Fossil hunters in China say they have found the earliest known forerunner of the Tyrannosaurus rex, the mighty flesh-ripping dinosaur beloved of children and Hollywood.
Uncovered in Wucaiwan in the western province of Xinjiang, the species has been dubbed Guanlong wucaii -- "crowned dragon of the five-colored rocks," a reference to the tint of the earth in which it was found.
It hails from the Late Jurassic period, around 161 million to 156 million years ago, according to the discoverers, led by Xu Xing (徐星) of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing.
By comparison, the T. rex lived much later, in the Late Cretaceous era, enjoying a 20-million-year reign of terror that ended with the extinction of the dinosaurs some 65 million years ago.
Nose to tail, T. rex measured up to 13m in length, whereas the best preserved of the two fossils unearthed in Wucaiwan suggest a creature that was about 3m long.
Despite these differences, the "crowned dragon" shows all the key ancestral hallmarks of the tyrannosaurids.
It shares their enlarged skull, two powerful rear feet, stubby forelimbs -- and long, blade-like teeth that suggests it, too, was a predator to be reckoned with.
The beast sported relatively long, three-fingered arms, rather than the two-fingered stubby arms T. rex had.
Scientists suspect it had feathers because related dinosaurs did.
But the "primitive" look of the pelvis also suggests something else, Xu said.
It supports a theory, first put forward in the 1990s, that the tyrannosaurids, despite their great size, evolved from a species of swift, small-bodied dinosaurs called "coelurosaurs."
The big surprise, said study co-author James Clark of George Washington University in Washington, was the narrow, delicate, largely hollow crest on its head. While other dinosaurs had similar features, this one was unusually large and elaborate for a two-legged meat-eater, Clark and co-authors wrote.
Nobody knows its purpose, but it was probably some kind of display to other members of its own species, said Clark, co-leader of 2002 expedition that found the beast.
This crest is "surprising," given that it would have surely hampered the beast in its hunt for food, the authors say.
They speculate that it was an ornament that may have been used to lure a mate or show off status. Many vertebrate species today use these tools, such as peacocks with their tails and elks with their antlers, even if the device carries a cost in movement.
Because it preserves anatomical features from its ancestors that were lost in T. rex and other tyrannosaurs, the primitive beast helps scientists understand where tyrannosaurs fit in the evolutionary tree, said an expert not involved in the discovery.
"This is the best look so far at the ancestral condition from which the tyrant dinosaurs, T. rex and company, evolved," said the expert, Thomas Holtz Jr. of the University of Maryland.
Along with some other finds, the creature helps illustrate the sequence of anatomical changes that occurred along the way to the later, more specialized tyrannosaurs, said Philip Currie of the University of Alberta in Canada.
Ken Carpenter, curator of lower vertebrate paleontology at the Denver Museum of Nature and Science, said he tentatively accepted the creature as a tyrannosaur but was not convinced of its age. It could be much younger, he said. Clark said that other data, not yet published, supported the proposed age of 160 million years.
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