Diet preferences and climate inferred from oxygen and carbon isotopes of tooth enamel of Tarbosaurus bataar (Nemegt Formation, Upper Cretaceous, Mongolia)

Abstract Stable isotopes of oxygen and carbon of tooth enamel are increasingly being used as tracers to study palaeoecology and the diet preferences of fossil vertebrates. We serially sampled tooth enamel carbonate along the growth axes of five Early Maastrichtian carnivorous dinosaur teeth ( Tarbosaurus bataar tyrannosaurid) from the Nemegt Formation, Mongolia, in order to identify seasonal climatic variations and determine the diet of this apex predator. Additional bulk samples of dentine, bone, and surrounding sediment were analyzed in order to exclude diagenetic obfuscation of the isotopic record. Enamel samples of potential prey species for dietary studies were also analyzed. In the case of the largest specimens, the sampled teeth usually recorded annual cycles ranging between two-thirds and a full year. Fluctuations in δ 18 O values in tyrannosaurid teeth suggest seasonality (high annual temperatures with distinct precipitation/humidity maxima during summer months) with mean annual temperatures (MAT) ten degrees higher than those of present-day Mongolia. The seasonal pattern of δ 18 O shows similarities to that of the modern-day Shijiazhuang Global Network of Isotopes in Precipitation station, northern China, and suggests that the Nemegt biota flourished when exposed to a cool temperate monsoon-influenced climate. Herbivore and carnivore carbon isotopes ( δ 13 C) values from tooth enamel imply the presence of a woodland ecosystem dominated by coniferous trees such as Araucariaceae, and are consistent with the hypothesis that large sauropods and hadrosaurids were the preferred prey of Tarbosaurus . Mean annual precipitation (MAP), based on the relationship between modern-day C3 gymnosperms and local average MAP, is estimated at 775–835 mm/yr. These results show that large theropod teeth can serve as valuable archives for palaeoenvironmental studies.