RECONSTRUCTING DINOSAUR ECOLOGY AND NICHE UTILIZATION IN THE JURASSIC USING C, O, AND CA STABLE ISOTOPES IN TEETH

Stable isotopes of carbon, oxygen, and calcium can preserve information about diet and ecosystem structure in the fossil record that might not be discernable from body fossils alone. Studying these isotopes has allowed for a greater understanding of many ecosystems, and here we apply it to an Late Jurassic North American ecosystem. Sauropod dinosaurs are the largest known terrestrial herbivores, and here we studied isotopes from the teeth of two sauropods, Camarasaurus lentus and Diplodocus longus, and one theropod, Allosaurus fragilis, to determine niche partitioning between herbivores and if these herbivores were being eaten by this significantly smaller carnivore.

The Morrison Formation preserves abundant large-bodied herbivores, including multiple types of sauropods. The large size of these animals suggests that food would be scarce in an environment with this many herbivores, and niche partitioning would be necessary to have so many large species in a single locality. Their large size also suggests that predators would not actively hunt large prey, but would preferentially seek out young, old, or injured individuals. We hypothesize that C. lentus and D. longus occupied different niches and will preserve isotope ratios indicative of feeding on upper and lower canopy, respectively. We also hypothesize that A. fragilis will preserve Calcium isotope ratios consistent with modern predator-prey isotope fractionation.

Here we examine δ¹⁸O, δ¹³C, and δ⁴⁴Ca of carbonate preserved in the enamel of C. lentus, D. longus, and A. fragilis. Higher C and Ca isotope ratios indicate higher browsing in the canopy, and modern predators preserve lower δ⁴⁴Ca values than their prey. Using this information, we will hypothesize the diet of these Late Jurassic dinosaurs. First, the level of diagenesis of the specimens must be determined, so we will examine the δ¹⁸O and δ¹³C values of the fossils to see if homogenization has occurred indicating diagenesis. If not, we will continue to analyze isotope values in each of our specimens, potentially targeting annual variation.