A 1-ton, potbellied vegetarian and a fierce, two-legged predator have surfaced from a 30-million-year gap in the dinosaur fossil record, and they are true-blooded Americans, chiseled from rock along the Arizona-New Mexico border.
That rock is one of the few sediments that has yielded fossils from the middle of the Cretaceous period, which spanned from 146 million to 65 million years ago. The dearth of mid-Cretaceous fossils has made it difficult for paleontologists to discern the origin of specialized horns, bills, claws, and other anatomic innovations apparent in the more plentiful fossil record beginning 75 million years ago.
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