Abstract
TarkaandTarkadectesare Middle Eocene mammals known only from the Rocky Mountains region of North America. Previous work has suggested that they are members of the Plagiomenidae, an extinct family often included in the order Dermoptera. Here we describe a new primate,Tarkops mckennaigen. et sp. nov., from the early Middle Eocene Irdinmanha Formation of Inner Mongolia, China. The new taxon is particularly similar toTarkaandTarkadectes, but it also displays many features observed in omomyids. A phylogenetic analysis based on a data matrix including 59 taxa and 444 dental characters suggests thatTarkops,TarkaandTarkadectesform a monophyletic group—the Tarkadectinae—that is nested within the omomyid clade. Within Omomyidae, tarkadectines appear to be closely related toMacrotarsius. Dermoptera, including extant and extinct flying lemurs and plagiomenids, is recognized as a clade nesting within the polyphyletic group of plesiadapiforms, therefore supporting the previous suggestion that the relationship between dermopterans and primates is as close as that between plesiadapiforms and primates. The distribution of tarkadectine primates on both sides of the Pacific Ocean basin suggests that palaeoenvironmental conditions appropriate to sustain primates occurred across a vast expanse of Asia and North America during the Middle Eocene.

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