Birds can fly; At least most of them can fly. Flightless birds such as penguins and ostriches have adapted to life without needing to fly. Despite this, there is a significant gap in the scientific understanding of the differences in the wings and feathers of flightless birds and flying birds.

A new study in the journal PNAS Scientists examined hundreds of birds in museum collections and discovered a number of feather characteristics common to all flying birds. These “rules” provide clues about how dinosaurs, the ancestors of today’s birds, first developed the ability to fly and which dinosaurs had the ability to fly.

Evolutionary origin of bird flight

Not all dinosaurs evolved into birds, but all living birds are dinosaurs. Birds belong to a group of dinosaurs that survived an asteroid hitting Earth 66 million years ago. Long before the asteroid impact, some members of a group of dinosaurs called penneraptorans began developing feathers and the ability to fly.

Members of the penneraptoran group began to develop feathers before flying; The primary purpose of feathers may be to provide insulation or to attract mates. Example, velocirpato It had feathers but could not fly.

Of course, scientists can’t get in a time machine and go back to the Cretaceous period to see if they can do it. velociraptors fly. Instead, paleontologists rely on clues such as the size and shape of arm/wing bones and crossed arms in fossilized animal skeletons and the shape of surviving feathers to determine which species was capable of true, powerful flight. For example, the long main feathers on the wing tips of birds are asymmetrical in flying birds and symmetrical in flightless birds.

Discovery in the evolution of the pen

The search for clues about dinosaur flight led to a collaboration between Jingmai O’Connor, a paleontologist at the Field Museum in Chicago, and Field doctoral student Yosef Kiat.

“Joseph, an ornithologist, studied characteristics such as the number of different types of wing feathers and the length of the humerus to which they attach, and the degree of asymmetry in birds’ flight feathers,” O’Connor said. a museum employee. Curator of fossil reptiles specializing in early birds. “Thanks to our collaboration, Yosef is able to track these features in fossils that are 160-120 million years old and thus study the early evolutionary history of feathers.”

Kiat conducted a study of the feathers of every living bird species, examining specimens of 346 different species kept in museums around the world. When he looked at the wings and feathers of hummingbirds, hawks, penguins, and pelicans, he noticed a number of consistent characteristics among flying species. For example, in addition to asymmetrical feathers, all flying birds had from 9 to 11 primary feathers. In flightless birds, their numbers vary greatly – penguins have more than 40 and emu have none. This is a deceptively simple rule that seems to have eluded scientists.

Implications for understanding dinosaur flight

“With so many flight styles we can find in modern birds, it’s really surprising that they all have between 9 and 11 primary feathers,” says Kiat. “And I’m surprised no one found it before.”

Applying information about the number of primary feathers to the common family tree of birds, Kiat and O’Connor also found that it took a long time for birds to develop other numbers of primary feathers. “This feature only changes over very long periods of geological time,” says O’Connor. “It takes a very long time for evolution to influence and change this trait.”

The researchers also examined 65 fossil specimens representing 35 different species of modern birds, as well as feathered dinosaurs and extinct birds. Using data from modern birds, the researchers were able to extrapolate information about the fossils. “Essentially, you can look at the overlap between the number of primary feathers and the shape of those feathers to determine whether a fossil bird could fly and whether its ancestors could fly,” O’Connor says.

For example, researchers looked at a feathered dinosaur caudipteryx. caudipteryx It had 9 primary feathers, but these feathers were almost symmetrical and the proportions of its wings made flying impossible. Researchers perhaps caudipteryx They had an ancestor with the ability to fly, but this ability was lost over time. caudipteryx arrived at the scene.

It is not volatile as it takes a long time for the number of primary feathers to change. caudipteryx It retained its 9 main feathers. Meanwhile, the wings of other feathered fossils, including the wings of the oldest known bird, also appeared ready for flight. archeopteryx And microraptorA small four-winged dinosaur that was not a direct ancestor of modern birds.

Integration of knowledge about evolution

Taken a step further, these data could spark a debate among scientists about the origins of dinosaur flight. “Only recently have scientists realized that birds were not the only dinosaurs that flew,” says O’Connor. “And there has been debate about whether flight evolved only once or several times in dinosaurs. Our results seem to suggest that dinosaur flight evolved only once, but in fact we must recognize that our understanding of flight in dinosaurs is only just beginning and that we are probably still missing some of the earliest stages of the evolution of feathered wings.” .”

“Our study, which combines paleontological data obtained from fossils of extinct species with information about living birds today, provides interesting information about feathers and plumage, one of the most interesting evolutionary innovations among vertebrates. In this way, it helps us learn about the evolution of these dinosaurs and their evolutionary processes.” It highlights the importance of integrating information from different sources to better understand,” says Kiat.

“Theropod dinosaurs, including birds, are among the most successful vertebrate lineages on our planet,” says O’Connor. “One of the reasons for their success is their flying. Another reason is probably their feathers, because they have a versatile structure. “So any information that can help us understand how these two important functions co-evolved to lead to this great achievement is really important.”