INTER-TOOTH VARIABILITY IN CA STABLE ISOTOPES COMPLICATES DINOSAUR PALEOECOLOGICAL RECONSTRUCTIONS

Accurately reconstructing animal ecology is incredibly important for understanding evolution. One method for evaluating vertebrate paleoecology is to use stable isotopes in fossil teeth or bone as indicators of diet and ecology. More specifically, stable isotopes of calcium isotopes (δ⁴⁴Ca) have been used to trace diet and niche partitioning in multiple clades of mammals and dinosaurs. When attempting to replicate the results of previous studies, however, we have found that δ⁴⁴Ca varies through the tooth growth axis in multiple clades of archosaurs. Through analysis of both Jurassic dinosaur teeth and modern crocodile teeth, we discovered that the δ⁴⁴Ca ratios of the teeth vary from the crown apex to the crown base of the enamel. This finding has serious implications for the use of δ⁴⁴Ca as a proxy for paleoecology and must be fully understood before this proxy can be used to its full extent. Here we present our findings of δ⁴⁴Ca variability in archosaur teeth, and suggest potential solutions through a protocol for subsampling tooth δ⁴⁴Ca in order to accurately reconstruct information about the diet and environment of modern and fossil archosaurs.