Late Cretaceous fluvial hydrology and dinosaur behavior in southern Utah, USA: Insights from stable isotopes of biogenic carbonate

During the Late Cretaceous, North America was flooded by the epieric Western Interior Seaway. Mountain building events on the western landmass fed sediment to broad, low relief fluvial systems, which preserve rich dinosaur-bearing fossil assemblages. In this study, stable isotope ratios of associated vertebrate and invertebrate material from the Kaiparowits Formation of southern Utah are used to investigate the nature of these hydrological systems and behavior of dinosaurs over these landscapes. Differences in stable isotope ratios of gar ganoine, enamel from hadrosaurid teeth, and authigenic micrite, in conjunction with previously published bivalve data, indicate a tripartite fluvial system consisting of large rivers draining upland areas, smaller streams draining the foreland basin, and lakes subject to unusual patterns of recharge. Specifically, mixing of water from large rivers and lakes occurred during seasonal flooding events analogous to processes taking place in modernday Tonle Sap Lake in central Cambodia. Episodic flooding created heterogeneity among soils, with those proximal to permanent lake shores saturated for a longer period of time compared to more distal localities. Hadrosaurids consuming vegetation closer to lake shores have higher carbon isotope ratios in their tooth enamel than hadrosaurids consuming vegetation from more distal areas suggesting a difference in habitat use. Thus, variations in the paleohydrology of these fluvial systems appear to have played an important role in determining the distribution of dinosaurs over the Kaiparowits floodplain.