A STUDY OF JURASSIC CAMARASAUR MIGRATION USING STABLE AND RADIOGENIC ISOTOPES

Sauropods were the largest animals to have ever walked on land, making them subjects of scientific study since they were first discovered. One of the most interesting aspects of sauropod paleontology is the paleoenvironmental context in which many sauropod remains are found, particularly in North America. These remains are common in the Jurassic Morrison formation, which is comprised of fossils and sediments that suggest terrestrial ecosystems resembling modern savannas, in that the vegetation was openly spaced in a semi-arid, hot, and seasonal climate setting, with tall trees common near rivers and floodplains. This association raises the question of how very large sauropods – which presumably required a great deal of forage – were able to sustain themselves over long periods of time. One possibility is that sauropods undertook long seasonal or longer time-period migrations that provided constant access to new food resources.

The goal of this study is to identify and characterize any such patterns of movement over the Morrison formation landscape by collecting carbon, oxygen, and strontium isotope data from sauropod tooth enamel and dentine, and from soil and lake carbonates. In particular we focused on one kind of sauropod – the camarasaur – whose fossil remains were obtained from a roughly north-south transect of three sites in Wyoming, Utah and Colorado. A geochemical comparison of tooth enamel data reveals significant geochemical differences among all three sites. In addition, significant oxygen isotope differences also exist between tooth enamel from Wyoming and Utah and authigenic carbonates from the same sites. The isotopic differences among populations of camarasaurs indicate that each was relying on a different source of drinking water and food. Therefore, it can be concluded that these populations were relatively isolated from each other. Although these populations were isolated from each other, some of them appear to have moved significant distances over time. In particular, the oxygen isotope differences between tooth enamel and authigenic carbonates suggests that Wyoming and Utah camarasaurs migrated from lowland to upland areas over the course of a year. In contrast, Colorado camarasaurs appear to have had a different pattern of movement, which kept them centered in lowland regions all year long.