A dinosaur track site discovered in Alaska's Denali National Park leads scientists to believe that many animals lived in the polar region millions of years ago. The thousands of tracks found are mostly from herds of duck-billed animals called hadrosaurs, among other species.

"We had mom, dad, big brother, big sister and little babies all running around together," paleontologist Anthony Fiorillo said. "As I like to tell the park, Denali was a family destination for millions of years, and now we've got the fossil evidence for it."

Fiorillo, who is studying the fossilized footprints, said the dinosaurs lived in the northern area 70 million years ago, during the Late Cretaceous Period. Fiorillo is the curator of earth sciences at the Perot Museum of Nature and Science in Dallas.

The track site, located in the northeast region of the park, also contains tracks from ceratopsians, therizinosaurs and the flying pterosaurs.

"Even back then the high latitudes were biologically productive and could support big herds of pretty big animals," Fiorillo said. Among the dinosaur fossils, scientists found evidence of clams, worms, bugs and birds within the same time period. Plant life like redwood cones and ferns allowed herbivore animals, like the hadrosaur, to survive.

Researchers organized the many footprints by size, which was difficult as the muddy ground was covered with layers of overlapping prints. While 80 percent of the impressions came from adult dinosaurs, the four distinct groups of tracks ranged in size from 5 inches to 24 inches in length.

The findings were published June 30 in the journal Geology.

"This is definitely one of the great track sites of the world," Fiorillo said. "We were so happy to find it."

Denali National Park & Reserve covers over 6 million acres of wild land and contains North America's highest mountain, Mt. McKinley.