A primitive form of feather may have evolved much earlier than was previously thought, according to an analysis of a dinosaur fossil that is more than 100 million years old. The specimen supports arguments that dinosaurs may have used feathers for display.
Finding feathers in dinosaurs is becoming a common occurrence. This is especially true in China’s Liaoning Province, where fine-grained sedimentary rocks often contain fossils with exquisite details still intact. But all of these feathered fossils have been of the bipedal, carnivorous theropod lineage, which includes Tyrannosaurus and Velociraptor.
Now, Xiao-Ting Zheng at the Shandong Tianyu Museum of Nature in China suggests that feathers were not limited to the theropods. He and his colleagues have discovered a dinosaur fossil in Liaoning that has long feather-like structures sticking up from its body. Based on the bones present, it looks like it was small, active, agile, and probably eating a mix of insects, small vertebrates and plants.
The team has identified the species as a heterodontosaurid from the Early Cretaceous period, which began about 144 million years ago. This in itself is remarkable as heterodontosaurids were most widespread during Late Triassic times, more than 65 million years earlier, and animal groups rarely survive for such long periods of geological time. “Heterodontosaurids are exceptionally rare, and previously unknown from Asia,” says Richard Butler at the Natural History Museum in London. This fossil “confirms that heterodontosaurids, one of the oldest groups of dinosaurs, survived into the Cretaceous”, Butler adds.
Dinosaurs are divided into two main orders: saurischians, which have forward-pointing pubic bones, and ornithischians, which have backward-pointing pubic bones. All previous feathered theropods belong to the saurischian order, whereas the new fossil belongs to the ornithischian.
The find “pulls the origin of feathers down into the Triassic, when the saurischian and ornithischian lineages of dinosaurs split”, says Philip Currie at the University of Alberta in Canada. The fossil is described this week in Nature1.
Birds of a feather
The feathery structures found on this heterodontosaurid, dubbed Tianyulong confuciusi, are not like those found on modern birds or even on some of the smaller, more bird-like theropods. Whereas modern feathers are flexible and have a central shaft with vanes that run off either side at angles, the feathers on T. confuciusi are all relatively stiff and lack vanes.
To date, only one ornithischian fossil find has suggested the presence of anything that approximates feathers: Psittacosaurus has bristle-like structures on its tail that have been hotly debated. T. confuciusi will no doubt add fuel to the debate about whether feathers evolved once, twice or many times.
Hai-Lu You, one of the palaeontologists who identified T. confuciusi, believes that the fossil supports the idea of a single evolution of feathers. “We still have some missing data between T. confuciusi and feathered theropod dinosaurs, but I think further discovery will fill these gaps,” he says. If this proves to be true, then many dinosaurs may once have sported feather-like structures, with descendant species losing the characteristic later on.
At present, no-one is sure of the function of the protofeathers. “If these are protofeathers, then they were not related in any way to flight,” explains Butler. “The fact that the filaments over the tail are so long and stiff suggests a possible display function.”
“Dinosaurs were clearly highly visual animals that not only modified their skeletons for show, but exaggerated their effect through external structures,” adds Currie. “It doesn’t take that much to imagine dinosaurs as colourful as their descendants — the birds.”