LASER-ABLATION MC-ICP-MS ANALYSIS OF ALASKAN EDMONTOSAURUS (LATE CRETACEOUS, PRINCE CREEK FORMATION) TO TEST ARCTIC DINOSAUR MIGRATION HYPOTHESES

During the Late Cretaceous, the Arctic had a rich dinosaurian fauna, in spite of a sub-freezing winter temperatures. This Late Cretaceous Arctic dinosaurian fauna includes not only theropods (including cf. Troodon), but also multiple juvenile individuals of the hadrosaurid Edmontosaurus sp. Discovery of dinosaurs from a high paleolatitude (~82° N) has been of interest for many researchers, because this suggests their metabolic rate was high enough to withstand the coldness. However, one counter hypothesis is that they migrated to the south during winter challenges, including low temperatures and darkness. To test this migration hypothesis, we analyzed and compared the strontium isotope ratio (⁸⁷Sr/⁸⁶Sr) of Edmontosaurus and cf. Troodon teeth. ⁸⁷Sr/⁸⁶Sr in animal’s body reflects that of the local sediment, and we assumed that Troodon were non-migratory, and therefore used cf. Troodon teeth as a proxy of the ⁸⁷Sr/⁸⁶Sr signal of the Late Cretaceous sediment. We analyzed seven Edmontosaurus teeth, five of which were extracted from two maxillae, and three isolated Trodon teeth. Since their enamel is very thin (~30 - 90 µm), we adapted laser-ablation MC-ICP-MS. To assess the alteration of the isotope signal due to diagenesis, we also compared the strontium signals between the dentine plus bone. We found the enamel preserves statistically significantly different ⁸⁷Sr/⁸⁶Sr value from those of dentine and bone, suggesting the enamel retains its original strontium signal. However, we did not find difference in the mean ⁸⁷Sr/⁸⁶Sr values between the Edmontosaurus and cf. Troodon teeth. The older teeth of the Edmontosaurus also have the same means as the younger teeth. Therefore, the Liscomb Bonebed Edmontosaurus were likely not migratory.