EARLY HOMINID EVOLUTION AND ECOLOGICAL CHANGE THROUGH THE AFRICAN PLIOPLEISTOCENE

The habitats in which extinct hominids existed has been a key issue in addressing the origin and extinction of early hominids, as well as in understanding various morphological and behavioral adaptations. Many researchers postulated that early hominids lived in an open savanna (D art, 1925; Robinson, 1963; Howell, 1978). However, Vrba (1985, 1988) h as noted that a major global climatic and environmental shift From mes ic, closed to xeric, open habitats occurred in the late African Plioce ne (approximately 2.5 m.y.a.), thus implying that the earliest hominid s existed in these mesic, wooded environs. This climatic shift is also suggested to have contributed to a pulse in speciation events with tu rnovers of many bovid and possibly hominid species. Previous environme ntal reconstructions of hominid localities have concentrated on taxono mic identities and taxonomic uniformitarianism to provide habitat reco nstructions (e.g., Vrba, 1975; Shipman & Harris, 1988). In addition, r elative abundances of species are often used to reconstruct a particul ar environment, when in fact taphonomic factors could be affecting the proportions of taxa. This study uses the morphological adaptations of mammalian assemblages found with early hominids to reconstruct the ha bitat based on each species' ecological adaptations, thus minimizing p roblems introduced by taxonomy and taphonomy. Research presented here compares east and south African Plio-Pleistocene mammalian fossil asse mblages with 31 extant mammalian communities from eight different habi tat types. All communities are analyzed through ecological diversity m ethods, that is, each species trophic and locomotor adaptations are us ed to reconstruct an ecological community and derive its vegetative ha bitat. Reconstructed habitats show that Australopithecus species exist ed in Fairly wooded,, well-watered regions. Paranthropus species lived in similar environs and also in more open regions, but always in habi tats that include wetlands. Homo is the first hominid to exist in area s of fairly open, arid grassland. This change from closed to open habi tats occurs gradually from about 4 m.y.a. until about 2 m.y.a. when th ere is a major increase in arid and grazing adapted mammals. Therefore , the appearance of open savannas do nor appear to have influenced the origination or adaptations of the earliest hominids, but could have c ontributed to their demise. As Stanley (1992) hypothesized, Homo speci es appear the first to be adapted to open, arid environments. (C) 1997 Academic Press Limited.