In July, scientists from the University of Alaska Museum of the North set out on a 500-mile trek down the Tanana and Yukon rivers, bringing back 2,000 pounds of dinosaur footprint fossils.
"We found dinosaur footprints by the scores on literally every outcrop we stopped at," expedition researcher Paul McCarthy of the University of Alaska Fairbanks said in a statement. "I've seen dinosaur footprints in Alaska now in rocks from southwest Alaska, the North Slope and Denali National Park in the Interior, but there aren't many places where footprints occur in such abundance."
"It took several years of dedicated looking before the first footprint was discovered in Denali [Alaska] in 2005, but since that time hundreds of tracks of dinosaurs and birds have been found," McCarthy said.
The prints found over the last decade at Alaska's Denali National Park were left in rocks that formed 65 million to 80 million years ago during the Late Cretaceous Period.
"In contrast, the tracks were so abundant along the Yukon River that we could find and collect as many as 50 specimens in as little as 10 minutes," McCarthy said.
The Yukon River prints may date back to 25 million to 30 million years earlier than the Denali prints.
Pat Druckenmiller, the museum's earth sciences curator, added that a find of this magnitude is rare today.
"This is the kind of discovery you would have expected in the Lower 48 a hundred years ago," Druckenmiller said in a statement. "We found a great diversity of dinosaur types, evidence of an extinct ecosystem we never knew existed."
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