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

重点研究北美洲中部晚中新世奥加拉拉组保存的土壤碳酸盐碳同位素组成。在此期间（约15-5 Ma），哺乳动物化石记录表明，包括北美在内的全球哺乳动物群落多样性显著减少，生态结构发生了变化。哺乳动物的变化与古土壤碳酸盐和哺乳动物食草动物牙齿化石碳同位素组成的变化大致相关。中新世晚期沉积在大陆古土壤碳酸盐和哺乳动物牙齿中的碳酸钙的碳同位素组成表明了植物群落组成的变化，并表明栖息地的变化可能至少是哺乳动物变化的一个促成因素。最近有人提出，中新世晚期全球大气CO2浓度的降低是植物群落变化的原因。这一解释预测了当地和全球动物和同位素记录的同步变化。该研究将对中新世晚期北美洲哺乳动物化石记录和古土壤稳定同位素记录的同步变化预测进行验证。如果变化不是同步的，则不支持严格的全球解释，必须寻求具有重要区域成分的替代办法。由于土壤碳酸盐是栖息地的直接反映，该项目还将测试气候、栖息地和哺乳动物区系变化之间的联系。

9901693FoxThe 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.