Africa's wild C 4 plant foods and possible early hominid diets

Abstract

A small minority of Africa's wild plant foods are C 4. These are primarily the seeds of some of the C 4 grasses, the rootstocks and stem/leaf bases of some of the C 4 sedges (especially papyrus), and the leaves of some of the C 4 herbaceous dicots (forbs). These wild food plants are commonly found in disturbed ground and wetlands (particularly the grasses and sedges). Multiple lines of evidence indicate that C 4 grasses were present in Africa by at least the late Miocene. It is a reasonable hypothesis that the prehistory of the C 4 sedges parallels that of the C 4 grasses, but the C 4 forbs may not have become common until the late Pleistocene. CAM plants may have a more ancient history, but offer few opportunities for an additional C 4-like dietary signal. The environmental reconstructions available for the early South African hominid sites do not indicate the presence of large wetlands, and therefore probably the absence of a strong potential for a C 4 plant food diet. However, carbon isotope analyses of tooth enamel from three species of early South African hominids have shown that there was a significant but not dominant contribution of C 4 biomass in their diets. Since it appears unlikely that this C 4 component could have come predominantly from C 4 plant foods, a broad range of potential animal contributors is briefly considered, namely invertebrates, reptiles, birds, and small mammals. It is concluded that the similar average C 4 dietary intake seen in the three South African hominid species could have been acquired by differing contributions from the various sources, without the need to assume scavenging or hunting of medium to large grazing ungulates. Effectively similar dominantly dryland paleo-environments may also be part of the explanation. Theoretically, elsewhere in southern and eastern Africa, large wetlands would have offered early hominids greater opportunities for a C 4 plant diet.