THE TRACE ELEMENT BIOGEOCHEMISTRY OF AFRICAN CARNIVORANS: THE RATIO OF STRONTIUM TO BARIUM AS AN INDICATOR OF WETLAND RESOURCE EXPLOITATION

Most early hominid fossil localities in Africa are associated with ancient wetlands, however the extent to which early hominids used wetland habitats and resources is not known. I have argued previously that the craniodental anatomy of robust australopithecines (Paranthropus) can be explained as an adaptation to a diet that included hard-shelled invertebrates such as freshwater crabs and molluscs. Here I test this “durophage model” by analyzing the trace element chemistry of extant African carnivorans, including aquatic, semi-aquatic, and terrestrial forms. The ratio of strontium to barium in bone tissue is found to distinguish taxa that forage primarily in freshwater (Hydrictis) from those that forage amphibiously on land and in freshwater (Aonyx, Atilax) from those that forage terrestrially (Genetta, Civettictis, Herpestes, Ichneumia, Galerella, Crossarchus, Bdeogale, Ictonyx) — the ratio of strontium to barium increases from freshwater aquatic to semi-aquatic to terrestrial ecologies. Coastal populations of Aonyx and Atilax that use marine resources have the highest Sr:Ba ratios. These overall biogeochemical patterns are evident in both equatorial and southern Africa. I compare these results with the published literature on fossil hominids, including Australopithecus and Paranthropus, and I conclude that the data are consistent with the durophage hypothesis.