Cercopithecines are common in hominid producing deposits and are a useful proxy for determining the ecological context of the early hominids. For this study, dental microwear is examined through low-magnification stereomicroscopy and used to reconstruct the diets of sampled primates. Those from the earliest sites, predominantly Parapapio, are primarily frugivorous while the incidence of gramnivory increases in the later Dinopithecus, Gorgopithecus, and Papio individuals denoting a general cooling and drying trend over the South African Plio-Pleistocene with a distinct pulse between 1.9-1.8 million years ago (mya). Australopithecus is reconstructed as a primary gramnivore which indicates that hominids adapted early in their evolution to expanding grasslands.