The effectiveness of oxygen isotopes in Spinosaurus tooth dentine for high-resolution palaeoenvironmental reconstructions

Abstract

Oxygen isotope compositions in tooth dentine of Spinosaurus aegyptiacus were investigated as a potential proxy for high-resolution reconstructions of palaeoenvironments in Cenomanian Cretaceous Morocco. The dentine was sampled sequentially along the tooth growth direction, and the successive δ¹⁸O values exhibited cycles which likely tracked the oxygen isotope compositions of ingested water and inferred changes in additional palaeoenvironmental properties. A conceptual model of catchment palaeohydrology was reconstructed to explain the mechanisms of isotopic variation. Seasonally variable water balance in the catchment or changes in water sources throughout the extensive deltaic environments are the most likely explanations for the seasonal profiles. With analysis of isotopic change in the conceptual model and comparison with data of modern tropical and subtropical deltas, we found similarities between palaeoclimates and modern data, and effectively identified the wet and dry seasons represented by troughs and peaks in the δ¹⁸O curves. These preliminary results demonstrated that palaeoenvironmental information at sub-seasonal resolution can be well preserved in theropod tooth dentine. The methodology developed in this study can be applied to the existing abundant reserves of theropod teeth to construct a Mesozoic palaeoclimatic database.