Dentition of Subengius mengi (Mammalia: Plesiadapoidea) and a reassessment of the phylogenetic relationships of Asian Carpolestidae

摘要: New fossils pertaining to the oldest known Asian plesiadapiform, the Gashatan carpolestid Subengius mengi, clarify aspects of the dental anatomy of this taxon. The dentition of S. mengi is substantially more primitive than previously recognized in retaining a lower dental formula of 2.1.3.3, a low-crowned p4 with three main cusps that are less fully connate than their counterparts in species of Elphidotarsius, P3 with a narrower and structurally simpler lingual margin, and in lacking widely splayed paraconid and metaconid on m1. The unique structure of P3 in S. mengi and a reassessment of P3 anatomy in Elphidotarsius sp., cf. E. florencae, suggest that certain cusp homologies on P3 in Carpolestidae have been misinterpreted in the past. Following a detailed character analysis, the phylogenetic relationships of carpolestids and their close relatives are reconstructed. The Bumbanian taxon Chronolestes simul is recovered as the most basal member of Carpolestidae. S. mengi and a second Bumbanian taxon, Carpocristes oriens, also appear to be relatively basal members of the carpolestid radiation, although none of these Asian carpolestid taxa seems to be specially related to each other. Dispersal of carpolestids between Asia and North America appears to have been restricted to earlier parts of the Paleocene, although carpolestids survived on both continents until sometime near the Paleocene–Eocene boundary.