Evidence for an Asian origin of stem anthropoids.

I n PNAS, Chaimanee et al. (1) report a previously undescribed species of primate, Afrasia, from the late Middle Eocene of Burma. They identify Afrasia as the sister taxon to the African genus Afrotarsius but slightly more primitive than it and allied with stem Anthropoidea of south Asia. Anthropoidea is the taxonomic group that today includes New and Old World monkeys, apes, and humans. If upheld, the biogeographic significance of these results is profound: If Afrasia and Afrotarsius are as closely related as Chaimanee et al. (1) propose, there must have been a late Middle Eocene geographic connection between the primate faunas of Asia and Africa. Further support for intercontinental connections between south Asia and Africa is found among other contemporaneous mammalian groups, including anomaluroid and hystricognathous rodents (2). More provocatively, Chaimanee et al. (1) consider the south Asian late Middle Eocene family Amphipithecidae to be a stem catarrhine clade and suggest that Catarrhini (the group of Old World anthropoids) also originated in south Asia and dispersed to Africa. A review of fossil evidence lends credence to the phylogenetic and biogeographic scenario of Chaimanee et al. (1). At the same time, it must be acknowledged that gaps in the Paleogene primate fossil record of south Asia and Africa allow for other plausible interpretations. Support for their scenario is not made any stronger by the fact that Afrasia djijidae and Afrotarsius libycus are known only from a few cheek teeth. For that matter, key anatomical evidence is lacking or incomplete for other Asian stem anthropoids (e.g., in the structure of the posterior wall of the orbit and middle ear) that would make their anthropoid status more certain.