Stable carbon isotope and molar microwear variability of South African australopiths in relation to paleohabitats and taxonomy

Stable carbon isotopes and occlusal microwear fabrics preserve direct, complementary evidence relating to the biogeochemistry and mechanical properties of foods that are consumed, and thus inform the diets of extinct individuals. We evaluate variation in microwear texture and carbon isotope composition in Australopithecus africanus and Paranthropus robustus in relation to paleoenvironmental reconstructions for the deposits from which these fossils derive. The distributions of microwear texture data for 44 Australopithecus specimens from Makapansgat and Sterkfontein, and 66 Paranthropus from Swartkrans, Kromdraai and Drimolen are compared with isotopic data for 25 A. africanus and 25 P. robustus from these same deposits. Makapansgat Member 3 is reconstructed as having witnessed more closed conditions than Sterkfontein Member 4. The A. africanus sample from Sterkfontein exhibits greater variation in δ¹³C and microwear complexity data, and both sets of values tend to be lower at Makapansgat, which might relate to a more appreciable reliance on C₄-based foods and the (perhaps seasonal) consumption of harder food items by the australopiths that were deposited at Sterkfontein. Swartkrans Member 1 appears to have been somewhat more open than Swartkrans Member 2, and while this is not reflected in microwear textures, the hominin δ¹³C values from Member 2 tend toward the lower side of the Member 1 range. Swartkrans Member 1 “Lower Bank” fossils display a wider range of δ¹³C values but a narrower range of microwear complexity values than those from Member 1 “Hanging Remnant.” Neither microwear texture nor carbon isotope data serve to differentiate specimens from Makapansgat and Sterkfontein that have been proposed to represent A. prometheus.