Fossils from a dinosaur species recently discovered in Liaoning province seem to fly in the face of everything the scientific community knows - or at least thought it did - about the evolutionary development of feathers.
The sub-adult Tianyulong Confuciusi, which was covered with feather-like structures, dates back to the early Cretacious Period (144-99 million years ago), when the first dinosaurs emerged - long before anything like feathers had been believed to have started developing.
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This artistic rendering of feathered dinosaurs is based on fossils recently discovered in Liaoning province.
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And the find, described in the journal Nature, presents another stumper: "This order of dinosaur was never supposed to have had anything like feathers," Chinese Academy of Geological Sciences paleontologist You Hailu said.
Tianyulong belonged to the Ornithischia, or "bird-hipped" order, which, despite what its Latin name might suggest, had been believed to have never developed any feather-like structures - that is, until Tianyulong was discovered with three patches of skin covered with "proto-feathers", more commonly known as "dino-fuzz".
The Ornithischia order also included lumbering armored sauropods, such as Triceratops and Stegosaurus.
It was theropods among the "lizard-hipped" Saurischia order that are known to have developed feathers and evolved into birds.
"Tianyulong is the first Ornithischian to have feather-like structures all over its body," You said.
"In addition, it belongs to the heterodontosaurids, the most evolutionarily basal branch of the entire great radiation of herbivorous dinosaurs, the Ornithischia."
Tianyulong had a gracile body, estimated to be 70 cm long, a 6-cm-long cranium and a 44-cm-long tail.