BioEd Online

Researchers in China have unearthed the bones of a gigantic bird-like dinosaur, dwarfing anything else in its category.

Alive, the beast is thought to have been 8 metres long, 3.5 metres high at the hip and 1,400 kilograms in weight — 35 times as heavy as its next largest family members and 300 times the size of smaller ones such as Caudiperyx. It has been classified as a new species and genus: Gigantoraptor erlianensis. The find is detailed this week in Nature.¹

The evolution of bird-like features had long been thought to be accompanied by a decrease in size, meaning the smaller the species, the more bird-like it is likely to be and vice versa. The new discovery shows that isn't necessarily true.

Gigantoraptor had long arms, bird-like legs, a toothless jaw, and probably a beak. There are no clear signs as to whether it was feathered. However, judging from its close affinity to other dinosaurs known to have been feathered, Xing Xu of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing speculates that it was.

The largest animal known to have had feathers is the extinct Stirton's thunder bird, which weighed in at 500 kilograms.

Comparison of the animal with other known dinosaurs — looking at more than a hundred characteristics, including limb proportions — puts Gigantoraptor firmly in the Oviraptoridae family. "We have really good diagnostic features for oviraptorosaurs," says Xu. The jaw, he notes, is particularly characteristic of this type of dinosaur.

"This is a dinosaur group we've known about for a hundred years. They are usually the size of a turkey or maybe an emu," says David Unwin, a dinosaur expert at the University of Leicester, UK. "No one would have predicted this. If they had, they'd be laughed at."

The bones date from the Late Cretaceous epoch, about 85 million years ago.

Accidental find

The animal was found by accident in April 2005, when Xu was re-enacting the find of a sauropod for a Japanese documentary film crew. While the cameras were rolling, Xu randomly picked out a bone from a dig site in the Gobi Desert, where a unique sauropod had previously been found. As he started clearing away the dirt, Xu soon realized that the bone was not from a sauropod. Its large size suggested a tyrannosaur, but he couldn't be sure. "I told them to stop filming," recalls Xu. "I said, 'This is not for your programme.'"

Xu's team later found an unusually complete collection of bones from the specimen, including a nearly complete forelimb, hind limb and lower jaw, a partial pelvis and some vertebrae.

The Gigantoraptor's diet is a mystery. It has the small head and long neck of a herbivore, but the sharp claws of a carnivore.

Several aspects of the skeleton are still confusing to the researchers. There's a large hole, of unknown purpose, in the vertebrae, Xu says.

Xu and his team also sliced through a bone to see how old the dinosaur was when it died: they think it was 11 years old, and despite its size was still a young adult at the time. The team says this means the animal grew much more rapidly than North American dinosaurs. They speculate that older creatures would have been even bigger.