Sexual dimorphism in the face of Australopithecus africanus

Recently discovered crania of Australopithecus africanus from Sterkfontein Member 4 and Makapansgat enlarge the size range of the species and encourag e a reappraisal of both the degree and pattern of sexual dimorphism. Resamp ling methodology (bootstrapping) is used here to establish that A, africanu s has a greater craniofacial size range than chimpanzees or modern humans, a range which is best attributed to a moderately high degree of sexual dimo rphism. Compared to other fossil hominins, this variation is similar to tha t of Homo habilis (sensu late) but less than that of A. boisei. The finding of moderately high dimorphism is corroborated by a CV-based estimate and r atios between those specimens considered to be male and those considered to be female. Inferences about the pattern of craniofacial dimorphism in the A. africanus face currently rely on the relationship of morphology and size . Larger specimens, particularly Stw 505, show prominent superciliary emine nces and glabellar regions, but in features related in part to canine size, such as the curvature of the infraorbital surface, large and small specime ns of A. africanus are similar. In this respect, the pattern resembles that of modern humans more so than chimpanzees or lowland gorillas. A, africanu s may also show novel patterns of sexual dimorphism when compared to extant hominines, such as in the form of the anterior pillar. However, males of t he species do not exhibit characteristics of more derived hominins, such as A. robustus. (C) 1999 Wiley-Liss, Inc.