Collaborative/RUI Research: Stable Isotope Reconstruction of North American Terrestrial Environments during the Late Cretaceous

摘要本项目的总体目标是利用北美晚白垩纪脊椎动物化石遗骸的碳氧同位素比值来研究陆地生态、水文和气候。初步获得了恐龙牙釉质的同位素数据，碳同位素比值在不同地区和不同恐龙类群之间存在差异。根据对现代陆生脊椎动物的了解，假设这些差异可以用于研究环境变化、C4植物的进化和恐龙的生态位划分。牙釉质中的氧同位素比率也存在空间差异，并且再次使用现代类似物，假设这些变化反映了各地之间的水文和气候差异。为了验证这些假设，额外的晚白垩纪恐龙牙齿将从四个环境和地理上不同的地方收集：(1)沿海朱迪思河地层及其同时代的高地地层；(2)蒙大拿州的两医药地层；(3)阿拉斯加的王子溪地层；(4)犹他州的凯帕洛韦茨地层。由于同位素数据的环境解释在缺乏背景信息（例如，准确的相关联）的情况下可能有些含糊不清，因此还将对取样地点进行详细的地层和沉积学分析，这是本研究的组成部分。通过将新的同位素和沉积学数据与现有的古生物学和古植物学信息进行比较，将有可能确定同位素比率与空间尺度上环境参数之间的关系。基于沉积学上约束良好的恐龙化石进行的古环境研究，是对来自较年轻的新生代沉积物的哺乳动物牙釉质进行的研究的合理延伸。因为恐龙和哺乳动物一样，有同样的氧和碳的一般来源，所以可以假设它们的碳和氧同位素比率也与环境参数有关。因此，中生代的陆地环境现在应该可以利用脊椎动物遗骸的稳定同位素比率进行研究。中生代稳定同位素数据的收集也有可能补充更传统的古生物学和古植物学研究。例如，我们的初步发现表明，不同草食性恐龙类群的碳同位素比率不同，这表明资源分配不同。同样，高碳同位素比率表明，具有C4光合作用途径的植物可能在中生代已经进化并丰富。此外，同位素数据可用于测试，从而改进这一时期生物群落分布和全球气候的模式模拟。拟议研究的知识分支是广泛的，我们相信该项目提供了一个很好的机会，以获得对晚白垩纪生态系统的新见解。更广泛的影响对许多对地球科学感兴趣的学生来说，有机会研究恐龙是一个令人兴奋的前景，这项拟议中的研究将由科罗拉多学院和马卡莱斯特学院的学生进行，作为他们地质学本科教育的一部分。因此，它将成为学习现场和实验室技术以及解释数据的绝佳工具。此外，学生将通过撰写毕业论文并在地区和国家会议上展示他们的成果来磨练他们的沟通技巧。在更一般的方式下，这里描述的研究将作为一个框架，在各种课程中介绍和讨论沉积学、同位素地球化学和古生物学的概念。这项研究的结果将通过发表在同行评议期刊上的报告传播给其他科学家。此外，我们计划将我们的工作总结提供给博物馆，以便将其纳入恐龙和晚白垩纪环境的展览中。

EAR-0319041ABSTRACTSummary The overall goal of this project is to use carbon and oxygen isotope ratios of vertebrate fossil remains from the Late Cretaceous of North America to study terrestrial ecology, hydrology, and climate. Preliminary isotope data from dinosaur tooth enamel has been obtained, and carbon isotope ratios vary from locality to locality and among dinosaur taxa. Based on what is known about modern terrestrial vertebrates, it is hypothesized that these differences can be used to investigate environmental change, evolution of C4 plants, and ecological niche partitioning by dinosaurs. Oxygen isotope ratios in tooth enamel also vary spatially, and using modern analogs again it is hypothesized that these variations reflects hydrological and climatological differences among localities.In order to test these hypotheses, additional Late Cretaceous dinosaur teeth will be collected from four environmentally and geographically diverse localities: (1) the coastal Judith River Formation and its contemporaneous, upland equivalent (2) the Two Medicine Formation of Montana, (3) the Prince Creek Formation of Alaska, and (4) the Kaiparowits Formation of Utah. Because environmental interpretations of isotopic data can be somewhat ambiguous in the absence of contextual information (e.g., accurate facies associations), detailed stratigraphic and sedimentological analyses of sampled localities will also be conducted, and is integral to this research. By comparing new isotopic and sedimentological data with existing paleontological and paleobotanical information, it will be possible to determine the relationships among isotope ratios and environmental parameters over a range of spatial scales.Intellectual MeritPaleoenvironmental research based on sedimentologically well-constrained dinosaur fossils is a logical extension of that being conducted using mammalian tooth enamel from younger, Cenozoic deposits. Because dinosaurs would have had the same general sources of ingested oxygen and carbon as mammals, it can be assumed that their carbon and oxygen isotope ratios would also be related to environmental parameters. As a result, terrestrial environments during the Mesozoic should now become available for study using stable isotope ratios of vertebrate remains.Stable isotope data collected for the Mesozoic also has potential to complement more traditional paleontological and paleobotanical research. For example, our preliminary findings indicate that carbon isotope ratios differ among herbivorous dinosaur taxa, which is suggestive of resource partitioning. Similarly, high carbon isotope ratios suggest that plants with C4 photosynthetic pathways may have evolved and been abundant during the Mesozoic. In addition, isotope data can be used to test and thus improve model simulations of biome distributions and global climate during this time period. The intellectual ramifications of the proposed research are extensive, and we believe that the project provides a wonderful opportunity to gain novel insights into Late Cretaceous ecosystems.Broader ImpactsAn opportunity to study dinosaurs is an exciting prospect to many students interested in the earth sciences, and this proposed research will be conducted by students at Colorado College and Macalester College as part of their undergraduate education in geology. As such it will serve as an excellent vehicle for learning field and laboratory techniques and interpreting data. In addition, students will hone their communication skills by writing a senior thesis and presenting their results at regional and national meetings. In a more general manner, research described here will serve as a framework for introducing and discussing concepts of sedimentology, isotope geochemistry, and paleontology in a variety of courses.Results of this research will be disseminated to other scientists via published reports in peer-reviewed journals. In addition we plan to make a general summary of our work available to museums so it can be incorporated into exhibits on dinosaurs and Late Cretaceous environments.