A new tracksite filled with hadrosaur footprints has been discovered in Denali National Park, Alaska, by a team of paleontologists led by Dr Yoshitsugu Kobayashi of Hokkaido University Museum, Japan.

“This tracksite occurs in the Upper Cretaceous Cantwell Formation in the Alaska Range and it is the largest tracksite known from this far north,” Dr Kobayashi and his co-authors wrote in a paper published in the journal Geology.

The discovery of the Denali tracksite shows that hadrosaurs – large, duck-billed, plant-eating dinosaurs – not only lived in multi-generational herds but thrived in the ancient high-latitude, polar ecosystem.

Preservation of the tracksite is exceptional – most tracks, regardless of size, contain skin impressions and co-occur with well-preserved plant fossils and traces of land and water insects.

“Denali is one of the best dinosaur footprint localities in the world,” said Dr Anthony Fiorillo from Perot Museum of Nature and Science in Texas, who is the first author of the paper. “What we found was incredible – so many tracks, so big and well preserved.”

Dr Fiorillo added: “many had skin impressions, so we could see what the bottom of their feet looked like. There were many invertebrate traces – imprints of bugs, worms, larvae and more – which were important because they showed an ecosystem existed during the warm parts of the years.”

Statistical analysis of the tracks also shows that individuals of four different age classes of hadrosaurids lived together in a large social group.

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Anthony R. Fiorillo et al. Herd structure in Late Cretaceous polar dinosaurs: A remarkable new dinosaur tracksite, Denali National Park, Alaska, USA. Geology, published online June 30, 2014; doi: 10.1130/G35740.1