New data on high-latitude hadrosaurid dinosaurs from the Upper Cretaceous Kakanaut Formation of Chukotka, Russia

Abstract

Fossils from high-latitude Mesozoic vertebrate localities provide a unique opportunity to reveal specific biological features and reconstruct adaptations to months of twilight and relatively low annual temperatures of polar dinosaurs. Here we provide morphological description of new hadrosaurid specimens (vertebrae, femora) and results of the histological analysis of hadrosaurid femora, proximal fragments of a humerus and a scapula from the Upper Cretaceous high-latitude (palaeolatitude estimate of 75°N) Kakanaut locality (Chukotka, Russia). The two studied hadrosaurid femora are different in size and form, but both are histologically mature and belong to fully grown adult individuals. This difference may indicate the presence of two different hadrosaurid taxa in the Kakanaut fauna. The bone histology of the Kakanaut dinosaurs does not differ from that of dinosaurs from lower latitudes and does not show specific histological features (namely, cyclic change of vascularization of the fibrolamellar bone, with sharply defined borders between cycles) found in polar Edmontosaurus from Alaska. This suggests that the Kakanaut hadrosaurid dinosaurs were not significantly stressed, and this may be the result of the local mild and weakly seasonal climate reconstructed from palaeobotanical data. We suggest that Arctic dinosaurs of Chukotka, like other polar dinosaurs, were year-round residents of paleopolar ecosystems.