Birds are a very special species, becoming a separate order in the phylum Chordata ( vertebra ) , ornithischia .
It was only in 1861 that Archaeopteryx with claws on its wings and long tail vertebrae was discovered in the Late Jurassic formation in Germany, about 146 million years old, that birds evolved from reptiles. But which of the reptiles evolved has been a hot topic of debate. It was not until the 1990s that a large number of extremely well-preserved small theropod dinosaurs with long hairs and long feathers and a large number of fossils of ancient birds were discovered in the Late Jurassic "Rehe Biota" in western Liaoning, China, about 145 million years ago, that a major breakthrough was made. Western scholars have to marvel: "The discovery of Long-haired and long-feathered dinosaurs in China has become the headlines of all countries in the world."
Taking the past year alone as an example, there have been 4 long ribbon-like tail feathers of "Hu's Yaolong", the woolly dinosaur "Tianyulong", which belongs to the ornithischian, and the world's earliest hairy dinosaur "Heshi near-bird" fossils, all published in the journal Nature. Now, let's comb through the fossil discoveries in recent years and explore the mystery of the origin of birds.
<h2 class= "pgc-h-arrow-right" > three hypotheses for the origin of birds</h2>
There are three different hypotheses about the origin of birds. One type of bird is believed to have originated as a small dinosaur among reptiles. The first to explicitly put this argument forward was the British paleontologist Huxley in 1868, who believed that the size and skeleton of Archaeopteryx were similar to those of it, but due to the lack of evidence, and many scholars believe that this skeletal similarity may also be the result of "convergent evolution", it is not recognized.
In 1973, Professor Ostrom, a well-known dinosaur expert in the United States, carefully analyzed its relationship with birds when studying dinosaurs, so as to more comprehensively discuss that birds should originate from small theropod dinosaurs; in addition, in 1986, Gaussyr in the United States also concluded from branching systematics that birds should originate from small theropod dinosaurs, thus reviving this hypothesis.
Another hypothesis holds that birds originated from slotted toothed species in reptiles.
This was proposed by Brom of South Africa in 1913 while studying a fossil of a false crocodile. This hypothesis is supported by many people, and even many textbooks cite this argument. In the 1980s, Feduccia, a famous American ornithologist, published "The Age of Birds" and "The Origin and Evolution of Birds", becoming the main representative of the opposition to the origin of birds from dinosaurs.
A third hypothesis holds that birds originated from crocodiles in reptiles, and in 1972 british paleontologist Valck proposed that birds and crocodiles could form a separate series. Although Valcke abandoned the hypothesis in 1985, martin, a well-known American paleornithologist, supported it.
The above controversy shows that the controversy is mainly caused by two major factions, dinosaur experts mostly support the origin of birds from dinosaurs, while bird experts mostly support the slotted tooth theory, the main basis of which is:
(1) Dinosaurs do not have a wishbone unique to birds on the chest (the wishbone is healed by the collarbone);
(2) Although the bones, teeth, phalanges, etc. of the waist and arms of dinosaurs are somewhat similar to birds, they do not have homologous relationships, such as dinosaurs and birds are 3 phalanges, but dinosaurs are degenerated by the 4th and 5th phalanges of the 5 phalanges, while the phalanges of 1 to 3 are retained, while birds are degenerate of 1 and 5 phalanges and retain 2 to 4 phalanges, which are significantly different;
(3) Small theropod dinosaurs are more specialized and appear later than Archaeopteryx, so they cannot evolve into birds. Because there are very few fossils found, there are not many reasons to prove or refute, and it is not expected to find long-haired and feathered dinosaurs in the future.
<h2 class= "pgc-h-arrow-right" > a dispute between "ground" and "arboreal"</h2>
Birds are mostly born by flight, while dinosaurs or slotted toothed birds are based on land, and it is not easy for them to evolve the ability to fly. Being able to fly means expanding the range of predation and increasing chances of escape, but it will also pay a huge price for overcoming strong gravity. So whether it is dinosaurs or slotted tooth, they are advanced and can glide, and then become flying. Do they start by running fast and glide? Or do you glide from a tree to another place and then fly? This has also caused a lot of controversy. Proponents of the dinosaur hypothesis tend to be ground-dwelling, while proponents of slotted toothed are inclined to arboreal.
The first to propose the ground type was the American dinosaur expert Willichski, who pointed out in 1879 that dinosaurs learned to glide short distances in a fast run; in 1907, Nopjo of Hungary also believed that dinosaurs fanned their forelimbs to increase their speed during the run, and then gradually evolved from the scales of the skin to feathers, so that they could fly; ostrom in the United States also strongly advocated the ground perch theory. The arboreal hypothesis was proposed by The American Poker, who is president of the International Bird Society. This view is that small theropod dinosaurs living in certain trees gradually developed the ability to glide among branches or toward the ground until they eventually became flying birds.
But as more fossils have been discovered from China, the line between the two factions has become increasingly unclear.
< h2 class="pgc-h-arrow-right" > evidence of fossils</h2>
In 1996, the Chinese dragon bird was found in the northwestern Liaoning region, which is more than 60 centimeters long, looks like a chicken, but has a long tail and long serrated fangs in the mouth, especially the filamentary hairs that have not yet evolved into feathers. Ji Qiang, director of the Geological Museum of China, believes that it is the most primitive bird, and after careful study by Chen Piji of the Nanjing Institute of Geology and Paleontology of the Chinese Academy of Sciences and foreign scholars, it is believed that its skeletal characteristics are extremely similar to those of the German Archaeopteryx, and the fur on the body is only subcutaneous fiber, so it should belong to the "theropod dinosaurs" in the jawed dragon.
As early as 1997, a new long-haired dinosaur was found in the area, and Xu Xing, a dinosaur expert at the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences, named it Beipiplex, which is a more specialized sickle dragon, and the fine hairs on the body are skin derivatives, closer to feathers. What was even more surprising was that in the same year, Ji Qiang and Ji Shu'an found dinosaurs with long feathers in the area! It is similar to the theropod dinosaur found in Central Asia and North America, Chiosaurus. However, it was originally thought to be a bird, so it was named the primitive ancestral bird, and some scholars still believe that it is indeed a real bird that has lost the ability to fly, just like the ostrich today.
In 1998, Xu Xing and others found a new long-haired dinosaur near the discovery of the Chinese dragon bird, which was named The Chinese Bird Dragon. The Chinese bird dragon belonging to the chiosaurus is very close to birds, and its hind skull morphology is very different from most dinosaurs, and it has early bird characteristics, especially it has the wishbones of birds and many previously unknown bird features, and the hair on its body is closer to the feathers of birds, so it provides an important basis for the evolution of feathers. Although the Chinese bird dragon is not yet able to fly, its skeletal system is fully equipped with the ability to flap its forelimbs.
In 1998, Ji Qiang, Ji Shu'an and scientists from the United States and Canada discovered another long-feathered dinosaur in Western Liaoning, the tail feather dragon, which had exactly the same feathers as the birds like the original ancestral birds, that is, the feathers on both sides of the feather shaft had exactly the same asymmetrical structure as the birds, resulting in the formation of the wing surface, ensuring the lift required for the birds to fly. Not only that, but it is also the same as birds, the first toe is degenerated, the teeth are also degenerated, but it is significantly different from birds in that the forelimbs are very short, while the forelimbs of birds, that is, the wings are very long.
What is even more breathtaking is that in 2000, Xu Xing, Zhou Zhonghe and Wang Xiaolin discovered the world's smallest dinosaur in Western Liaoning, Zhao's little robber, which was only 39 centimeters long, belonged to the Chilong family, and was closely related to the Velociraptor, but its toe position, the length of the toe segment, the shape of the terminal toe segment, and the structure of the hind feet were different from other Chilong who were good at running, but had the ability to climb trees.
When Xu Xing and others carefully studied some small robber dragon specimens, they found that a kind of feathers with the same as birds, especially the hind limbs of some individuals grew at the hip socket, and the hind limbs and forelimbs had long feathers, becoming a four-winged "monster". Their hind limbs claws are like birds that can hold branches, obviously they live in trees, and can fly short distances, so the strange discovery of this class called Gu's little thief has surprised well-informed paleontologists.
From the many small theropod dinosaurs with long hairs and feathers found above, it is not difficult to conclude that the line between them and birds has become increasingly difficult to distinguish. As Xu Xing points out, "In the past, it was thought that the wishbones, sternum, hollow bones, very long forearms, and wrists that could be retracted laterally were skeletal features of birds. But now these small theropods also have these characteristics: in the past, it was thought that only birds had the behavior of incubating eggs and caring for young chicks, and now small theropods also have these characteristics; what used to be thought to be unique to birds, these dinosaurs now have them. "In addition, in the past it was thought that the toes of birds were 1 and 5 toes degenerate, and now some dinosaurs also have this phenomenon ... All this fully shows that birds did evolve from small theropod dinosaurs.
As for the evolution of arboreal or ground-dwelling theropod dinosaurs, a large number of data indicate that both possibilities exist. For example, tail feather dragons, bird dragons and Chinese hunting dragons may be running in a short distance gliding, especially the dragons are less than 1 meter long, the body is also long, the forelimbs will be laterally folded and opened like bird wings, and the hind limbs are slender, which is very suitable for running, obviously belonging to the ground-dwelling type. And Gu's little raptor, Zhao's little thief, and Archaeopteryx (some people think it is 80%.)
<h2 class="pgc-h-arrow-right" > unsolved mystery remains</h2>
Birds originated from dinosaurs, but what kind of dinosaurs did they originate from? The 3 species of long-haired dinosaurs found in western Liaoning - Chinese dragon bird, Beipiao dragon, Chinese bird dragon and 4 kinds of long-feathered dinosaurs - tail feather dragon, primitive ancestral bird, small robber dragon, Chinese hunting dragon, etc. belong to the megalosaur class, sickle dragon, egg stealing dragon, chi dragon, galloping dragon, etc., which type of birds belong to? A series of studies on the evolution of birds is needed to unravel the mystery.
It is well known that few fossils formed by birds are formed. Fortunately, there are many bird fossils found in China. Hou Lianhai, a famous paleoornithologist in China, pointed out in his monograph that there are not only many fossil types of ancient birds in northern China, but also the sum of the ancient bird species found in the world is not as much as that of China. In terms of the suborder Archaeopteryx (Ornithopods), only 4 genera have been found so far, of which 3 are in China, and only 1 genus of Archaeopteryx is found in Germany. Moreover, the fossil sequence of ancient birds in various periods of the Mesozoic Era in northern China is very complete, Only 145 million years from the Late Jurassic to the Early Cretaceous of 100 million years ago can be divided into 3 different categories of bird fauna, the number of their genera accounted for almost 2/3 of the number of genera found in the world during this period; 100 million to 65 million years ago The late Cretaceous ancient birds are also the most in the world; not only that, the Cenozoic paleobirds are also the most in the world, especially from 65 million to 60 million years ago in the early Cenozoic, which was the most scarce period of ancient birds after the extinction of dinosaurs, and many ancient birds were still found in the north of China.
Therefore, the north of our country can be called the home of the world's ancient birds, and the biggest problem now is that the earliest birds and earlier feathered dinosaurs have not yet been found.
The world's earliest "bird" is the proto-bird found in the Late Triassic strata of the United States about 223 million years ago, but most scholars do not recognize it as a bird; followed by the German Archaeopteryx, but because it is too specialized and very rare, it is unlikely to be a bird ancestor. China's Liaoxi discovered Confucius bird in 1996, it is somewhat similar to Archaeopteryx, such as the skull is not completely healed, the humerus is longer than the scratching bone, there are 3 claws on the wings, etc., its individual is similar to the chicken, there is no tooth in the mouth, it is a beak, the tail vertebrae are degenerated, the tail is short, and the sternum is developed. From an evolutionary point of view, it is more advanced than Archaeopteryx, dating back 140 million years, slightly later than Archaeopteryx, so it is not enough to be the ancestor of birds, although its fossils are extremely numerous and well preserved.
As early as 2013, Ji Qiang and others found an auspicious bird in western Liaoning, which is very close to the Confucius bird and is slightly earlier than the Confucius bird. A few years later, the team discovered a more primitive bird, the Huameijin hummingbird, in Fengning County, Hebei Province, and thought it might be the ancestor of birds.
What is even more exciting is that Xu Xing and others recently found a new feathered dinosaur in the northeast region, they call it "Heshiu proorosaurus", it can be vaguely seen that it has 4 wings, the whole body is covered with feathers, even the feet have, especially its feathers can be divided into two kinds, one is "dinosaur fluff", growing on the head and neck, the other is similar to the structure of modern bird feathers, there are many fine hairs growing from the feathers, and each forelimb has about 24 feathers, and the calves and feet also grow a similar number of feathers. It has been found that the feathered dinosaurs have feathers that generally grow on the forelimbs, but it grows on the wrist joints of the hind limbs, and the feathers of the legs and feet cover each other, which has a stronger ability to fly, and it is obvious that it is an arboreal type. What is particularly important is that its age is 151 million to 160 million years ago, which is older than archaeopteryx and goldenrod, which completely solves the problem of "time inversion" of the earliest birds that evolved earlier than the long-feathered dinosaurs that evolved into it, that is to say, it is logical that the older near-bird dragons will evolve the newer Archaeopteryx and goldenrod.
The continental strata of the Mesozoic Era in northern China are very developed, widely distributed, and the stratigraphic series is complete, and it is entirely possible to find old birds, especially older long-feathered dinosaurs, to make new contributions to solving this problem.