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Scientists Uncover Earliest Known Ancestor to Tyrannosaurus Rex


Chinese and U.S. scientists have uncovered the earliest known ancestor to the giant, fearsome Tyrannosaurus rex dinosaur. This 160-million-year-old primitive tyrannosaur was much smaller and looks more like a predecessor to a rooster than a T-rex.

The far western reaches of China's Gobi Desert, the same region depicted in the movie Crouching Tiger, Hidden Dragon, have yielded a pair of small hidden dragons, long buried in a mixture of sand, clay, and volcanic deposits. In fact, the researchers who dug up the three-meter-long creatures have named them, meaning Crested Dragon.

That is because the most striking feature of the two nearly complete skeletons is a strange crest at the front of the head like that of a rooster, only with a straight top edge rather than a wavy one. A U.S. member of the research team, James Clark of George Washington University, says the structure was unusual among this branch of theropod dinosaurs, the broader line believed to be related to birds. The crest dwindled in size to just a faint ridge in the next known tyrannosaur descendant, a feathered tyrannosaur unearthed in 2004 called Dilong. It was completely gone by the time of T-rex, 90 million years after Guanlong.

"This tall crest on the skull is unique for a tyrannosaur and may have been primitive for the whole group, that is, something that was there at the beginning and then lost later on," he said. "It was probably a display structure, although this is something we really don't have a good handle on [don't understand]."

Clark says no one knows if the crest belonged to only the male tyrannosaur like a rooster because the gender of the two fossils cannot be determined.

The scientists say they did not immediately recognize the beast as an early tyrannosaur because many of its features are so primitive. But closer study in a Beijing laboratory showed the relationship to its gigantic descendant, such as similarities in the jaw, teeth, and pelvis. Clark says the finding extends the tyrannosaur record back to about the time in the Middle Jurassic period when the species branched off from an earlier line.

"We don't know a lot about these early tyrannosaurs because we have this huge gap in tyrannosaur fossils," he said. "So here we have them way back almost into the Middle Jurassic, and yet the Late Jurassic record and Early Cretaceous record is very, very slight. So we know now the early tyrannosaurs really did come off very early and we're just missing a big chunk."

By the time of the 14-meter-long T-rex, tyrannosaurs were the dominant predators in eastern and central Asia and North America. They remained so for the last 20 million years of the Late Cretaceous era, which ended at the time all dinosaurs became extinct 65 million years ago.

Although fearsome, T-rex had comparatively puny, shrunken arms for its size, with only two fingers. Co-discoverer Mark Norell of the American Museum of Natural History in New York says the crested Guanlong had long, thin forelimbs with three fingers, more akin to modern birds, which have remnants of three fingers.

"This is almost like a very gracile [graceful] animal as opposed to a more elephantine Tyrannosaurs rex," he said. "How that relates exactly to prey capture we really don't know because we don't really have good evidence of what these animals ate yet."

They are known to have been meat-eaters, however, and the scientists suspect that the new discoveries had feathers because related dinosaurs did. They report their findings in the journal Nature.

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