This evolutionary journey has taught us that dinosaurs and birds are related

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Compiled by New Media Editor Li Yunfeng

On April 17, Zhou Zhonghe, an academician of the Chinese Academy of Sciences, expressed his opinion in the open class "Academicians are teaching!" that dinosaurs are not completely extinct because birds are descendants of dinosaurs. Considering that domestic chickens originated from wild birds, many netizens said that chickens are also "transformed" from dinosaurs? Professor Hu Xiaosong of China Agricultural University also clearly stated in a program that chickens are direct descendants of dinosaurs.

Many people may know that birds evolved from dinosaurs, but do you know where this saying comes from? What are the similarities between birds and dinosaurs? How did dinosaurs "transform" into birds step by step? Let me show you how and why.

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Archaeopteryx: Related to carnivorous theropod dinosaurs

Since we are talking about birds and dinosaurs, our first reaction should be a name that everyone is familiar with - Archaeopteryx. In our cognition, it is a species that is very distant from us, just like dinosaurs.

The discovery of Archaeopteryx has a great influence on proving the statement that birds are descendants of dinosaurs. In the mid-19th century, Darwin put forward a view that species are not static, and that all animals and plants have evolved from earlier forms. Those animals and plants that adapt to the environment can survive. At that time, this view was opposed by many people, who believed that it was a fantasy.

It was not until 1861, two years after Darwin published The Origin of Species, that German paleontologist Meyer reported the discovery of Archaeopteryx fossils in Germany. Wasn't this the transitional species between birds and reptiles that Darwin predicted?

▲The Archaeopteryx fossil named "Imprinting Stone Archaeopteryx" in 1861 (Source: "Earth Magazine" WeChat official account)

In recent years, paleontologists have discovered more Archaeopteryx fossils, which have partially proved that Archaeopteryx and carnivorous theropod dinosaurs are closely related, supporting the theory that birds originated from dinosaurs.

▲Archaeopteryx specimen in the Life Exhibition Hall of Wuhan Science and Technology Museum (Photo source: "Wuhan Science and Technology Museum" WeChat official account)

The unearthed fossils show that the feet of Archaeopteryx are very different from those of modern birds and are closer to those of theropod dinosaurs. The most obvious feature is that its second toe can be overextended, which is almost the same as the feet of dinosaurs such as Microraptor and Ornithopod. In addition, the first toe of Archaeopteryx grows inwards, unlike the toes of birds that extend outwards, and is somewhat similar to the thumb of the human hand. Moreover, its jawbone grows radially in all directions, with obvious theropod dinosaur genetic characteristics. Scientists say that these fossils not only show that birds originated from theropod dinosaurs, but also show that Archaeopteryx does not have toes that can climb branches like modern birds, so it will not perch on branches. Rather than saying that Archaeopteryx is a bird, it is better to say that it is more like theropod dinosaurs such as Velociraptor and Deinonychus.

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Sinosauropteryx: A small carnivorous dinosaur

For a long time, there have been different opinions on whether birds are descendants of dinosaurs. Until 1996, the fossils of Chinese dragon bird were discovered in the Jehol Biota in western Liaoning, China, which provided strong evidence for the theory of dinosaur evolution of birds.

▲Sinosaur bird fossil (Source: Visual China)

The Sinosauropteryx fossil is about 68 centimeters long, with a low and long skull, a small brain, long hind limbs, short and strong forelimbs, a long tail, long and dense hair on its body, and sharp teeth in its mouth. It was initially thought to be a bird, but after careful research, Chinese paleontologists classified it as a dinosaur and named it "Sinosauropteryx". Only a few fragments of dinosaur skin fossils have been found in the world, and they are all hairless. The hairy Sinosauropteryx is an important basis for studying biological evolution.

Research has shown that the morphological characteristics and body size of Sinosauropteryx are similar to those of Compsognathus, a small theropod dinosaur native to Germany, and they can be classified as one. Sinosauropteryx is a bipedal animal, and an adult can grow to 2 meters long.

On its back, there is a row of epidermal derivatives similar to "hair". Some paleontologists believe that this is a primitive "feather", so Sinosauropteryx should be a primitive bird; other paleontologists believe that this skin derivative does not have the characteristics of feathers, but is similar to the epidermal derivative structure on the back of some living reptiles (such as lizards) - keratinous bristles, or it may be fibrous tissue.

The discovery of Sinosauropteryx spread all over the world immediately because it provided new evidence for the evolution from reptiles to birds. After research, Chinese paleontologists pointed out that Sinosauropteryx not only retained some characteristics of small theropod dinosaurs, but also had some basic characteristics of birds, becoming an intermediate link in the evolution of dinosaurs to birds. The "feathers" of Sinosauropteryx were in the form of sheets and had feather shafts. These feathers were different from the feather structure of modern birds and represented the initial stage of early bird evolution. Judging from the characteristics displayed by Sinosauropteryx, it was more ancient and primitive than the Archaeopteryx in Germany. The skeletal characteristics of Sinosauropteryx were like those of dinosaurs, with a large head, teeth, a large number of tail vertebrae, and agility, but it did not have the ability to fly.

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Meilong: has the same sleeping state as birds

In 2004, Chinese paleontologist Xu Xing and American scholar Norell discovered a very special dinosaur fossil specimen in a place called Lujiatun, Beipiao City, Liaoning Province, China. Scientists found that this fossil is not only well preserved, but also retains the posture of sleeping. Its overall shape looks like a big bird, with a small skull, a pair of striking big nostrils on the skull, and sharp teeth in its mouth, just like other small carnivorous dinosaurs. It curled up, curled its legs under its body, and buried its head under one arm, the same sleeping posture as birds.

▲Meilong fossil (Photo source: WeChat public account of "China Paleozoological Museum")

Further research has shown that Meilong was a small troodontid dinosaur that lived in the early Cretaceous period about 125 million years ago. The body shape and sleeping state of this dinosaur are similar to those of modern birds, a typical bird-like behavior, which can indicate that the two animals have a common ancestor.

▲Reconstruction of the Meilong (Source: WeChat official account of "Wuhan Science and Technology Museum")

Meilong was very light and should have been very agile. Its forelimbs were relatively long and had three fingers, which could be used to grasp food. Its hind limbs were relatively strong and it should have been able to run very fast. Did Meilong have wings? It is speculated that it did, but no conclusive evidence of feathers has been found so far.

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Anchiornis hercules: the earliest living feathered dinosaur

In September 2009, Chinese scientists discovered the fossil of a hairy dinosaur, Anchiornis hurricanei, about 160 million years old, in the Linglongta area of ​​Jianchang County, Liaoning Province. As of September 27, 2009, this was the earliest known feathered dinosaur in the world.

▲Anchiornis hercules fossil (Source: Nitu.com)

Anchiornis huxleyi is a small theropod dinosaur, less than 40 cm long, and is one of the smallest dinosaurs discovered so far. Like many typical Jehol Biota dinosaurs of the early Cretaceous period, Anchiornis huxleyi was covered with feathers, but it lived earlier, from the late Jurassic period more than 160 million years ago, earlier than Archaeopteryx.

The genus name of Anchiornis huxley means "close to bird", because this dinosaur has many characteristics that are very similar to birds. In addition, it lived a long time ago, which is of great significance in filling the gap in the evolution of dinosaurs into birds. The species name "Hexley" is to commemorate the famous evolutionary biologist Huxley, who was the first person to propose that birds may have evolved from dinosaurs through the Archaeopteryx fossils.

▲Full body color restoration of Anchiornis huxleyi [Image source: Li et al./ Science (2010)]

Anchiornis huxleyi had flaky feathers on its forelimbs and hindlimbs, so it was a four-winged dinosaur like Microraptor, but its arms were shorter and the feathers on its arms were symmetrical, unlike modern birds, which have longer forelimbs and asymmetrical flight feathers. Based on these morphologies, scientists have determined that Anchiornis huxleyi had limited flying ability and may have only simple gliding ability, which was a primitive stage for dinosaurs to fly towards the blue sky.

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(Sources: Global Magazine, Tencent News, Dinosaur World, China Geological Museum, China Paleozoological Museum, Species Calendar, Explorers, Science Decoding, Baidu Encyclopedia, Wuhan Science and Technology Museum)

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