Scientists have discovered a new, unusually well-preserved track site of hadrosaur dinosaur footprints in Alaska, showing that hadrosaurs likely traveled in herds.

"We had mom, dad, big brother, big sister and little babies all running around together," said paleontologist Anthony Fiorillo, curator of earth sciences at the Perot Museum of Nature & Science in Dallas, who is studying the dinosaur tracks. "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."

The footprints date back to roughly 70 million years ago, and tell us more about the ways that dinosaurs lived. Fiorillo believes that dinosaurs lived in polar regions during the Late Cretaceous.

"Even back then the high latitudes were biologically productive and could support big herds of pretty big animals," Fiorillo said.

Thousands of hadrosaur tracks were discovered in the track site, along with traces of other life such as birds, clams, worms and bugs. Other dinosaur tracks were found there as well, but the majority were from hadrosaurs, a duck-billed dinosaur. Scientists found four distinct size ranges, from 5 inches to 24 inches. Because most of the tracks are from larger hadrosaurs, scientists theorized that baby hadrosaurs grew very quickly, minimizing the amount of time they spent as vulnerable youth. This theory is backed up by studies done previously on hadrosaur bones.

How did so many hadrosaurs get to Alaska? They migrated, most likely, scientists say. "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."

The Alaska these dinosaurs lived in was warmer than it is today, but still had extremes of light and dark. The tracks were likely made in a muddy stream during summer, according to research from Fiorillo and his team, so the dinosaurs were walking under long sunny Alaskan days.

Fiorillo and his team have been working since 2011 to document and preserve the track site. They have just published their findings recently in the journal called Geology. The paper delves into the likely herd structure of the hadrosaurs, and how they thrived in a polar ecosystem. This research is an exciting development in the world of dinosaur history, and adds a wealth of knowledge to what we already knew about hadrosaurs.

"On one of the last nights, as work was coming to a close, I was lying in my tent and woke up to an earthquake in the park," Fiorillo said. "For the first time in my life, I wasn't worried about a big rock [hitting me]. I was worried about my track site sliding down the mountain."