Modern birds originated from a theropod dinosaur whose members included the familiar T. rex and velociraptor.
Compared with modern birds, even the smallest theropod dinosaurs are usually about 45 to 220 kilograms, which is far from today's birds, but since the disaster of 65 million years, modern birds seem to have completed the transition from dinosaurs to birds in an instant in the gap between evolutions, but in fact this transformation may have undergone a long series of incredible changes.
Surprise from "feathers"
In the first half of the 20th century, paleontologists believed that the only fossil link between birds and dinosaurs was Archaeopteryx, a creature first found in Germany with feathered wings, but also dinosaur teeth and long bone tail. They seem to have acquired several important characteristics of birds in just 10 million years — wings, feathers and flight — a "metamorphic rate of development" that amphibians can only bow to the wind when they look at it.
With the unearthing of fossils from all over the world, there has been a new development in the story of how dinosaurs became birds. Scientists speculate that bird-specific traits, such as feathers, existed long before the first "birds" appeared, suggesting that this dinosaur population that evolved toward birds already had some pre-existing traits, only later had new uses.
But the fossils that support this hypothesis did not come until 1996, when a large number of fossils unearthed in Yixian County, Liaoning Province, China, provided a surprise from "feathers", many dinosaur fossils, including the Chinese dragon bird, although they did not have wings, they had a full set of feathers, and from the surface of the fossil, their bodies were covered by long filamentous structures, which belonged to the homologous structure with the feathers of birds, and the discovery of these new intermediate species filled the concept of the transition from dinosaurs to birds.
Stephen Brussart, a paleontologist at the University of Edinburgh in Scotland, said: "A bird did not evolve from a Tyrannosaurus rex overnight, but the classic characteristics of birds evolved one by one, first bipedal movements, then feathers, then fork bones and feathers that look more complex than feathers, then wings, and other 'parts' that make up birds." ”
When all these features are in place, the birds will fly.
Unusual "getting smaller"
Although feathers, wings and other characteristics are the characteristics of birds that most people pay attention to, it is also very important to have a "small" body, although a body of tens of kilograms can glide for a short time, but the real flight still requires a certain proportion of body weight and wing size.
A study published in the journal Science found that the bodies of theoptera suborder Hypochonosaurus began to shrink more than 200 million years ago, 50 million years before the advent of Archaeopteryx, when most dinosaurs were on the road to "getting bigger" and the osteoplenosaurs were shrinking their bodies.
Rapid miniaturization suggested that at the time, perhaps smaller sizes had certain advantages over larger sizes, such as opening up new habitats and new ways of life in tall trees, and even related to changes in the physiological structure of the body, but whatever the reason, smaller body size may be a precursor to starting flight.
Beak – a pair of hands that grow on the face
The problem with salvaging a "fallen leaf" in a long river of evolution is that the exact time of the fall is not known, so it is almost difficult for scientists to accurately decipher the full details of the evolution of birds from dinosaurs. But as the three fields of evolution, genetics, and developmental biology intersect, the exploration of certain traits becomes relatively simple.
Birds' beaks have the versatility of finding food, cleaning themselves, nesting, and caring for their cubs, and after the birds' ancestors completed their flight evolution, the skills that have been able to reproduce on Earth to this day are derived not only from their excellent flight ability, but also from their powerful beaks.
It is no exaggeration to say that the beak of a bird is equivalent to a pair of hands growing on the face.
In modern birds, the two premaxillas merge to form a beak, a structure that is very different from dinosaurs, alligators, ancient birds and most other vertebrates, because scientists speculate that this may be a puzzle that forms birds, and along the course of bird evolution, they uncover the genetic mechanisms that form beaks, and only a little genetic adjustment is required to make dinosaur faces appear on bird faces.
Completing this "back-to-ancestor" phenomenon was the embryo of a chicken, and by using chemical inhibitors at the embryonic stage to allow the chicken to replicate the expression of ancient ancestral amniotic tissue, the foremandible was unable to form a beak, but instead the skeletal phenotype of the most ancient palate form, and as a result, the treated embryo grew a face more like a dinosaur.
Artistic creation diagrams, avoiding ethical issues
Specifically, small changes from the interior of an object have also driven macroscopic evolution, and the so-called micro-knowledge, for hundreds of millions of years, has been a natural and unchanging law of survival.
Resources:
https://www.science.org/doi/abs/10.1126/science.1252243
https://pubmed.ncbi.nlm.nih.gov/25264248/
https://onlinelibrary.wiley.com/doi/abs/10.1111/evo.12684