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

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.

KEYWORDS:

• Phenacodontidae
• Lophocion
• Ectocion
• late Paleocene
• Clark’s Fork Basin

Acknowledgments

We thank Fang-Yuan Mao (IVPP) and Alana Gishlick (AMNH) for acquisition of the label information of AMNH FM 16060 and access to the AMNH collections; Wei Gao and Yemao Hou (both IVPP) for the photographs and CT scanning, respectively. The review comments of two anonymous reviewers greatly improved the final manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Funding was provided by grants from the Strategic Priority Research Program of Chinese Academy of Sciences [XDB26000000]; the National Natural Science Foundation of China [41672014, 41572021], the Special Fund for Fossil Excavation and Preparation, CAS, Youth Innovation Promotion Association of the Chinese Academy of Sciences [2017101], China Scholarship Council [201204910062], and Frick Funds from the Division of Paleontology, American Museum of Natural History.