RESUMO
The earliest platyrrhines have been documented from the late Oligocene of Bolivia (Salla) and from the early and early middle Miocene of middle and high latitudes (central Chile and Argentinean Patagonia). Recent paleontological field expeditions in Peruvian Amazonia (Atalaya, Cusco; Upper Madre de Dios Basin) have led to the discovery of a new early Miocene locality termed MD-61 ('Pinturan' biochronological unit, ~18.75-16.5 Ma [millions of years ago]). Associated with the typical Pinturan dinomyid rodent Scleromys quadrangulatus, we found a well-preserved right talus of a small-bodied anthropoid primate (MUSM-2024). This new platyrrhine postcranial element displays a combination of talar features primarily found among the Cebidae, and more especially in the Cebinae. Its size approximates that of the talus of some living large marmosets or small tamarins (Cebidae, Callitrichinae). MUSM-2024 would thus document a tiny Saimiri-like cebine, with the body size of a large marmoset. Functionally, the features and proportions of MUSM-2024 indicate that this small primate was arboreal and primarily quadrupedal, agile, with frequent horizontal leaping and vertical clinging in its locomotor repertoire. This small talus is the first platyrrhine fossil to be found from Peru and the earliest primate fossil from northern South America. This new early Miocene taxon could be a stem cebid, thereby providing new evidence on the existence of some long-lived clades of modern platyrrhines.