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Raptorex Shows Tiny Arms Came Before T. rex

A new tyrannosaurid, Raptorex, may help solve a long-standing mystery about when the arms of large carnivorous dinosaurs, such as T. rex,  became puny. (See Raptorex's full body below). Shown here is Raptorex’s skull reconstruction and a flesh model. All images courtesy of Paul Sereno. Photo © Mike Hettwer, courtesy of Project Exploration.

Today, a terrific new dinosaur specimen was announced by Paul Sereno and colleagues. It is Raptorex kriegsteini, a 3 meter-long, 65 kg. (10 feet long, 140 lbs.) tyrannosaurid found in 125 million years old sediments in China. Whereas other early relatives of Tyrannosaurus rex, such as Guanlong and Dilong, were small-bodied and had long arms, Raptorex was small-bodied with small arms like T. rex. What Sereno et al. propose in their paper is that tyrannosaurids evolved into their more familiar 10 to 13 meter-long, 4,000 to 7,000kg. (32 to 40 feet-long, 4.4 to 7.7 ton) form through a series of three stages, and that the trademark small forelimbs of T. rex evolved before the final stage, which was when tyrannosaurids evolved their gigantic sizes. This provides new evidence toward answering long-standing questions about  when and why short limbs evolved in large carnivorous dinosaurs, of which T. rex is just one example.

Unfortunately, this unique specimen of Raptorex was excavated and exported illegally. The area where it was discovered in northern China, the Lujiatun Beds of the Yixian formation near the borders of Liaoning Province and the Nei Mongol Autonomous Region (Inner Mongolia), is a hot spot for the illegal trade of fossils. Although the flow of internationally exported specimens has declined with the imposition of stiff penalties and more careful border inspections, the international demand continues as well as a robust domestic demand. The Chinese central government, the provinces, and paleontologists in museums and institutions in the region and in Beijing have been largely unsuccessful in stopping the flow of fossils from this area.

Knowing where fossils come from is a key part of paleontology. When a fossil is excavated illegally, it is easy to lose its geological context, which can make it difficult to date or to say anything about the environment the animal lived in. Information about how the creature may have died can also be lost.

Fortunately, Raptorex was excavated in a block, so when Sereno was contacted by Henry Kriegstein, an eye surgeon and avid fossil collector who had purchased the specimen several years ago, Sereno was able to deduce the general area and specific rock layer where the fossil was found. Its environmental context  could be determined from fossil fish bones and clams that were still associated with the bones of the dinosaur. "If the specimen had not come out as intact as it was, any claims as to where it was from would have been highly questionable," says Sereno.

Also fortunately, Sereno was able to convince Kriegstein that to return the fossil to China was the best for all concerned. "I'm hoping this can be a model for how a few other such unique specimens might find their way back to China and take their rightful place in dinosaur history," says Sereno.

Unfortunately, however, contraband will flow to where there is a demand. Just this week, a huge cache of illegally exported Chinese fossils intercepted at Chicago's O'Hare airport was returned to China. As long as there is a market demand for fossils from other countries—and our own public lands—there will be someone ready to risk digging them up illegally.

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