Almost all dinosaurs were probably covered in feathers, Siberian fossils of a tufted, two-legged running dinosaur dating from roughly 160 million years ago suggest.

Over the past two decades, discoveries in China have produced at least five species of feathered dinosaurs. But they all belonged to the theropod group of "raptor" dinosaurs, ancestors of modern birds. (Related: "Dinosaur-Era Fossil Shows Birds' Feathers Evolved Before Flight.")

Now in a discovery reported by an international team in the journal Science, the new dinosaur species, Kulindadromeus zabaikalicus (KOO-lin-dah-DRO-mee-us ZAH-bike-kal-ik-kuss), suggests that feathers were all in the family. That's because the newly unearthed 4.5-foot-long (1.5 meter) two-legged runner was an "ornithischian" beaked dinosaur, belonging to a group ancestrally distinct from past theropod discoveries.

"Probably that means the common ancestor of all dinosaurs had feathers," says study lead author Pascal Godefroit of the Royal Belgian Institute of Natural Science in Brussels. "Feathers are not a characteristic [just] of birds but of all dinosaurs." (Related: "Dinosaur Feathers Changed With Age.")

The fossils, which included six skulls and many more bones, greatly broaden the number of families of dinosaurs sporting feathers—downy, ribboned, and thin ones in this case—indicating that plumes evolved from the scales that covered earlier reptiles, probably as insulation. In addition to its feathers, Kulindadromeus also had scales, notably arched ones that appeared in rows on its long tail.

"It's really fantastic that dinosaurs with 'fluff' are found outside of China," says paleontologist Jakob Vinther of the United Kingdom's University of Bristol, who was not on the discovery team. "The material and specimens are nothing short of fantastic; their age and sheer number are rarely to be expected."

Kulindadromeus adds a whole new dimension to understanding feather evolution, Vinther says, pointing to the fact that the three feather types found as imprints with the fossils are different from ones found on feathered dinosaurs or modern birds.

What exactly did all these different feathers do? "I don't know; nobody knows for sure," Godefroit says. "These animals couldn't fly, that's all we can tell you."

Jurassic Peeps

During the Jurassic, Kulindadromeus lived near what is now Siberia's Kulinda River, sporting feathery tufts on its legs and elbows, as well as more streamlined feathers on its back. Its shins had "ribbon-shaped" feathers of a type never seen before.

At least six skulls of the species, along with hundreds of bones, have turned up in a fossil bed that was once a lake bottom and is now a Siberian hillside. Most of the fossils were juveniles, which suggests that they died in single events, not in a mass catastrophe, according to Godefroit.

The dinosaur's name essentially means "Kulinda River running dinosaur." Zabaikalsky Krai is the region of Siberia where it was discovered (which explains its species name, zabaikalicus).

"There were lakes and there were volcanoes there, lots of volcanoes," Godefroit says. The plant-eating dinosaurs likely died and fell to the lake bottom, where eruptions soon after covered them with a fine ash. That is what preserved the feather imprints with the fossil bones.

"We don't know how big this fossil bed is, and it is likely we will find more when we go back," Godefroit says.

The Feather Connection

The scales on Kulindadromeus resemble the scaly skin seen on some birds, the study says, which also argues for a deep genetic root linking dinosaurs to birds.

Two earlier ornithischian dinosaur discoveries, both from China, had hinted that featherlike bristles had covered dinosaurs, notes paleontologist Stephen Brusatte of the United Kingdom's University of Edinburgh.

"But the new Siberian fossils are the best example yet that some ornithischian [beaked] dinosaurs had feathers, so it wasn't only the theropods that had downy coats," Brusatte says.

"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," he adds. "I think that the common ancestor of dinosaurs probably had feathers, and that all dinosaurs had some type of feather, just like all mammals have some type of hair."

Even so, Godefroit suggests that the largest dinosaurs likely had the fewest feathers, as they wouldn't have needed them for insulation. "Just like elephants in Africa don't need fur," he says.