Researchers from the Perot Museum of Nature and Science in the US discovered the first North American co-occurrence of hadrosaur and therizinosaur tracks in the Denali National Park in Alaska, US.
Hadrosaur was an unusual predatory dinosaur thought to have become a herbivore, while as therizinosaurs are best known from Asia.
"This discovery provides more evidence that Alaska was possibly the superhighway for dinosaurs between Asia and western North America 65-70 million years ago," said Anthony R Fiorillo from the Perot Museum of Nature and Science.
Fiorillo and a colleague published on a distinct single footprint in Denali National Park in 2012 that they determined to be made by a therizinosaur.
In 2013 and 2014, they conducted a more detailed analysis of the area, and unearthed dozens more tracks of therizinosaurs.
What surprised Fiorillo and his 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 Denali," said Fiorillo.
"From our research, we have determined that this track association of therizinosaurs and hadrosaurs is currently the only one of its kind in North America," he said.
The plant-eating therizinosaurs are rare and unusual creatures in the fossil record.
The strange-looking dinosaurs 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.
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.
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