All babies have a moment before hatching when their hip bone is a tiny replica of a dinosaur’s pelvis.
That’s one of the findings of a new study led by Yale in the journal Nature which explores the evolutionary foundations of the avian hip bone. It’s also a modern look at the dramatic transformation that led from dinosaurs to birds over tens of millions of years.
“Every bird, in its early years of life, possesses this dinosaur shape,” said Bhart-Anjan S. Bhullar, assistant professor of earth and planetary sciences at Yale and lead and corresponding author of the new study. “Then at the last minute, it’s like he remembers he’s a bird and needs a bird’s pelvis.”
Over the past decade, Bhullar and his collaborators have conducted ground-breaking research on key evolutionary transitions between species of dinosaurs, reptiles and birds, including the development of the dinosaur inner ear, the beak of birds, the jaw rolling of mammals and sight in vertebrates.
Bhullar’s lab is particularly known for its innovative use of computed tomography (CT) and microscopy to create 3D images of animal embryos.
Christopher Griffin, a postdoctoral associate in Bhullar’s lab, is the lead author of the study. He and Bhullar, with colleagues, looked at pelvic development in alligators, domestic chickens, Japanese quail, Chilean tinamous and parakeets, and compared their developmental stages with those of dinosaurs, including the feathered species Archeopteryx .
For the study, the team labeled embryonic hip bones with antibodies to look for proteins that are expressed in developing cartilage, connective tissue, skeletal muscles and nerves. The researchers created 3D images of the bones, muscles and nerves of the hip using confocal microscopes and CT scans.
They found that the bird’s pelvis is an example of “terminal addition,” a biological mechanism in which ancestral traits appear in an animal late in its development. That was a surprise, Griffin noted, because many features important in the dinosaur-to-bird transition, 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. “In just two days, the developing embryo changes in a way that reflects how they changed in evolution, going from looking like an early dinosaur to looking like a modern bird.”
The hip bone is the core of a bird’s body. It runs the length of the avian structure, engulfing the torso, while allowing the bird to stand, move, and bear the weight of its entire body.
“The bird’s body is incredibly modified in virtually every way to create an optimized flying machine,” Bhullar explained. “Its body structures are strongly constrained by the needs of aeronautical design.”
The new study also looked at the avian muscles and nerves involved in hip development. The researchers said that the development of these systems was not synchronous with bone development, implying that each system was somewhat “decoupled” from the others.
Scientists find the first bird beak, right under their noses
Christopher T. Griffin et al, The developing bird pelvis passes through conditions ancestral to dinosaurs, Nature (2022). DOI: 10.1038/s41586-022-04982-w
Provided by Yale University
Summons: Developing bird pelvis goes through ancestral dinosaur conditions (2022, August 5) Retrieved August 6, 2022, from https://phys.org/news/2022-08-bird-pelvis-ancestral- dinosaurian-conditions.html
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