Mitra is the earliest terrestrial vertebrate on earth, which flourished in Carboniferous and Permian, and a few species continued into Triassic. Its conical tooth cross section has a labyrinth structure, hence the name. The skull is composed of hard and coarse bone fragments, so it is also called scleroderma. Compared with fleshfin fish, the skull is flat, the bone fragments are reduced, the tongue and jaw retreat to the middle ear to form the stapes, and the stapes has an auditory recess. In addition, most of them have heavy scales. In the prosperous times, this kind of animal can be found everywhere in swamps, rivers and lakes on the earth. In the late Paleozoic and Triassic, they were distributed in all continents of the earth. Newts are divided into three orders: Fishiopoda, separated vertebrates and Carboniferous salamanders.
Iguana in the suborder Iguana is a special amphibian, and it can be seen that it has some characteristics of amphibians and reptiles. This phenomenon provides strong evidence that reptiles originated from amphibians.
The origin of amphibians may have occurred in the late Devonian. At that time, a certain species of fleshfin fish landed on land, creating a new direction of adaptation and evolution. This is an adventure of early vertebrates, and a bold step towards a completely unfamiliar and only partially adapted new environment. However, once this progressive air-breathing fish took this step, it quickly became a primitive amphibian. Since then, many new possibilities have emerged in the evolutionary development of vertebrates.
Some scientists believe that the motivation for letting fleshfin fish leave water and land may be precisely to get more water. It is speculated that some long-bearded fishes in the late Devonian were probably threatened by extreme drought, forcing them to try to find new ponds or streams to survive in them, which forced them to climb the dry land first. As a result, some finned fish have found new water sources, so they can continue their fish life. Most explorers are likely to die tragically; However, the most successful people are probably those individuals and their descendants who have learned a new way of life on land. They created a brand-new living space on land, got rid of the restriction of water on vertebrates, and laid the foundation for a more advanced evolutionary direction. So far, the earliest vertebrate discovered by scientists on land is a primitive amphibian called "fish-stone salamander".
The skull structure of ichthyosaur is solid, and the position and shape of each bone block on the top cover are similar to those of progressive fleshfin in fish, and of course it is more progressive. The skeletal characteristics of ichthyosaurs show the wonderful combination of amphibians and fish. The spine is slightly better than fish, but the tail still retains the fins like fish's tail. Strong shoulder straps, belts and fully developed front and rear limbs related to them show that ichthyosaurs can walk on all fours. Since the ancestors of ichthyosaurs, amphibians (classes) have differentiated into three subclasses in the process of adapting to the land environment: Echinoptera, Cladocera and Slippery. The earliest representative of lungfish is the Middle Devonian double-fin fish. On this basis, lungfish once flourished from late Devonian to Carboniferous, and only a few highly specialized representatives live in the equatorial regions of Africa, Australia and South America. Australian lungfish is the most primitive lungfish in three regions. They live in a river in Queensland. When the river volume decreases in the dry season, they live in isolated puddles, come to the surface to breathe air, and breathe with their single lung with many blood vessels. However, this kind of fish can't live without water. African lungfish and South American lungfish can survive for several months after the rivers in which they live completely dry up. When the dry season comes, these lungfish get into the mud and wrap themselves up, leaving only one or several holes to ventilate with the outside world for breathing. Unlike Australian lungfish, both lungfish have a pair of lungs. The ability of lungfish to breathe air naturally reminds us that they may be the intermediate link between fish and terrestrial vertebrates. In particular, the lateral fin of Australian lungfish evolved to look like thin legs, and they can even use this lateral fin to move their bodies, just like walking at the bottom of a river or pond. This body structure and behavior vividly reflect the early form of terrestrial quadruped vertebrates. Compared with other fish families, lungfish has always been a small family. From the trunk of this evolutionary route, Ceratosaurus was developed. In Triassic and late Mesozoic, Ceratosaurus was widely distributed in most continental waters of the world. Modern Australian lungfish is a direct descendant of hornfish. African lungfish and South American lungfish are branches differentiated from the evolutionary trunk of lungfish. The lateral fin of African lungfish degenerated into a slender whip, while the lateral fin of South American lungfish also shrank obviously and became a fairly small appendage. The distribution of lungfish on the southern hemisphere continent makes some geologists think that this proves that the southern hemisphere continent was once closely related. However, some scientists believe that because all kinds of lungfish once spread all over the world in geological history, the distribution of modern lungfish only represents the remains of the once extensive lungfish habitat in modern times. The existence of lungfish provides a reference for us to understand the transition from fish to primitive amphibians in the past. However, there is still not enough evidence to show that lungfish is the ancestor of amphibians. For example, the ossification of their skulls is very low, which is very different from the hard bones of amphibians. Moreover, the lateral fin of lungfish is so specialized and delicate that it is difficult for people to associate it with the strong limbs of amphibians.
There is a Seymour city in Texas, USA, and a large area of early Permian sediments is exposed in the north of the city. The famous fossil between reptiles and amphibians represents lizards found here. On the one hand, iguanas are very similar to an amphibian called Carboniferous lizard. For example, the top of its skull is completely covered, and all the bone fragments of the tooth fan skull are still preserved; There are also sharp teeth similar to hypnotic teeth on the edge of the upper and lower jaws, especially some typical big teeth similar to hypnotic teeth on the palatal bone; Moreover, it connects the occipital condyle of the skull and cervical vertebra, and only one is like a Carboniferous lizard.
On the other hand, however, the bones on the lizard's body (anatomically called the bones behind the head) show a series of progressive features similar to those of early reptiles. For example, the composition and shape of its spine, the clavicle in the shoulder strap connecting its forelimbs and spine, and the humerus are all very similar to reptiles; Intestinal bones are much larger than those of amphibians; There are two recommended vertebrae, only one different from amphibians. Although its ankle is still an amphibian, the arrangement of phalanges is similar to that of early reptiles: the thumb and big toe have two phalanges, the second toe has three phalanges, the third toe has four phalanges, and the fourth toe has five phalanges. This arrangement of phalanges is typical of primitive reptiles, which can be expressed by numbers as 2-3-4-5-3 (4). So, are lizards amphibians or reptiles? The best answer to this question obviously depends on whether iguanas lay eggs on land like modern reptiles or return to the water to lay eggs like modern amphibians. Unfortunately, paleontology has not provided us with clues to this problem so far. However, Dr. White, a paleontologist, has made a detailed study of iguanas and found that many fossil materials show that iguanas have hermaphroditic characteristics-the first arch protruding from the bottom of some individuals' coccyx is far from the back of the belt, while the corresponding arch of others is closer to the back of the belt. Based on this, it is speculated that those individuals whose vascular arches are far away from the trailing edge of the belt indicate that there must be a considerable gap between the vascular arches and the trailing edge of the belt. Such individuals represent females, and the large gap reflects the adaptation of large chorionic eggs to cloacal passages. If we analyze this speculation in connection with the reptilian characteristics of the bones behind the head, there is no doubt that lizards should belong to reptiles. But judging from the characteristics of skulls and teeth, lizards and amphibians really can't be completely separated. Moreover, some genera similar to iguanas still retain some obvious amphibian characteristics. For example, the larvae of sauropod found in Europe still breathe through gills. However, it is this seemingly contradictory evidence that illustrates the true meaning of animal evolution. Even the evolution of a species is not consistent in all aspects. An animal may be progressive in some features, but primitive in others. This situation is called "mosaic evolution". This mosaic evolution of lizards shows that they are a wonderful intermediate type between amphibians and reptiles. Therefore, we can safely speculate that reptiles originated from lizards or amphibians similar to lizards.
Some more progressive teleost fishes appeared in the Middle Devonian. Some or all of their bones ossify into hard bones. The outer layer of the skull is connected by a large number of bone fragments to form a complex pattern, covering the top of the head and sides, and covering the cheeks backwards. Branchial arch consists of a series of bone chains connected by joints; The whole gill is covered by a whole bone-the operculum. Therefore, they form a single outlet of gill at the moving edge of the back of gill cover. Their spray holes are greatly reduced or even disappeared. Most teleost fish connect their jaws with craniolingual joints through their tongues and jaws. The spine of these teleost fish has a central bone body in the shape of a spool, which is called the vertebral body. The vertebral bodies are interconnected and connected into a dynamic trunk to support the body. The spines protruding upward from the vertebral body are called medullary spines; The vertebral body at the tail also protrudes downward with spines, which are called vein spines. Both sides of the thoracic vertebral body are related to the ribs. The "redundant" fins degenerate and disappear; All functional fins are supported by bone fins. The scales covered in vitro are completely ossified. The scales of primitive teleost fish are thick and usually rhombic, which can be divided into two types: one is dentate scales represented by early fleshfin fish, and the other is hard scales represented by early radial fin fish. With the evolution and development of teleost, the thickness of scales gradually becomes thinner, and finally, the advancing teleost has only a thin layer of bone scales. Primitive teleost fish had functional lungs, but most later teleost fish's lungs became swim bladders that helped to control buoyancy.
1990, Yu Xiaobo, a researcher at the Institute of vertebrate paleontology and Paleoanthropology, Chinese Academy of Sciences, discovered the spotted scale fish in the western suburbs of Qujing, Yunnan Province, and was identified as a primitive meat scale fish that lived in the early Devonian more than 400 million years ago. Meat fin fish is one of the big families of teleost fish, and the other big family of teleost fish is radial fin fish. From April 65438 to April 0999, Zhu Min, a researcher at vertebrate paleontology Institute of China Academy of Sciences, made a further study on Lepidoptera punctata, and found that Lepidoptera punctata may be not only the most primitive fleshy fish, but also the most primitive representative of the whole bony fish. Many characteristics of non-bony fishes retained by Lepidoptera punctata fill the morphological gap between bony fishes and non-bony fishes. In the Middle Devonian, teleost fish differentiated into two branches: Actinidia (subclass) and Carnivora (subclass).
Generally speaking, no animal living in water on earth can achieve evolutionary success like teleost. Even the most fully developed aquatic invertebrates, such as various mollusks and ammonites, developed very complicated in Mesozoic, and were far from being able to adapt to the aquatic life of teleost fish. Bony fish have occupied all kinds of niches in all waters on the earth, from streams to rivers, from small ponds in the depths of the mainland to various lakes, from shallow bays to waters of various depths in the vast ocean, where bony fish roam everywhere. The size of teleost species also varies greatly. Some small fish never grow more than 1 cm, but tuna can grow very big. The body shape and ecological adaptation types of teleost are also very different, each with its own advantages. Moreover, the species and individuals of teleost far exceed the sum of many other vertebrates. Therefore, bony fish is the real water conqueror on the earth.
The sharks we are familiar with belong to cartilaginous fish.
Chondroid fish are almost all marine animals. In the whole life history (the whole process of a living body from the beginning to the end), their bones are always cartilaginous, and the hard parts are usually only teeth and spine. Most cartilaginous fish fossils are learned from these things, and occasionally completely calcified skulls, jaws and spines are preserved as fossils. The most primitive cartilaginous fish is represented by split shark, and its most complete fossil is found in Griffin black shale in the late Devonian on the south bank of Lake Erie in the United States. Interestingly, the mouth of modern sharks is usually split horizontally, while that of split sharks is straight. The maxilla of the cleft shark is connected with the skull through two joints, one is the posterior orbital joint, which is directly behind the orbit; The other is located at the back of the skull, where the skull is connected with the connecting rod at the back of the hyoid mandible. This connection between the maxilla and the skull is called double connection, which is quite primitive. The split shark has a high tooth tip in the middle and a low tooth tip on both sides, which is the tooth structure of many ancient cartilaginous fish. The structure of split shark represents the original model of cartilaginous fish in many aspects, and it can be considered that it is close to the basic point of the main line of the evolution system of cartilaginous fish, and the sharks in the later period may have developed along their respective evolutionary directions from here, including Acanthosauroptera, Archaea, Heterodonta, Hexagora, Cuttlefish and Raya. These orders constitute the most prosperous class of cartilaginous fishes: Claudibranchia. Another kind of cartilaginous fish, with fewer species, lives in the deep sea. Because of its unique self-connecting craniomandibular connection, it forms a separate cartilaginous fish group: Cephalopoda. Silver mackerel is a representative of cephalopod, and its evolutionary history can be traced back to the early Jurassic. A large number of toothed plates suitable for grinding were also found in the late Paleozoic strata, which were collectively called slow-toothed sharks, and their genetic relationship was uncertain. The tooth fossils of the cracked shark were found in Carboniferous strata in Zhanyi, Yunnan, China. A spiny fossil of Sparus macrocephalus was found in the Late Triassic strata of Kunming.
English name: giant feather-winged horseshoe crab
Time: 460-445 million years ago in Ordovician.
Typical body length: 1-2m long.
Chinese name: Nautilus
Time: 470-440 million years ago, from the late Ordovician to the early Silurian (it is said that there are still, but no one has seen it alive. It is said that once a China sailor caught a live one, and because he didn't know what it was, he cooked it and ate it. It was said to be delicious.
Typical body length: about 1 1 meter long.
Chinese name: horseshoe crab
Time: 438 million years to 4 1 1 100 million years ago.
Typical body length:1.5m.
Common name: trilobite
Age: Devonian
Typical body length:
Name of species: teleost
Age: Middle Devonian-Late Devonian
Typical body length: .....
Chinese name: Dungeon Fish
Time: Late Devonian, 370-360 million years ago.
Typical body length: 8- 10 meter long.
Chinese name: breast shark
Time: Late Devonian to Carboniferous from1.700 million years ago to 345 million years ago.
Typical body length: 0.7-2m long.
Name: Blacet Tron
Body length: 3 meters long
Survival time: Late Permian-Early Triassic
Chinese name: magic dragon.
Time: Triassic 240 million -2 1 100 million years ago.
Typical body length: 3-4 meters long.
Time: Triassic 240 million -2 1 100 million years ago.
Chinese name: ichthyosaur
Time: Late Triassic, 240-265,438+0 billion years ago.
Typical body length: 10 meter long.
Dinosaur name: ichthyosaur
Dinosaur length: There are many kinds of ichthyosaurs, ranging from 3m to15m.
Age of existence: Jurassic
Name: Pterosaur
Body length: wings can reach 30 to 700 cm.
Age of existence: Jurassic
Chinese name: tooth dragon
Time: 654.38+0.6 billion -654.38+0.5 billion years ago in the middle and late Jurassic.
Typical body length: 25 meters long (controversial, the body length of plesiosaur that can be confirmed now is only about 10 meters)
Chinese name: saurosuchus.
Time: Middle Jurassic1.600 million years ago-1.500 million years ago.
Typical body length: 3 meters long
Chinese name: Leeds fish
Time: Late Jurassic10.65 million-10.55 million years ago.
Typical body length: 27 meters long
Title: Swordfish
Age: 87-65 million years ago in the late Cretaceous.
Typical body length: 6 meters long
Name: Long-headed Dragon
Body length: 9 meters
Age of existence: Early Cretaceous
Chinese name: crocodile
Age: Early Cretaceous
Typical body length: 12m long.
Comparison of skulls between crocodile and live crocodile
Chinese name: Film Dragon
Age: Late Cretaceous 85-65 million years ago.
Typical body length: 15m long.
Chinese name: black dragon.
Age: Late Cretaceous from 85 million to 65 million years ago.
Typical body length: 9- 17m long.
Chinese name: Dayanglong
Age: Late Cretaceous from 85 million to 65 million years ago.
Typical body length: 3 ~ 4m long.
Chinese name: ancient turtle
Age: Late Cretaceous 75-65 million years ago.
Typical body length: 4.6 meters long.