Paleoclimate Reconstruction Based on the Stable Carbon Isotopic Composition of Bone Collagen from Small Herbivores Recovered in Archaeological Assemblages

在国家科学基金会的支持下，Raymond Mauldin，Debajyoti Paul和Robert Hard博士将进行合作研究，重点是利用从考古遗址的小型食草动物中提取的胶原蛋白中的稳定碳同位素模式，开发过去生态条件的短期本地措施。这个为期两年的项目汇集了稳定同位素地球化学实验室（LSG）的工作人员，德克萨斯大学圣安东尼奥（UTSA）地质系的研究生和本科生，考古研究中心（CAR）的研究人员，以及UTSA人类学系的研究生和本科生。考古学中的大多数古气候重建都是在大的时间尺度（数百年）和未知的、定义不清的或非常大的空间尺度上进行的。然而，人类觅食者并不是为了应对几个世纪以来发生的变化而启动适应性转变，而是为了应对通常在季节性或年度时间范围内运作的短期事件，并且覆盖公里而不是大陆。 虽然长期、大规模的气候变化肯定会影响哪些适应性战略最终取得成功，但正是在这些较小的时间和空间尺度上启动了适应性决策。这项研究与大多数其他考古古气候调查不同，因为它针对的是小型食草动物，如杰克兔和棉尾兔，它们可以提供适合探索人类适应的气候数据。这些食草动物消耗各种植物，这些植物使用两种不同的光合途径之一，称为C4或C3，从环境中提取二氧化碳。从食草动物骨骼中提取的胶原蛋白中的碳同位素比率的测量可以提供C4或C3植物在食草动物饮食中的相对贡献的估计。由于这两种不同的植物途径受到不同环境条件的青睐，C4植物在温暖，干旱的环境中更常见，C3植物在凉爽，潮湿的环境中更常见，C4或C3植物在杰克兔和棉尾骨胶原蛋白中的相对贡献可以提供数据来重建过去的植被和气候方面。 杰克兔和棉尾兔在发展过去气候的适当空间和时间措施方面有许多明显的优势。它们的寿命很短，很少超过3年。寿命范围大小通常小于1平方公里。 因此，这些小型食草动物的饮食反映了当地的短期植被模式。从杰克兔和棉尾兔的骨头中提取的胶原蛋白，从年代久远的考古学背景中收集，可以提供植被的记录，以及植被的变化，在短时间和小空间尺度上直接与理解人类适应有关。 虽然使用从德克萨斯州三个生态不同地区获得的考古样本，并专注于过去4,000年的狩猎-采集适应，但这项研究对人类适应的调查具有广泛的影响。小型食草动物存在于世界各地的考古和古生物遗址中，并且来自各种时间背景。 因此，UTSA的LSG（地质学），人类学和CAR之间的这项合作研究的结果将引起全国和全球更广泛的科学界的兴趣。

With National Science Foundation support, Drs. Raymond Mauldin, Debajyoti Paul, and Robert Hard will conduct collaborative research focused on developing short-term, local measures of past ecological conditions using patterns of stable carbon isotopes in collagen extracted from small herbivores from archaeological sites. The two year project brings together staff from the Laboratory for Stable Isotope Geochemistry (LSG), graduate and undergraduate students from the Department of Geology at the University of Texas at San Antonio (UTSA), researchers from the Center for Archaeological Research (CAR), and graduate and undergraduate students from the Department of Anthropology at UTSA. Most paleoclimate reconstructions in archaeology operate at large temporal scales (hundreds of years) and unknown, poorly defined, or extremely large spatial scales. Human foragers, however, do not initiate adaptive shifts in response to changes that occur over centuries, but in response to short term events that commonly operate at a seasonal or yearly timeframes, and that cover kilometers rather than continents. While long-term, large scale climate changes will certainly influence which adaptive strategies are ultimately successful, it is at these smaller temporal and spatial scales that adaptive decisions are initiated. This research differs from most other archaeological paleoclimate investigations in that it targets small herbivores, such as jack rabbits and cottontails, which can provide data on climate at scales appropriate for exploring human adaptations. These herbivores consume a variety of plants that use one of two different photosynthetic pathways, termed C4 or C3, to extract carbon dioxide from their environment. Measurements of carbon isotope ratios in collagen extracted from herbivore bones can provide an estimate of the relative contribution of C4 or C3 plants in herbivore diet. As these two different plant pathways are favored by different environmental conditions, with C4 plants more common in warm, arid settings, and C3 plants more common in cooler, moister settings, the relative contribution of C4 or C3 plants in jack rabbit and cottontail bone collagen can provide data to reconstruct aspects of past vegetation and climate. Jack rabbits and cottontails have a number of distinct advantages in the development of appropriate spatial and temporal measures of past climates. They have short life spans, seldom exceeding 3 years in length. Lifetime range sizes are commonly less than 1 square kilometer. As such, the diets of these small herbivores reflect local, short-term patterns of vegetation. Collagen extracted from jack rabbit and cottontail bones, collected from well-dated archaeological contexts, can provide a record of vegetation, and shifts in vegetation, at short temporal and small spatial scales directly relevant to understanding human adaptations. While using archaeological samples obtained from three ecologically distinct areas of Texas, and focused on hunter-gather adaptations that span the last 4,000 years, this research has broad implications for investigations of human adaptation. Small herbivores are present in archaeological and paleontological sites throughout much of the world, and from a variety of temporal contexts. Therefore, the findings of this collaborative research between the LSG (Geology), Anthropology, and CAR at UTSA will be of interest to the broader scientific community, both nationally and globally.