Jul 09, 2014 03:47 PM EDT By Russell Westerholm, UniversityHerald Reporter

Scientists have identified a trove of dinosaur footprints in Alaska's Denali National Park painting a picture of a herd of the ancient animals.

According to LiveScience.com, the team of researchers believes the discovery means the dinosaurs lived in polar latitudes around the calendar late in the Cretaceous period. About 70 million years ago, the team determined, a herd of duck-billed hadrosaurs left footprints with impressions of the skin and nails.

The team published their study in the journal Geology.

"Denali is one of the best dinosaur footprint localities in the world. What we found that last day was incredible - so many tracks, so big and well preserved," Anthony R. Fiorillo, curator of earth sciences at the Perot Museum of Nature and Science, said in a press release. "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."

Among the dinosaur tracks, the team identified evidence of birds, clams, worms and other bugs, depicting a healthy ecosystem in the late-Cretaceous period. The hadrosaur footprints were so compressed, the scientists could not separate them for individual examination. Instead, they counted them up and separated them based on size.

"Even back then the high latitudes were biologically productive and could support big herds of pretty big animals," Fiorillo told LiveScience.com. "This is definitely one of the great track sites of the world. We were so happy to find it."

Based on the size of the footprints, the researchers say 80 percent of the herd were adult hadrosaurs and the rest were either juveniles or less than a year old. The lack of younger hadrosaurs led the team to conclude that the dinosaurs grew up quickly.

"If you take a great big herd of plains eaters, they have to move at some level, otherwise they strip out all the vegetation," Fiorillo said. "But there's a growing data set that suggests they didn't do the thousand and thousands of miles of migration that was originally considered."

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