Some researchers have speculated that dinosaurs migrated north to Alaska, perhaps even coming from Canada like huge caribou herds.
"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."
During the Late Cretaceous, Alaska sat at about the same latitude as today, but it was a tectonic jigsaw puzzle that had yet to assemble into today's stunning topography. Mountain-fed rivers and streams flowed through Denali, but not the same mountains: the Alaska Range was just being born. Mount McKinley, now the tallest mountain in North America, didn't exist. The climate was warmer, similar to coastal Washington and Oregon, but sunlight still flipped between extremes, with lengthy summer days and long, dark winters. (In Images: How North America Grew as a Continent)
Despite the dark winters, scientists such as Fiorillo have uncovered scores of dinosaur fossils and tracks across Alaska in recent decades, from quarries near the North Slope oil fields down to Denali's spectacular mountains.
Fiorillo and colleagues from Texas, Japan and Alaska have been documenting the new Denali track site since 2011. Exhibits featuring copies of the Denali dinosaur fossils and hadrosaur footprints are on display in the park and at the Perot Museum in Texas.
The trampled ground sits at the top of a steep ridge and is exposed on a cliff face about 590 feet (180 meters) long. The tracks were made within a short time range, between 69 million to 72 million years ago, likely in a muddy river or stream bank during the height of summer, the researchers said. (The bugs and plants help pin down the time of year.)
The outcrop was revealed by a rockfall and could be destroyed by another landslide in the future, so researchers scanned the area with lidar (a high-resolution laser-scanning technique) to preserve the site forever.
"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."
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