The phylogenetic significance of strepsirhinism in Paleogene primates

Two lines of evidence reviewed here argue against the recent proposal that strepsirhinism is an apomorphous feature in primates, shared only by adapiforms and lemuriforms. These are (1) the presence of strepsirhinism in several extant taxa of nonprimate mammals, including Tupaiidae, Tenrecidae, Erinaceus,and Didelphis,and (2) the inferred presence of strepsirhinism not only in adapiforms, but also in all plesiadapiforms and omomyids for which the relevant anatomical regions are known. Therefore, strepsirhinism cannot be invoked as an adaptive innovation underlying the initial strep-sirhine/haplorhine dichotomy. Likewise, the apparent retention of strepsirhinism in omomyids suggests either that the haplorhine oronasal configuration of extant tarsiids and anthropoids was acquired independently or that tarsiids and anthropoids form a clade to the exclusion of omomyids.