PALEODIETARY RECONSTRUCTION USING STABLE ISOTOPES OF HERBIVORES FROM THE SHUNGURA FORMATION, ETHIOPIA: IMPLICATIONS FOR HOMININ ENVIRONMENTS

Environmental changes in the Pliocene and Pleistocene are among the key drivers that are believed to have shaped the course of human evolution. Well-dated, continuous and prolific hominin bearing sites which span this critical time period in human evolution offer the unique opportunity of investigating temporal trends in paleoenvironments. One approach which is commonly used to make paleoenvironmental reconstructions is looking at the dietary adaptation of fossil herbivores and how these adaptations change through time. As plants are the primary source of carbon for herbivores, such changes in dietary patterns may be recorded in the carbon isotopic composition of herbivore tissues. Here, we present stable isotopic study of tooth enamel of fossil herbivores from several members of the Shungura Formation, which is a well dated site with an abundant fossil record in this northern area of the Omo-Turkana Basin. A total of 1034 samples, comprised of molars and molar fragments, were collected and the isotopic ratios were analyzed. Based on the stable carbon isotope results, the time period from 3.5 - 2.9 Ma shows a higher proportion of mixed-feeders compared to grazers or browsers. From ~2.8 - ~2.0 Ma, there appears to be an increase in the proportion of C₄ resource consumption with some decline in the proportion of mixed feeders. After 1.8 Ma there is a further decline in browsers and an increase in the proportion of grazing taxa. These patterns are similar to results previously reported from the southern Omo-Turkana Basin and indicate a non-analogous faunal composition in the Pliocene compared to modern faunal compositions in contemporary African ecosystems. Also, intra-basinal comparisons show that the Shungura Formation had a higher proportion of mixed feeders compared to fauna from contemporaneous strata in the southern Omo-Turkana Basin. This might reflect the presence of broad gallery forests and a relatively closed and wet environment in the Shungura area, which supports a previous hypothesis that proposed the paleo-Omo river might have provided a relatively stable refugium for the mammalian community.