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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.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