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T. Rex Had Humble Origins

The most famous of all the giant meat-eating predators that walked the Earth -- Tyrannosaurus rex -- started out rather small, at least as dinosaurs go.

The latest fossil discovery from China has turned up a dinosaur believed to be the earliest ancestor of T. rex. The ancestor is no more than 10 feet long and sports a large crest on top of its head, leading its discoverers to call it Guanlong, meaning "crowned dragon."

Its discovery has raised as many questions as it answers.

Just over a year ago, scientists announced they'd found the "oldest" ancestor of T. rex: a feathered dinosaur uncovered in China. Now scientists have discovered an even older ancestor. It was toothy, to be sure, but about one-fourth the size of T. rex.

And, says lead scientist James Clark of George Washington University, it wasn't alone.

"We have two skeletons preserved, the larger lying on top of the other one," Clark explains. The dinosaurs were 7 and 12 years old when they died, but they're 90 million years older than T. rex.

Finding the apparent Adam of the T. rex family is remarkable enough, but finding two of them, one on top of the other is, as one team member described it, "weird." Their grave site is a mystery; there's no sign of a struggle, and their deaths were probably years apart.

Guanlong looks like a smaller, more graceful T. rex. It has steak-knife-like teeth, but with longish arms instead of the short, rather pathetic arms of T. rex. It had three claws, like modern birds, and might have had feathers, says Clark, though he didn't find any.

Guanlong suggests that nature had a basic design that worked for predators. But this discovery suggests that over time, size became the favored trait.

Team member Gregory Erickson is with Florida State University.

"Maybe it's just a case of these animals tracking larger prey," says Florida State University's Gregory Erickson. As herbivores got bigger, larger predators would have had an advantage.

There's another mystery about this creature. It had something unique to tyrannosaurs: a large crest on its head. It's like the crest many birds have, but bony inside.

Tom Holtz, a dinosaur scientist at the University of Maryland, says lots of dinosaurs are believed to have had display ornamentation, such as plates along the back or bony frills around the neck.

"If you've got a big showy display structure, at least in certain seasons, you've got a lot of color on it to say, 'Ha, look at me, I'm ready from breeding,' or 'Hey, stay away from me, I'm dangerous,'" says Holtz.

Scientists say the past decade of discoveries, especially in China, has revealed a menagerie of tyrannosaur ancestors: smaller, quicker, feathered, and now crested. And they were by no means top dog when they started out in the Jurassic Period, some 180 million years ago.

["In the case of tyrannosauroids, we see they spent a long period of their history as secondary predators -- as minor components in the predatory guilds," Holtz says. "And it's only at the very end -- only the last 15 years of the Cretaceous, really -- did they take off as the top. This helps reinforce the idea that the tyrannosaurs that we know and love -- the great T. rex -- was in a sense a really late experiment."

An experiment that came to a screeching halt, fortunately for humans, 65 million years ago.

The new discovery is described in the most recent issue of the journal Nature.

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Christopher Joyce is a correspondent on the science desk at NPR. His stories can be heard on all of NPR's news programs, including NPR's Morning Edition, All Things Considered, and Weekend Edition.