Hominid phylogenetics and the existence of Homo in Member I of the Swartkrans formation, South Africa

The geology, biochronology and history of hominid systematics at Swartkrans is reviewed and morphological evidence is presented which confirms the existence of two contemporaneous hominid species at this site. A phylogenetic analysis of the Swartkrans hominid material supports the allocation of the composite SK-847 cranium to the genus Homo rather than Paranthropus and suggests on the basis of synapomorphous features that two other crania from Member I, SK-27 and 47, should also be included in the hypodigm of this taxon. Some of these specializations are discussed in terms of their functional and adaptive significance and it is concluded that a dietary rather than a tool utilization model best explains the selective pressures that initiated the evolutionary dichotomy of the Paranthropus and Homo clades. SK-27, 47 and 847 from Swartkrans and other early Pleistocene hominid specimens from South and East Africa are specifically attributed to Homo (Australopithecus) africanus and the evolutionary affinities and systematic position of this taxon within the Hominidae are examined. The major sources of difficulty which have arisen in the palaeontological recognition of the genus Homo are reviewed and a cladistic definition of this genus is proposed along with a phylogenetic classification of the Hominidae.