MOSASAUR LIFESTYLES: FLUCTUATIONS OF STABLE OXYGEN ISOTOPES IN TOOTH ENAMEL AS A PROXY FOR MIGRATORY BEHAVIOR

Stable oxygen isotope analyses in teeth of Platecarpus mosasaur specimens from the Late Cretaceous Niobrara Chalk of Kansas yield potential information on mosasaur behavior. Our technique analyzes phosphate oxygen from enamel of the tooth crown to elucidate isotopic fluctuations preserved during tooth ontogeny. Based on daily growth lines in the teeth, the estimate for duration of tooth growth is about 1 to 2 months. Analysis of teeth from individual Platecarpus jaws allows for splicing multiple isotopic records generated by the analysis of each tooth to produce a long-term isotopic record for each mosasaur specimen. There are two noteworthy features present in the spliced isotopic record. The first is a long-term trend enrichment of about 2 ‰ in 18O that may represent an organized change in location of the mosasaur to more open marine environments and reduced fresh-water influence. Superimposed on the long-term trend are 18O negative spikes of ~ 1 to 2 ‰ that are repeated nearly every week. These weekly spikes are consistent with changes in water temperature and depth, and are most likely due to the foraging behavior of the mosasaur.