Miocene Continental Paleoclimate and Fossil Horse Evolution:Trace Element and Stable Isotope Geochemistry of Enamel- Phosphate

我们建议通过建立北美化石马骨和牙齿磷酸盐中痕量元素和同位素保存的系统学来探索中中新世古气候与马演化联系的可能性。我们将测试釉质磷酸盐是否提供了关于古环境(温度、水文)、古饮食(放牧与浏览)和进化(马的中中新世辐射)的定量信息，或者骨骼和牙齿磷酸盐是否在成岩上不透明。这项初步工作可能为揭示中新世大陆古气候变化提供新的途径，中新世大陆古气候变化是全球气候恶化的重要时期，大陆记录缺乏定量的古地球化学信息。化石马特别适合研究，因为它们在地理上分布广泛，在始新世至晚更新世的化石组合中很常见，并具有现代相似性。马匹在中新世中期(16-12 Ma)经历了爆炸性的适应性辐射和推测的饮食转变，可能是对古气候变化和稀树草原的扩张做出了反应。这种气候变化是从古海洋学数据中推断出来的；饮食变化是从对牙齿功能形态的研究中推断出来的。我们希望确定在化石牙齿的化学成分中是否存在明显的古饮食变化；大陆古气候记录是否在幅度、方向和时间上证实了海洋记录；以及古气候变化是否与古环境和演化变化同时发生。在这个初步的项目中，我们将探索成岩作用、种间和种内差异的影响，并描述Burge采石场的马牙和骨骼化石的del 18Opo4，Burge采石场是中中新世(-12 Ma)马动物群中含量最丰富、保存最完好的之一。成岩作用将通过釉质磷酸盐的微量元素、扫描电子显微镜和X射线衍射仪分析进行评估，并与现代马进行比较。如果成岩作用被证明是可以忽略的，那么现代牙齿和化石牙齿中的牙釉质Del 18Opo4将确立重建大陆古气候记录的适宜性。

We propose to explore the potential for linking mid-Miocene paleoclimate and horse evolution by establishing the systematics of trace elemental and isotopic preservation in the bone and tooth phosphate of North American fossil horses. We will test whether enamel phosphate provides quantitative information about changes in paleoenvironment (temperature, hydrology), paleodiet (graze vs. browse), and evolution (the mid-Miocene radiation of horses), or if bone and tooth phosphate is diagenetically opaque. This preliminary work could catalyze new avenues for unraveling Miocene continental paleoclimate changes, an important period of global climatic deterioration with scant quantitative paleogeochemical information from continental records. Fossil horses are particularly suitable for study because they are geographically widespread and common in fossil assemblages from the Eocene to late Pleistocene and have modern analogues. Horses underwent an explosive adaptive radiation and presumed dietary shift in the middle Miocene (16-12 Ma) perhaps responding to paleoclimatic changes and the spread of savannah grasslands. This climatic shift is inferred from paleoceanographic data; the dietary shift, from studies of the functional morphology of teeth. We wish to determine if a paleodietary shift is evident in the chemistry of the fossil teeth; if the continental paleoclimate record corroborates the marine record in magnitude, direction, and timing; and if paleoclimatic change occurred concurrently with paleoenvironmental and evolutionary changes. In this preliminary venture, we will explore the effects of diagenesis, inter- and intraspecific variations, and characterize the del 18Opo4 of fossil horse teeth and bones from the Burge Quarry, one of the richest and best-preserved middle Miocene (-12 Ma) horse faunas. Diagenesis will be evaluated with trace element, SEM, and XRD analyses of enamel phosphate and compared to modern horses. If diagenesis proves to be negligible, del 18Opo4 of tooth-enamel in modern and fossil teeth will establish the suitability of reconstructing the continental paleoclimate record.