Doctoral Dissertation Improvement Grant: Experimental Determination of Tooth Mineralization Patterns in Ungulates for Application to Paleoseasonality Reconstruction

一个多世纪以来，学者们一直在争论导致人类大型大脑和独特行为进化的条件，包括复杂的石器使用和语言。一种有影响力的理论提出，这些特征是对过去500万年来非洲季节性资源可获得性的回应。地质和古生物数据表明，不断变化的降雨模式可能产生了更干旱的非洲生态系统和新颖的觅食行为，尽管记录古代降水模式的方法仍然很初级。在Tanya Smith博士的指导下，Daniel Green致力于利用新的实验室技术和实验来改进季节性重建的方法，促进对人类进化关键时期古代气候变化的研究。通过对牙齿进行化学分析，可以重建气候模式，这些分析记录了牙齿形成期间的环境化学，并在死亡和石化后保持不变。牙齿的增量，类似于树上的年轮，在儿童时期每天都会从与当地水源平衡的矿物质中形成。随着季节的推移，同位素(原子变种)的组成会发生变化，牙齿会记录这些变化。重要的是，牙齿中的同位素记录了与时间标记相关的季节性变化，有助于准确估计环境变化。该项目将通过精确绘制牙齿矿化的几何图形和时间来改善气候重建。结合尖端同步加速器成像和扫描电子显微镜对发育中的绵羊牙齿进行扫描，将会产生随着时间的推移矿物质密度的变化。然后，该项目使用受同位素水开关影响的动物来测试这些结果，实验证明牙齿化学和接近季节性变化的水分变化之间的关系。最终，对环境敏感矿物如何添加到牙齿中的具体理解将改善季节性重建，并将使人们能够调查显著的气候变化是否伴随着独特的人类解剖和行为的发展。该项目将培养研究生和本科生，并加强与欧洲和非洲学者的合作。这项研究的结果将在专业期刊和会议上广泛传播，并向公众展示。

Scholars have been debating the conditions that led to the evolution of humans' large brains and unique behaviors, including complex stone tool use and language, for more than a century. One influential theory proposes that these features emerged in response to seasonal resource availability in Africa over the last five million years. Geological and paleontological data suggest that changing rainfall patterns might have produced more arid African ecosystems and novel foraging behaviors, although approaches for documenting ancient precipitation patterns remain rudimentary. Under the direction of Dr. Tanya Smith, Daniel Green aims to improve methods of seasonal reconstruction with new laboratory techniques and experimentation, facilitating research on ancient climate change during key periods in human evolution.Climatic patterns may be reconstructed through chemical analysis of teeth, which record environmental chemistry during formation and remain unchanged after death and fossilization. Tooth increments, analogous to rings in trees, form every day during childhood from ingested minerals that are in equilibrium with local water sources. As seasons pass, the composition of isotopes (atomic variants) change, and teeth record these changes. Importantly, isotopes in teeth record seasonal changes that can be related to time markers, facilitating precise estimates of environmental change. This project will improve climate reconstruction by precisely mapping the geometry and timing of tooth mineralization. A combination of cutting-edge synchrotron imaging and scanning electron microscopy of developing sheep teeth will yield mineral density change over time. This project then tests these results using animals subject to an isotopic water switch, experimentally demonstrating the relationship between tooth chemistry and changes in water that approximates seasonal variation.Ultimately, a concrete understanding of how environmentally sensitive minerals are added to teeth will improve seasonal reconstruction, and will allow one to investigate if marked climatic change accompanied the development of unique human anatomy and behaviors. This project will train graduate and undergraduate students, and enhance collaborations with scholars in Europe and Africa. Results of this research will be broadly disseminated in professional journals and meetings, and presented to public audiences.