Herd structure in Late Cretaceous polar dinosaurs: A remarkable new dinosaur tracksite, Denali National Park, Alaska, USA

The discovery of a new tracksite of mostly hadrosaurid dinosaur footprints, made by a herd living in an ancient high-latitude continental ecosystem, provides insight into the herd structure and behavior of northern polar dinosaurs and perspective on populations of large-bodied herbivores in an Arctic greenhouse world. This tracksite occurs in the Upper Cretaceous Cantwell Formation in the Alaska Range (Denali National Park, Alaska, United States), and it is the largest tracksite known from this far north. Preservation of the tracksite is exceptional: most tracks, regardless of size, contain skin impressions and they co-occur with well-preserved plant fossils and invertebrate trace fossils of terrestrial and aquatic insects. Statistical analyses of the tracks show that individuals of four different age classes of hadrosaurids lived together in a large social group. Our research results independently corroborate the growth curve for hadrosaurids proposed by paleohistologists that suggests that these dinosaurs experienced a period of rapid growth early in their life history.