African Pliocene and Pleistocene cercopithecid evolution and global climatic change

Vrba, 1992, 1995a has put forth a series of hypotheses about the evolution of African mammals, which she has termed "habitat theory" This theory posits that changes in global climate cause "turnover pulses", within relatively short periods of time during which occur large numbers of first and last appearances of species. The present study examines whether a turnover pulse, or other forms of faunal change, occurred in the Cercopithecidae, 2.8-2.5 Ma at a time of major global cooling. The East African cercopithecid fossil record is well suited to this analysis because cercopithecids occur at most East African Pliocene and Pleistocene sites and are relatively speciose (Szalay and Delson, 1979; Delson, 1984; Jablonski, 2002). Several approaches are used including examination of cercopithecid species ranges as well as the abundance of larger taxonomic units. Both appearance and abundance data are examined for the Afar Depression and Turkana Basin, whereas only the species range data are studied for all East African and complete sub-Saharan analyses. The results provide no support for a turnover pulse 2.8-2.5 Ma. In fact, the largest number of first and last appearances are clustered around 3.4 and 2.0Ma, with a shift in abundance at 3.4Ma in both samples examined. These results are consistent with a relatively constant rate of turnover of cercopithecids between about 4 Ma and the Holocene.