Wednesday, May 7, 2014

New tyrannosaur was the Dobermann of the dinosaur era

We have found a lost cousin of Tyrannosaurus rex, and it was a far more graceful creature than its more famous relative. Because of its long snout, its discoverers have nicknamed it "Pinocchio rex".

Big tyrannosaurs like T. rex in North America and Tarbosaurus in Asia are famed for their massive, bone-crunching jaws. These made them apex predators, the terrors of the late Cretaceous world.

Now Junchang Lü of the Institute of Geology in Beijing, China, and his colleagues have described a new species called Qianzhousaurus sinensis. It had an unusually long and narrow jaw that marks it as a different type of predator.

"This is a Dobermann pinscher with a long, narrow snout, as opposed to T. rex and Tarbosaurus, which is a pit bull," says Tom Holtz of the University of Maryland in College Park, who was not involved in the research. "It's another variation on being a tyrannosaur."

Construction workers found the fossil while excavating in Ganzhou in southern China. It is a nearly complete tyrannosaur, 8 to 9 metres long and with a 90-centimetre-long skull (see picture, below). It weighed about 750 kilograms; lightly built compared to the big guys.

Qianzhousaurus "breaks the mould for what we expect tyrannosaurs to be", says co-author Stephen Brusatte of the University of Edinburgh, UK. With longer legs and a lighter skeleton than T. rex, "it probably was a second-tier predator relying more on speed than on brute strength". And it probably hunted smaller prey than Tarbosaurus did.

Brusatte previously described examples of small and long-snouted tyrannosaurs called Alioramus from Mongolia, but both were young, and young tyrannosaurs go through a long-snouted stage. The new fossil is nearly full-grown, which means the long-snouted state persisted into adulthood, and so it is the hallmark of a previously unrecognised group.

It is not clear why Qianzhousaurus had such a long face. The long snout would not have been able to resist the high loads and stresses that the skull of T. rex could handle, says Thomas Carr of Carthage College in Kenosha, Wisconsin, who was not involved in the research.

Another family of fierce predatory dinosaurs, the spinosaurs, had a snout that was even longer and thinner. But spinosaurs mostly ate fish, so their jaws had enlarged tips with teeth arranged to help trap fish. The jaws of Qianzhousaurus curve smoothly and have buck teeth like T. rex, suggesting its mouth did not evolve to catch fish.

Journal reference: Nature Communications, DOI: 10.1038/ncomms4788

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