Palaeo-ecology of the Sterkfontein hominids: a review and synthesis

Abstract

Excavations at the Sterkfontein hominid fossil site have yielded a rich and revealing faunal assemblage. Evolutionary transitions are evident in early hominids and associated fauna between the times represented by Members 4 and 5. Member 4 has yielded a large and variable sample of Australopithecus africanus as well as evidence of considerable species diversity among the artiodactyls, carnivores and primates. The appearance of early Homo along with stone and bone tools in Member 5 coincides with a reduction of species representation in the orders of larger mammals as well as with the occurrence of new derived species and apparent extinctions. Three hypotheses have been suggested to account for the trends seen in the hominid-bearing members of the Sterkfontein Formation. The 'Climatic Change Hypothesis' accounts for the evolutionary trends by the causal factors of global and local cooling and aridification with evidence of savanna-grasslands supplanting an earlier environment with a denser cover of vegetation. The 'Taphonomic Hypothesis' explains changes in relative species representation at Sterkfontein in terms of the bone-accumulating agents; in Member 4 primary carnivores were largely responsible for the deposition of large mammalian fauna, whereas the scavenging activities of early Homo would have accounted for much of the bone and all of the artefacts found in Member 5. A third proposition is the 'Species Interaction Hypothesis', a derivative of the ' Red-Queen Hypothesis'; here the dynamics of species interaction, including competition and commensalism among hominids, carnivores and cercopithecids, propel the evolutionary changes and cause the extinctions. These hypotheses are not mutually exclusive, but the relative effects of the factors involved must be verified or refuted with better chronological controls and further analyses of the African fossil sites. The Sterkfontein Formation represents a microcosm in which various scenarios of African mammalian evolution can be tested