Testing Stable Isotopes of Human Dental Calculus as a Nondestructive Proxy for Paleodiet

三十多年来，生物考古学家一直使用稳定的碳和氮同位素来评估早期人类的饮食习惯。鉴于骨骼在大多数化石学环境中比皮肤、指甲和头发保存得更好，所以在同位素分析中使用的主要生物材料是胶原蛋白。这种蛋白质是钙化骨骼的有机部分，不能直接用于分析，因此用于分离胶原蛋白的方法是破坏性的。与胶原蛋白不同，牙菌斑是一种生物膜，形成于人类和其他动物的牙齿上。当菌斑积聚而不被清除时，它就会钙化，形成牙结石。2008年，从西班牙维托利亚的中世纪和后中世纪巴斯克骨骼中收集了微积分，目的是分离植物植硅体。该项目的目标是确定研究人员是否可以直接观察到从新大陆引入西班牙的可食用植物，特别是玉米。不幸的是，处理微积分样本以发现植硅体的成功微乎其微。带着58个样本，发现植硅石的希望变得渺茫，5个结石样本被送到里诺内华达大学的地球化学实验室进行稳定同位素分析。研究人员在文献中找不到任何证据表明有人曾试图从微积分中获得稳定的同位素特征，因此他们并不乐观，没有足够的碳和氮来从主要由钙和磷酸盐矿物组成的生物材料中获得良好的信号。对五个样本的初步分析得出了令人惊讶的结果。碳的含量比预期的要多，它产生的比率可以在重复试验中复制，这些比率接近早期欧洲人从骨胶原中获得的值。当对样本进行氮测试时，也发现了类似的结果。微积分中有足够的氮来获得良好的同位素估计，结果与基于骨胶原的早期欧洲人群的值一致。这个项目并不是以稳定的碳和氮同位素在古饮食分析中的用途为中心的，这一点在过去35年的数百项研究中得到了证明。该项目的目标是确定一种新的生物材料是否？牙科微积分？可用于估计C和N比率，特别是在禁止破坏性分析的情况下。关键是，牙石不是骨骼或牙齿系统的一部分，而是现代人类群体中经历(由牙齿卫生员)添加和移除的循环的附加组件。在牙齿卫生之前，重点更多地放在添加上，而不是去除上，所以牙结石在早期人类的牙齿上很常见。虽然到目前为止的结果令人鼓舞，但该项目将进行必要的额外测试，以确定牙结石是否可以作为同位素分析的一致和有效的替代品。微积分样本将从具有不同生存模式的人类群体中获得，包括格陵兰因纽特人、格陵兰北欧人、经典和殖民地玛雅人以及史前秘鲁人，以确定微积分中的同位素是否显示出蛋白质消耗的差异以及C3和C4植物的不同用途。如果能够获得一致的结果，牙科微积分可能会提供一个更容易获得的数据来源，还可能避免美国原住民群体对使用人类骨骼遗骸破坏性分析技术进行这种分析的抵制。该项目将验证一种同位素分析方法，该方法比目前标准的骨胶原检测方法更快、非破坏性和成本更低，这将是对古饮食研究子领域的重大贡献。

For over thirty years, bioarchaeologists have used stable carbon and nitrogen isotopes to evaluate the dietary habits of earlier human populations. Given that bone preserves better than skin, fingernails, and hair in most taphonomic contexts, the primary biomaterial used in isotope analysis is collagen. This protein, the organic fraction of calcified bone, is not directly available for analysis so methods used to isolate collagen are destructive. In contrast to collagen, dental plaque is a biofilm that forms on the teeth of humans and other animals. When plaque accumulates and is not removed, it calcifies to form dental calculus. In 2008, calculus was collected from medieval and post-medieval Basque skeletons from Vitoria, Spain with the aim of isolating plant phytoliths. The goal of this project was to determine if researchers could observe directly the introduction of edible plants from the New World to Spain, with special emphasis on maize. Unfortunately, processing calculus samples to find phytoliths was minimally successful. With 58 samples and diminished hopes of finding phytoliths, five calculus samples were sent to the geochemistry lab at the University of Nevada, Reno for stable isotope analysis. The researchers could find no evidence in the literature that anyone had ever attempted to obtain stable isotope signatures from calculus, so they were not optimistic there would be enough carbon and nitrogen to get a good signal from a biomaterial primarily made up of calcium and phosphate minerals. The initial analysis of five samples yielded surprising results. There was more carbon than anticipated, it yielded ratios that could be replicated on repeated trials, and these ratios were close to the values obtained from bone collagen for earlier European populations. When the samples were tested for nitrogen, a similar result was found. There is sufficient nitrogen in calculus to get a good isotope estimate and the results were consistent with values for earlier European populations based on bone collagen. This project does not center on the utility of stable carbon and nitrogen isotopes in paleodietary analysis as that has been demonstrated in hundreds of studies over the past 35 years. The project goal is to determine whether a new biomaterial ? dental calculus ? can be used to estimate C and N ratios, especially in instances where destructive analysis is prohibited. The key is that calculus is not part of the skeletal or dental system but is an add-on that goes through a cycle of addition and removal (by a dental hygienist) in modern human populations. Prior to dental hygiene, emphasis was more on addition and less on removal so calculus is common on the teeth of earlier humans. While results to date are encouraging, this project will conduct the necessary additional tests to determine if dental calculus can be a consistent and effective proxy for isotope analysis. Calculus samples will be obtained from human groups with divergent subsistence patterns, including Greenlandic Inuit, Greenlandic Norse, classic and colonial Maya, and prehistoric Peruvians, to determine if isotopes from calculus exhibit differences in protein consumption and the varied use of C3 and C4 plants. If consistent results can be obtained, dental calculus might provide a much more accessible source of data and may also avoid resistance by Native American groups to this sort of analysis using destructive analyses techniques on human skeletal remains. The project will validate a method of isotopic analysis that is faster, non-destructive and less expensive than the current standard testing bone collagen, which would be a major contribution to the sub-field of paleo-diet studies.