New specimens of Neosaimiri fieldsi from La Venta, Colombia: a middle Miocene ancestor of the living squirrel monkeys

Abstract

Abstract During the 1989 and 1990 field seasons, more than 200 new specimens of Neosaimiri fieldsi were recovered from the middle Miocene Villavieja Formation in La Venta, Colombia, South America. The stratigraphic horizon for new materials is about 100 meters above that of the type locality. New radioisotopic dates obtained from tuffaceous beds just above the present materials horizon are 12-13 Ma. The holotype of Neosaimiri, which was recovered in 1949, is an incomplete mandible and dentition, while new materials include not only lower but also upper dentition and deciduous teeth. The present materials closely resemble Saimiri in the shape and size proportion of molar series and in the basic crown morphology of other teeth, suggesting a close relationship to extant Saimiri. However, these materials are differentiated from Saimiri in the proportions of tooth series, with smaller incisors and larger molars; in the structure of the P4 hypocone; and in the morphology of M1-2, which shows strong polymorphism. Therefore, the present materials are identified as an independent genus, Neosaimiri, which is a middle Miocene ancestor of Saimiri . Laventiana annectens, which was recovered at the same location as the present materials in 1988, is concluded to be a junior synonym of Neosaimiri. A close relationship between Saimiri and a late Oligocene form from Bolivia, Branisella, which has been suggested by several researchers, is refuted by the crown structure of P4 in Neosaimiri . The Neosaimiri-Saimiri lineage needs another Oligocene ancestor.