A new Yale-led study in the journal Nature that explores the evolutionary foundations of the avian hip bone, have identified that birds in their embryonic phase form a pelvis like that of the dinosaurs.
“Every bird, in its early life, possesses this dinosaur-like shape,” Bhart-Anjan S. Bhullar, assistant professor of Earth and planetary sciences at Yale and lead and corresponding author of the new study, said in a statement. “Then at the last minute, it’s like he remembers he’s a bird and he needs a bird’s pelvis.”
Over the past decade, Bhullar and his collaborators have conducted groundbreaking research on key evolutionary transitions between dinosaur, reptile, and bird species, including the development of the inner ear of dinosaurs, the beak of birds, the movable jaw of mammals and sight in vertebrates.
Christopher Griffin, a postdoctoral associate in Bhullar’s lab, is the lead author of the study. They looked at pelvic development in alligators, domestic chickens, Japanese quail, Chilean tinamou, and parakeets, and compared their developmental stages to those of dinosaurs, including the feathered species Archeopteryx.
They found that the avian pelvis is an example of “terminal addition,” a biological mechanism in which ancestral features appear in an animal until late in its development. This was a surprise, Griffin noted, because many important features in the transition from dinosaur to bird, such as the bird’s beak, are seen early in a bird’s embryonic development.
“It was unexpected to find that these early stages of bird development looked so much like the hips of an early dinosaur,” Griffin said. “Over just two days, the developing embryo changes in a way that mirrors how it changed in evolution, going from resembling an early dinosaur to resembling a modern bird.”
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