Pediomys clemensi

DISTRIBUTION: Judith River Formation, Montana.

DESCRIPTION: Two labial fragments of upper molars, AMNH 77373 and 77374, are similar to each other. Specimen AMNH 77373, however, has conules (fig. 13 P), whereas the other, AMNH 77374, lacks conules and is slightly larger. The stylar shelf in the specimens is not bilobate and the stylar shelf is weakly developed. Cusp A is better developed than in the other contemporary metatherian genera, and a crest connects it to the paraconule. Cusp B is small and posterolabial to the paracone. The stylar shelf narrows labial to the paracone, and the external rim of the paracone extends to the shelf. Cusp C is posterior to cusp B and slightly larger. The stylar shelf widens posteriorly just lingual to the prominent stylar cusp D, which is the largest stylar cusp. The metastyle is weakly developed and linked to the metacone by a high ridge. The paracone is situated more labial to the metacone and is about the same height. There are five lower molars that can be referred to Pediomys by use of the criterion developed by Clemens (1966), which is the position of the crista obliqua on the posterior wall of the trigonid. The crista obliqua in pediomyid molars intersects the trigonid wall at the protoconid, a position labial to the usual position in other Cretaceous marsupials. These pediomyid lower molars are small, ranging in length from 1.8 to 2.6 mm. The paraconid is a slender, conical, anteriorly directed cusp in AMNH 77377 (fig. 13 S, T). It is only slightly smaller than the metaconid and well separated from it. The protoconid is anterior and taller than the metaconid, and has a small anterobasal cingulum. The talonid is wide, and the hypoconid is a large, high cusp, which is well separated from the twinned hypoconulid and the broken entoconid. The hypoconulid is a small pointed cusp, directed posteriorly and linked to the entoconid by a short ridge. A broad cingulum is present on the posterolabial side of the crown. AMNH 77376 (fig. 13 Q, R) is a larger lower molar than AMNH 77377.

Figure 13 P-T

DIAGNOSIS: A small Campanian pediomyid most closely similar to P. elegans from the Maestrichtian. Stylar cusp A (parastyle) and D are well developed. Cusp B is feebly formed and is situated posterolabial to the paracone, close to the equally small stylar cusp C.

ETYMOLOGY: For W. A. Clemens, University of California, Berkeley.

HOLOTYPE: AMNH 77373, an upper molar (M 2 or M 3). TYPE LOCALITY: Clambank Hollow, Chouteau County, Montana.