Friday, July 22, 2016

New Evidence About the Emergence of New World Monkeys During the Oligocene Paleogene

Neotropics provide insights into the emergence of New World monkeys: New dental evidence from the late Oligocene of Peruvian Amazonia


Marivaux et al


Recent field efforts in Peruvian Amazonia (Contamana area, Loreto Department) have resulted in the discovery of a late Oligocene (ca. 26.5 Ma; Chambira Formation) fossil primate-bearing locality (CTA-61). In this paper, we analyze the primate material consisting of two isolated upper molars, the peculiar morphology of which allows us to describe a new medium-sized platyrrhine monkey: Canaanimico amazonensis gen. et sp. nov. In addition to the recent discovery of Perupithecus ucayaliensis, a primitive anthropoid taxon of African affinities from the alleged latest Eocene Santa Rosa locality (Peruvian Amazonia), the discovery of Canaanimico adds to the evidence that primates were well-established in the Amazonian Basin during the Paleogene. Our phylogenetic results based on dental evidence show that none of the early Miocene Patagonian taxa (Homunculus, Carlocebus, Soriacebus, Mazzonicebus, Dolichocebus, Tremacebus, and Chilecebus), the late Oligocene Bolivian Branisella, or the Peruvian Canaanimico, is nested within a crown platyrrhine clade. All these early taxa are closely related and considered here as stem Platyrrhini. Canaanimico is nested within the Patagonian Soriacebinae, and closely related to Soriacebus, thereby extending back the soriacebine lineage to 26.5 Ma. Given the limited dental evidence, it is difficult to assess if Canaanimico was engaged in a form of pitheciine-like seed predation as is observed in Soriacebus and Mazzonicebus, but dental microwear patterns recorded on one upper molar indicate that Canaanimico was possibly a fruit and hard-object eater. If Panamacebus, a recently discovered stem cebine from the early Miocene of Panama, indicates that the crown platyrrhine radiation was already well underway by the earliest Miocene, Canaanimico indicates in turn that the “homunculid” radiation (as a part of the stem radiation) was well underway by the late Oligocene. These new data suggest that the stem radiation likely occurred in the Neotropics during the Oligocene, and that several stem lineages independently reached Patagonia during the early Miocene. Finally, we are still faced with a “layered” pattern of platyrrhine evolution, but modified in terms of timing of cladogeneses. If the crown platyrrhine radiation occurred in the Neotropics around the Oligocene–Miocene transition (or at least during the earliest Miocene), it was apparently concomitant with the diversification of the latest stem forms in Patagonia.

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