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

这个项目的总体目标是利用北美晚白垩世脊椎动物化石的碳和氧同位素比值来研究陆地生态、水文学和气候。已获得恐龙牙釉质的初步同位素数据，碳同位素比率因地而异，在恐龙类群之间也不同。根据对现代陆地脊椎动物的了解，可以假设这些差异可以用来研究环境变化、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在空间上也不同，再次使用现代类似物，假设这些变化反映了不同地区之间的水文和气候差异。为了验证这些假设，将从四个环境和地理不同的地点收集额外的晚白垩世恐龙牙齿：(1)沿海的朱迪斯河地层及其同期的高地相当于(2)蒙大拿州的两个梅迪奇地层，(3)阿拉斯加的普林斯克里克地层，和(4)犹他州的凯帕罗维茨地层。由于在缺乏背景信息(例如准确的相关联)的情况下，对同位素数据的环境解释可能有些模棱两可，因此还将对采样地点进行详细的地层和沉积学分析，这是这项研究的组成部分。通过将新的同位素和沉积学数据与现有的古生物和古植物学信息进行比较，将有可能在一系列空间尺度上确定同位素比率和环境参数之间的关系。智力价值基于沉积学良好约束的恐龙化石进行的古环境研究是使用来自较年轻的新生代沉积物的哺乳动物牙釉质进行的逻辑扩展。由于恐龙摄入的氧气和碳的一般来源与哺乳动物相同，因此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，现在应该可以利用脊椎动物遗迹的稳定同位素比率来研究中生代的陆地环境。为中生代收集的稳定同位素数据也有可能补充更多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。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进化并丰富。此外，同位素数据可以用来测试并改进这段时间内生物群分布和全球气候的模型模拟。这项拟议的研究具有广泛的学术意义，我们相信，该项目提供了一个极好的机会，可以对晚白垩世生态系统有新的见解。广泛的影响对于许多对地球科学感兴趣的学生来说，研究恐龙的机会是一个令人兴奋的前景，这项拟议的研究将由科罗拉多学院和马卡莱斯特学院的学生进行，作为他们本科地质学教育的一部分。因此，它将成为学习现场和实验室技术以及解释数据的极好工具。此外，学生将通过撰写一篇高级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能。更广泛地说，这里描述的研究将作为一个框架，在不同的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在同行评议期刊上发表的报告传播给其他科学家。此外，我们计划向博物馆提供我们工作的总体总结，以便将其纳入关于恐龙和晚白垩世环境的展览。

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.