Wisdom teeth: refining our understanding of mammalian evolution through dating dental enamel

直接测定哺乳动物化石的年代比放射性碳测年的限制（~5万年）更早是非常具有挑战性的，这使得研究重点集中在最近的过去，以形成我们对哺乳动物对变化环境的反应的理解。然而，如果我们的目标是了解气候变化对陆地生物的影响，或者解开我们自己的进化史，这个狭窄的时间窗口是极其有限的。我们很难确定非洲哺乳动物的主要进化驱动因素，并在一个庞大而多样的大陆上比较模式。这个问题包括我们的祖先。阻碍所需的比较的根本问题是年代学，特别是一种可以直接确定化石年代的方法。我们的项目团队一直在开发和采用通过化石中原始蛋白质的分解来确定年代的方法。令人兴奋的是，我们刚刚在方法上取得了突破，使氨基酸（一种蛋白质分解产物）的年代测定能够对残留在牙釉质（一种由磷酸钙和少量蛋白质组成的抗性晶体材料）中的少量氨基酸进行测定。牙釉质定年具有巨大的优势，可以为哺乳动物的牙齿（重要的化石）提供直接的日期，而新方法现在可以进行常规的氨基酸分析，成功地确定了英国材料的年龄，可达300万年。这项技术已经成熟，可以发展到一系列哺乳动物物种和其他地理区域，有可能彻底改变我们对哺乳动物（包括人类）在过去几百万年里的进化的理解，以及它们在当地和全球范围内对环境变化的反应。这项提议将解决常规使用这种测年方法所需的三个技术发展领域，但它开辟的时间框架（过去~ 400万年）将使我们能够解决的研究问题范围发生重大转变。提出的三种技术进步是：1)微流体（“芯片上的实验室”）方法，这将大大减少所需的物理样本量，以及在专业实验室之外进行的准备/分析；2)结合有机和无机组分的分析和成像，了解它们的结构、功能以及对蛋白质分解的影响；3)利用先进的化学模型来理解击穿反应。然后，我们将把这些方法应用到非洲的两个特别感兴趣的进化地区：东非（包括裂谷）和南部非洲（包括“人类的摇篮”）。最初，我们在可靠的年代材料上校准了定年方法，然后将其扩展到目前未知年代的材料。发展的年表还将使人类与环境相互作用的模型得到检验，为我们对人类进化历史的理解提供一个突破。因此，该项目将采用年代测定方面的最新进展，并将其应用于一个地区，在那里，古环境记录可以帮助人们了解非洲生物群（植物和动物）对温度和降雨模式变化的敏感性。了解大型哺乳动物对环境和气候变化的反应对于制定适当的保护措施至关重要，我们也将深入了解人类血统进化的时间和驱动因素。

Directly dating mammal fossils older than the limit of radiocarbon dating (~50,000 years) is very challenging, and this has led to a research focus on the most recent past in forming our understanding of mammalian response to changing environments. However this narrow time window is extremely limiting if we aim to understand the effects of climate change on land-based organisms, or unpick our own evolutionary history. We are hard-pressed to pinpoint the major evolutionary drivers for African mammals, and to compare patterns across a large, diverse continent. This problem notably includes our own ancestors. The fundamental problem preventing the required comparisons is chronology, and specifically a method that can date fossils directly. Our project team has been developing and employing methods for dating using the breakdown of the original proteins trapped within fossils. Excitingly, we have just made a methodological breakthrough which enables amino acid (a protein breakdown product) dating to be undertaken on the small amounts of amino acids remaining in tooth enamel (a resistant crystalline material composed of calcium phosphate with small amounts of protein). Dating enamel has the enormous advantage of providing a direct date on mammal teeth (critical fossils of interest) and the new method now enables routine amino acid analysis, successfully dating UK material up to 3 million years in age. This technique is ripe for development to a range of mammalian species and additional geographic regions, potentially revolutionising our understanding of mammalian evolution (including humans) during the last few million years, and their response to environmental change, at the local and the global scale.This proposal will address the three areas of technology development needed for this dating method to be used routinely, but the time frame it opens up (the last ~4 million years) will enable a significant shift in the range of research questions we can address. The three strands of technological advance proposed are: 1) a microfluidics ("lab on a chip") approach, which will enable both a significant decrease in the physical sample size needed, as well as preparation / analyses to be undertaken outside specialist labs; 2) combining analysis and imaging of both the organic and inorganic fractions to understand their structure, function and any impact on the protein breakdown; and 3) using advanced chemical models to understand the breakdown reactions.We will then apply these methods to two regions of Africa of particular evolutionary interest: east Africa (including the Rift Valley) and southern Africa (including the 'Cradle of Humankind'). Initially calibrating the dating approach on reliably dated material, we will then expand it to material that is currently of unknown age. The developed chronology will also enable models of human-environment interaction to be tested, providing a breakthrough in our understanding of our evolutionary past. This project will therefore take the latest advances in dating and apply them to a region where the palaeoenvironmental record can help shape the understanding of the sensitivity of Africa's biota (plants and animals) to changes in temperature and rainfall patterns. Understanding large mammals' responses to environmental and climate change is critical for developing appropriate conservation measures, and we will also gain insights into the timings and drivers of the evolution of our human lineage.