New discovery shows how scales became feathers in dinosaurs

At some point hundreds of millions of years ago, dinosaur scales evolved into feathers. New research sheds some light on how this happened.

It is widely accepted that modern birds are descendants of dinosaurs. One need only look at a bird’s foot to see the unmistakable similarity to that of a theropod dinosaur such as Tyrannosaurus rex or Velociraptor.

When we think of birds, the first thing we think of is feathers.

Somewhere on their evolutionary journey, dinosaurs’ scales must have developed into these filaments which today help birds dazzle, impress, stay warm and, of course, fly.

New research published in Nature Communications might help explain how and when that transition occurred.

Palaeontologists from University College Cork (UCC) in Ireland have found that some feathered dinosaurs had scaly skin like reptiles. Their results are based on an analysis of a new specimen of the feathered dinosaur Psittacosaurus.

These creatures were ceratopsians – related to the Triceratops. But, unlike their massive, horned relatives, Psittacosaurus were small, bipedal nimble dinosaurs, weighing no more than 100kg. They lived roughly 135–100  million years ago during the early Cretaceous of what is now Asia. This is about the time in which dinosaurs were evolving into animals that would be recognisable today as birds.

There are up to 12 known species of Psittacosaurus – the most of any dinosaur genus. One specimen made waves when it was discovered with preserved filaments on its tail – early feathers.

By the time Psittacosaurus came around, many dinosaurs already had feathers. In fact, some palaeontologists suggest that most, if not all, dinosaurs had at least some feathers by the time of the mass extinction event 66 million years ago.

It is believed that modern birds are descendants of feathered theropods, not ceratopsians. Nevertheless, studying the development of feathers in Psittacosaurus could help explain how the transition from scales to feathers occurred.

A new Psittacosaurus fossil specimen found in northeastern China, dated to between 133 and 120 million years ago, was analysed by the UCC team, along with researchers from Nanjing University in China.

The team used ultraviolet light to identify patches of preserved skin. Further X-ray and infrared analysis revealed spectacular detail of the cell structure of the fossilised skin.

Dinosaur fossil under uv light
Studied Psittacosaurus specimen NJUES-10 under natural (upper half) and UV light (lower half) showing the orange-yellow fluorescence of the fossil skin. Credit: Dr. Zixiao Yang.

“The fossil truly is a hidden gem,” says lead author Zixiao Yang from UCC. “The fossil skin is not visible to the naked eye, and it remained hidden when the specimen was donated to Nanjing University in 2021. Only under UV light is the skin visible, in a striking orange-yellow glow.”

“The evolution of feathers from reptilian scales is one of the most profound yet poorly understood events in vertebrate evolution,” adds senior author Maria McNamara, also at UCC. “While numerous fossils of feathers have been studied, fossil skin is much more rare.”

“Our discovery suggests that soft, bird-like skin initially developed only in feathered regions of the body, while the rest of the skin was still scaly, like in modern reptiles,” McNamara adds. “This zoned development would have maintained essential skin functions, such as protection against abrasion, dehydration and parasites. The first dinosaur to experiment with feathers could therefore survive and pass down the genes for feathers to their offspring.”

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