Cranial anatomy and implications of Dolichocebus, a late Oligocene ceboid primate

THE very scarce fossil record of Cainozoic New World monkeys(1,2) has contributed little to knowledge of the history of platyrrhine primates, an important element of both the neotropical mammal fauna(3) and the pantropical primates, as a whole. Only the affinities of the Middle Miocene Colombian fossils Neosaimiri, Stirtonia and Cebupithecia seem reasonably well established(4), though not without dissent(5), and these are clearly linked with the modern squirrel, howler and sakiuakari monkeys, respectively. After completion of a survey of the morphology and interrelationships of the platyrrhines, to be detailed elsewhere (A. L. R., in preparation), it is now possible to discuss the evolutionary implications of the terminal Oligocene Dolichocebus gaimanesis of Patagonia, represented by a nearly complete cranium only recently prepared fully, although first described in 1942 (ref. 6). This specimen strongly suggests that Dolichocebus is a member of the Saimiri lineage, which thus becomes the oldest generic lineage known for the primates, dating from about 25 Myr ago(7). Its affinities also imply that the two major monophyletic divisions of Ceboidea were already established by late Oligocene times, as were the marmosets and tamarins.