"It was a hothouse planet," he said.

North America was flooded, with a seaway stretching through the center of the continent from the Arctic to the Gulf of Mexico. In the western section, dinosaurs lived between the sea that reached to eastern Utah and a line of mountains.

That means the new finds come from "a really important place and time," Sampson said.

Strangely, dinosaurs from southern Utah at that time differ from those discovered in Montana and Canada. New finds have raised more questions than they have given answers.

The site is near the center of the 1.9-million-acre monument.

"It can take you hours and hours to walk a mile" in the steep terrain, Sampson said.

Sometimes, he said, "if we're really lucky, we find a complete skeleton . . . and the preservation turns out to be impressive."

Sampson showed a photo of rock containing dinosaur skin impressions, which were notably knobby.

The skull of a yet-unnamed new duckbill dinosaur, which is on display at the museum, is 7 feet long.

Speaking of the raptor, Zanno said, "We know now that Hagryphus had feathers on its body."

Getty noted that a main reason the national monument was created "was to protect the paleontological resources."

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E-mail: bau@desnews.com