Biogenic and diagenetic Sr/Ca in Plio-Pleistocene fossils of the Omo Shungura Formation

Abstract

Under conditions of normal calcium metabolism, strontium/calcium ratios (Sr/Ca) have been shown to reflect the trophic level of contemporary and recent terrestrial fauna. These ratios therefore offer a potential means of studying fossil ecosystems and the diet of prehistoric humans. In cases in which suitable controls have demonstrated the preservation of biogenic Sr/Ca, it has been possible to investigate the proportionate importance of meat vs. vegetable foods in the diets of prehistoric humans. However, diagenetic change after interment has made it impossible to discern biogenic Sr/Ca in faunal and human skeletons over 15,000 y b.p. A procedure is investigated for the analysis of biogenic and diagenetic apatite in vertebrate fossils, on the basis of solubility differences among carbonate, hydroxy-, and fluorapatites. When applied to the 2 ma b.p. fauna of the Omo Basin (Ethiopia), distinct characterization of the herbivore, omnivore, and carnivore fauna in conformity with trophism was discerned, in spite of anomalous Sr/Ca of one highly specialized carnivore,Homotherium.Possible metabolic and/or taphonomic explanations of this anomaly are discussed, and future basic research into the solubility profile procedure is outlined.