-

tion, southwestern Utah, UCM locality 85358, MNA localities 939, 1067.

Revised Diagnosis - Paraconid equal to or larger than metaconid on m2-4 as in stagodontids and unlike other marsupial families, but lacking the extreme enlargement of the paraconid seen in Eodelphis or Didelpho- don. Paracristid and protocristid notches well-developed on unworn specimens. Cristid obliqua originates medially on ml, m3, and m4 like alphadontids but unlike stagodontids or pediomyids, and labially on m2, unlike alphadontids. Cusps of m 1-3 talonids close to subequal in height, in unworn specimens entoconid slightly taller than hypoconulid. hyoconulid taller than




A

B B

GSH

1mm

FIGURE 8. Periadens kirklandi. A, V5843, LMx, occlusal view (stereopair); B, same, labial oblique view (stereopair); C, V6024, LMx, occlusal view (stereopair); D, V5373, RMx (labial part), occlusal view (stereopair); E, V5842, Lml, occlusal view (stereopair); F, V6090, Rmx, occlusal view (stereopair); G, same, lingual view; H, V5836, Rmx, occlusal view (stereopair); I, same, lingual view.

hypoconid. On m4, entoconid tallest cusp of the talonid. Molars increase in size posteriorly as in stagodontids, but unlike alphadontids and pediomydis.

Referred Specimens -Loc. 1067: V5353, LMx; V5373, RMx (labial part); V5383, RMx; V5833, Lmx; V5834, LMx; V5836, Rm3?; V5837, Lm3?; V5838, Lmx; V5839, Lm3?; V5840, Lm3?; V5841, Lmx; V5850, talonid Rmx; V6019, LMx; V6024, LMx (labial part); V6058, LM3?; V6090, Rm2?; V6092, Lmx; V6093, Rm3?; V6388, Lmx; V6341, Lmx. Loc. 939: V5632, Lmx; V5633, Lmx; V5842, Lm l, V5843, LMx.

Description--V5843 (Figs. 8A, B), a possible M3,

has a stylar cusp A, subequal cusps B and D, and two cusps in the C region. One of the "C" cusps is a small, low cusp immediately posterior to cusp B; the other is lingual to the other stylar cusp and is a buccolingually oriented crest-like cusp that terminates just labial to

the centrocrista notch. This buccolingually oriented cusp is similar to cusps found on Eodelphis (Fox, 198 1: figs. 3c, e). A small cusp is present posterior to cusp D and three cuspules are present on the postmetacrista. There is only a hint of a preparacrista connecting the paracone to the anterior of stylar cusp B. The paracone and metacone are subequal in height, with the metacone having a broader base. Well-developed, unwinged paraconule and metaconule are present, and the protocone is slightly lower than the paracone and metacone. V6024 (Fig. 8C) is a partial upper molar having a strongly expanded stylar cusp B and a large stylar cusp C positioned at the well-developed ectoflexus. A weak preparacrista connects the paracone to stylar cusp B.

V5373 (Fig. 8D), the labial half of an upper molar, has a small, low cusp A; cusp B is subequal with D,



120 JOURNAL OF VERTEBRA TE PALEONTOLOG Y, VOL. 13, NO. 1, 1993

TABLE 5. Measurements (in mm) of Pariadens kirklandi.


V5373 RMx 3.10 * V5383 RMx * 3.05 V5834 LMx * 3.28 V5843 LMx 3.63 3.81 V6019 LMx * 3.41


V5632 Lmx 3.78 1.70 1.72 V5633 Lmx 3.2* 1.6* 1.7* V5833 Lmx 2.3* 1.21* 1.2* V5836 Rm3? 2.80 1.40 1.53 V5837 Lm3? 3.08 1.78 1.75 V5839 Lm3? 2.96 1.58 1.52 V5840 Lm3? 2.90 1.60 1.55 V5841 Lmx 3.90 2.12 2.10 V5842 Lml 2.69 1.22 1.39 V6058 Lm3? 3.19 1.72 1.72 V6090 Rm2? 2.85 1.53 1.65 V6092 Lmx 3.38 1.82 1.85

three "C" cuspules are present in the ectoflexus region, and there is no E cusp. A low preparacrista connects the paracone to stylar cusp B. The paracone and metacone are subequal in size and height. Two other partial upper molars, V5834 and V6019, have a C cusp equal in size to cusp D.

V5842 (Fig. 8E) is an ml with a worn paraconid which appears to be lower than the metaconid. The trigonid is relatively open (650). The cristid obliqua originates medially, at the protocristid notch. The hypoconulid is in a medial position, distinctly separated from the entoconid. The entoconid is slightly taller than the hypoconulid, the hypoconid is the lowest cusp.

V6090 (Figs. 8F, G), is an m2 or m3, probably an m2, with a paraconid slightly taller than the metaconid (also true of V5632, V5837, V5840). A crest descends on the posterior wall of the trigonid labial to the protocristid notch, connecting labially to the convex cristid obliqua and forming a broad, open talonid basin. The hypoconulid is well-separated from the subequal entoconid and both are slightly taller than the hypoconid.

V5836 (Figs. 8H, I), possibly an m3, has a moderately compressed trigonid (530). The paraconid and metaconid are subequal (as they are in another possible m3, V6058). The anterior face of the paraconid is convex near the cusp apex and is slightly concave near the terminus of the anterior cingulum. The cristid obliqua originates medially, forming a smaller talonid basin than in m2?. The hypoconid, hypoconulid, and entoconid are subequal in height.

Discussion--The upper molars are tentatively referred here to Pariadens on the basis of their large size (as with the lower molars, the largest in the sample) and the larger metacone than paracone on M 1. Due to the considerable variation in tooth shape and stylar

cusp configuration, it is possible that more than one taxon is represented in this sample of upper molars. Alternatively, the upper molars of this species may be highly variable or variation may be related to tooth position. For these reasons, the revised diagnosis does not include upper molar morphology.

Three lower molars (V5633, V5841, V6092) have been tentatively referred to this species. All three of these teeth are worn but appear to have trigonids more tightly compressed (about 40") than in the holotype. Two of the teeth (V5841, V6092) are 10/o-20% larger than the m2-3 of the holotype of Pariadens, and do not appear to be m4s. The range of variation present in the lower molars, as is the case in the upper molars, may imply the presence of another species in this sample.

When the type specimen (m2-4) of the species was described by Cifelli and Eaton (1987), it was suspected that the specimen had suffered postmortem shear on the lingual side. The recovery of unsheared specimens indicates that this was indeed the case. As a result, the description of the type overemphasized the crest-like nature of the entoconid as well as its height relative to the hypoconid and hypoconulid. The cusps of the talonid are subequal in height except for the m4. No new m4s were recognized in this sample, but the m4 of the type shows less damage by shear than the other molars and has a strongly elevated entoconid. It is possible that on the m4 the entoconid is significantly taller than the other talonid cusps.

Pariadens lacks several characters typical of latest Cretaceous stagodonts in that the trigonids are not anteroposteriorly shortened, paraconids are not consistently enlarged, the cristid obliqua does not originate in a labial position on all lower molars, paracones are not reduced (except on M 1), and the conules are not winged. Consistent with placement in the Stagodon- tidae, however, Pariadens does have progressively larger molars posteriorly, subequal or larger paraconid than metaconid, and a labially oriented origin for the cristid obliqua on some lower molars. The larger paraconid than metaconid may be primitive for the Meta- theria if the Deltatheroida is indeed a sister group of marsupials (Kielan-Jaworowska and Nessov, 1990) and may not confer any relationship of Pariadens to the Stagodontidae. As Pariadens lacks several derived characters considered to be definitive of the Stagodon- tidae its assignment to that family is questionable. Al- though the teeth of Pariadens exhibit a few stagodontid characters, ultimately the genus may be more appropriately placed in a new family.

If Pariadens is a stagodontid, it may be closer to Didelphodon than is Eodelphis. Pariadens is more like Didelphodon than like Eodelphis in having a weakly developed preparacrista and a well-developed stylar cusp D. Upper molars of Eodelphis have a relatively strong preparacrista and a series of cuspules posterior of the well-developed stylar cusp B (lacking a distinct stylar cusp C or D). This may cast some doubt on the direct ancestor-descendent relationship ofEodelphis to




Didelphodon suggested by Fox (1981) and Fox and Naylor (1986).

PHYLOGENETIC RELATIONSHIPS

Dakota Therians

Analysis of the dental characters of therians in this fauna has shed little light on which characters are primitive and which are derived. The lower molars ofDako- tadens are primitive(?) relative to marsupials in not having a postcristid (the lack of which was considered to be primitive by Clemens and Lillegraven, 1986) and share derived characters (also based on Clemens and Lillegraven, 1986) with Late Cretaceous marsupials (but not Deltatheroida) in having approximated entoconid and hypoconulid and subequal paraconid and metaconid. The last character would indicate that Da- kotadens is derived relative to stagodontids if the large size of the paraconid of deltatheroids is indeed primitive for the Metatheria, as would be suggested if the Deltatheroida is the sister group of the Marsupialia as proposed by Kielan-Jaworowska and Nessov (1990); alternatively, if the nearly subequal paraconids and metaconids are primitive for Late Cretaceous marsupials (as suggested by Clemens and Lillegraven, 1986) then stagodontids are derived in this regard relative to Dakotadens.

The presence of Dakotadens, Pariadens, Alphadon and Protalphadon together in the Cenomanian, without any documentation of earlier definite marsupials, provides little clues as to the relationships of these genera to each other. The presence of pediomyid-like marsupials (Pediomys or Iqualadelphis) in this fauna is not well-established and therefore provides no information regarding the phylogentic or temporal relationship of pediomyids to other marsupials. The diversity of marsupials and marsupial-like taxa in this fauna of Cenomanian age suggests that the origin of the order may be as old as Neocomian.

Bearing on the Ancestral Marsupial Morphotype

The presence of at least eight taxa of, or approaching, metatherian grade (dental formula of three premolars, four molars; twinned hypoconulid, entoconid; approximately subequal paracone-metacone, paraconid- metaconid; upper molars long labially relative to buccolingual dimension; wide stylar shelves bearing at least stylar cusps A, B, and D; large protocone) in the Cen- omanian was an unexpected result of this research. The morphologic characters present in the teeth of these therians, such as the relative positions, sizes, and heights ofcusps, as well as overall tooth shape, are much closer to those of later Cretaceous marsupials described from the Campanian (e.g., Fox, 1971; Cifelli, 1990b) or the Maastrictian (e.g., Clemens, 1966; Lillegraven, 1969) than they are to those of known Albian-Aptian (latest Early Cretaceous) Trinity fauna (e.g., Slaughter, 1971). As the fauna is not remarkably primitive, it sheds less

light than anticipated on the ancestral condition of marsupials.

Simpson (1928, 1945) considered the molar morphology of Pediomys to represent the primitive condition for marsupials, implying that the molars were gaining rather than losing the stylar shelf. Discovery of the Early Cretaceous Trinity faunas, with all tribosphenic upper molars having broad stylar shelves (Patterson, 1956), allowed refutation of this interpre- tation. The relationship of Trinity therians such as Holoclemensia to later therians has been problematic.

Aplin and Archer (1987) established a family Hol- oclemensiidae and considerated the possible relationship of Holoclemensia to several later Cretaceous genera. Although Holoclemensia could possibly be considered a metatherian, I doubt that it has any special relationship to any later marsupial (for recent reviews of this topic also see Jacobs et al., 1989; Cifelli, 1990c). The upper molars of Holoclemensia have very large stylar cusps A, C, and E, and small cusps B and D. Either Holoclemensia does not represent the ancestral condition for marsupials or there was a sub- sequent reduction of stylar cusps A, C, and E, and a concurrent enlargement of the B and D cusps, which seems a less likely alternative. Both Pappotherium and Holoclemensia are unusual, and not marsupial-like, in the extreme development of certain stylar cusps (A and B in Pappotherium; A and C in Holoclemensia) that exceed the heights of the principal cusps of the trigon and in the retention of the primitive character (Clem- ens and Lillegraven, 1986) of the much taller paracone than metacone.

The lower molars assigned to Holoclemensia have characters not present in any of the marsupials recovered from the Dakota Formation, including the com- pression of the trigonid and lack of a postcristid. A lower molar (FMNH 965) figured by Patterson (1956) is much more marsupial-like in having equal-sized metaconid and paraconid, uncompressed trigonid, and the initial development of a postcristid, though the hypoconulid is not positioned close to the entoconid. The tooth represents a more reasonable ancestral morphotype for lower molars of marsupials than those attributed to Holoclemensia.

Clemens (1966, 1968) considered the structure of the Alphadon upper molar to represent the ancestral morphology of all marsupials. He later (1979) modified this concept by suggesting that the ancestral Alphadon may have had well-developed stylar cusps B and D but lacked stylar cusp C. Fox (1987a), based on the lack of a stylar cusp C in Iqualadelphis (Fox, 1987b) (Iqualadelphis = "unnamed species resembling P. prokrejcii" in Fox, 1987a, fig. 5; "Milk River" molar of Fox 1987a, fig. 6) suggested that the absence of a stylar cusp C was the ancestral condition for marsupials. The taxonomic status ofl Iqualadelphis is unclear. The narrow stylar shelf (broad stylar shelves are regarded as primitive, Clemens and Lillegraven, 1986) and the short labial and long lingual portions of both the paracone and metacone are here considered de-




rived with the last character being unlike that found in any other Cretaceous marsupial. Fox (1987a) and Marshall et al. (1990) consider the morphology of Iqualadelphis to represent the ancestral condition for pediomyids in the reduction of the stylar shelf and the large bladelike stylar cusp D. For this to be true, pediomyids would have to be derived relative to Iquala- delphis in the erect cone shape of the metacone and paracone. As the metacones and paracones of Ceno- manian marsupials are also erect and conical (unlike Iqualadelphis) then this shape would represent paral- lelism in pediomyids if the Fox (1987a) and Marshall et al. (1990) sequence is accepted. Pediomyids must also shift the angle formed by the centrocrista from being parallel to the anteroposterior axis of the tooth row to being oblique to it. Also, pediomyids parallel to and independent of alphadontids would have had to enlarge the protocone and shift the conules closer to the base of the metacone and paracone. For these reasons, I doubt that Iqualadelphis has any special ancestral relationship to pediomyids or any other family of Cretaceous marsupials.

Fox (1987a) has suggested that Pediomys (excluding the type of the genus P. elegans), the Stagodontidae and Alphadon were all derived from a condition in which stylar cusp C was undeveloped. In that scenario, Pediomys was not derived from an Alphadon type morphology. I would agree with Fox (1987a) in this regard, but for different reasons. The taxon described here as Protalphadon sp. (and other alphadontids), Iqualadel- phis, and pediomyids may have arisen independently from a primitive morphotype with a broad stylar shelf having distinct stylar cusps A, B, and D, as well as a series of indistinct cuspules between cusps B and D. In this view, Pariadens and Didelphodon retain the primitive condition of a broad stylar shelf with distinct stylar cusps A, B, and D with an indistinct series of cuspules intermediate between cusps B and D. Eodel- phis is derived in the loss of a distinct stylar cusp D. Iqualadelphis retains stylar cusps A, B, and D and simplifies the cusp series between cusps B and D to a continuous ridge and reduces the width of the stylar shelf. Pediomyids retain the complex series of stylar cusps (Fox, 1987a:fig. 5, "un-named species resembling P. florencae") or simplify them to swellings on a continuous ridge along the labial margin of the stylar shelf(P. cooki, Clemens, 1966:fig. 24) accompanied by narrowing the anterior part of the stylar shelf. In alphadontids, the broad stylar shelf is retained and, over time, the cusps between B and D consolidate into a single mesostyle.

The stylar shelf of Sulestes karakshi, a Coniacian deltatheroid (an order Kielan-Jaworowska and Nes- sov, 1990, considered to be a sister-group of marsupials), has a complexly cuspate labial margin along the stylar shelf, as might be expected for a primitive metatherian, but has no distinct stylar cusp D which would not be expected. Prokennalestes trofimovi, an Early Cretaceous eutherian, has several cuspules between distinct stylar cusps D and B (Kielan-Jaworowska and

Dashzeveg, 1989:fig. 1), suggesting that a series of cusps between stylar cusps B and D may have been primitive for the last common ancestor of eutherians and metatherians. Many of the upper molars of Alphadon, Prot- alphadon, Pariadens, and Dakotadens from the Cen- omanian have more than one cusp between stylar cusps B and D which may represent retention of the primitive condition. In stagodontids, this condition appears to be retained throughout the history of the family with the exception of the lack of a distinct stylar cusp D in Eodelphis (similar to Sulestes in this regard). In alphadontids, the situation appears to stabalize over time such that a single well-developed cusp consistently occurs in the C position.

Marshall et al. (1990:454) stated that ". . . prolifer- ation of cuspules between stylar cusp B and D is a precursor condition to the development of a distinct stylar cusp C." I would agree with this statement, but would also suggest that the absence of cusps between cusps B and D may also reflect a loss of cusps and hence also be derived. Alternatively, there could have been Early Cretaceous metatherians possessing a series of cuspules along the labial margin of the stylar shelf which gave rise to stagodontids and alphadontids and another group of metatherians with a simple, continuous labial ridge along the margin which gave rise to Iqualadelphis (and "pediomyids"?). There is no basis on which to suggest which of these two conditions might have been the ultimate ancestral condition.

Pediomys cooki, P. krejcii, P. hatcheri, and P. florencae are weakly cuspate or uncuspate along the anterior margin of the stylar shelf. Fox (1987a) suggested that P. elegans, because of its more distinctly cuspate stylar shelf, may have been derived from an Alphadon- like morphology and does not share the same ancestry as other "pediomyids" (the quotes are required as P. elegans is the type species for the genus); however, Pediomys elegans retains the anteriorly directed preparacrista, anteriorly narrow stylar shelf (Clemens, 1966:fig. 21 b), and the labial origin for the cristid obliqua characteristic of the Pediomyidae. It may be that P. elegans is the least derived pediomyid, and the great- er distinction of the stylar cusps is a retention of the complex of cusps along the margin of the stylar shelf primitive for marsupials (a possibility suggested here). This is supported by the diverse arrangement of stylar cusps on upper molars assigned to P. elegans (Clemens, 1966:fig. 21b; Lillegraven, 1969:fig. 22). This would require a scenario in which pediomyids (if P. elegans is in the same family as other "pediomyids") arose from something more Alphadon-like than Iqualadel- phis-like. Alternatively, pediomyids could have arisen from an ancestor lacking strong stylar cusps (although probably not Iqualadelphis) and P. elegans is derived in redeveloping a more distinct stylar cusp series.

As recognized by Kielan-Jaworowska et al. (1979), there are no compelling reasons to regard any of the Trinity therians as true eutherians (contra Aplin and Archer, 1987). Reports by Nessov (1984, 1985), though in need of better documentation of age and taxa pres-




ent, suggest that eutherians were diverse in the middle Cretaceous of Asia. This and the lack of middle Cre- taceous eutherians in North America (Eaton and Ci- felli, 1988) may indicate that the separation of metatherian and eutherian lineages long predated the appearance of either (as currently defined) and that the divergence of these lineages may be as old as the earliest Cretaceous (Neocomian).

ACKNOWLEDGMENTS

Jim Kirkland and Jared Morrow are thanked for their help and assistance in the field and the lab, and Malcolm McKenna for his support of field research. Rich Cifelli is thanked for providing casts of specimens and manuscripts prior to publication. Reviews of the manuscript by William Clemens, Jason Lillegraven, Rich Cifelli, Louis Jacobs, and Judd Case were con- structive and helpful. Discussions and comparisons of material with David Archibald and Lev Nessov were instructive. This research was funded by National Geo- graphic Society grant 3965-88 and National Science Foundation grant EAR-9004560.

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Received 4 September 1991; accepted 5 March 1992.



Documents

Therian Mammals from the Cenomanian (Upper Cretaceous) Dakota Formation, Southwestern Utah