Dinosaur feathers may have been more birdlike than previously thought

Feather proteins can change during fossilization, a study finds

An illustration of the nonavian dinosaur Sinornithosaurus seen running in profile on a white background.

An analysis of fossilized feathers, including one from the nonavian dinosaur Sinornithosaurus (illustrated), suggests that the fossilization process can leave misleading clues about the evolution of feathers.

FunkMonk/Wikimedia Commons (CC BY-SA 3.0)

Many feathered dinosaurs couldn’t fly — at least, not like birds do today. But the reptiles’ feathers may have been more birdlike than scientists thought.

In 2019, fossil analyses found that feathers from a flightless dinosaur mostly contained a different, more flexible form of the keratin protein that makes up modern bird beaks, scales and feathers. Researchers suggested then that feathers had evolved molecularly over time to become stiffer as birds — the last living dinosaurs — took to the skies (SN: 7/31/14).

Yet fossilization can change feather proteins, making one keratin protein resemble another, researchers report in the October Nature Ecology & Evolution.  The team also presented their findings on October 19 at the Society for Vertebrate Paleontology’s annual meeting in Cincinnati.

The study raises the possibility that dinosaur feathers may have mainly contained the beta-keratin proteins found in bird feathers. While such a finding would not imply all feathered dinosaurs flew, it does raise new questions about feather evolution.

The work also gives scientists valuable insight into one way the fossil record may transform over time, says Julia Clarke, a vertebrate paleontologist at the University of Texas at Austin who was not involved in the new research. “There’s still a lot more to discover about the process of chemical alteration that all structures undergo during the process of rock formation, liquification and burial,” she says.

For the new study, paleontologist Tiffany Slater of University College Cork in Ireland and colleagues placed modern bird feathers under heat conditions that mimic what deeply buried dinosaur feathers may have endured during fossilization. Beta-keratins in the feathers unfolded and reformed in the shape of alpha-keratins, the more flexible form previously found to be dominant in dinosaur feathers, suggesting that a similar process had occurred in those feathers.

The researchers next examined a roughly 50-million-year-old bird feather and a 125-million-year-old feather from the nonavian dinosaur Sinornithosaurus. To their surprise, the bird feather seemed to consist mainly of alpha-keratins. Since it should have been rich in the beta variety, the team suspects that the proteins transformed during fossilization. The dinosaur feather, by contrast, contained mainly beta-keratins, suggesting it wasn’t exposed to enough heat to morph its proteins.

The simplest interpretation is that the distorting effects of fossilization led previous researchers astray in thinking dinosaur and bird feathers were so different molecularly, Slater says.

But the conditions the team tested in the new study may not accurately replicate what occurred during centuries of burial, says molecular paleontologist Mary Schweitzer of North Carolina State University in Raleigh, who was involved in the 2019 research.

In her own work, feathers exposed to even higher temperatures preserved their proteins well when kept in sediment, rather than removed from it as in the current study. The effect fossilization has on feather proteins may be more complex and as yet misunderstood, she believes.

Scientists increasingly think that feathers did not evolve for flight. Instead, they probably kept dinosaurs warm and helped them attract mates (SN: 2/4/10). But some nonavian dinosaurs did launch themselves into the air and glide from place to place (SN: 10/28/16). And some that couldn’t fly still flapped their wings as they ran (SN: 5/2/19).

If feathers are only one piece of the puzzle of how flight evolved, keratin composition may be an even smaller sliver, says Matthew Shawkey, a biologist at Ghent University in Belgium, who wasn’t involved in the new research. “Would a feather made of alpha-keratin really be so flimsy?” he asks. “I just don’t know.”

More important for the evolution of flight, he thinks, may be the shape of feathers, whether they have veins, and how they are arranged relative to one another.

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