9310546 Cerling This proposal is to study the carbon isotopic composition of fossil tooth enamel to determine the diet of mammals in the last 20 million years. C4 plants are isotopically different from C3 plants. Therefore, this study will determine the timing of development of C4 ecosystems, which are usually dominated by grasses. The proposed research has three parts: 1) to identify diagenic changes that may alter the isotopic concentration of tooth enamel, 2) to precisely determine the time that C4 ecosystems developed on several continents, and 3) to establish the variability of diet in horses of North America. Based on preliminary data, the apparent synchronous development of C4 ecosystems in the Old and New Worlds suggests a global ecological change, perhaps related to changes in atmospheric changes in CO2. This research will establish the time of the first significant appearance of C4-dominated ecosystems on different continents. Specifically, fossil horses from North America, Europe, Asia, and Africa will be studied. %%% This research represents the first attempt to document the development of grassland ecosystems worldwide. Given that these C4 ecosystems developed simultaneously on different continents, then their evolution is most likely closely tied to global ecological change. Understanding such changes and their consequences is vital to predicting and preparing for future changes as atmospheric CO2 levels continue to rise. ***
