The Fossil Record and Primate Phylogeny

Fossils provide the only direct evidence of the evolutionary history of primates. A method of phylogeny reconstruction is outlined which is based on an evaluation ofphenetic resemblances of fossils interpreted in their stratigraphiccontext. This stratopheneti¢ approach to phylogeny involves three successive steps: (1) organization of fossils stratigraphically, (2) phenetie linking of similar forms from adjacent stratigraphic intervals, (3) critical testing--Is the density and continuity of the fossil record sufficient to support the proposed linkings?--Does the proposed phylogeny make sense cladistically?-Does it make sense paleogeographicaUy? Evaluation of the known fossil record of primates, following the stratophenetic approach outlined here, has suggested that microsyopoids are primitive primates and that fossil tarsioids and ples-. iadapoids form a closely linked group. Early anthropoids link most closely with Eocene adapoids, supporting an adapoid origin of Anthropoidea. Large gaps remain in the fossil record of lemuroid and lorisoid primates: they may have been derived from an Adapislike Eocene genus, or they may possibly have evolved independently of other primates since the late Cretaceous or the Paleocene. This question is closely related to the problem of whether living Tarsius or modern lemurs and lorises are more closely related to the living higher primates. The fossil record and the paleogeography of Central America suggest that platyrrhines eyolved from an early anthropoid stock and may have entered South America from Asia via North America at about the end of the Eocene. Dental remains are the only evidence of Plio-Pleistocene hominids known in sufficient quantities from successive stratigraphic intervals to permit stratophenetic analysis. Studying the stratigraphic distribution of measurements of tooth size in the East Rudolf sample of fossil hominids and comparing this with dental variation in a modern human population suggests the probable presence of two hominid lineages in East Africa throughout much of the Plio-Pleistocene. Study of all dental and skeletal remains in an explicitly stratigraphic and temporal context should help to clarify the course and complexity of early hominid evolution.