Discovery overturned long-held assumption about the role of feathers.
When it comes to dino outerwear, shag might be the new scales. Fossil evidence from a trio of 125-million-year-old dinosaurs that were relatives of Tyrannosaurus rex indicate the giant creatures had a fluffier side -- that they wore primitive feathers.
The three tyrannosauroids -- one adult and two juveniles -- belong to a newly described species discovered in northeastern China. The full-grown Yutyrannus huali weighed 3,000 pounds and stretched about 30 feet from nose to tail. The younger ones were still impressive at about 1,100 and 1,300 pounds. The fossils are described in Thursday's journal Nature.
The dinosaurs are noteworthy for being such complete specimens, scientists said. But the most eye-catching part of the find might well be the patchily preserved signs of fossilized feathers around different parts of the animals' bodies.
The feathers varied in length. Some on the tail were about 6 inches long; others, hanging from the neck, measured about 8 inches.
Given that the three dinosaurs had feathery patches in different locations -- adorning, among their collected parts, the hips, foot and forelimbs -- and given that feathers are known to be preserved in bits and pieces even in birds with full plumage, it's likely that Y. huali wore a full feather coat too, said Corwin Sullivan, a vertebrate paleontologist. "It was quite clear we had something impressive," said Sullivan, who is based at the Institute of Vertebrate Paleontology and Paleoanthropology in the Chinese Academy of Sciences in Beijing.
The ancient feathers are not like those seen today. These plumes weren't used for flight; they were filamentary, giving the dinosaurs who wore them more of a fuzzy appearance. (Think of the fuzzy down of a modern baby chick more than the plumes of an adult bird.) "I think this animal would have looked quite shaggy in life," Sullivan said.
These dinosaurs hail from a group known as theropods, which include both T. rex and the ancestors of modern birds. But the findings overturn the long-held assumption that feathers were primarily a feature of smaller dinosaurs rather than larger ones, experts said. Most theories presume that feathers arose for some purpose other than flight. A leading idea is that they provided insulation for the cold-blooded creatures, much the way hair and fur keep mammals warm.
If so, this would have been especially useful for smaller animals; the extra protection from the elements would have come in handy.
But this isn't a big problem for larger animals. With comparatively less surface area in relation to the size of their bodies, they are able to retain heat much more effectively. Fur or hair thus becomes less necessary, and perhaps, in warmer climes, even a little uncomfortable. It's not a hard-and-fast rule, but it is a strong tendency, one that should hold for feathers as well. "That makes Yutyrannus, which is large and downright shaggy, a bit of a surprise," Sullivan said.
But he pointed out that in this particular region of modern-day China, near North Korea, the climate would have been relatively cooler than in surrounding areas. The average temperature where Y. huali roamed was about 50 degrees, compared with 64 degrees elsewhere, so a downy coat could have come in handy.
"It's pretty exciting," said Thomas Holtz, a dinosaur paleontologist at the University of Maryland who was not involved. "Finding a complete articulated skeleton of a large dinosaur is fairly rare, and here there are three almost complete skeletons found. That's pretty amazing."
It open up the possibility that other large dinosaurs -- perhaps even the fearsome T. rex, about six times as massive as Y. huali -- might have been feathered as well. Scientists said the evidence is trending in that direction. "People need to start changing their image of T. rex," said Luis Chiappe, director of the Dinosaur Institute at the Natural History Museum of Los Angeles County, who was not part of the discovery team.
Just don't mistake fuzzy for cuddly. The predatory dinosaur would have been just as menacing. Having feathers, Holtz said, "doesn't make it less threatening or less fearsome."
The Associated Press and New York Times contributed to this report.