So, what kind of dinosaurs did Archaeopteryx evolve from? The answer is theropod dinosaurs. The similarities between theropoda and birds include: the sole of the foot has three toes, the chest has a "fork bone", and the bone is full of air.
Among the family members of theropods, there are giant Tyrannosaurus Rex and smaller Raptors. Tyrannosaurus rex is about 13 meters long and weighs about 6.8 tons. Needless to say, even the young velociraptor weighs about 15 kg, which is simply a monster compared with modern birds. So, how did such a huge dinosaur evolve into a bird now?
Gene mutation?
In the first 30 years of the 20th century, the mainstream explanation was "Hope Monster Theory".
This theory holds that, unlike the slow evolution within a species, the major changes of a species must be due to large-scale genetic variation. For example, the carnivorous dinosaur of 136 kg turned into a prehistoric Iberian bird the size of a sparrow, and the scales of the dinosaur suddenly evolved into feathers, and the genetic material in it must have changed greatly.
However, in 1990s, China discovered a new dinosaur fossil-Confucius bird fossil. Although this fossil shows that dinosaurs had no wings at that time, they were actually covered with feathers. In the past, feathers were thought to be unique to birds.
Later, researchers also found that the respiratory system of birds had already appeared in dinosaurs. Archaeopteryx and the ancestor of more than 9300 kinds of modern birds-Bone Dragon (a special small dinosaur, later evolved from theropod dinosaur) are not very different in bone structure. These findings run counter to the monster theory of hope: dinosaurs evolved into birds without mutation. So, if it's not a genetic mutation, what is it?
If you want to be a bird, lose weight first.
In 20 14, researchers from Australia, Britain and Italy discovered the mystery of the successful evolution of theropod dinosaurs-"slimming" movement according to the anatomical characteristics of 1500 of 20 kinds of dinosaurs. It turns out that theropod dinosaur is the only dinosaur whose size is shrinking while other dinosaurs are still growing. Their contraction speed is 160 times that of other dinosaurs. Its average weight was163kg 2100000 years ago, and it has dropped to 0.8kg when it evolved into Archaeopteryx about1600kg years ago.
For dinosaurs, it is very important to be very small, which may be the most critical step in the evolution of birds, because small size may be the premise of flight. Although it is huge and can glide, the real flight with wings needs to generate thrust by flapping wings, which requires maintaining a special ratio between the size and weight of wings. Therefore, before the big dinosaur became a bird, it went through a long process of "slimming". Researchers estimate that this "slimming exercise" took about 50 million years for the theropod dinosaur family.
However, how did theropod dinosaurs successfully "slim down"? The researchers found that in theropod dinosaurs, a wonderful evolutionary process took place-the continuation of childhood.
Juvenile continuation is a phenomenon that species retain the characteristics of infancy or even fetus until adulthood. For example, human beings are typical young animals. Human newborns have sparse body hair, big brains and strong brain learning ability. This is a young state. When they are adults, these characteristics still exist, and the learning ability of the brain is very strong throughout their lives.
It was found that theropod dinosaurs also had a continuation of childhood. After they were born, they didn't grow up much. With the passage of time, the face and bones of theropod dinosaurs are shrinking and getting smaller, and the leg bones are becoming slender, but the eyes and brains have been developing and beaks have begun to appear. Comparing bird fossils with dinosaur fossils, it is found that the skulls of small dinosaur fossils are very similar to those of adult birds, while the earliest birds are almost the same as the embryos of raptors. It is through this process that theropod dinosaurs retained their small size in their infancy, thus successfully slimming down and creating an evolutionary miracle.
Remodeling details: the appearance of bird's beak
So, how do other details, such as the beak, a very important organ of birds, come into being?
Birds can use their beaks to find food, clean their bodies, build nests and take care of their young. Birds have different habitats, and many birds rely on very special beaks to survive. Therefore, the viability of birds not only stems from their flying ability, but also their amazing multifunctional beaks play an important role.
In modern birds, two maxillae are fused to form a beak. Its structure is completely different from that of vertebrates such as dinosaurs, alligators and ancient birds. In order to find out how this change happened, researchers from Yale University in the United States studied a series of existing species related to ancient birds: alligators, chickens, mice, lizards, turtles and emus.
They found that birds have a unique gene cluster related to facial formation compared with creatures without beaks. Subsequently, the researchers used chemicals to inhibit the protein products of some genes in chicken embryos in eggshells, and found that when chicken embryos began to develop, they grew short round bones instead of long and narrow bones of birds. Finally, the beak tissue of the embryo and the palatine bone above the mouth returned to the same state as the dinosaur, and a chicken grew a dinosaur face. However, due to the consideration of experimental morality, the researchers euthanized the chicken embryo and failed to make it develop into a complete chicken.
This discovery shows once again that the transition from the snout to the beak of a dinosaur does not require a special evolutionary leap or large-scale gene changes, but only the activity of protein, who is responsible for gene expression, is different. In this way, the smallest changes within the species can also drive macroevolution, so that the species can evolve new features and new populations.
The researchers speculate that it may be because of the slight change in the genetic control mode within this species that dinosaurs gradually evolved bird characteristics in the process of "slimming", such as first evolving bipedal walking, then feathers, wishbones, more complicated stems, and finally wings. The final result is a seamless and perfect transition from dinosaurs to birds.