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Title: OCCURRENCES OF PANTOLAMBDA INTERMEDIUM IN THE SAN JUAN BASIN, NEW MEXICO, USA
In the wake of the end-Cretaceous extinction, pantodonts were among the first mammals to achieve truly large body sizes. Paleocene pantodonts occupied large herbivore niches across North America, Asia, and Europe. In North America, the Torrejonian genus, Pantolambda, encompasses three species ranging from large dog- to small cow-sized. Of the three species, P. intermedium is the most poorly represented with known material consisting of a fragmentary dentary with m1-2 and isolated lower premolars. All the originally referred material was recovered from the Gidley Quarry, Montana. We describe cranial and postcranial fragments of the species from the Nacimiento Formation of the San Juan Basin (SJB), New Mexico. Interestingly, although it is intermediate in size between P. bathmodon and P. cavirictum, P. intermedium occurs lower in the stratigraphy (Tj2) than these other species and is the first appearance of pantodonts in the SJB. The presence of P. intermedium in the SJB is validated with a worn dentary (NMMMNH P-19774) containing m1-2. A pronounced entoconid on m1 and m2 distinguishes these teeth from those of P. cavirictum, whose entoconid is weakly developed, and from those of P. bathmodon, which lacks an entoconid on the anterolingually-sloping postcristid. An isolated m3 (NMMNH P-72117) shows a partial, narrow trigonid with a wide talonid basin that is shallower than in P. bathmodon. A concreted, partial braincase (NMMNH P- 21646) bears low sagittal and nuchal crests similar to P. bathmodon. A partial scapula (NMMNH P-21647) preserves the glenoid region and the distal portion of the scapular body. The glenoid cavity is an elongated oval that tapers anteriorly to a prominent, triangular supraglenoid tubercle. A coracoid process distinct from the tubercle is not present. A similar pattern is observed in P. bathmodon. The condition observed in Pantolambda contrasts with other pantodonts. Alcidedorbigna possesses a relatively small tubercle distinct from a rounded coracoid process and the larger-bodied pantodonts, Barylambda and Coryphodon, exhibit both a prominent tubercle and a well-developed coracoid process. A prior hypothesis posited that P. intermedium from Montana could simply represent larger morphs of P. bathmodon following Bergmann’s Rule. However, the presence of P. intermedium in New Mexico in a similar environment to and at the same latitude as P. bathmodon and P. cavirictum supports its distinction from the other two morphs as a unique species. Funding Sources European Research Council Starting Grant (ERC StG 2017, 756226, PalM); National Science Foundation (NSF; EAR 1654952, DEB 1654949)  more » « less
Award ID(s):
1654952
NSF-PAR ID:
10480915
Author(s) / Creator(s):
; ; ;
Publisher / Repository:
Society of Vertebrate Paleontology
Date Published:
Journal Name:
Journal of vertebrate paleontology
ISSN:
1937-2809
Format(s):
Medium: X
Location:
Toronto, Ontario, Canada
Sponsoring Org:
National Science Foundation
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