Thousands of dinosaur tracks found in a remote area on the Yukon River are "evidence of an extinct ecosystem," University of Alaska researchers say.

The tracks were discovered by a team from the university's Museum of the North in Fairbanks after a 500-mile boat trip, the university said last week. Earth Sciences Curator Pat Druckenmiller said the tracks were left by a diverse group of dinosaurs, both carnivores and herbivores.

"We found a great diversity of dinosaur types, evidence of an extinct ecosystem we never knew existed," Druckenmiller said.

Paul McCarthy of the department of geology and geophysics said he has seen dinosaur footprints elsewhere in Alaska. But those were not as numerous.

"We found dinosaur footprints by the scores on literally every outcrop we stopped at," he said.

McCarthy said the tracks in the Yukon are probably 25 million to 30 million years older than those in Denali National Park, hundreds of miles to the south. The species that have been identified are also different from earlier finds in Alaska.