New species of Peradectes and Swaindelphys (Mammalia: Metatheria) from the Early Paleocene (Torrejonian) Nacimiento Formation, San Juan Basin, New Mexico, USA

Thomas E. Williamson and Louis H. Taylor

ABSTRACT

Three new metatherian taxa are reported from the early Paleocene (Torrejonian) of the Nacimiento Formation, San Juan Basin, New Mexico; two new species of Swaindelphys, S. encinensis and S. johansoni, and one new species of Peradectes, P. coprexeches. Most of the new specimens consist of isolated teeth. Both new species of Swaindelphys are larger than S. cifellii, previously the only reported species of Swaindelphys, and the first report of this genus outside of Wyoming. S. johansoni is approximately intermediate in size between S. encinensis and S. cifellii. P. coprexeches is nearly the same size as P. elegans, but differs in the more buccally expanded and convex outline of the upper molar metastylar lobe, and relatively larger stylar cusp C.

This provides new information on early Paleocene metatherian morphology and significantly increases their known diversity. New significant morphology reported here includes that of a dP3 not previously reported for early Paleocene metatherians. Moreover, this study helps to clarify taxonomic issues related to the validity of other Paleocene metatherians and is relevant to the origins and morphology of basal Herpetotheriidae and Peradectidae.

Thomas E. Williamson, New Mexico Museum of Natural History and Science, 1801 Mountain Road, NW, Albuquerque, New Mexico 87104-1375, USA.
Louis H. Taylor, Denver Museum of Nature and Science, 2001 Colorado Boulevard, Denver, Colorado 80205-5798, USA.

KEY WORDS: New species; metatheria; Paleocene; Torrejonian; San Juan Basin