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

这个项目调查了在古新世-始新世最热时期(PETM，大约5580万年前)，植被结构对全球变暖5-10摄氏度和大气二氧化碳增加的响应，以及这是否反过来影响了以这种植被为食的动物。PETM中的冠层结构对于几个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的意义。三维植被结构之所以重要，原因有很多。它影响地表的反照率、水文循环、地球表面附近的大气循环和碳储存。所有这些都影响着全球范围内的气候和生物地球化学循环。植被也是陆地生物移动和获取食物的栖息地，它从根本上影响它们的运动适应和饮食。这个项目验证了这样的假设，即植被结构在PETM期间从开阔的林冠转变为封闭的林冠。这对已知的最古老的真正灵长类(真灵长类)、周趾类(奇趾有蹄类)和偶蹄类(双趾有蹄类)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期间的北美。最早的真灵长类是高度专业化的树上现实主义者，它们的扩散可能是由于封闭树冠的发展而促进的。郁闭林林下植被的13C/12C比值低于开阔环境中的植被。以林下植被为食的哺乳动物在它们矿化的组织(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稳定的碳同位素比率(13C/12C)来推断牙冠结构。化石牙齿从PETM之前、期间和之后的间隔中采集了约16个物种的样本。这些牙齿来自大角盆地东南部(SBB)，那里的PETM在生物地层和地球化学上受到碳同位素漂移的限制。这一地区拥有唯一已知的PETM大型植物群，这有助于古环境和古气候的解释。该项目还从新热带地区现有的哺乳动物动物群中采集牙齿和骨骼样本，以更好地限制用于解释树冠结构和资源分配的同位素参数。树冠效应在东半球动物群中得到了很好的记录，特别是在非洲，但在新热带动物群中受到的限制很少。然而，晚古新世和PETM的动物群可能更类似于现代新热带动物群，因为它们缺乏专有的叶，这可能会减弱树冠效应，缩小动物群同位素变异性的范围。因此，新热带动物群的研究应该加强解释。更广泛的影响包括对本科生进行野外和实验室技术方面的培训，以及在数据库创建、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、妇幼保健部网站在线可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最终可能有助于预测全球变暖的长期后果，并日益引起政策制定者和公众的兴趣。

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.