Down-Covered Dinosaur

The once radical notion that birds descended from dinosaurs--or may even be dinosaurs, the only living branch of the family that ruled the earth eons ago--has got stronger and stronger since paleontologists first started taking it seriously a couple of decades ago. Remarkable similarities in bone structure between dinos and birds were the first clue. Then came evidence, thanks to a series of astonishing discoveries in China's Liaoning province over the past five years, that some dinosaurs may have borne feathers. But a few scientists still argued that the link was weak; the bone similarities could be a coincidence, they said. And maybe those primitive structures visible in some fossils were feathers--but maybe not. You had to use your imagination to see them.

Not anymore. A spectacularly preserved fossil of a juvenile dinosaur, announced by a team of paleontologists from the Chinese Academy of Geological Sciences and New York City's American Museum of Natural History in the latest issue of Nature, is about as good a missing link as anyone could want. "It has things that are undeniably feathers," exults Richard Prum, of the University of Kansas Natural History Museum, an expert on the evolution of feathers. "But it is clearly a small, vicious theropod similar to the velociraptors that chased the kids around the kitchen in Jurassic Park."

In fact, this duck-size relative of Tyrannosaurus rex, dating from 124 million to 147 million years ago, has no fewer than three different types of feathers. The head sports a thick, fuzzy mat of short, hollow fibers ("like a butch cut," says Prum), while the shoulders and torso have plumelike "sprays" of extremely thin fibers up to 2 in. long. The backs of its arms and legs, meanwhile, are draped in multiple filaments arranged in a classic herringbone pattern around a central stem. Even the tail is covered with feathers, with a fan, or tuft, at the end. "It doesn't look anything like what most people think dinosaurs look like," explains the American Museum's Mark Norell, one of the team's co-leaders. "When this thing was alive, it looked like a Persian cat with feathers."

The find helps cement the dinosaur-bird connection, but it also casts new light on the mystery of why nature invented feathers in the first place. For the better part of a century, biologists have assumed that these specialized structures evolved for flight, but that's clearly not true. "The feathers on these dinosaurs aren't flight-worthy, and the animals couldn't fly," says paleontologist Kevin Padian, of the University of California, Berkeley. "They're too big, and they don't have wings." So what was the original purpose of feathers? Nobody knows for sure; they might have been useful for keeping dinos dry, distracting predators or attracting mates, as peacocks do today.

But many biologists suspect that feathers originally arose to keep dinosaurs warm. The bone structure of dinosaurs shows that, unlike modern reptiles, they grew as fast as birds and mammals--which dovetails with a growing body of evidence that dinos were, in fact, warm-blooded. Says Padian: "They must have had a high basal metabolic rate to grow that fast. And I wouldn't be surprised if they had some sort of skin covering for insulation when they were small." Says Norell: "Even baby tyrannosaurs probably looked like this one."

At the rate feathered dinosaurs are turning up, it shouldn't take long to solidify scientists' understanding of precisely how and why feathers first arose and when the first birdlike creature realized they were useful for flight. Meanwhile, kids had better get used to the idea that T. rex may have started life looking an awful lot like Tweety Bird.