Every Bird Has A Dinosaur Moment Just Before Hatching

By D.C. Demetre •  Updated: 08/06/22 •  6 min read

The long morph that started with dinosaurs and led to birds across tens of millions of years got a second look in new research using laser scanning confocal microscopy of animal embryos. The study found that all baby birds have a moment before hatching when their hip bone is a tiny replica of a dinosaur’s pelvis.

“Every single bird, in its early life, possesses this dinosaurian form. Then, at the last minute, it’s like it remembers it’s a bird and needs a bird’s pelvis,”

said Bhart-Anjan S. Bhullar, assistant professor of Earth & planetary science at Yale and senior and corresponding author.

Bhullar’s lab is renowned for its ingenious use of computed tomographic (CT) scanning and microscopy to produce 3D images of animal embryos. They have done groundbreaking research on key evolutionary transitions between dinosaur, reptile, and avian species — including the development of the dinosaurian inner ear, the bird beak, the mammalian rolling jaw, and eyesight in vertebrates.

Bird Pelvis Development

Embryonic budgerigar parakeet

Embryonic budgerigar parakeet imaged using laser scanning confocal microscopy. The skeleton is in green, nerves are in blue, and muscles are in red.
Credit: Christopher T. Griffin, Daniel Smith-Paredes, and Bhart-Anjan S. Bhullar

Lead author Christopher Griffin is a postdoctoral associate in Bhullar’s lab. He and Bhullar, along with their colleagues, investigated how pelvises developed in alligators, domestic chickens, Japanese quail, Chilean tinamou, and parakeets.

They compared the developmental stages of these modern-day animals with those of dinosaurs, including the feathered species Archaeopteryx, a transitional fossil between non-avian dinosaurs and birds.

The team tagged embryonic hip bones with antibodies to look for proteins that are expressed in developing cartilage, connective tissue, skeletal muscles, and nerves. The researchers then created 3D images of the hip bones, muscles, and nerves with confocal microscopes and CT scanning.

Terminal Addition

They found that the bird pelvis is an example of terminal addition, a biological mechanism in which ancestral features continue to appear in an animal until late in its development. It was surprising, Griffin pointed out, since many essential components 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 these initial stages of bird development look so much like the hips of an early dinosaur. During just two days, the developing embryo changes in a way that reflects how they changed in evolution, transitioning from looking like an early dinosaur to looking like a modern bird,”

Griffin said.

The hip bone is the core of a bird’s body. It runs the length of the avian frame, engulfing the torso while enabling a bird to stand, move, and carry the weight of its entire body. Its body structures are highly constrained by the necessities of aeronautic design, according to Bhullar.

Likewise, many bones in birds are hollow, with crisscrossing struts or trusses for added structural strength, much like the metallic ribs in an aircraft wing. The number of hollow bones varies among species, with large gliding and soaring birds tending to have the most.

Bird Coloring And Climate Change

Another recent study looked at a faster form of bird evolution- changes in feather colours in a species called the blue tit (Cyanistes caeruleus). The work was conducted over 15 years (2005-2019) through a partnership between scientists from the UPV/EHU and the Centre d’Ecologie Fonctionnelle et Évolutive in Montpellier (CEFE-CNRS).

The team focused on two populations of blue tits in the south of France, one living on the outskirts of Montpellier and the other in the northwest of the island of Corsica.

“Our work suggests that environmental changes, and specifically climate change, could be the main reason why birds such as the blue tit are undergoing a change in their physical features, more specifically in the brightness and intensity of their colouration,”

said UPV/EHU’s David López-Idiáquez.

The blue crests and yellow breasts of blue tits in these two populations are on average less colourful right now than when the research began. It may seem like a purely aesthetic change, but this change in plumage may have an effect on the mating patterns of the species.

“In these birds, traits such as colouring function as signals to indicate to other individuals the quality of the specimen, which are decisive, for example, when it comes to breeding,”

explained David López.

Plastic Vs. Genetic Change

When there is a variation in the environment, animal populations have 4 options:

The change the blue tit opted for is not genetic but plastic. The long change that modern birds’ ancestors opted for was genetic. Unfortunately, the fourth option is the trendiest nowadays.

Bird species are currently going extinct at a far greater rate than any possible generation of new species, and the disappearance of a population, subspecies, or species means the permanent loss of an array of unique genes.

According to a recent study in the journal Annual Review of Environment and Resources, approximately 48% of existing bird species worldwide are known or suspected to be undergoing population declines.

Populations are stable for 39% of species. Only 6% are showing increasing population trends, and the status of 7% is still unknown.

The findings mirror the results of a 2019 study which determined that nearly 3 billion breeding birds have been lost during the past 50 years across the United States and Canada alone. Despite their findings, study authors say there is hope for avian conservation efforts, but transformative change is needed.

“The fate of bird populations is strongly dependent on stopping the loss and degradation of habitats,” said lead author Alexander Lees. “That is often driven by demand for resources. We need to better consider how commodity flows can contribute to biodiversity loss and try to reduce the human footprint on the natural world.”

Information is key in this challenge. The study authors note that the growth of public participation in bird monitoring and the growth of easy-to-use tools, like the Cornell Lab’s eBird database, make continental-scale breeding bird surveys, distribution atlases, and abundance models possible and help inform conservation efforts.

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