Dietary adaptations of South African australopiths: inference from enamel prism attitude.

The angle at which enamel prisms approach the wear surface holds information with regard to the stiffness of the tissue, as well as its wear resistance. Hence, analyses of prism orientation may shed light on questions of whether the thick enamel in hominins has evolved to confer stiffness or wear resistance to the teeth and may thus inform about the diet and behavioural ecology of these species. This was explored for Paranthropus robustus and Australopithecus africanus, whereby a distinction was made between prisms at the Phase I and Phase II facets. The results were compared with those obtained for Theropithecus, Macaca, and Potamochoerus for whom behavioural and/or experimental data are available, and were interpreted against simple mechanical principles. The South African hominins differ significantly in their relationships between wear facets and prism angulations. Teeth of P. robustus are better adapted to more vertical loads during mastication (Phase I), whereas those of A. africanus are better adapted to cope with more laterally-directed loads (Phase II) commonly associated with roll-crush and mastication. Overall, teeth of P. robustus appear stiffer, while those of A. africanus seem more wear resistant.