PRELIMINARY INVESTIGATION OF SEASONAL PATTERNS RECORDED IN THE OXYGEN ISOTOPE COMPOSITIONS OF THEROPOD DINOSAUR TOOTH ENAMEL

Oxygen isotope compositions of tooth enamel increments in theropod dinosaurs are investigated as potential climate seasonality. Six teeth of large carnivorous theropods collected from four Cretaceous formations deposited under contrasted climates have been sampled. These teeth have been analyzed for the oxygen isotope compositions of their apatite phosphate (delta O-18(p)) through incremental sampling performed along the major growth axis. Significant fluctuations in oxygen isotope compositions along the growth axis of each tooth are observed and interpreted as reflecting seasonality in ingested local surface water delta O-18(w) values. Fluctuations in delta O-18(p) values of theropod teeth from the Aptian of Thailand and Cenomanian of Morocco vary similarly to meteoric water d delta O-18(mw) values occurring today in sub-tropical regions subjected to large seasonal amounts of precipitations. A dinosaur tooth recovered from the more inland and mid-latitude Nemegt Formation of Mongolia shows a seasonal pattern similar to present-day cold temperate and continental climate. Finally, the high latitude and coastal Kakanaut Formation (Russia) experienced strongly dampened seasonal variations, most likely due to the influence of warm Pacific oceanic currents. Such conditions occur today in high latitude regions submitted to marine influence. These results further highlight the potential of using the oxygen isotope compositions of large theropod teeth to reconstruct past seasonal variations of terrestrial climates. Increased knowledge of past seasonality may help to better understand the complex interactions between climate and the dynamics of land biodiversity in terms of ecological adaptations, biogeography and the evolutionary history of organisms.