In July, the scientists from the University of Alaska Museum of the North embarked on a 500-mile (800 kilometers) journey down the Tanana and Yukon rivers; they brought back 2,000 pounds (900 kilograms) 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." [See Photos of the Dinosaur Tracks Along the Yukon River]
In the last decade, dinosaur footprints have been found in Alaska's Denali National Park, left in rocks that formed 65 million to 80 million years ago, during the Late Cretaceous Period. The new prints along the Yukon River might date back 25 million to 30 million years earlier, McCarthy said.