Scientists have long known that very early dinosaurs, the ancestors of today's birds, have been covered with feathers, probably for warmth and for attracting friends. But no one knows exactly when – and how – these feathered dinosaurs took flight. Now, the molecular evidence from fossil fossils of dinosaurs reveals how key proteins that make up feathers become lighter and more flexible in time, as non-flying dinosaurs develop to flying birds and later birds.
All modern terrestrial animals with a backbone have keratin, proteins that make up everything – from nails and beaks, to scales and feathers. In humans and other mammals alpha-keratins form the 10-nanometer threads that make up hair, skin and nails. In crocodiles, turtles, lizards and birds, beta-keratins form even the narrower, firmer fibers that build nails, beaks and feathers.
Using all genomes of dozens of live birds, crocodiles, turtles and other reptiles, scientists have built a family tree of these animals over the last decade, based on how their beta-keratin changes over time. Among the findings: Modern birds have lost most of their alpha-keratin, but beta-keratins in their feathers have become more flexible due to the missing portion of glycine and tyrosine amino acids that make nails and beaks stiff. This suggests that the transition to the field requires both changes to take place.
Researchers have shown this directly, analyzing alpha and beta-keratins in a handful of extremely fossilized fossils from China and Mongolia. Researchers led by paleontologists Pan Yanghong of the Chinese Academy of Sciences in Beijing and Mary Schweitzer of the State University of North Carolina in Rallye created separate antibodies that bind to identifying segments of different alpha and beta-keratin proteins preserved in fossilized feathers of five species that lived between 160 and 75 million years ago. The antibodies were labeled with fluorescent labels that illuminate each time they bind to them.
The Pen of Anchiornisa wild-type dinosaur that lived 160 million years ago, illuminated to reveal the flexible cut beta-keratin found in modern birds, scientists today Notifications of the National Academy of SciencesBut the dinosaurs that preceded the first known bird, archeopteryx, with 10 million years – had even more alpha-keratins, which today are largely lacking in bird feathers. Considering that apart from the structural differences found by electronic microscopic analysis, this is likely Anchiornis Shakespeare says the feathers are not suitable for flight, but they are an intermediate stage in the evolution of flight crews.
Petrified feathers from a small 130-year-old dinosaur without a flight called Shuvuya (which is not the ancestor of today's birds) reveal that, like modern birds, it lacks alpha-keratins. But unlike Anchiornishis feathers were still composed of the larger, harder beta-keratin. "We begin to reveal the mosaic pattern of feather evolution," says Schweitzer, suggesting that the feather transition to the field requires both the mutations that eliminate most alpha-keratin and the truncated flexible beta-keratin.
"This kind of work is the dream of every evolutionary biologist," said Matthew Greenwalk, an evolutionary biologist at the University of South Carolina, Colombia, who helped build the former beta-keratin family tree. Taken together with modern genetic evidence, the new discovery suggests that during the transition to the flight the beta-keratin gene has been duplicated many times in the genomes of some dinosaurs. As the animals develop, some of the extra specimens then mutate in a truncated form that makes the flight possible. This not only allows feathered dinosaurs like archeopteryx to circle the sky about 150 million years ago, but it also generates all the crows, snakes, starlings and eagles that we have with us today.