Newly discovered dinosaur footprints suggest the Arctic was a land bridge in Cretaceous times, too

The Bering Land Bridge linked Asia and North America millions of years ago, just as it did in recent ice ages.

By Yereth Rosen - August 22, 2018
An artist’s rendition suggests what dinosaurs in Alaska may’ve looked like. New findings suggest that dinosaurs crossed between Asia and North America via a Beringian land bridge. (Perot Museum of Nature and Science)

As ancient humans used a Beringian land link to migrate between Asia and North America, so did much older forms of life.

The Bering Land Bridge, which appeared and disappeared several times in earth’s geologic history, was used to make Alaska part of a dinosaur migration highway, new evidence from Denali National Park indicates.

“Just like people and mammoths and woolly rhinos and what have you made use of this land bridge, dinosaurs did too,” said paleontologist Tony Fiorillo, curator of the Perot Museum of Nature and Science and an expert on Alaska dinosaurs.

The evidence comes from a collection of mingled, 70 million-year-old footprints from duck-billed hadrosaurs, common in Cretaceous Alaska, and another dinosaur, a long-clawed animal that was much more Asian — the therizinosaur.

That mixture of hadrosaur and therizinosaur tracks found in Denali’s Cantwell formation — described in a study led by Fiorllo and newly published in the Nature journal Scientific Reports — had never been seen before in North America.

Exactly why the two very different dinosaurs trekked the same route is yet unknown, the study says. “Whether the animals interacted in a complex social manner or received mutually beneficial predatory avoidance for the combined herd is unresolved,” it says.

While duckbilled and horned dinosaurs are known to have roamed Alaska and the rest of North America, Asia was the territory for therizinosaur, an unusual-looking creature with knife-like long claws on its three-fingered hands and a name translates in Greek to “scythe lizard.” The therizinosaurs had an interesting evolutionary history as well. They started out as predators but, for some natural-selection reasons yet unknown, evolved into vegetarians, Fiorillo said.

Only a few signs of therizinosaur presence have been found in North America. Their fossils are much more plentiful in Asia, notably in Mongolia. Consequentially, discovery of therizinsour tracks in Alaska, which in the late Cretaceous was not exactly in the same shape and location as today but fairly similar, is significant.

Credit for the first discovery of a therizinosaur track in Denali, Fiorillo said, goes to David Tomeo of Alaska Geographic, a science and educational program that works with national parks, refuges and forests and in the state.

Fiorillo’s previous work in Denali found evidence that hadrosaurs traveled across the landscape in multigenerational groups, much as elephants do today. Analysis of thousands of fossilized prints in the Cantwell formation found a mixture of hadrosaur age groups, from very young to full-grown adults, that appeared to be walking together as socialized herds.

Denali has turned out to be a rich trove of dinosaur fossils. That is probably not because dinosaurs preferred that territory to other parts of what is now Alaska, Fiorillo said. It is likely the product of mountain formation, which thrust up Cretaceous rock that is now exposed and available for present-day inspection, he said.

The location within a national park also helps. Some of the most important finds have been near sites used by Denali tourists, most of whom travel into the park on shuttle buses that drive on the single 92-mile road.

The first discovered Denali dinosaur print, a 2005 find that that started a stampede of paleontological expeditions to the park, was within about 50 yards of that road, Fiorillo said.

“The vast majority of the people who ride those buses don’t realize how many dinosaurs they’re riding by,” he said.

In addition to his work in Denali and elsewhere in interior Alaska and Alaska’s North Slope, Fiorillo has been focusing in recent years on Aniakchak National Monument and Preserve. In 2001, he found a dinosaur track there, the first found in any National Park Service unit in Alaska. He was back in Aniakchak last summer and this summer, but there was little interaction with tourists. Aniakchak is one of the least-visited national park sites in the nation.