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Mini T. Rex Unearthed

September 18, 2009

The Tyrannosaurus Rex is characterized by its big head, packed with sharp teeth, and tiny arms. However, a new ancestor has been dug up in China that was only 10 feet tall and 150 pounds, aptly nicknamed “Raptorex.”

Though the mini Raptorex is almost 100 times smaller than the T. rex, it is practically identical in structure, even sporting the same little arms and all the fortunate traits that made it such a successful predator, said lead author Paul Sereno from the University of Chicago and National Geographic explorer-in-residence.

The findings of Sereno and his colleagues were first described in the journal Science at the Science Express website on Thursday.

“It really is the blueprint for the later (T. rex) dinosaurs,” Sereno said, “it was a blueprint that was scalable.”

The tiny terror was a surprise link in the evolution of the notorious predator, which at one time dominated the northern half of the globe and has given researchers a whole new perspective on how the T. rex evolved.

“Raptorex, the new species, really throws a wrench into the observed pattern,” said co-author Stephen Brusatte of the American Museum of Natural History.

“Here we have an animal that’s 1/100th of the size of T. rex…but with all of the signature features, big head, strong muscles, tiny little arms — that were thought to be necessary adaptations for a large-body predator.”

The fossil of the Raptorex reveals that the scrawny arms, which were previously believed to have helped balance overall bodyweight, rather evolved as a tradeoff for agility and speed.

The large, powerful back leg muscles would have given the T. rex an edge on chasing down prey, while the tiny front legs gave it the ability to stand upright to attack with its steel jaws.

The Raptorex fossil, which is about 125 million years old, is thought to have been a juvenile around the age of five or six when it met its end.

The T. rex species only reached its full size about 85 million years ago and died out about 65 million years ago during the in the great extinction that brought the Cretaceous Period to a close.

“What that means is that for most of their evolutionary history, about 80 percent of the time that they were on earth, tyrannosauruses were small animals that lived in the shadow of other types of very large dinosaur predators,” Brusatte told reporters in a conference call.

It appears that the only reason the T. rex was able to reach its gigantic stature was because competing predators died off.

“We cannot say that this incredibly successful, scalable blueprint for a predator was responsible for their total domination…because we never saw them cohabiting in environments with these other, earlier types of predators,” he said.

Once the tyrannosauruses got bigger, “there was no turning back until the asteroid hit because they really had it down pat.”

The unearthed fossil, which was unbelievably well-preserved and nearly complete, had actually been illegally excavated and snuck out of China for sale on the private market.

Thankfully, an American eye surgeon and dinosaur enthusiast Henry Kriegstein bought the fossil because he knew it was valuable to science.

Kriegstein  contacted Sereno, who then agreed to study the fossil under the condition that it was returned to China after being analyzed.

“We rapidly achieved that agreement and Raptorex sees the light of day,” Sereno said.

“I hope this is a pathway (which can be used again so) that other important specimens that do find their way out of the ground in the dark of night do not get lost to science.”

The full name of the new genus is Kriegsteini, to honor Kriegstein’s contribution to science and the connection it has to raptors and the T-Rex.

Image 1: Entombed in the sediment of an ancient lake margin in northern China 125 million years ago, the bones of the long-legged predator Raptorex are remarkably preserved. (Mike Hettwer)

Image 2: Weighing as little as 1/100th that of its descendant T. rex, the 125-million year old Raptorex shows off the distinctive body plan of this most dominant line of predatory dinosaurs. This image is based on a fossil skeleton discovered in Inner Mongolia, China. (Todd Marshall)

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Mini T Rex Unearthed


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