ABSTRACT
An ecological approach to evolutionary interpretations of the platyrrhines avoids the many assumptions inherent in the purely morphological, gradistic approach and provides testable hypothesis at various levels. There is very strong evidence of a close cladistic relationship between the late Oligocene Dolichocehus and Saimiri, whose crania bear several hallmarks of the light-weight Frugivorous-Insectivorous Zone feeding mechanism. The recovery of good Oligocene catarrhine material contests such a gradistic ranking by illustrating that early undoubted catarrhines cannot be distinguished by the traditional suite of craniodental characters and are in fact more similar to some platyrrhines than to eucatarrhines in certain postcranial features. This implies that both Cebus, the closest living relative of Saimiri, and callitrichines, the sister-group of cebines, had already differentiated as lineages.
