Now, the discovery of six new dinosaur fossils in Siberia suggests feathers weren't exclusive to theropods. Paleontologists recently wrapped up their analysis of six Kulindadromeus zabaikalicus specimens, and the scientists say the 4.5-foot-long, two-legged species not only had feathers and ate plants but also belonged to a dino lineage distinct from theropods.
"Probably that means the common ancestor of all dinosaurs had feathers," explained lead researcher Pascal Godefroit, a paleontologist at the Royal Belgian Institute of Natural Science in Brussels. "Feathers are not a characteristic [just] of birds but of all dinosaurs."
The discovery is detailed in the latest issue of Science Magazine.
The scientists say they're not sure what purpose the feathers played, as most dinosaurs could not and did not take to the air. But the evidence is now pretty clear, they say: feathers have deep evolutionary roots.
"This does mean that we can now be very confident that feathers weren't just an invention of birds and their closest relatives, but evolved much deeper in dinosaur history," said Stephen Brusatte, researcher at the United Kingdom's University of Edinburgh.
The scientists liken the revelation to the concept of all mammals having hair. But just like some of the world's largest mammals have very little hair, like elephants, researchers say the biggest dinosaurs probably had few noticeable feathers.