Found! Father of T-Rex
It had an odd-looking crest and long arms, but a fossil dug up in a remote Chinese desert is the earliest example yet found of a tyrannosaur, scientists report.
The creature, named Guanlong wucaii, lived 160 million years ago, more than 90 million years before Tyrannosaurus rex.
It shows the tyrannosaur family had an extensive history, the researchers report in today's issue of the journal Nature.
"Guanlong is the oldest and most primitive tyrannosaur," says Professor James Clark of George Washington University, who helped to lead the study.
T. rex, the best-known tyrannosaur, lived 65 million to 70 million years ago, during the Cretaceous period. This latest find is 90 million years older.
"It is really pushing the record of tyrannosaurs back into the Jurassic," Clark says.
Clark's team found two examples of the early tyrannosaur in the Junggar Basin in northwestern China, a largely unexplored cold desert.
Back in the Jurassic, the area would have been a large wetland bounded by mountains, says geologist Dr David Eberth of the Royal Tyrell Museum in Alberta, Canada.
It would have been warm, with sporadic volcanic explosions, he says.
"These animals were found in mud rock," says Eberth, adding the deposits were made of sand, clay and volcanic material that secured the fossilised bones for millennia.
The wind has now eroded the dried deposits of tens of millions of years. "It is very easy to see what is in the rocks, what is coming out of the rocks," Clark says.
The researchers camp out in the desolate region in the summers, working between sandstorms. They hire local people to walk across the rocks, systematically searching for protruding fossils.
It was one such employee who spotted a bit of Guanlong sticking out and eventually the palaeontologists dug up two nearly complete skeletons, one on top of another.
"We knew right away that this was a theropod dinosaur," Clark says. It had sharp teeth and clearly was a two-legged animal.
But one of the two specimens had an unusual, thin crest on its head, and there was a place on the second skull where one appeared to have been broken off.
"It's a very unusual skull with this crest coming off it," Clark says. "It doesn't immediately shout tyrannosaur when you first see it."
But other identifiers marked it as a tyrannosaur, including distinctive structures in the pelvis.
The thin crest probably was used for display, Clark says. It has been coloured red in the reconstruction, although scientists have no idea what colour it would have been.
They have also given the animal bright purple feathers.
"We have no evidence of feathers in this species," Clark says. "But there is evidence of feathers in another primitive tyrannosaur. We are fairly confident that it did have feathers."
Dr Gregory Erickson of Florida State University studied the 'growth rings' in the animals' shin bones and determined that one specimen would have been about seven years old and thus a juvenile, and the other a 12-year-old adult.
The creatures were about 3 metres long, compared to T. rex, which reached lengths of 14 metres. They do not have T. rex's shortened forelimbs.
The researchers, led by Dr Xu Xing of the Institute of Vertebrate Palaeontology and Palaeoanthropology at the Chinese Academy of Sciences in Beijing, named the new dinosaur Guanlong wucaii.
The genus name is derived from the Mandarin word for 'crowned dragon' and species name refers to the region where it was found.