5.8 MA CARBON ISOTOPE RECORDS OF EAST AFRICAN MAMMALIAN DIET AND THEIR MODERN RELATIVES

Analyzing carbon isotopes (δ¹³C) of fossilized tooth enamel can aid in understanding dietary adaptations of mammalian fauna and reconstructing paleoenvironmental conditions. Carbon isotopic composition of tooth enamel is based on differences in carbon isotope discrimination between plants that use the two major photosynthetic pathways (C3 and C4) and the transfer of isotopic signature from plants to tooth enamel. The fossil enamel record has the potential to provide detailed information about dietary adaptations and track diet changes of C3 browsing, C4 grazing, or relative contribution of C3 and C4 based diets in the mixed feeders. Here, we used new and compiled modern and fossil tooth enamel δ¹³C data from seven different herbivores fauna (i.e., Bovids including Alcelaphini, Tragelaphini, Reduncini, Aepycerotini and Bovini and non-bovids including Equids and Hippos). The fossil tooth enamel samples were collected from five different sites in the Awash Basin, Ethiopia representing nine time periods spanning from Late Miocene to Pleistocene in the last 5.8 Ma. Our results indicate that C4 grasses were a significant part of the mammalian diet throughout the record. Equids and Alcelaphini exhibited a consistent C4-dominated diet throughout the record, while Aepycerotini and Tragelaphini were mainly fed on C3/C4 mixed diet. Hippos and Bovinis adopted C3/C4 mixed diets prior to 3Ma but they shifted to exclusively C4-dominated diet. On the other hand, most of the modern herbivore taxa show relatively similar diet as compared to their fossil closest relatives, except Tragelaphini, which relies on pure C3 diet. These diverse diets observed in the mammalian fauna since Late Miocene indicates the presence of both C3 and C4 vegetation and the significance of C4 grasses on the paleolandscape, which further provides an insight to the resources available for early hominin. Finally, the fact that the fossil diet of some of the mammals changed with time, and in some cases differ from their closest modern relatives caution the use of modern mammals to interpret paleoecology of the fossil record.