Science: Fossils Suggest Feathers Were Widespread Among Dinosaurs

The new finds from two sites in Russia suggest that all major groups of dinosaurs may have had at least a few feathered species.
Artist's reconstruction of Kulindadromeus zabaikalicus, from the Jurassic period, in its natural environment. | Andrey Atuchin

Fossils unearthed in Siberia suggest that feathers may have been more widespread among dinosaurs than scientists have thought. Instead of being limited to theropods, the dinosaur group associated with the first bird, feathers may have been present among all dinosaur groups, a new study in the 25 July issue of Science reports.

In recent years in China, quill-like structures have been found in ornithischian dinosaurs, the group of herbivorous creatures that served as prey for the mostly flesh-eating theropods. But, it has been unclear whether the structures found in ornithischian dinosaurs are true feathers.

"Here, for the first time, we found compound, feather-like structures resembling those found in theropod dinosaurs, in the ornithischian clade," explained the study's lead author Pascal Godefroit, head of the Directorate Earth and History of Life at the Royal Belgian Institute of Natural Sciences in Brussels. "So we can now confidently suppose that feathers characterize the whole dinosaur group."

Feathers are often seen as the defining feature of birds. But, scientists have known for some time that feathers evolved in dinosaurs long before birds arrived on the scene, and that feathers are part of the evidence suggesting that birds are direct dinosaur descendants.

Charles Darwin was the first to propose this; he compared the skeletal structure of a small theropod dinosaur with that from one of the earliest known birds, Archaeopteryx, and showed that the two were quite similar.

Then, in the 1990s, well-preserved theropod fossils with feathers of all kinds — from simple bristles to fully elaborated flight-type feathers — were found in China, providing evidence for birds as direct descendants of theropods.

 
In this episode of Science with a Twist, Marshall Bradshaw explains why feathers may have evolved long before they were used for flight. | AAAS/ Carla Schaffer

Now, based on six partial skulls and several hundred skeletons unearthed from two locations in Russia, Godefroit and his colleagues describe a new dinosaur outside the theropod group that displays feather-like structures.

"The structures resemble those found in relatively advanced theropod dinosaurs," Godefroit explained. "It was a true surprise to find them associated with the fossils of a plant-eating ornithischian dinosaur."

They call the ornithischian creature they found Kulindadromeus zabaikalicus. It had tiny, feather-like filaments on its head and back, and more complex, grouped filaments — 10 to 15 millimeters long — around the humerus, femur, and tibia bones. The grouped filaments were the most feather-like of all, the researchers say, resembling the down feathers of some modern chicken breeds such as the Silkie, a fluffy bird thought to have originated in China.

Godefroit and his team found the bones of Kulindadromeus zabaikalicus side by side with fossils of plants, insect larvae, and freshwater crustaceans, leading them to believe they were in what once was a lake. Curiously, their new specimen's soft tissue of scales and feather-like structures were exceptionally well-fossilized. The bones, by contrast, were less well preserved.

"Our next step," Godefroit explained, "is to study the most complete material discovered on this expedition and to explain the unusual fossilization conditions, why the soft tissues are so exquisitely preserved although the bones are not. For the moment, we have no answers to this."

The work of Godefroit and his team supports earlier suggestions that feathers didn't first arise for purposes of flight, but instead, existed for many millions of years before birds evolved. They may have been adapted for insulation purposes or for signaling to attract mates, the researchers said, and only later co-opted for flight.