Environmental and Climatic Change Across the Paleocene-Eocene Boundary in the Continental Interior of North America

该项目调查了植被结构如何应对全球变暖5-10 C和古新世-始新世热最大期（PETM，约5580万年前）大气中二氧化碳的增加，以及这是否反过来影响了以这种植被为食的动物群。在PETM的冠层结构具有重要的意义，最早的几个现代哺乳动物分支的代表的扩散和随后的进化。三维植被结构是重要的原因有很多。它影响陆地表面的湿度、水文循环、地球表面附近的大气环流和碳储存。所有这些都在全球范围内影响气候和地球化学循环。植被也是陆地生物移动和获取食物的栖息地，它从根本上影响着它们的运动适应和饮食。该项目测试的假设，植被结构从开放到封闭的冠层森林在PETM。这对全球扩散和随后的辐射有重要的影响，这些最古老的灵长类动物（Euprimates），奇趾（奇趾有蹄类动物）和偶蹄（偶数趾有蹄类动物），最早出现在北美的PETM。最早的优灵长类动物是高度专业化的树栖动物，它们的扩散可能是由封闭的树冠的发展所促进的。生长在林下植被的封闭冠层森林有较低的13 C/12 C比生长在开放环境中的植被。吃林下植被的哺乳动物在它们的矿化组织（如牙齿）中记录了这种“树冠效应”。该项目通过分析哺乳动物牙釉质中的稳定碳同位素比率（13 C/12 C）来推断冠层结构。化石牙齿采样约16个物种的间隔之前，期间和之后的PETM。这些牙齿来自东南部的大角盆地（SBB），在那里，PETM在生物地层学和地球化学上受到碳同位素偏移的限制。这一地区包含了从古新世以来唯一已知的大型植物群，这有助于古环境和古气候的解释。该项目还对新热带区现存哺乳动物动物群的牙齿和骨骼进行采样，以更好地约束用于解释冠层结构和资源分配的同位素参数。林冠效应在旧大陆动物群中有很好的记录，特别是在非洲，但在新热带区动物群中没有得到很好的限制。然而，古新世晚期和古新世始新世晚期的动物群可能更类似于现代新热带区动物群，因为它们缺乏专性食叶动物，这可能会减少冠层效应并缩小动物群同位素变异的范围。因此，对新热带区系的研究应加强解释，更广泛的影响包括对本科生进行野外和实验室技术以及数据库创建、管理和网络界面方面的培训。项目成果将通过专业会议、出版物、FLMNH网站在线搜索数据库和公开讲座广泛传播。研究古新世时期的环境变化可能最终有助于预测全球变暖的长期后果，并越来越受到政策制定者和公众的关注。

This project investigates how vegetation structure responded to global warming of 5-10 C and increased atmospheric CO2 during the Paleocene-Eocene Thermal Maximum (PETM, approximately 55.8 million years ago), and whether this in turn affected the fauna feeding on this vegetation. Canopy structure in the PETM has important implications for the dispersal and subsequent evolution of the earliest representatives of several modern mammalian clades. Three dimensional vegetation structure is important for many reasons. It affects the albedo of land surfaces, hydrologic cycling, atmospheric circulation near the earth's surface, and carbon storage. All of these affect climate and biogeochemical cycles on a global scale. Vegetation also forms the habitat in which terrestrial organisms move and acquire food, and it fundamentally influences their locomotor adaptations and diet. This project tests the hypothesis that vegetation structure changed from open- to closed-canopy forests during the PETM. This has important implications for the global dispersal and ensuing radiations of the oldest known true primates (Euprimates), perissodactyls (odd-toed ungulates), and artiodactyls (even-toed ungulates), which first appeared in North America during the PETM. The earliest euprimates were highly specialized arborealists and their dispersal may have been facilitated by the development of a closed canopy. Vegetation growing in the understory of closed canopy forests has lower 13C/12C ratios than vegetation growing in open environments. Mammals that consume understory vegetation record this 'canopy-effect' in their mineralized tissues (like teeth). This project infers canopy structure by analyzing stable carbon isotope ratios (13C/12C) in mammalian tooth enamel. Fossil teeth are sampled for ~16 species from intervals before, during, and after the PETM. The teeth come from the southeastern Bighorn Basin (SBB) where the PETM is constrained biostratigraphically and geochemically by a carbon isotope excursion. This area contains the only macrofloras known from the PETM, which aids paleoenvironmental and paleoclimatic interpretations. The project also samples teeth and bone in extant mammalian faunas from the Neotropics to better constrain isotopic parameters that are used to interpret canopy structure and resource partitioning. The canopy effect is well documented in Old World faunas, especially from Africa, but is poorly constrained in Neotropical faunas. However, faunas in the late Paleocene and PETM may have been more analogous to modern Neotropical faunas, in that they lacked obligate folivores, which could diminish the canopy effect and narrow the range of faunal isotopic variability. Thus, study of Neotropical faunas should strengthen interpretations.Broader impacts include the training of undergraduate students in field and laboratory techniques, and in database creation, management, and web interface. Project results will be broadly disseminated through professional meetings, publications, the FLMNH website on-line searchable database, and public lectures. Study of environmental change during the PETM may ultimately be useful for predicting the long-term consequences of global warming and is of growing interest to policy makers and the public.