USING OXYGEN, CARBON AND STRONTIUM ISOTOPE RATIOS OF TOOTH ENAMEL FROM DINOSAURS TO INFER PATTERNS OF MOVEMENT OVER THE LATE JURASSIC LANDSCAPE OF CO, UT AND WY

Patterns of movement are a critical component of animal behavior that are in turn related to their biology, diet and ecology, but are hard to infer for extinct organisms such as dinosaurs. Fortunately, stable isotope ratios of vertebrate fossils, in particular tooth enamel, can be used to infer patterns of movement for such organisms. This is possible because oxygen, carbon and strontium isotope ratios of bioapatite that makes up enamel are influenced by the ratios of ingested food and water. In turn, these ratios vary significantly over terrestrial landscapes. For example, oxygen isotope ratios of surface waters decrease as elevation increases, strontium isotope ratios of surface waters flowing over older rocks are higher than those flowing over younger rocks, and carbon isotope ratios of water-stressed plants are higher than those that are not.

To date, this type of isotopic approach has been used to study movement of two populations of sauropod dinosaurs that lived on the late Jurassic landscape of North America. Oxygen isotope data indicate that Camarasaurus dinosaurs from Utah and Wyoming migrated hundreds of kilometers each year from the Morrison basin to western highlands. The goal of this study is to expand this research by (1) collecting strontium and carbon isotope data from these same Camarasaurus teeth, (2) collecting oxygen, strontium and carbon isotope data from co-existing Diplodocus and Allosaurus teeth, and (3) by expanding this multi-isotope, multi-taxa approach to include samples from two new sites in Colorado.

Preliminary results suggest that the carnivorous Allosaurus from Utah, Wyoming and eastern Colorado followed the west-east, upland-lowland migrations of Camarasaurus, possibly because Camarasaurus was their main food source. In contrast to these localities, there is little evidence that either Camarasaurus or Diplodocus from western Colorado undertook seasonal migrations. This behavior may be explained by the existence of a large lake system in the region that would have made migration unnecessary. Allosaurus from western Colorado appear to have spent time in uplands away from the lake system, but these uplands were the nearby erosional remnants of the Ancestral Rocky Mountains rather than active arc-related mountains to the west.