Many dinosaurs may have been covered in elaborate feathers similar to those of modern-day birds, according to a study of new fossils. The finding raises the possibility that the very earliest dinosaurs had feathers, and that such plumage was much more common than thought.
The prevailing theory is that the only feathery dinosaurs were two-legged flesh-eaters called theropods, such as Velociraptor. Ultimately, some theropods evolved into today’s birds via intermediates such as Archaeopteryx.
Theropods belong to one of the two major dinosaur groups, the saurischians. Now new fossils suggest that the other major group, the ornithischians, also bore feathers. Ornithischians were plant-eaters and include famous dinosaurs such as Triceratops, Iguanodon and Stegosaurus.
Recently, ornithischians have been found with what appear to be bristly feathers. But these putative feathers were very simple compared with those of theropods and birds. The latest fossil finds are far more elaborate.
Feathers, feathers everywhere
Pascal Godefroit of the Royal Belgian Institute of Natural Sciences in Brussels and his colleagues analysed six partial skulls and several hundred other fossils of limb and other bones from two sites in south-east Siberia. They all belong to a new ornithischian called Kulindadromeus zabaikalicus, which lived 160 million years ago.
K. zabaikalicus was about 1.5 metres long. It was bipedal, with a small, coot-like head and a pointed tail. It foraged for plants in swamps, using its front limbs to manipulate its food.
Uniquely, it had three kinds of preserved feather protruding from its bones. The simplest were bristle-like filaments like those of other ornithischians, covering its head, back and most of its body. “I think their function was primarily for insulation,” says Godefroit.
The second type of feather resemble the downy feathers found on modern-day birds. They sheathed the top halves of K. zabaikalicus‘s limbs.
The third kind were the most unusual, and were restricted to part of the animal’s lower legs. “They consist of clusters of six or seven ribbon-shaped elements bundled together,” says Godefroit. “There’s nothing like it in modern birds.” He suggests the second and third types of feathers were probably used for display.
The rest of the animal’s lower legs and feet, and the tail, were covered in scales, not feathers.
Origin of feathers
“This discovery provides the first convincing evidence that feathers were present in many groups of dinosaurs, and not only in the theropods most closely related to birds,” says Darla Zelenitsky at the University of Calgary in Alberta, Canada. Evidence of feathers on ornithischians may have been overlooked or dismissed, she says.
“This research provides the clearest evidence to date that feathers were present within the ornithischian half of the dinosaur family tree,” says Ryan McKellar of the Royal Saskatchewan Museum in Regina, Canada, who was not involved in the research. “Ornithischian plumage has the potential to be a much closer structural match to theropod proto-feathers [than the filaments seen before].”
Godefroit suggests that the earliest dinosaurs may have had feathers, before they split into ornithischians and saurischians around 220 million years ago.
McKellar is not convinced about that. He says the groups could have evolved feathers independently. “Until more groups are discovered with plumage associated there will be some room for debate,” he says.
Journal reference: Science, DOI: 10.1126/science.1253351
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