New species of Trogosus (Tillodontia, Mammalia) from the Green River Basin, Wyoming, U.S.A.

ABSTRACT

A new species, Trogosus gazini, is represented by eleven upper teeth (I2, P3–M3), eleven lower teeth (i2, i3, c1, and p3–m3), and some fragmentary postcrania of a single individual (USNM 364762), from the Blacks Fork Member of the Bridger Formation, Green River Basin, Wyoming, U.S.A. The new species has unique dental characters with a diminutive parastyle on the P3 and the asymmetrical pattern of the P4 lingual crests (reduced preprotocrista and expanded postprotocrista), in addition to having brachydont molars with dominant shearing wear facets. A phylogenetic analysis based on dental morphology places T. gazini as the sister taxon to either Trogosus latidens or Tillodon fodiens. The result also produces a solution for previously unresolved phylogenetic relationships among Kuanchuanius, Trogosus, and Tillodon. Although the result requires more morphological data to enhance the credibility of relationships among trogosine tillodont species, Trogosus gazini may represents a transitional form to Tillodon fodiens, which is most likely a descendant from a paraphyletic Trogosus with some autapomorphies. On the contrary, Kuanchuanius is allocated as a sister taxon to the Trogosus + Tillodon clade.