Editor's note: Fish climbed onto land, and human evolution began here. Lu Jing, Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences, opened a strange cabinet at the Voice of the Chinese Academy of Sciences. Her strange object cabinet will contain some knowledge related to the evolution of life and paleontology that everyone may be interested in, thinking, and even gossip, and everyone is welcome to come and visit!
What is the relationship between people and fish?
A simplified version of the answer to this question is: man evolved from fish and does not accept rebuttals. But to be more rigorous, it should be said that today's humans and today's fish have a series of common ancestors, of which the most recent common ancestor form is much closer to fish than to humans. Fish here are defined as non-tetrapod vertebrates, while tetrapods include all vertebrates that have landed on land, such as frogs, lizards, birds, beasts, and their descendants who return to the water, such as ichthyosaurs, whales, sea snakes, etc. Humans belong to the quadruped-mammal-primates.
Vertebrates of all kinds (image from the Internet)
These realizations are the product of a series of recent scientific advances that have finally sent thousands of years of mermaids, krakens, and dragon palaces into the world of legends and myths. At the beginning of the 19th century, during Napoleon's expedition to Egypt, the French biologist Étienne Geoffroy Saint-Hilaire found a strange fish in the Nile, which was polypterus bichir bichir (PBB dinosaur king). The multifin fish, with a slender body, a head that looks like a lizard, and a section of the pectoral fin wrapped in muscle, inspired St. Elier, who proposed that animals such as fish, whales, birds, people, monkeys, etc. are actually very similar in nature, with anatomical structures such as heads, limbs/fins, and vertebrae.
Saint-Hilaire (Image from the web)
Multifin fish found in Saint-Hilaire (image from the web)
In the decades that followed, the famous naturalist and anatomist Richard Owen noticed the same phenomenon and proposed archetype, that is, all kinds of animals, at least vertebrate bodies, can change from an ideal archetype. Archetype theory actually acknowledges the existence of evolution, and if you've seen Owen's vertebrate archetype, it basically looks like a fish. But the conservative Owen eventually missed the opportunity to break through the last layer of window paper, and evolution, the greatest biological phenomenon, was finally proposed by Darwin and Wallace. The existence of evolution gives a perfect explanation for the inherent similarity between man and fish. Over the next two hundred years, the question to be solved becomes: What fish, when, and how did it evolve into quadrupeds?
What fish, when and how did it evolve into tetrapods?
With two "living fossil" finned fish, lungfish and lattimer known to the scientific community in the second half of the 19th century and the first half of the 20th century, modern ichthyologists once thought they could answer the above question. In terms of species, about half of the vertebrates on Earth are fish, but the vast majority of them belong to ray-finned fish, including our common fish, such as crucian carp, silver carp, grass carp and so on.
Comparison of rayfin fish fins and meat fin fish fins (image from the network)
In contrast, modern finned fish lungfish and lattimers have muscular even fins, in which the fin bones and other forms of the lattimer are closer to the appearance of limb bones, but the lattimahfish live in the deep sea far from the terrestrial environment, while the lungfish are very adapted to the environment of shallow water and the intersection of land and water. As a result, some scholars at the time were mired in the debate that "lungfish or Ratimi fish are more closely related to land vertebrates", and the end result is that lungfish are closer. However, modern lungfish have become so specialized that modern ichthyologists have been unable to deduce how fish evolved into tetrapods, and this question has been answered mainly by paleontologists.
Live flesh-finned fish. Latimer (top) and Australian lungfish (bottom) (image from the internet)
Paleontologists have long noted that a large class of fossil finned fish, formerly known as "total fin fish," is closely related to the evolution of tetrapods. Until now, some popular science books will write that "the total fin fish landed on land and evolved tetrapods.". However, later research found that the concept of "total fin fish" is not rigorous, it includes some fossil fin fish that are far related to each other, but there is indeed a class of tetrapods that are closely related to tetrapods, in fact, quadrupeds themselves are included in this category, which is tetrapodomorphs.
The four-legged flesh-finned fish that eventually landed
Foreign cartoon, the first fish to go ashore (image from the Internet)
The earliest tetrapod-finned fish were similar in appearance to other flesh-finned fish, such as the exotic eastern sassyllus and Ken's fish found in China, but they have evolved the glandular pituitary nodules that sense the circadian rhythm of the land and the inner nostrils that can breathe air, and later came in handy in land life. Most tetrapod finned fish may live in very shallow water and are ferocious ambush hunters. The root-toothed fish, which have large fangs and stiff fins, seem to have become very well adapted to crawling under shallow water, rushing out to catch prey.
By the Mid-Late Devonian, a class of tetrapod-shaped flesh-finned fish known as the Hope Salamander evolved, with a flattened head like a crocodile, bulging eyes, and a vanished dorsal fin, apparently living a way of life very close to crocodiles, hippos, and four-eyed fish, moving on the surface of shallow water bodies. Hopefully, salamanders already possess most of the features of tetrapods, except for the limbs that do not have long toes. Even a recent study suggests that the fins of the salamander muscles have grown rudimentary shapes of toe bones, and that the most recent common ancestor of true tetrapods, all land vertebrates, including humans, has been revealed. Saint-Ele would have laughed if he had seen the salamander appear in his vertebrate skeleton comparison chart between man and fish.
Evolution of tetrapod-finned fish
Source: Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences