Preservation of primary stable isotope signals in dinosaur remains, and environmental gradients of the Late Cretaceous of Montana and Alberta

Although the use of stable isotope data from vertebrate remains is becoming common for the Cenozoic, their application to Mesozoic environments has been rare, in part due to the perception that diagenesis has obfuscated all potential primary signal. In this paper, we illustrate how stable isotope data collected from dinosaur and other vertebrate remains can in fact be used to reconstruct paleoenvironmental conditions during the Mesozoic.Carbon and oxygen isotope ratios were measured from tooth enamel of hadrosaur dinosaurs and from scales of freshwater fish that were collected from sites in the Two Medicine, Judith River, and Dinosaur Park Formations of Montana and Alberta. These formations represent a coastal to upland gradient along the western margin of the Late Cretaceous inland seaway. Isotopic comparisons among skeletal components and among taxa are used as evidence that primary paleoenvironmental information, as recorded by isotope data, is preserved in tooth enamel and freshwater fish scales. A comparison of carbon isotope ratios between hadrosaur tooth enamel and sedimentary organic matter indicates that these animals had a larger isotopic offset compared to bulk diet than modern mammals, and that all hadrosaurian isotope data are consistent with the existence of C3-only ecosystems.Higher and more variable carbon and oxygen isotope ratios from animals occupying the coastal Judith River region are interpreted to reflect a range of freshwater to brackish water conditions and plants that were undergoing water stress. Lower and less variable carbon and oxygen isotope ratios from the upland Two Medicine and intermediate Dinosaur Park areas are interpreted to reflect a gradual rainout of moisture from air masses moving inland and more uniform environmental conditions. Overall, these results indicate that stable isotopes from dinosaur and other vertebrate remains have the potential to expand our understanding of terrestrial environments and ecosystems during the Mesozoic.