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

Macalester College, Saint Paul MN

Investigators

Abstract

EAR-0319041 ABSTRACT Summary 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 Merit Paleoenvironmental 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 Impacts An 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.