Three sympatric fossil cercopithecoid genera (Cercopithecoides, Parapapio, and Theropithecus) occur in Members 3 and 4 at the Makapansgat Limeworks hominin locality, South Africa, and their presence in a single ecosystem suggest a certain degree of ecological and/or dietary differentiation between taxa. Here, we explore the extent of dietary niche separation amongst these taxa using stable isotope (13C/12C, 18O/16O) and trace-element (Sr, Ba, Ca) analyses of fossil tooth enamel. In particular we searched for evidence of subtle niche separation between the more closely related, morphologically similar taxa of the genus Parapapio, as uncertainties exist around their taxonomy and taxonomic identification. Given these uncertainties, craniometric analyses were also performed to ground the dietary interpretations in a morphological context. The results found no clear taxonomic signal in the craniometric data for the Parapapio sample, and further indicate that this sample was no more variable morphologically than a single, geographically circumscribed, extant chacma baboon sample. In contrast, two overlapping dietary ecologies were found within this same Makapansgat Parapapio sample. Additionally, two widely differing dietary ecologies were found within the Cercopithecoides williamsi sample, while results for Theropithecus darti indicate a predominantly C4 diet. Hence, although biogeochemical dietary indicators point towards distinct dietary ecologies within and between fossil genera at Makapansgat, within the genus Parapapio disjunctions exist between the dietary categories and the taxonomic assignment of specimens. Am J Phys Anthropol, 2008. © 2007 Wiley-Liss, Inc.