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

该项目研究了古新世-始新世极热期（PETM，约5580万年前）全球变暖5-10℃和大气二氧化碳增加对植被结构的响应，以及这是否反过来影响了以这些植被为食的动物群。PETM的冠层结构对几种现代哺乳动物分支的早期代表的扩散和随后的进化具有重要意义。三维植被结构的重要性是多方面的。它影响地表反照率、水文循环、近地表大气环流和碳储量。所有这些都在全球范围内影响着气候和生物地球化学循环。植被也构成了陆生生物活动和获取食物的栖息地，并从根本上影响了它们的运动适应和饮食。本项目验证了始新世新元时期植被结构由开放冠层森林向封闭冠层森林转变的假说。这对于已知最古老的真灵长类动物（真灵长类动物）、异趾目动物（奇趾有蹄类）和偶蹄目动物（偶趾有蹄类）的全球扩散和随后的辐射具有重要意义，这些动物最早出现在PETM时期的北美。最早的灵长类动物是高度专业化的树栖动物，封闭树冠的发展可能促进了它们的扩散。封闭林下植被的13C/12C比值低于开放林下植被。消耗下层植被的哺乳动物在其矿化组织（如牙齿）中记录了这种“冠层效应”。本项目通过分析哺乳动物牙釉质的稳定碳同位素比值（13C/12C）来推断冠层结构。从始新世纪之前、期间和之后的时间间隔中取样了大约16个物种的化石牙齿。这些齿来自Bighorn盆地东南部（SBB），该盆地的PETM受到碳同位素漂移的生物地层和地球化学限制。这一地区包含了唯一已知的始新世（PETM）时期的大型植物群，这有助于解释古环境和古气候。该项目还对来自新热带地区的现存哺乳动物的牙齿和骨骼进行了采样，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。冠层效应在旧大陆的动物群，特别是非洲的动物群中有很好的记录，但在新热带动物群中却很少受到限制。然而，古新世晚期和始新世晚期的动物群可能更类似于现代新热带动物群，因为它们缺乏专性叶食动物，这可能会减弱冠层效应，缩小动物群同位素变化的范围。因此，对新热带动物的研究应加强解释。更广泛的影响包括培训本科生野外和实验室技术，以及数据库创建、管理和网络界面。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。对PETM期间环境变化的研究可能最终有助于预测全球变暖的长期后果，并引起决策者和公众越来越大的兴趣。

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.