Tyrannosaur design evolved at 'punk size'

A new dinosaur shows that tyrannosaur design evolved at 'punk size.' The creature, Raptorex, from NE China had evolved all the hallmark anatomical features of Tyrannosaurus rex at least 125 million years ago. A paper in the 17 September issue of Science Express titled 'Tyrannosaurid Skeletal Design First Evolved at Small Body Size' by Paul Sereno and colleagues describes the newly discovered species.

Raptorex shows that tyrannosaur design evolved at 'punk size,' basically our body weight. And that's pretty staggering, because there's no other example that I can think of where an animal has been so finely designed at about 100th the size that it would eventually become,' said Sereno.

Raptorex was approximately 9 feet in length, with a large head, tiny arms and lanky feet, also with enlarged olfactory bulbs - as in T. rex - indicating a highly developed sense of smell.

Sereno, a well-known University of Chicago palaeontologist, marvels at the scalability of the tyrannosaur body type, which when sized up 90 million years ago completely dominated the predatory eco-niche in both Asia and North America until the great extinction 65 million years ago at the end of the Cretaceous Period.

'On other continents like Africa, you have as many as three large predators living in the same areas that split among them the job of eating meat,' he said. But in Africa, the allosaurs never went extinct, as they did in North America, possibly presenting an evolutionary opportunity for Raptorex. 'We have no evidence that it was a competitive takeover,' said Sereno, 'because we have never found large tyrannosaurs and allosaurs together.'

It is interesting to mention that Henry J. Kriegstein, one of the co-authors and a private fossil collector, brought the nearly complete Raptorex skeleton to Sereno's attention after buying it from a vendor. It is expected that the fossil will be returned to a museum in Inner Mongolia, where it was illicitly excavated. Raptorex will also appear on the National Geographic Channel at 8:00 PM ET Sunday, 11 October.