Isotopic evidence for the timing of the dietary shift toward C₄foods in eastern African Paranthropus

New approaches to the study of early hominin diets have refreshed interest in how and when our diets diverged from those of other African apes. A trend toward significant consumption of C₄foods in hominins after this divergence has emerged as a landmark event in human evolution, with direct evidence provided by stable carbon isotope studies. In this study, we report on detailed carbon isotopic evidence from the hominin fossil record of the Shungura and Usno Formations, Lower Omo Valley, Ethiopia, which elucidates the patterns of C₄dietary utilization in the robust hominin Paranthropus. The results show that the most important shift toward C₄foods occurred at ~2.37 Ma, within the temporal range of the earliest known member of the genus, Paranthropus aethiopicus, and that this shift was not unique to Paranthropus but occurred in all hominins from this fossil sequence. This uptake of C₄foods by hominins occurred during a period marked by an overall trend toward increased C₄grazing by cooccurring mammalian taxa from the same sequence. However, the timing and geographic patterns of hominin diets in this region differ from those observed elsewhere in the same basin, where environmental controls on the underlying availability of various food sources were likely quite different. These results highlight the complexities of dietary responses by hominins to changes in the availability of food resources.