It isn't clear how and when feathered dinosaurs, the ancestors of present day birds, started to fly. Analysis of the fossilized remains of a winged dinosaur that lived in China 160 million years ago, however, offered clues on the evolution of flight.
The crow-sized dinosaur called Anchiornis lived 10 million years before the Archaeopteryx, the first recognized bird.
Modern vertebrates that walk on land have the protein called keratin. Alpha-keratins (α-keratins) are in the 10 nanometer-wide filaments of the hair, skin, and nails of humans and other mammals.
In reptiles and birds, beta-keratins (β-keratins) form the narrower but more rigid filaments that make up the beaks, claws, and feathers.
Study researcher Mary Schweitzer, from North Carolina State University in Raleigh, explained that modern bird feathers are primarily composed of β-keratin. Feathers, however, differ from other beta-keratin tissues because the feather protein is modified in a way that made it more flexible and more conducive to flight.
"At some point during the evolution of feathers, one of the β-keratin genes underwent a deletion event, making the resultant protein slightly smaller. This deletion changed the biophysics of the feather to something more flexible — a requirement for flight," Schweitzer said.
The researchers said that knowing when and in what organisms the deletion event occurred can provide researchers a better understanding of how flight evolved when dinosaurs transitioned to birds.
Anchiornis Feathers Have Both Alpha-keratins And Beta-keratins
Using high-resolution electron microscopy, as well as chemical and immunological techniques, researchers took a closer look at the fossilized feathers of the Anchiornis and compared these to those of younger fossil birds and modern birds at the molecular level.
The researchers found that the feathers of the Anchiornis is composed of both β-keratins and α-keratins, which is surprising since α-keratin is present in only small amounts in modern feathers. The Anchiornis feathers has also already undergone the deletion event that made feathers different from other tissues.
The findings suggest that during the transition to flight, the β-keratin gene was duplicated many times in the genomes of some dinosaurs. As these animals evolved, some of the extra copies mutated into the truncated form that made flight possible.
This allowed the feathered dinosaurs such as the Archaeopteryx to take flight around 150 million years ago and gave rise to modern-day birds.
Researchers said that the Anchiornis feathers were not likely suitable for flight, but represents an intermediate stage in the evolution toward flight feathers.
The findings were published in the Proceedings of the National Academy of Sciences.