The remains of a giant, birdlike dinosaur as tall as the formidable tyrannosaur have been found in China, a surprising discovery that indicates a more complicated evolutionary process for birds than originally thought, scientists said on Wednesday.
Fossilised bones uncovered in the Erlian Basin of northern China's Inner Mongolia region show that the specimen was about 26 feet in length, 16 feet tall and weighed three-thousand pounds, said Xu Xing, a paleontologist at the Institute of Vertebrate Paleoanthropology in Beijing.
The height is comparable to the meat-eating tyrannosaurs, but the dinosaur, called Gigantoraptor elrianensis, also had a beak and slender legs and likely had feathers, making it 35 times larger than its likely close relation, the Caudiperyx, a small, feathered dinosaur species, Xu said.
That puts the Gigantoraptor's existence at odds with prevailing theories that dinosaurs became smaller as they evolved into birds and that bigger dinosaurs have less birdlike characteristics, he said.
Xu, who co-authored a paper on the finding published on Thursday in the journal Nature, said it was like finding "a mouse that is the size of a horse or a cow."
He added that the find was important in trying to trace the evolution process of dinosaurs to birds.
"As dinosaurs evolved to great size the theory was they would loose the birdlike characteristics. But Erlian Gigantoraptor is an exception. Its body was very big, but it is more birdlike even than many of its smaller cousins. So it has complicated the theory," said Xu.
The Caudiperyx and the Gigantoraptor belong to a group of dinosaurs called oviraptors, which tend to be human-sized or smaller.
In recent years paleontologists have found turkey-sized, feathered representatives of the group, but they've never found anything close to the scale of Gigantoraptor.
Animals tend to become bigger with evolution because larger creatures have an easier time getting food, impressing potential mates and avoiding predators.
But size has disadvantages, too. Bigger animals need more food and territory. They have fewer offspring and reproduce less frequently than smaller animals do.
That means they are particularly vulnerable when environmental conditions change, as they abruptly did about 65 (m) million years ago.
Just a few (m) million years after Gigantoraptor evolved, it and every other dinosaur species on Earth became extinct.
On Wednesday, reporters were given a look at the Gigantoraptor's remains, two yellowing, rough-edged leg bones both a little over one-meter (3.2 feet) long and believed to be those of a young adult.
It hasn't been determined if the Gigantoraptor was a herbivore, which have small heads and long necks, or a carnivore, which have sharp claws.
The dinosaur has both, Xu said.
Xu and his team, which discovered three other specimens in the fossil-rich Erlian Basin, were being interviewed by Japanese media in 2005 when they discovered the Gigantoraptor remains.
They had chosen a random site to illustrate how one of the previous fossils had been discovered and hit upon a bone while on camera, Xu said.
The team originally thought that it belonged to a tyrannosaur because of its size, but realised upon examination that it was an oviraptor.