Revelado o surpreendente precursor pequeno do T. rex?

Unveiled: The Surprisingly Small Precursor of T. Rex

By Joel Achenbach
Washington Post Staff Writer
Friday, September 18, 2009
Tyrannosaurus rex -- the most fearsome predator ever to have trod the Earth -- had a pint-sized precursor, remarkably similar in appearance but no heavier than a human being, according to a new report from a team of scientists. The creature was what Austin Powers might call T. rex's Mini-Me.

The new animal, based on a single fossil smuggled out of China and eventually sold to a private collector, has been named raptorex. It lived 125 million years ago in a lake-dotted region of northern China.

Raptorex had a big head, tiny forelimbs, and a body built for sprinting, just like T. rex. But this fossil is of a young adult dinosaur, nearly full-grown, that at maturity would have been only about 9 feet long, compared with about 40 feet for an adult T. rex, according to a paper published Thursday in the online edition of the journal Science. It would have weighed only 150 pounds. An adult T. rex could reach 13,000 pounds.

This scrambles the picture of mega-predator evolution and raises the question of whether other jumbo dinosaurs also materialized in a pipsqueak version.

The orthodoxy in paleontology has been that T. rex got its peculiar body shape -- the colossal head, powerful jaws, slashing teeth, and comically short forelimbs, among other features -- as a side effect of evolving into a giant animal. The small arms have been seen as a natural trade-off for the big head. The fossil record shows the limbs becoming shorter as T. rex evolves to monstrous dimensions between about 90 million and 65 million years ago, when it went extinct along with every other species of dinosaur, other than birds.

Raptorex, however, shows that having the jaws as the first line of attack rather than the forelimbs worked for bodies at the much smaller scale, and tens of millions of years before T. rex's giant phase. Like T. rex, raptorex had a bite force so powerful it could chomp through bone.

"What we're looking at is a blueprint for a fast-running set of jaws," University of Chicago paleontologist Paul Sereno, the lead author of the Science paper, said this week. The blueprint works at multiple scales and across tens of millions of years of the Mesozoic, he added. "This animal really changes the way we look at all tyrannosaur evolution."
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Uma pergunta ingênua deste blogger: um T. rex bebê nunca existiu??? Se existiu, este fóssil não poderia ser de um T. rex bebê???