Dietary adaptations of early hominids are generally understood to have played a crucial role in hominid evolution. The dietary habits of Australopithecus robustus are of special interest because the robust masticatory apparatus and characteristic dental features point to a distinctive dietary niche. Suggestions have ranged anywhere between carnivory and specialist herbivory, but current consensus has focused mainly on small hard items within the context of a vegetarian diet, and more particularly, frugivory. Few studies have challenged this perspective, although the results of a recent Sr/Ca study of A. robustus at Swartkrans were found to be inconsistent with herbivory. Here we address the question of A. robustus diet using 13C/12C ratio analysis of structural carbonate in tooth enamel, which has been shown to retain biogenic isotopic composition over long periods, contra earlier arguments based on bone apatite. Results for A. robustus, compared with other fauna from Swartkrans, show a mixed diet including both C3 and C4 foods. Since the C4 contribution must derive from consumption of grass or grazing animals, the data do not support either a specialist frugivorous or graminivorous niche for A. robustus
rather, they suggest a more generalized or omnivorous diet.