Pterosaurs, those flying reptiles that soared over the heads of dinosaurs, have long been depicted with scaly skin and bat-like, hairless wings. But a new study paints them as far cuddlier creatures than we might have thought. According to an international team of palaeontologists, pterosaurs were covered in no less than four different types of feathers, pushing back the origin of this bodily covering by about 70 million years.

It's long been known that pterosaurs were at least partly covered in fuzzy stuff called "pycnofibers," but more details on the nature of it has only really come to light in the past few years. It was thought that the coat only covered the animals' heads and part of the body, but not the wings, and was made up of filaments far simpler than the complex structures that modern feathers have become.

But the new discovery turns both of those ideas upside down. Not only did the pycnofibers cover almost all of the pterosaurs' bodies, but they consisted of four distinct types of feathers. There are simple, hair-like filaments; brush-like bunches that split at the ends; filaments that have a little tuft about halfway down the length; and soft, downy feathers like those on modern bird chicks.

These different types were found on different parts of the body. The individual filaments were spread almost everywhere. The brush-tipped feathers covered parts of the head, limbs and tail. The tufted form were found only on the head. And finally, the down was on the wing membranes.

The discovery was made by examining two pterosaur fossil specimens found in the Daohugou Formation in Mongolia. The researchers, hailing from the Universities of Nanjing, Bristol, Cork, Beijing, Dublin and Hong Kong, used high-powered microscopes to look over the fossils to reveal the structure, distribution and even color of the feathers.

"Some critics have suggested that actually there is only one simple type of pycnofiber, but our studies show the different feather types are real," says Maria McNamara, an author of the study describing the find. "We focused on clear areas where the feathers did not overlap and where we could see their structure clearly. They even show fine details of melanosomes, which may have given the fluffy feathers a ginger color."

The find doesn't just give us a more accurate understanding of what pterosaurs looked like – it actually rewrites the history of the feather itself. It's long been known that two major groups of dinosaurs, including the ancestors of birds, sported feathers. But pterosaurs aren't dinosaurs, so the fact they were also dressed in feathery pelts means the feature must have come from an earlier ancestor common to both pterosaurs and dinosaurs. The researchers estimate that feathers must be 70 million years older than previously thought.

"We ran some evolutionary analyses and they showed clearly that the pterosaur pycnofibers are feathers, just like those seen in modern birds and across various dinosaur groups," says Mike Benson, an author of the study. "Despite careful searching, we couldn't find any anatomical evidence that the four pycnofiber types are in any way different from the feathers of birds and dinosaurs. Therefore, because they are the same, they must share an evolutionary origin, and that was about 250 million years ago, long before the origin of birds."

The research was published in the journal Nature Ecology & Evolution.

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