Dietary adaptations of Plio-Pleistocene Bovidae: implications for hominid habitat use.

Abstract

Detailed reconstructions of vegetation structure are critical to understanding morphological and behavioral adaptations of Plio-Pleistocene African hominids, Savanna grassland habitats are often postulated as being influential in the evolution of many hominid adaptations (e.g., bipedality, foraging behaviors), yet the existence of this habitat type throughout the African Plio-Pleistocene has not been clearly established. Broad-scale reconstructions of hominid habitats as "savanna-mosaic" do not account for the fact that African grasslands may be classified into at least two different types: edaphic grasslands, which include seasonally flooded valley grasslands; and secondary grasslands, which include vast, relatively dry savanna grasslands. Though edaphic grasslands have existed for millions of years, it is unknown when secondary grasslands became widespread. The presence of specific microhabitats, including secondary grasslands, at a number of hominid sites was investigated in this study through reconstruction of diet and habitat preference in five extinct bovid taxa that were contemporaneous with early hominids. To reconstruct diet in extinct taxa, morphological correlates of dietary preferences were identified through a comparative study of cranial form in extant bovids. Metric data from cranial material of the five African Plio-Pleistocene bovid taxa were compared with extant bovid results, which yielded information of specific feeding behaviors of the extinct taxa. Reconstructed diets suggest that the earliest taxa to inhabit secondary grasslands in East Africa were Connochaetes gentryi and Parmularius altidens at around 2 m.y.a. It may therefore be inferred that secondary grasslands became prevalent at this time. This inference of secondary grassland development suggests that adaptations to this habitat type were not related to the origin of the Hominidae or to the evolution of bipedality in hominids. However, evidence suggests that this habitat type was influential in the evolution of Homo erectus sensu lato just after 2 m.y.a. in East Africa.