New Mexico Geological Society Annual Spring Meeting — Abstracts

A new tillodont is described from the northwestern San Juan Basin of New Mexico. Represented by a crushed maxillary fragment preserving LP2-M2, the new genus corresponds in size to North American Paleocene Deltatherium, but is smaller than the tillodont Esthonyx (late Paleocene-late Eocene). Comparable to several Asian alleged tillodonts (e.g. late Paleocene Meiostylodon), the new tillodont appears temporally and morphologically intermediate between the earliest Esthonyx (E. xenicus) and Deltatherium. Similar to Deltatherium in premolar morphology, the new genus is advanced in acquisition of a distinct P3 lingual cone, further development of the P4 protocone, reduction of the metastylar lobe, and augmentation of the hook-shaped parastyle in P3-4. The wide, wing-like stylar shelves of Deltatherium's primitive triangular molar dentition are superseded in the new tillodont by subrectangular, anteroposteriorly-compressed molars. Exhibiting greater posterolingual hypocone flare, crown hypsodonty, and moderately wide, bilobate stylar shelves, the new genus approaches in form the cosmopolitan undisputed tillodont Esthonyx. Resemblances among North American and Asian Late Paleocene assemblages indicate faunal interchange. However, confirmation of the new North American genus as a late Paleocene tillodont transitional to Esthonyx confounds generic derivation from the oldest putative tillodont, the Asian early Paleocene Lofochaius. Lending decisive support to Deltatherium's recent inclusion within Tillodontia, discovery of the new tillodont resuscitates a North American origination of the order, defies tillodont classification of aforementioned Asian specimens, and complicates conventional theories of speciation, radiation, immigration, and timing during the Paleocene-Eocene faunal turnover.