Paleontologists have discovered a duck-size dinosaur they believe died while catching some z's. Researchers found the creature's fossilized remains curled up with its head tucked under a forelimb, a pose that today is unique to sleeping and resting birds.

"I never expected we'd find a sleeping dinosaur in general, let alone with the tuck-in position," said Xu Xing, a curator at the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, China.

Mark Norell, chairman of the division of paleontology at the American Museum of Natural History in New York, said the discovery further strengthens the chain linking dinosaurs and birds, suggesting this birdlike sleeping posture first evolved in dinosaurs.

"This is another stereotypical bird behavior in another nonavian theropod," he said. Theropods are meat-eating dinosaurs characterized by short forelimbs and powerful hind legs. Many scientists believe small theropods are ancestors to the first birds.

Xu and Norell describe the new dinosaur in tomorrow's issue of the science journal Nature. The pair named the 21-inch-long (53-centimeter-long) creature Mei long, Chinese for "soundly sleeping dragon."

Mei long is a troodontid, one of the most birdlike types of theropods. Several other features of Mei long support theories that nonavian dinosaurs were warm-blooded and that small size was a prerequisite for flight, according to the paleontologists.

The research was supported, in part, by a grant from the National Geographic Society's Committee for Research and Exploration.

Hans-Dieter Sues, the associate director for research and collections at the Smithsonian Institution's National Museum of Natural History in Washington, D.C., said the fossil does appear to be preserved in a resting or sleeping posture.

"One should keep in mind, however, that this could have been a death posture as well," said Sues, who is a member of the National Geographic Society's Committee for Research and Exploration.

Sues and Philip Currie, curator of dinosaurs at the Royal Tyrell Museum in Alberta, Canada, point out that an incomplete troodontid skeleton from Mongolia, Sinornithoides, was discovered in 1994 in a similar pose.

"Overall, I think [Mei long] is a very remarkable find and is especially amazing because it is the second small troodontid in this pose," Currie said. "Not much doubt that this is the way they slept."

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SOURCES AND RELATED WEB SITES Nature Royal Tyrrell Museum NGS Committee for Research and Exploration: Hans-Dieter Sues American Museum of Natural History: Division of Paleontology