COLLABORATIVE RESEARCH: Isotopic Composition of Equus Tooth Enamel and Its Relationship to Diet

马类化石牙釉质中构造碳酸盐（和磷酸盐）的C和O同位素组成已被广泛应用于南亚、非洲和北美的新生代古环境研究。然而，对于现代马（Equus），人们对(1)马利用周围生态系统的哪一部分作为它们的食物，(2)饮食摄入的同位素组成与体内水和血液中溶解的二氧化碳的同位素组成的关系，以及(3)特定个体的牙齿间和牙齿内同位素变化的认识不足。更好地了解这些不确定性对于破译釉质C和O同位素组成的环境意义具有重要意义。我们建议通过以下两方面的研究来回答这些问题：(1)加州大学戴维斯分校兽医学院对实验马进行对照饮食研究；(2)对两个野生马群进行为期两年的研究，其中我们(a)同位素表征周围生态系统，(b)监测每月的植物物种组成和马饮食的同位素组成，(C)监测水体的O同位素组成，(d)检查选定个体的齿间同位素变异。(e)检查牙内形态和同位素变化。这项研究的推动力之一是动物科学和古生物学文献中报道的观察结果（以及同位素化学家最近的发现），即马的牙齿是在个体生命的重要时期形成的。虽然确切的年代有些不确定，但我们相信牙齿可能潜在地记录了饮食和水摄入量的同位素组成的年度和季节性变化。如果这是真的，马科动物的牙齿可能提供了比以前认识到的更详细的过去同位素记录。同样重要的是，必须认识到个体内部由生理而非饮食摄入引起的潜在同位素变化，才能正确解释这一同位素代用物。这项研究建立在对环境水与磷酸釉质O同位素组成之间关系的开创性研究，以及对化石和现代生物牙齿内同位素变化的最新研究的基础上。我们的目的是将现有的知识整合到一个有凝聚力的实验设计中，以充分回答关于马的牙釉质及其作为环境条件同位素代理的相关性的问题。

9706653 Amundson The C and O isotope composition of structural carbonate ( and phosphate) in the tooth enamel of fossil Equids has become widely used in Cenozoic paleoenvironmental studies in south Asia, Africa, and North America. Yet, with respect to modern horse (Equus), there is insufficient knowledge of (1) what portion of the surrounding ecosystem the horses utilize for their diet, (2) the relationship of the isotopic composition of dietary intake to the isotopic composition of body water and dissolved CO2 in blood, and (3) the inter-and intra-tooth isotopic variability in a given individual. A better understanding of these uncertainties is important to decipher the environmental significance of the C and O isotope composition of enamel. We propose to conduct a two pronged study to answer these questions through: (1) controlled dietary studies on experimental horses at the UC Davis School of Veterinary Medicine and (2) a two year study of two feral horse herds in which we (a) isotopically characterize the surrounding ecosystem, (b) monitor the monthly plant species composition, and isotopic composition, of the horse diet, (C ) monitor the O isotope composition of body water, (d) examine inter-tooth isotopic variability in selected individuals, and (e) examine intra-tooth morphological and isotopic variations. One impetus for this research are the observations reported in the animal science and paleontological literature (as well as recent findings by isotope chemists) that Equus teeth form over a significant period of an individual's life. While the exact chronology is somewhat uncertain, we believe that teeth may potentially record both annual and seasonal variations in the isotopic composition of diet and water intake. If this is true, Equid teeth may provide a more detailed isotopic record of the past than previously recognized. Equally important, potential isotopic variations within an individual caused by physiology, rather than dietary intake, must be recognized for ade quate interpretation of this isotopic proxy. This research builds on pioneering studies of the relationship between environmental water and the O isotope composition of enamel phosphate, and on recent studies of in-tooth isotopic variability in fossil and modern organisms. Our purpose here is to consolidate this existing knowledge into a cohesive experimental design that will adequately answer the question that remains about Equus tooth enamel and its relevance as an isotopic proxy for environmental conditions.