Scientists have unveiled significant insights into the evolutionary history of flight in birds and their dinosaur ancestors, shedding light on a previously overlooked aspect of their anatomy: the number and characteristics of their flight feathers.
The research was led by Jingmai O’Connor, a renowned paleontologist at the Field Museum in Chicago, and Yosef Kiat, a postdoctoral researcher at the same institution.
By analyzing the intricate details of feather evolution from dinosaurs to modern birds, the team has gained a new perspective on how these creatures developed the ability to fly.
The experts meticulously examined specimens from 346 species of living birds housed in museum collections worldwide, alongside 65 fossil specimens representing 35 different species of feathered dinosaurs and extinct birds.
“Yosef, an ornithologist, was investigating traits like the number of different types of wing feathers in relation to the length of arm bone they attach to, and the degree of asymmetry in birds’ flight feathers,” said O’Connor. “Through our collaboration, Yosef is able track these traits in fossils that are 160-120 million years old, and therefore study the early evolutionary history of feathers.”
The extensive study revealed a striking commonality among all flying birds: the presence of between 9 and 11 primary feathers on their wings.
This characteristic contrasts sharply with flightless birds, where the number of primary feathers can significantly vary. Penguins, for example, boast more than 40 primary feathers, while emus have none. This finding suggests a fundamental “rule” that had been overlooked by scientists until now.
“It’s really surprising, that with so many styles of flight we can find in modern birds, they all share this trait of having between 9 and 11 primary feathers,” said Kiat. “And I was surprised that no one seems to have found this before.”
The significance of this discovery extends beyond the mere count of feathers. It provides invaluable insights into the evolutionary processes that govern bird physiology.
According to the researchers, the number of primary feathers changes over extensive time periods, indicating a slow evolutionary pace for this trait.
Such slow evolution suggests that the primary feather count is a stable characteristic within bird lineages. By applying these insights to the fossil record, the team could infer the flight capabilities of ancient birds and dinosaurs.
The feathered dinosaur Caudipteryx, despite possessing the requisite number of primary feathers, had almost symmetrical feathers and wing proportions that would have made flight impossible. This anomaly suggests that Caudipteryx might have descended from an ancestor capable of flight but lost this ability over time.
Conversely, the presence of flight-ready wing features in other fossils, such as Archaeopteryx and Microraptor, supports the notion of a single evolutionary origin for flight among dinosaurs.
“It was only recently that scientists realized that birds are not the only flying dinosaurs,” said O’Connor. “And there have been debates about whether flight evolved in dinosaurs just once, or multiple separate times.”
“Our results here seem to suggest that flight only evolved once in dinosaurs, but we have to really recognize that our understanding of flight in dinosaurs is just beginning, and we’re likely still missing some of the earliest stages of feathered wing evolution.”
“Our study, which combines paleontological data based on fossils of extinct species with information from birds that live today, provides interesting insights into feathers and plumage – one of the most interesting evolutionary novelties among vertebrates,” said Kiat.
“Thus, it helps us learn about the evolution of these dinosaurs and highlights the importance of integrating knowledge from different sources for an improved understanding of evolutionary processes.”
O’Connor noted that theropod dinosaurs, including birds, are one of the most successful vertebrate lineages on our planet.
“One of the reasons that they’re so successful is their flight. One of the other reasons is probably their feathers, because there’s such versatile structures. So any information that can help us understand how these two important features co-evolved that led to this enormous success is really important.”
The study is published in the journal Proceedings of the National Academy of Sciences.
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