FUNCTIONAL-MORPHOLOGY OF THE POSTCRANIUM AND LOCOMOTOR BEHAVIOR OF NEOSAIMIRI-FIELDSI, A SAIMIRI-LIKE MIDDLE MIOCENE PLATYRRHINE

A number of postcranial specimens of Neosaimiri fieldsi, a Middle Mioc ene platyrrhine, were discovered in 1988, 1989, and 1990 at La Venta, Colombia. Until recently only three postcranial specimens of this spec ies had been discovered and the present material adds further informat ion about this taxon's postcranial morphology. In overall skeletal dim ensions and in postcranial features, Neosaimiri is most similar to Sai miri among extant medium-sized platyrrhines, but differs from Saimiri in having more rugose surface markings, a longer olecranon, a smaller anterior process of the distal tibia, an absence of a distal surface e xtension on the anterior tibial shaft, an absence of an anterior midtr ochlear depression of the talus, and a shorter distal calcaneus relati ve to the calcaneal tuberosity. These differences suggest that Neosaim iri was relatively heavily built, possessed a more dominant forelimb i n quadrupedal progression, and utilized a less stabilized upper ankle joint, and a shorter power arm for plantarflexion. Neosaimiri is inter preted as an arboreal quadruped with frequent leaping across arboreal gaps, as in extant Saimiri, with perhaps less frequent running and lea ping than in Saimiri. As with the dentition, the postcranial specimens suggest the close relationship between Neosaimiri and extant Saimiri. (C) 1997 Wiley-Liss, Inc.