Cretaceous Alaska Was ‘Superhighway’ for Migrating Dinosaurs, Paleontologists Say

Paleontologists have discovered the first North American co-occurrence of hadrosaur and therizinosaur tracks, providing more evidence that Alaska was the ‘superhighway’ for dinosaurs between Asia and western North America 65-70 million years ago (Late Cretaceous epoch).

Life reconstruction of hadrosaur-therizinosaur co-occurrence based on tracks described in this study. Image credit: Karen Carr.

In 2012-2014, Dr. Anthony Fiorillo from the Perot Museum of Nature and Science and colleagues discovered distinct footprints in Denali National Park, central Alaska Range, that they determined to be made by therizinosaurs, unusual predatory dinosaurs thought to have become herbivores.

What surprised the team most was the co-occurrence of dozens of hadrosaurs, also known as duck-bill dinosaurs.

“Hadrosaurs are very common and found all over Denali National Park. Previously, they had not been found alongside therizinosaurs in the park,” Dr. Fiorillo said.

“In Mongolia, where therizinosaurs are best known — though no footprints have been found in association — skeletons of hadrosaurs and therizinosaurs have been found to co-occur from a single rock unit so this was a highly unusual find in Alaska, and it prompted my interest.”

“From our research, we’ve determined that this track association of therizinosaurs and hadrosaurs is currently the only one of its kind in North America.”

The first North American co-occurrence of hadrosaur and therizinosaur tracks: (a) photo of large block in study area that demonstrates the co-occurrence of both hadrosaurid (in blue) and therizinosaurid (in yellow) tracks on the same bedding plane; (b) line drawing of tracks on the slab in (a), with hadrosaurid tracks in blue, therizinosaurid tracks in yellow; note the different sizes of hadrosaur tracks indicating multiple generations of this type of dinosaur. Image credit: Fiorillo et al, doi: 10.1038/s41598-018-30110-8.

The plant-eating therizinosaurs, which are rare and unusual creatures in the fossil record, had long skinny necks, little teeth, a small beak for cropping plants, and big torsos accompanied by large hind feet and long arms.

Though therizinosaurs are known from Asia and North America, the best and most diverse fossil record is from Asia – even up to the time of extinction – and therein is the connection.

Dr. Fiorillo has long postulated that Cretaceous Alaska could have been the thoroughfare for fauna between Western North America and Asia — two continents that shared each other’s fauna and flora in the latest stages of the Cretaceous.

“This study helps support the idea that Alaska was the gateway for dinosaurs as they migrated between Asia and North America,” said co-author Dr. Yoshitsugu Kobayashi, of Hokkaido University Museum in Japan.

To support the theory, the researchers worked to establish if the tracks were those of a therizinosaur and to study any unique aspects of the ecosystem.

They determined that this particular area of Denali was a wet, marsh-like environment and that one fossil in particular looked like a water lily, which supported the theory that there were ponds and standing water nearby. They suspect that both therizinosaurs and hadrosaurs liked these wetter locations.

“This Alaskan discovery may connect these animals environmentally and perhaps behaviorally to other therizinosaurs in central Asia,” Dr. Fiorillo said.

The research appears in the journal Scientific Reports.

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Anthony R. Fiorillo et al. An unusual association of hadrosaur and therizinosaur tracks within Late Cretaceous rocks of Denali National Park, Alaska. Scientific Reports 8, article number: 11706; doi: 10.1038/s41598-018-30110-8