Tracking changing environments using stable carbon isotopes in fossil tooth enamel: an example from the South African hominin sites.

The environmental contexts of the karstic hominin sites in South Africa have been established largely by means of faunal associations; taken together these data suggest a trend from relatively closed and more mesic to open, drier environments from about 3 to 1.5 Ma. Vrba argued for a major shift within this trend ca. 2.4-2.6 Ma, an influential proposal that posited links between bovid (and hominin) radiation in Africa and the intensification of Northern Hemisphere Glaciation. Yet faunal approaches often rely on habitat and feeding preferences of modern taxa that may differ from those of their extinct predecessors. Here we explore ways of extending (13)C/(12)C data from fossil mammals beyond denoting "presence" or "absence" of C(4) grasses using the evolution of open environments in South Africa as a case study. To do so we calculated the relative proportions of C(3)-, mixed-, and C(4)-feeding herbivores for all the hominin sites for which we have sufficient data based on (13)C/(12)C analyses of fossil tooth enamel. The results confirm a general trend towards more open environments since 3 Ma, but they also emphasize a marked change to open grassy habitats in the latest Pliocene/early Pleistocene. Mean (13)C/(12)C for large felids also mirrored this trend.