Birds are much more like dinosaurs than we thought
This was discovered by an international research team who observed that before the egg hatches, the bird's hip bone is a tiny replica of a dinosaur's pelvis.
The embryo of a parakeet was imaged by laser scanning confocal microscopy. The skeleton is in green, the nerves are in light blue and the muscles are in red. The pelvis of this embryonic bird resembles that of early dinosaurs such as Velociraptor / Credit: Griffin et al., Yale University.
In the life of birds, there is a time when all the species in existence today are much more dinosaur-like than previously assumed. This was discovered by an international research team led by evolutionary biologists at Yale University in the United States, which observed that, before the egg hatched, the hip bone of all birds was a tiny replica of a dinosaur pelvis.
To arrive at this conclusion, described in detail in a study recently published in Nature the researchers examined the pelvic development of alligators, domestic chickens, Japanese quail, Chilean tinamou, and parakeets, comparing their stages of formation with those of dinosaurs, including the feathered species. Archeopteryx.
For the study, the team labeled the embryonic hip bones with antibodies to look for proteins expressed in developing cartilage, connective tissues, skeletal muscles, and nerves and create 3D images of the hip bones and muscles and nerves. nerves, using confocal microscopes and computed tomography techniques. This approach made it possible to detect that the bird basin is an example of "terminal addition" a biological mechanism in which ancestral characteristics appear in an animal until the end of its development.
Pelvic bones of reptiles, dinosaurs, and birds / Credit: Griffin et al., Nature, 2022.
For scholars, the identification of such a mechanism came as a surprise, because many important features of the evolutionary transition of dinosaurs to birds, such as beak formation, are only observed at the beginning of the embryonic development of birds.
"It was unexpected to find that these early stages of birds development look so much like the pelvis of early dinosaurs - said Christopher Griffin, a postdoctoral research associate at Yale University and lead author of the study. In just two days, the developing embryo changes in a way that reflects how it changed during evolution. passing from the appearance of an early dinosaur to that of a modern bird”.
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The hip bone is at the base of a bird's body. It travels the length of the avian structure, including the torso, allowing it to stand, move and support all the weight. “The bird's body is modified in virtually every way to create an optimized flying machine - explained Bhart-Anjan S. Bhullar, assistant professor of Earth and planetary sciences at Yale University and senior author and correspondent of the study. Its facilities are strictly constrained by the needs of flight”.
They also examined the birds' muscles and nerves related to hip development, noting that the formation of these systems is not synchronous with bone development, which implies that each system is somehow "decoupled" from the others. "Each individual bird, in its embryonic stages, has a dinosaur-like hip - added Bhullar -. Then, at the last minute, it's as if he remembers he's a bird and needs a bird's basin”.
The findings thus show a previously unknown mechanism of terminal addition, suggesting that the maintenance of ancestral states in development is common during evolutionary transitions. According to the researchers, there may also be other cases of terminal addition in nature, which could be common in major evolutionary transitions.