Late Middle Eocene primate from Myanmar and the initial anthropoid colonization of Africa

Abstract

Reconstructing the origin and early evolutionary history of anthropoid primates (monkeys, apes, and humans) is a current focus of paleoprimatology. Although earlier hypotheses frequently supported an African origin for anthropoids, recent discoveries of older and phylogenetically more basal fossils in China and Myanmar indicate that the group originated in Asia. Given the Oligocene-Recent history of African anthropoids, the colonization of Africa by early anthropoids hailing from Asia was a decisive event in primate evolution. However, the fossil record has so far failed to constrain the nature and timing of this pivotal event. Here we describe a fossil primate from the late middle Eocene Pondaung Formation of Myanmar, Afrasia djijidae gen. et sp. nov., that is remarkably similar to, yet dentally more primitive than, the roughly contemporaneous North African anthropoid Afrotarsius . Phylogenetic analysis suggests that Afrasia and Afrotarsius are sister taxa within a basal anthropoid clade designated as the infraorder Eosimiiformes. Current knowledge of eosimiiform relationships and their distribution through space and time suggests that members of this clade dispersed from Asia to Africa sometime during the middle Eocene, shortly before their first appearance in the African fossil record. Crown anthropoids and their nearest fossil relatives do not appear to be specially related to Afrotarsius , suggesting one or more additional episodes of dispersal from Asia to Africa. Hystricognathous rodents, anthracotheres, and possibly other Asian mammal groups seem to have colonized Africa at roughly the same time or shortly after anthropoids gained their first toehold there.

Evidence for an Asian origin of stem anthropoids

“…Others allocate a strepsirrhine-like calcaneus and humerus from Burmese sites to amphipithecids and conclude that amphipithecids are strepsirrhines (19). Even accepting the specimen allocations (I do) of Chaimanee et al (1), the Bremer support for a stem catarrhine placement of amphipithecids is very weak, which perhaps explains why the family has variously been identified as stem anthropoids (11,20) or placed in an unresolved trichotomy with platyrrhines and catarrhines (16). In any case, in figure 3 in ref. 1, amphipithecids are nested within an otherwise African clade consisting of oligopithecids, propliopithecids, parapithecids, and proteopithecids.…”

“…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.…”

“…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).…”

“…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.…”