A large male hominin cranium from Sterkfontein, South Africa, and the status of Australopithecus africanus

Stw 505 is the most complete hominin cranium discovered in Sterkfontein Mem ber 4 since Broom's excavations. It was found in situ in Member 4 breccia i n 1989 and is larger, on the whole, than any other cranium from Sterkfontei n that has comparable parts. Displacement due to breakage, as well as plast ic deformation, has affected Stw 505 in several areas, especially the face and the vault. Diagnostic morphology is nevertheless abundant in the specim en. In several areas-the distinct anterior pillar, the straight inferior bo rder of the zygoma, the pattern of cresting on the naso-alveolar clivus, th e basal aspect of the temporal bone-Stw 505 closely matches the morphology of specimens of Australopithecus africanus and is distinct from other homin ins. Some isolated characters overlap with other groups, mainly early Homo and/or A. robustus. However, only the hypodigm of A, africanus can accommod ate the entire suite of morphology. In some cases, Stw 505 introduces more variation into the Sterkfontein samp le. For example, prominent superciliary eminences occupy the medial portion s of the supraorbital region and flow medially into a strongly protruding g labellar mound. These characteristics are probably attributable to sexual d imorphism. In many respects, Stw 505 highlights similarities between A. afr icanus and early Homo. Comparison with other species suggests that males of A. africanus do not show derived features of A. robustus that are not also present in females, and that cranial differences between A. afarensis and A. africanus have, if anything, been understated. (C) 1999 Academic Press.