Scientists have uncovered a huge surprise in the Inner Mongolia region of northern China: the fossil skeleton of an unusually robust birdlike dinosaur that lived 70 million years ago. The animal appeared to be a young adult 25 feet long and weighing 3,000 pounds and, if it had lived longer, would probably have grown even larger.
Paleontologists said the discovery contradicted widely held theories that carnivorous dinosaurs got smaller as they evolved more birdlike characteristics. But they emphasized that the new specimen did not challenge the theorized link between dinosaurs and birds.
The Chinese scientists who made the discovery, being reported Thursday in the journal Nature, said the skeleton belonged to a dinosaur family that included the beaked, birdlike oviraptor. This family was not closely related to the dromaeosaurid dinosaurs generally thought to be ancestors of modern birds. Still, the scientists concluded that the new skeleton "is an exception to some general patterns" during the evolution of related dinosaurs, including the "trend of size decrease" that is associated with the origin of birds. They said it was significant that the large specimen "shows many birdlike features absent" in smaller relatives.
Impressed by the size and puzzling character of their find, the team led by Xing Xu, a paleontologist at the Chinese Academy of Sciences in Beijing, classified the animal as a new genus and species. It was given the name Gigantoraptor erlianensis, the specific name recognizing the Erlian basin of Inner Mongolia, where the skeleton was excavated.
Gigantoraptor appears in an artist's reconstruction to have cut a menacing figure on the Cretaceous landscape. Rearing on its hind limbs, it spread out forelimbs tipped with sharp claws and prepared to pounce on prey with an open mouth and strong beak. Independent dinosaur experts said the description of the fossils of the half-complete skeleton appeared to support the discoverers' interpretations. They said Gigantoraptor probably had some feathers, though none were preserved.
"The specimen is quite convincingly diagnostic," said Peter Dodson, a paleontologist at the University of Pennsylvania and co-author of the authoritative reference book "Dinosauria." "This was on the line leading toward birds, though not itself the closest relative to birds by any means."
Mark A. Norell, a dinosaur paleontologist at the American Museum of Natural History, said the find was "pretty unexpected" and showed "how little we know about the diversity in the dinosaur world."