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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The two newly discovered dinosaur species, found by a team of paleontologists led by Doug Wolfe of the Mesa Southwest Museum in Mesa, Ariz., represent the first of their kind in North America. Bits of similar fossils have been found in China, the probable ancestral home of the roughly 90-million-year-old fossils. Wolfe and several of his colleagues announced their findings this week in Washington, D.C. The work is funded by the Discovery Channel, which is airing a special on the finds on July 15.
Catherine Forster of the State University of New York at Stony Brook says, “They’ve come up with some good material.”
The herbivore, dubbed Nothronycus, is, all the scientists say, just plain “bizarre.” The paleontologists picture it as a feather-coated biped with a tiny head and long neck. Each of its neck vertebrae is bigger than its skull. Huge claws protruded from its forelimbs, possibly for defense or ripping up vegetation.
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“It walked like Godzilla with this big gut,” says team member Jim Kirkland, the Utah Geological Survey’s paleontologist. Nothronycus‘ 12-foot-tall form towers over similar species uncovered in the early Cretaceous, and the dinosaur probably links early and late Cretaceous species of the therizinosaur group. Nothronycus‘ description, based on scattered bones of one individual, will appear in the Journal of the Society of Vertebrate Paleontology this fall.
Kirkland describes the new predator, a yet-unnamed type of Coelurosaur, as “the coyote of the Cretaceous.” Like coyotes, he speculates, it consumed a variety of prey. As a group, the Coelurosaurs–which include duck-billed dinosaurs, oviraptors, and even Tyrannosaurus rex–sport a variety of special features, including beaks and horns. The new creature lacks adornments.
The group used information from Chinese fossils to reconstruct the new Coelurosaur from the remains of two individuals.
The original Coelurosaur ancestor may have looked a lot like this new find did. The species is too young to have been the original ancestor of the Coelurosaurs, Wolfe says, but “this dinosaur is a good example of what we hope might be the rootstock.”
Many paleontologists speculate that modern-day birds emerged from Coelurosaur rootstock, an idea bolstered by recent finds in China of early Cretaceous fossils of what were apparently feathered Coelurosaurs (SN: 4/28/01, p. 262).
The sediments from the Arizona-New Mexico site will probably continue to yield surprises. The researchers have already spied some promising new bones waiting to be retrieved.