An eosimiid primate of South Asian affinities in the Paleogene of Western Amazonia and the origin of New World monkeys

Western Amazonia has recently revealed that two distinct anthropoid primate clades of African origin colonized South America near the Eocene/Oligocene transition (ca. 34 Ma). Here, we report a new fossil primate from Brazilian Amazonia pointing to a third clade involved in that colonization. Surprisingly, this taxon has strong affinities with eosimiid anthropoids of South Asian origin. These data highlight some of the life history traits (very-small-bodied size and insectivory/frugivory) that would have increased the chances of survival on a natural raft during this extraordinary transatlantic journey from Africa to South America. Estimated splits between New and Old World taxa indicate that the dispersal(s) coincides with the late middle Eocene climatic optimum (ca. 40.5 Ma), which generated intense flooding events.