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

Recent fossil discoveries in Western Amazonia revealed that two distinct anthropoid primate clades of African origin colonized South America near the Eocene/Oligocene transition (ca. 34 Ma). Here, we describe a diminutive fossil primate from Brazilian Amazonia and suggest that, surprisingly, a third clade of anthropoids was involved in the Paleogene colonization of South America by primates. This new taxon, Ashaninkacebus simpsoni gen. et sp. nov., has strong dental affinities with Asian African stem anthropoids: the Eosimiiformes. Morphology-based phylogenetic analyses of early Old World anthropoids and extinct and extant New World monkeys (platyrrhines) support relationships of both Ashaninkacebus and Amamria (late middle Eocene, North Africa) to the South Asian Eosimiidae. Afro-Arabia, then a mega island, played the role of a biogeographic stopover between South Asia and South America for anthropoid primates and hystricognathous rodents. The earliest primates from South America bear little adaptive resemblance to later Oligocene-early Miocene platyrrhine monkeys, and the scarcity of available paleontological data precludes elucidating firmly their affinities with or within Platyrrhini. Nonetheless, these data shed light on some of their life history traits, revealing a particularly small body size and a diet consisting primarily of insects and possibly fruit, which would have increased their chances of survival on a natural floating island during this extraordinary over-water trip to South America from Africa. Divergence-time estimates between Old and New World taxa indicate that the transatlantic dispersal(s) could source in the intense flooding events associated with the late middle Eocene climatic optimum (ca. 40.5 Ma) in Western Africa.

A reassessment of the cranial morphology of Neoepiblema acreensis (Rodentia: Chinchilloidea), a Miocene rodent from South America.

The rodent Neoepiblema acreensis (Chinchilloidea: Neoepiblemidae) is member of a lineage that reached gigantic dimensions during the Late Miocene of South America-the Neoepiblemidae. In this paper, the cranial anatomy of this rodent is reviewed. Noninvasive imaging is used to reveal internal structures. Our review is based mainly on an almost complete cranium from the Upper Miocene deposits of the western Amazonia of Brazil. The cranium has an elongated rostrum, large frontal sinuses, a deep temporal fossa, well-developed sagittal, nuchal, medial occipital, and secondary crests, and a tympanic fenestra connected to the external acoustic meatus by a thin ventral cleft. Remarkably, the cranium shows the presence of fossae on the posterior region of the frontal and parietal bones, and a "W-shaped" fronto-parietal suture, which are not present in other analyzed chinchilloids. This study contributes to the knowledge of the morphology of this extinct rodent as well as to the phylogenetic relationships and paleobiology of neoepiblemids.