A new late Paleocene phenacodontid 'condylarth' Lophocion from the Clark’s Fork Basin of Wyoming

Abstract

ABSTRACT Phenacodontidae are a group of archaic ungulates in the early Paleogene and are considered to play an important role in the origin of some other ungulates, including perissodactyls. The early Eocene Lophocion asiaticus, the only unequivocal phenacodontid from Asia, is most closely related to North American Ectocion and probably closer to perissodactyls than is the latter, as evidenced by its more lophodont teeth. Here we named a new species of Lophocion, L. grangeri sp. nov., from the latest Paleocene (Clarkforkian 3) deposit in the Clark’s Fork Basin of Wyoming. Although the holotype of the new species is only known by a right maxilla with P4-M2, its degree of lophodonty is similar to that of Lophocion but diverges from Ectocion in having the incipient protoloph and metaloph on upper molars. In dental morphology, Lophocion grangeri is somewhat intermediate between Ectocion and L. asiaticus, and probably gave rise to the latter during the Paleocene-Eocene transition. Both Lophocion and Ectocion are included in Phenacodontinae rather than Meniscotheriinae, but their phylogenetic relationship with other ungulates still remains obscure.