Stable Carbon Isotope Variation in Late Miocene Paleosol Carbonates from North America: Habitat Change and Mammalian Evolution

9901693

Fox

The research will focus on the carbon isotope composition of soil carbonates preserved in the late Miocene Ogallala Formation of central North America. During this interval (approximately 15-5 Ma), the mammalian fossil record indicates significant decreases in diversity and changes in the ecological structure of mammal communities globally, including North America. The changes among mammals broadly correlate with changes in the carbon isotope composition of both paleosol carbonates and fossil mammalian herbivore teeth. The carbon isotope composition of calcium carbonate deposited in paleosol carbonate and mammal teeth on a number of continents during the late Miocene indicate shifts in the composition of plant communities and suggest that habitat changes may have been at least a contributing factor in the changes among mammals. It has recently been proposed that a global lowering of the concentration of atmospheric CO2 during the late Miocene is the cause of the changes in plant communities. This explanation predicts synchronous changes in faunal and isotopic records, both locally and globally. The research will test the prediction of synchrony of change in the mammalian fossil record and the stable isotope record of paleosols in North America during the late Miocene. If the changes are not synchronous, a strictly global explanation is not supported and alternatives, with significant regional components, must be sought. As soil carbonates are a direct reflection of the habitat, the project will also provide a test of connections between climate, habitat, and faunal changes among mammals.