9604024 Cerling The PIs will study the carbon and oxygen isotopic composition of fossil tooth enamel on a global scale to determine changes in the diets of African mammals over the past 20 million years. The PIs have established that the carbon isotopic composition of enamel from equids and other large mammals changes dramatically between about 7 and 5 million years ago in widespread parts of the world. We propose: 1) to examine the transition to C4 diet in East Africa for the last 20 million years for different mammal groups, including bovids, suids, rhinos, and proboscideans; 2) to gather data on extant mammals from the East African ecosystem to develop the use of d13C and d180 as a paleoecologic indicator. The PIs will examine the development of different ecological niches in rhino, proboscidean, suid, and bovid lineages using the stable carbon isotopic composition as a measure of the diet (hence habitat) of these groups. We will examine the shift in conjunction with morphologic change in these animals. In addition, the PIs will examine three different communities: the semi-desert region near Lake Turkana, a savanna plains community, and an equatorial forest community. Forest communities may preserve a closed canopy signal in the d13C signal, and resource partitioning in carbon and oxygen should be distinguishable in all communities.
