Bird-like behemoth joins pantheon of dinosaurs

Never mind Sesame Street. One of the world's most renowned fossil hunters has discovered the original Big Bird -- a partly-feathered but flightless dinosaur that weighed about 3,100 pounds and was nearly 26 feet long.

Gigantoraptor erlianensis, discovered in China's Inner Mongolia, is the largest bird-like dinosaur ever found, capable of going eyeball to eyeball with the fearsome Tyrannosaurus rex, according to researchers. It haunted the Late Cretaceous period some 70 million years ago.

Scientists worldwide were stunned by the size of the beast, the largest new dinosaur dug up in years and the first true behemoth of the bird-like dinosaurs. Such creatures were usually much smaller, topping out at 90 pounds.

"Imagine finding a mouse the size of a very big pig," said paleontologist Xu Xing in an interview from Beijing. "We were most amazed to find this."

Xu, of China's Academy of Sciences, described his discovery in an article in yesterday's issue of Nature, the British science journal.

The discovery appears to contradict prevailing evolutionary theories that dinosaurs grew smaller as they became more bird-like, according to Xu. Compared with its close relatives, Gigantoraptor has some features -- such as long forelimbs -- suggesting it was becoming more bird-like even as it bulked up over vast periods of time.

"Dinosaur evolution is a complicated process," he said. "There are still species that are beyond imagination. We need to work even harder to find even more fossils of this fascinating group."

Scientists believe that dinosaurs and birds have common evolutionary roots. But paleontologists stressed that Gigantoraptor was only "bird-like," not a true bird -- and may not necessarily belong in the family tree of modern birds.

Gigantoraptor possessed a parrot-like beak, no teeth, and may have sported a fringe of feathers on arms that ended in wickedly sharp claws, according to an analysis of the fossils Xu found. It was more than 35 times heavier than similar known "oviraptors," bird-like dinosaurs that stalked the fern thickets and forests of the Late Cretaceous.

"Usually, oviraptors are pretty small animals, but this beast was huge," said Mark A. Norell, paleontologist at the American Museum of Natural History in New York City and himself a top fossil hunter who has worked with Xu, but not on this particular find. "This shows the incredible body diversity among these creatures."

Big as it was, the Gigantoraptor wasn't even fully grown, according to Xu. The dinosaur was "only age 11 when it died, it had not reached its full size, it had some growing to do, and a full-sized Gigantoraptor would have been considerably heavier," he said. "This was basically a growing adolescent."

Gigantoraptor erlianensis was so difficult to classify -- because of its bulk combined with a bird-like structure -- that it took two years of intensive study before Xu and his colleagues felt confident enough to pronounce it both a new genus and new species.

The flightless creature's feathers, Xu speculated, might have been for show -- perhaps mating display -- and possibly for keeping eggs warm. It had a small head and long neck, characteristic of herbivorous species. But it also had big talons, capable of ripping flesh, and long legs suitable for chasing prey.

In size, Gigantoraptor is comparable to the giant meat-eaters, like T-rex. But the creature's bird-like beak suggests it may have foraged on plants. "We don't know what kind of food it ate," said Xu.

The creature was unearthed by accident.

Two years ago, Xu was participating in a documentary film about one of his earlier dinosaur finds. Poking around a hillside in the Erlian Basin of the Gobi desert -- near the "dinosaur city" of Erenhot, famed for fossils since the 19th century -- Xu happened upon a large femur while showing a Japanese film crew how a paleontologist's work is done. It turned out to belong to a species unknown to science.

The discovery marked the 25th dinosaur species find credited to Xu, an extraordinary record.

The region where Gigantoraptor lived is today desert, but 70 million years ago it was a floodplain containing numerous ponds and thickets, cut by a broad river. It was great country for dinosaurs, said Xu: "Duckbilled dinosaurs, primitive tyrannosaurs, some ankylosaurs, and a kind of small titanosaurian sauropod -- that's what we know of" inhabiting the same area.

Xu said it's uncertain why this dinosaur grew so huge.

"But being big has advantages," he said. "You can get food that may be unavailable to smaller animals, and you don't have as many predators to eat you."

Gigantoraptor's days on earth were numbered. Most dinosaurs met their doom during a mysterious mass extinction at the end of the Cretaceous, about 65 million years ago.