ISOTOPE RECORDS OF PLIOCENE MAMMALIAN TOOTH ENAMEL AS PALEONVIRONMENTAL AND PALEOCLIMATIC INDICATOR FROM DIKIKA, ETHIOPIA

Analyses of the isotope ratios of mammalian fossil tooth enamel have increasingly been used to reconstruct paleoecological and paleoclimatic conditions. Although there are many approaches to reconstruct environmental and climatic conditions at fossil localities, there are certain advantages and limitations of each methodology. Here, we use stable isotopes of carbon and oxygen of tooth enamel from Dikika, Ethiopia, a method which has a advantage of being derived empirically without any assumption about the animal behavior or consideration of the habitat preference of modern faunal analogues. A weighted average d¹³C_ecosystem value was calculated using the average d¹³C_enamel of each taxon weighted by faunal abundance and the estimated daily food intake of large vertebrates. The resulting d¹³C_ecosystem value was used to asses shifts in the floral composition of the ecosystem, which follows climate conditions since the C3/C4 ratio of local vegetation is determined by temperature and precipitation. We analyzed the isotopic composition of a total of 210 herbivorous tooth enamel samples, which archive the dietary preferences and drinking behavior between 3-4 Ma. The carbon isotopic data signify a wide range of foraging strategies, characterized by a mixed C3/C4 to C4-dominated diets in a wooded grassland to open woodland environmental setting. Similarly, the oxygen isotope composition of tooth enamel is a function of the isotopic composition of the body water, which in turn is a function of drinking water, which may also reflect local climatic conditions. We use the oxygen isotopic enrichment (e_ES-EI) between evaporation sensitive and insensitive fauna, which provides an estimated water deficit of 1217 mm. Thus, paleoclimatic conditions based on the water deficit and the δ¹⁸Oenamel value from the Pliocene Dikika fauna indicate wetter and humid as compared to the middle Pleistocene site at Asbole and many other Pliocene sites in the Awash Valley.