Proteins found in fossil dinosaur feathers shed light on links to birds

Analysis of proteins from fossilised dinosaur feathers from China have revealed that we may have misjudged our fine feathered dino friends.

Previously, studies have suggested that the proteins recovered from dinosaur fossils indicate that the animals tended to have feathers that were less stiff than those of a modern bird. But a study published in the journal Nature Ecology and Evolution uses a new approach to propose that dinosaur feathers were actually very similar in their protein composition to those of modern birds.

“It’s really exciting to discover new similarities between dinosaurs and birds,” says lead author and University College Cork (UCC) palaeontologist Dr Tiffany Slater. “Using X-rays and infrared light, we found that feathers from the dinosaur Sinornithosaurus contained lots of beta-proteins, just like feathers of birds today. This finding validates our hypothesis that dinosaur birds had stiff feathers – like in modern birds.”

Today’s birds evolved from small two-legged theropod dinosaurs that evolved feathers and even flight long before the extinction event which saw the end of the “Age of the Dinosaurs” 66 million years ago.

In fact, birds are living dinosaurs.

But exactly when powered flight evolved among these pioneering bird-dinosaurs remains a mystery. It is believed that dinosaurs first evolved feathers as insulation to keep warm. They then would have developed into ornamental and locomotive tools later.

Earlier tests found dinosaur feathers tended to have alpha-keratin proteins. This made their feathers less stiff, whereas birds today have feathers rich in beta-keratin proteins making them stronger and more suited for flight.

What was not clear, however, was whether the alpha-keratin richness of dino feathers was actually because of the fossilisation process, rather than being part of the feathers in life.

Slater led a team which analysed 125-million-year-old feathers from dinosaur Sinornithosaurus and the early bird Confuciusornis, both from China. They also examined a 50-million-year-old feather from the US.

The researchers placed the fossilised feathers in front of the powerful X-rays at the Stanford Synchrotron Radiation Light Source (SSRL) at the Department of Energy’s SLAC National Accelerator Laboratory. Separate experiments also simulated the temperatures the fossils would have been subjected to over time.

The analysis revealed that, while some fossil feathers do show signs of having a lot of alpha-keratin, they likely formed over time rather than being present originally. It is believed they could have formed due to the high extreme heat that fossils experience.

“Our experiments help explain that this weird chemical discrepancy is the result of protein degradation during the fossilisation process,” Slater says. “So, although some dinosaur feathers do preserve traces of the original beta-proteins, other fossil feathers contain alpha-proteins that formed during fossilisation.”

“The idea that original protein compositions may change over time is an often-overlooked aspect of looking at biomarkers from deep time,” says SSRL Scientist Sam Webb. “Comparing our X-ray spectroscopy results to the additional lab measurements of experimentally heated feather samples helped calibrate our findings.”

“Traces of ancient biomolecules can clearly survive for millions of years, but you can’t read the fossil record literally because even seemingly well-preserved fossil tissues have been cooked and squashed during fossilisation,” says senior author and UCC professor Maria McNamara. 

“We’re developing new tools to understand what happens during fossilization and unlock the chemical secrets of fossils. This will give us exciting new insights into evolution.”