Evolutionary development of reptiles. Origin and evolution of reptiles Origin and evolution of reptiles
In the Upper Triassic, from carnivores, moving mainly on their hind limbs, pseudosuchians (thecodonts); two more groups separated: lizards and ornithischians - dinosaurs that differ in the details of the structure of the pelvis. Both groups developed in parallel; in the Jurassic and Cretaceous periods, they gave an extraordinary variety of species, ranging in size from a rabbit to giants weighing 30-50 tons; lived on land and coastal shallow waters.
By the end of the Cretaceous period, both groups became extinct, leaving no descendants. Big part was a predator moving on its hind limbs (a heavy tail served as a counterweight); the forelimbs were shortened, often rudimentary. Among them there were giants up to 10-15 m long, armed with powerful teeth and strong claws on the fingers of the hind limbs, like a ceratosaurus; despite the big dimensions, these predators were very mobile. Part of the lizard dinosaurs switched to eating plant foods and moving on both pairs of limbs. These include the largest land animals that have ever existed. So, diplodocus, which had a long tail and a long, mobile neck, carrying a small head, was 30 m long and probably weighed about 20-25 tons, and a more massive and short-tailed brachiosaurus, with a length of about 24 m, probably weighed at least 50 tons. Such giants, apparently, moved slowly over land and most of the time, like modern hippos, stayed in the coastal areas of water bodies, eating aquatic and above-water plants. Here they were protected from the attack of large land predators, and their enormous weight made it possible to successfully withstand the blows of the waves.
Ornithischian dinosaurs were probably herbivores. Most of them retained a bipedal type of movement with noticeably shortened forelimbs. Among them, giants 10-15 m long arose, for example iguanodons, in which the first limb turned into a powerful spike, apparently helped defense against predators. Duck-billed dinosaurs stayed along the banks of water bodies and could run and swim. The front part of the jaws formed a wide duck-like beak, and in the depths of the mouth there were numerous flattened teeth that ground plant food. Other ornithischians, having retained herbivory, again returned to the four-legged walking. They often developed protective education against large predators. So, in a stegosaurus that reached 6 m - on back there were two rows of large bone triangular plates, and on a powerful tail there were sharp bone spikes more than 0.5 m long. Triceratops had a powerful horn on the nose and on the horn above the eyes, a the widened posterior edge of the skull that protected the neck bore numerous pointed processes.
Finally, the last branch of reptiles - a subclass of animal-like, or synapsids - was almost the first to separate from the common trunk of reptiles. They separated themselves from the primitive Carboniferous cotylosaurs, which apparently inhabited humid biotopes and still retained many amphibian features (skin rich in glands, structure of the limbs, etc.). Synapsids began a special line of development of reptiles. Already in the Upper Carboniferous and Permian, various forms arose, united in the order of pelycosaurs. They are had amphicoelous vertebrae, a skull with a poorly developed one fossa and one occipital condyle, there were also teeth on the palatine bones, there were ventral ribs. In appearance, they looked like lizards, their length did not exceed 1 m; only single species reached 3-4 m in length. Among them were real predators and herbivorous forms; many led a terrestrial way of life, but there were near-aquatic and aquatic forms.
To end perm pelycosaurs died out, but earlier the animal-toothed reptiles, therapsids, separated from them. The adaptive radiation of the latter proceeded in the Upper Permian, with continuously increasing competition from progressive reptiles, especially archosaurs. Therapsid sizes varied widely: from a mouse to a large rhinoceros. Among them were herbivores - moschops; and large predators with powerful fangs - foreigners (skull length 50 cm) and others. Some small forms, like rodents, had large incisors and, apparently, led a burrowing lifestyle. By the end of the Triassic and the beginning of the Jurassic, diversely and well-armed archosaurs had completely replaced the animal-toothed therapsids. But already in the Triassic, some group of small species, probably inhabiting damp, densely overgrown biotopes and capable of digging shelters, gradually acquired the features of a more progressive organization and gave rise to mammals.
Thus, as a result of adaptive radiation, already at the end of the Permian - the beginning of the Triassic, a diverse fauna of reptiles (approximately 13-15 orders) had developed, displacing most groups of amphibians. The flowering of reptiles was secured a number of aromorphoses that affected all organ systems and ensured an increase in mobility, intensification of metabolism, greater resistance to a number of environmental factors (to dryness in the first place), some complication of behavior and better survival of offspring. The formation of the temporal pits was accompanied by an increase in the mass of chewing muscles, which, along with other transformations, made it possible to expand the range of feeds used, especially plant foods. Reptiles not only widely mastered the land, populating a variety of habitat, but returned to the water and rose into the air. Throughout the Mesozoic era - for more than 150 million years - they occupied the dominant position in almost all terrestrial and many aquatic biotopes. At the same time, the composition of the fauna changed all the time: the ancient groups were dying out, being replaced by more specialized young forms.
By the end of the Cretaceous period on earth started a new powerful cycle of mountain building (Alpine), accompanied by extensive transformations of landscapes and the redistribution of seas and land, an increase in the general dryness of the climate and an increase in its contrasts both in seasons of the year and and by natural areas. At the same time, the vegetation was changing: the dominance of cycads and conifers is replaced by the dominance of the angiosperm flora, the fruits and seeds of which have a high stern value. These changes could not but affect the animal world, especially since by this time two new classes of warm-blooded vertebrates had already formed - mammals and birds. The specialized groups of large reptiles that survived to this time could not adapt to the changing conditions of life. In addition, increasing competition with smaller but active birds and mammals played an active role in their extinction. These classes, having acquired warm-bloodedness, persistently high metabolic rates, and more complex behavior, have increased in numbers and importance in communities. They quickly and efficiently adapted to life in changing landscapes, more quickly mastered new habitats, intensively used new food and exerted an increasing competitive impact on more inert reptiles. The modern Cenozoic era began, in which birds and mammals occupied a dominant position, and only relatively small and mobile scaly (lizards and snakes), well-protected turtles survived among reptiles. and a small group of aquatic archosaurs - crocodiles.
Literature: Zoology of vertebrates. Part 2. Reptiles, birds, mammals. Naumov N. P., Kartashev N. N., Moscow, 1979
Varanus niloticus ornatus at London ZooPermian period
From the upper Permian deposits of North America, Western Europe, Russia and China, remains of Cotylosauria (Cotylosauria) are known. In a number of ways, they are still very close to stegocephals. Their skull was in the form of a solid bone box with holes only for the eyes, nostrils and parietal organ, the cervical spine was poorly formed (although there is a structure of the first two vertebrae characteristic of modern reptiles - atlanta and epistrophy), the sacrum had from 2 to 5 vertebrae; in the shoulder girdle, a kleytrum was preserved - a skin bone characteristic of fish; the limbs were short and widely spaced.
The further evolution of reptiles was determined by their variability due to the influence of various living conditions that they encountered during reproduction and settlement. Most groups have become more mobile; their skeleton became lighter, but at the same time stronger. Reptiles used a more varied diet than amphibians. The technique of obtaining it has changed. In this regard, the structure of the limbs, the axial skeleton and the skull underwent significant changes. Most of the limbs became longer, the pelvis, acquiring stability, was attached to two or more sacral vertebrae. In the shoulder girdle, the "fish" bone of the kleytrum disappeared. The solid shell of the skull has undergone a partial reduction. In connection with the more differentiated muscles of the jaw apparatus in the temporal region of the skull, pits and bone bridges separating them appeared - arcs that served to attach a complex system of muscles.
synapsids
The main ancestral group that gave all the diversity of modern and fossil reptiles was probably cotylosaurs, but the further development of reptiles followed different paths.
Diapsides
The next group to separate from the cotylosaurs were the Diapsida. Their skull has two temporal cavities located above and below the postorbital bone. Diapsids at the end of the Paleozoic (Permian) gave extremely wide adaptive radiation to systematic groups and species, which are found both among extinct forms and among modern reptiles. Among the diapsids, two main groups have emerged: lepidosauromorphs (Lepidosauromorpha) and archosauromorphs (Archosauromorpha). The most primitive diapsids from the group of lepidosaurs - the Eosuchia squad - were the ancestors of the Beakhead order, of which only one genus is currently preserved - tuatara.
At the end of the Permian, squamates (Squamata) separated from primitive diapsids, which became numerous in
Some representatives of this group of historical animals were the size of an ordinary cat. But the height of others can be compared with a five-story building.
Dinosaurs... This is probably one of the most interesting groups of animals in the entire history of the development of the Earth's fauna.
The ancestors of reptiles are considered batrachosaurs - fossil animals found in the Permian deposits. This group includes, for example, seymuria. These animals possessed intermediate characters between amphibians and reptiles. The outlines of their teeth and skull were typical of amphibians, and the structure of the spine and limbs was typical of reptiles. Seymouria spawned in the water, although she spent almost all her time on land. Its offspring developed into adults through the process of metamorphosis, which is typical for modern frogs. The limbs of Seimuria were more developed than those of early amphibians, and she easily moved on muddy soil, stepping over her five-fingered paws. It fed on insects, small animals, sometimes even carrion. The fossilized contents of the stomach of Seymouria indicate that sometimes she happened to eat her own kind.
Batrachosaurs gave rise to the first reptiles, the cotylosaurs, a group of reptiles that included reptiles with a primitive skull structure.
Large cotylosaurs were herbivorous and lived, like hippos, in swamps and river backwaters. Their heads had outgrowths and ridges. They could probably burrow into the silt up to the very eyes. Fossil skeletons of these animals have been found in Africa. Russian paleontologist Vladimir Prokhorovich Amalitsky was fascinated by the idea of finding African lizards in Russia. After four years of research, he managed to find dozens of skeletons of these reptiles on the banks of the Northern Dvina.
From cotilosaurs during the Triassic period (during the Mesozoic era), many new groups of reptiles appeared. Turtles still retain a similar skull structure. All other orders of reptiles also originate from cotilosaurs.
Animal lizards. At the end of the Permian period, a group of animal-like reptiles flourished. The skull of these animals was distinguished by one pair of lower temporal pits. Among them were large quadrupedal forms (it is even difficult to call them "reptiles" in the exact meaning of the word). But there were also small forms. Some were carnivores, others were herbivores. The predatory lizard Dimetrodon had powerful wedge-shaped teeth.
A characteristic feature of the animal is a leathery crest starting from the spine, resembling a sail. It was supported by long bone processes extending from each vertebra. The sun warmed the blood circulating in the sail, and it transferred heat to the body. With teeth of two kinds, Dimetrodon was a ferocious predator. Razor-sharp front teeth pierced the body of the victim, and short and sharp rear teeth served for chewing food.
Among the lizards of this group, animals with different types of teeth first appeared: incisors, fangs and molars. They were called animal-toothed. A predatory three-meter lizard with fangs more than 10 cm long got its name in honor of the famous geologist Professor A.A. Foreigners. Predatory animal-toothed lizards (theriodonts) are already very similar to primitive mammals, and it is no coincidence that the first mammals developed from them by the end of the Triassic.
Dinosaurs are reptiles with two pairs of temporal pits in their skulls. These animals, having appeared in the Triassic, received significant development in subsequent periods of the Mesozoic era (Jurassic and Cretaceous). For 175 million years of development, these reptiles have given a huge variety of forms. Among them were both herbivorous and predatory, mobile and slow. Dinosaurs are divided into two orders: lizards and ornithischians.
Lizard dinosaurs walked on their hind legs. They were fast and agile predators. Tyrannosaurus (1) reached a length of 14 m and weighed about 4 tons. Small carnivorous dinosaurs - coelurosaurs (2) resembled birds. Some of them had a coat of hair-like feathers (and possibly a constant body temperature). The largest herbivorous dinosaurs, brachiosaurs (up to 50 tons), which had a small head on a long neck, also belong to the lizards. 150 million years ago, a thirty-meter diplodocus lived in lakes and along river banks - the largest animal ever known. To facilitate movement, these huge reptiles spent most of their time in the water, that is, they led an amphibious lifestyle.
Ornithischian dinosaurs ate exclusively plant foods. Iguanodon also moved on two legs, its forelimbs were shortened. There was a large spike on the first toe of its forelimbs. Stegosaurus (4) had a small head and two rows of bony plates along the back. They served as protection for him and carried out thermoregulation.
At the end of the Triassic, the first crocodiles originated from the descendants of cotylosaurs, which profusely spread only in the Jurassic period. Then flying lizards appear - pterosaurs, also leading their origin from thecodonts. On their five-fingered forelimb, the last finger was able to make a special impression: very thick and equal in length to ... the length of the animal's body, including the tail.
A leathery flying membrane was stretched between it and the hind limbs. Pterosaurs were numerous. Among them were such species that are quite comparable in size to our ordinary birds. But there were also giants: with a wingspan of 7.5 m. Among the flying dinosaurs of the Jura, the most famous are rhamphorhynchus (1) and pterodactyl (2), of the Cretaceous forms, the relatively very large Pteranodon is most interesting. By the end of the Cretaceous, flying lizards had become extinct.
Among the reptiles there were also water lizards. Large fish-like ichthyosaurs (1) (8–12 m) with a fusiform body, flippers, and a fin-tail resembled dolphins in general outline. Plesiosaurs (2) with elongated necks probably inhabited coastal seas. They ate fish and shellfish.
It is interesting that the remains of lizards, very similar to modern ones, were found in the Mesozoic deposits.
In the Mesozoic era, which was distinguished by a particularly warm and even climate, primarily in the Jurassic period, reptiles reached their peak. In those days, reptiles occupied the same high place in nature that belongs to mammals in modern fauna.
About 90 million years ago, they began to die out. And 65-60 million years ago, only four modern orders remained from the former splendor of reptiles. Thus, the extinction of reptiles continued for many millions of years. This was probably due to the deterioration of the climate, the change of vegetation, competition from animals of other groups, which had such important advantages as a more developed brain and warm-bloodedness. Of the 16 orders of reptiles, only 4 have survived! About the rest, only one thing can be said: their adaptations were clearly not enough to meet the new circumstances. A vivid example of the relativity of any devices!
However, the rise of reptiles was not in vain. After all, they were the necessary link for the emergence of new, more advanced classes of vertebrates. Mammals originated from animal-toothed lizards, and birds originated from lizard dinosaurs.
). They lived near reservoirs and were closely associated with them, since they bred only in water. The development of spaces remote from water bodies required a significant restructuring of the organization: adaptation to protecting the body from drying out, to breathing atmospheric oxygen, efficient movement on a solid substrate, and the ability to reproduce outside water. These are the basic prerequisites for the emergence of a qualitatively different group of animals - reptiles. These restructurings were quite complex, for example, it required the design of powerful lungs, a change in the nature of the skin.
Carboniferous period
The remains of the most ancient reptiles are known from the Upper Carboniferous (about 300 million years ago). It is assumed that separation from amphibian ancestors should have begun, apparently, in the Middle Carboniferous (320 million years), when from anthracosaurs, like Diplovertebron, forms were isolated, apparently better adapted to the terrestrial way of life. From such forms, a new branch arises - seymuriomorphs ( Seymouriomorpha), the remains of which were found in the Upper Carboniferous - Middle Permian. Some paleontologists classify these animals as amphibians.
Permian period
From the upper Permian deposits of North America, Western Europe, Russia, and China, remains of cotylosaurs are known ( Cotylosauria). In a number of ways, they are still very close to stegocephals. Their skull was in the form of a solid bone box with holes only for the eyes, nostrils and parietal organ, the cervical spine was poorly formed (although there is a structure of the first two vertebrae characteristic of modern reptiles - atlanta and epistrophy), the sacrum had from 2 to 5 vertebrae; in the shoulder girdle, a kleytrum was preserved - a skin bone characteristic of fish; the limbs were short and widely spaced.
The further evolution of reptiles was determined by their variability due to the influence of various living conditions that they encountered during reproduction and settlement. Most groups have become more mobile; their skeleton became lighter, but at the same time stronger. Reptiles used a more varied diet than amphibians. The technique of obtaining it has changed. In this regard, the structure of the limbs, the axial skeleton and the skull underwent significant changes. Most of the limbs became longer, the pelvis, acquiring stability, was attached to two or more sacral vertebrae. In the shoulder girdle, the "fish" bone of the kleytrum disappeared. The solid shell of the skull has undergone a partial reduction. In connection with the more differentiated muscles of the jaw apparatus in the temporal region of the skull, pits and bone bridges separating them appeared - arcs that served to attach a complex system of muscles.
synapsids
The main ancestral group that gave all the variety of modern and fossil reptiles were cotylosaurs, however, the further development of reptiles went in different ways.
Diapsides
The next group to separate from the cotylosaurs were the diapsid ( Diapsida). Their skull has two temporal cavities located above and below the postorbital bone. Diapsids at the end of the Paleozoic (Permian) gave extremely wide adaptive radiation to systematic groups and species, which are found both among extinct forms and among modern reptiles. Among the diapsids, there are two main groups of Lepidosauromorphs ( Lepidosauromorpha) and Archosauromorphs ( archosauromorpha). The most primitive diapsids from the Lepidosaur group are the Eosuchia order ( Eosuchia) - were the ancestors of the order Beakheads, of which only one genus is currently preserved - tuatara.
At the end of the Permian, squamosals separated from primitive diapsids ( Squamata), which became numerous during the Cretaceous period. Towards the end of the Cretaceous, snakes evolved from lizards.
Origin of archosaurs
see also
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Notes
Literature
- Naumov N. P., Kartashev N. N. Part 2. Reptiles, birds, mammals // Vertebrate Zoology. - M .: Higher School, 1979. - S. 272.
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An excerpt characterizing the origin of reptiles
He wanted to say something else, but at that time Prince Vasily and his daughter got up, and two young men got up to give them way.“Excuse me, my dear viscount,” said Prince Vasily to the Frenchman, gently pulling him by the sleeve down to the chair so that he would not get up. “This unfortunate feast at the Messenger’s is depriving me of my pleasure and interrupting you. I am very sad to leave your delightful evening,” he said to Anna Pavlovna.
His daughter, Princess Helen, lightly holding the folds of her dress, went between the chairs, and the smile shone even brighter on her beautiful face. Pierre looked with almost frightened, enthusiastic eyes at this beauty when she passed him.
“Very good,” said Prince Andrei.
“Very,” said Pierre.
Passing by, Prince Vasily grabbed Pierre by the hand and turned to Anna Pavlovna.
“Educate me this bear,” he said. - Here he lives with me for a month, and for the first time I see him in the light. Nothing is so necessary for a young man as a society of smart women.
Anna Pavlovna smiled and promised to take care of Pierre, who, she knew, was a paternal relative of Prince Vasily. The elderly lady, who had previously been sitting with ma tante, hastily got up and overtook Prince Vasily in the hall. All the old pretense of interest was gone from her face. Her kind, weepy face expressed only anxiety and fear.
- What will you tell me, prince, about my Boris? she said, catching up with him in the front. (She pronounced the name Boris with a special emphasis on o). – I cannot stay longer in Petersburg. Tell me, what news can I bring to my poor boy?
Despite the fact that Prince Vasily listened reluctantly and almost impolitely to the elderly lady and even showed impatience, she smiled affectionately and touchingly at him and, so that he would not leave, took his hand.
“That you should say a word to the sovereign, and he will be directly transferred to the guards,” she asked.
“Believe me that I will do everything I can, princess,” answered Prince Vasily, “but it’s hard for me to ask the sovereign; I would advise you to turn to Rumyantsev, through Prince Golitsyn: that would be smarter.
The elderly lady bore the name of Princess Drubetskaya, one of the best families in Russia, but she was poor, long gone from the world and lost her former connections. She has come now to secure a position in the guards for her only son. Only then, in order to see Prince Vasily, did she name herself and come to Anna Pavlovna's for the evening, only then did she listen to the history of the viscount. She was frightened by the words of Prince Vasily; once her beautiful face expressed anger, but this lasted only a minute. She smiled again and gripped Prince Vasili more firmly by the arm.
“Listen, prince,” she said, “I never asked you, I will never ask, I never reminded you of my father’s friendship for you. But now, I conjure you by God, do this for my son, and I will consider you a benefactor,” she added hastily. - No, you are not angry, but you promise me. I asked Golitsyn, he refused. Soyez le bon enfant que vous avez ete, [Be a good fellow, as you were,] she said, trying to smile, while there were tears in her eyes.
“Papa, we will be late,” said Princess Helene, turning her beautiful head on antique shoulders, who was waiting at the door.
But influence in the world is a capital that must be protected so that it does not disappear. Prince Vasily knew this, and once he realized that if he began to ask for everyone who asks him, then soon he would not be able to ask for himself, he rarely used his influence. In the case of Princess Drubetskaya, however, after her new call, he felt something like a reproach of conscience. She reminded him of the truth: he owed his first steps in the service to her father. In addition, he saw from her methods that she was one of those women, especially mothers, who, once taking something into their heads, will not lag behind until they fulfill their desires, otherwise they are ready for daily, every minute pestering and even on the stage. This last consideration shook him.
“Chere Anna Mikhailovna,” he said with his usual familiarity and boredom in his voice, “it is almost impossible for me to do what you want; but in order to prove to you how much I love you and honor the memory of your late father, I will do the impossible: your son will be transferred to the guards, here is my hand to you. Are you satisfied?
- My dear, you are a benefactor! I did not expect anything else from you; I knew how kind you are.
He wanted to leave.
- Wait, two words. Une fois passe aux gardes ... [Once he goes to the guards ...] - She hesitated: - You are good with Mikhail Ilarionovich Kutuzov, recommend Boris to him as adjutant. Then I would be calm, and then I would...
Prince Vasily smiled.
- I don't promise that. You do not know how Kutuzov has been besieged since he was appointed commander in chief. He himself told me that all the Moscow ladies conspired to give him all their children as adjutants.
“No, promise me, I won’t let you in, dear, my benefactor…
- Dad! - the beauty repeated again in the same tone, - we will be late.
- Well, au revoir, [goodbye,] goodbye. See?
- So tomorrow you will report to the sovereign?
- Certainly, but I do not promise Kutuzov.
“No, promise, promise, Basile, [Vasily],” Anna Mikhailovna said after him, with a smile of a young coquette, which once must have been characteristic of her, but now did not suit her emaciated face.
She apparently forgot her years and used, out of habit, all the old women's means. But as soon as he left, her face again assumed the same cold, feigned expression that had been on it before. She returned to the circle, in which the viscount continued to talk, and again pretended to be listening, waiting for the time to leave, since her business was done.
“But how do you find all this latest comedy du sacre de Milan?” [Milanese anointing?] – said Anna Pavlovna. Et la nouvelle comedie des peuples de Genes et de Lucques, qui viennent presenter leurs voeux a M. Buonaparte assis sur un trone, et exaucant les voeux des nations! Adorable! Non, mais c "est a en devenir folle! On dirait, que le monde entier a perdu la tete. [And here is a new comedy: the peoples of Genoa and Lucca express their desires to Mr. Bonaparte. And Mr. Bonaparte sits on the throne and fulfills the wishes of the peoples. 0! It's amazing! No, it's crazy. You'll think the whole world has lost its head.]
Prince Andrei grinned, looking directly into the face of Anna Pavlovna.
- “Dieu me la donne, gare a qui la touche,” he said (the words of Bonaparte, spoken at the laying of the crown). - On dit qu "il a ete tres beau en prononcant ces paroles, [God gave me the crown. Trouble for the one who touches it. - They say he was very good pronouncing these words,] - he added and repeated these words again in Italian: "Dio mi la dona, guai a chi la tocca".
- J "espere enfin," continued Anna Pavlovna, "que ca a ete la goutte d" eau qui fera deborder le verre. Les souverains ne peuvent plus supporter cet homme, qui menace tout. [I hope that it was finally the drop that would overflow the glass. Sovereigns can no longer tolerate this man who threatens everything.]
– Les souverains? Je ne parle pas de la Russie,” said the viscount politely and hopelessly: “Les souverains, madame!” Qu "ont ils fait pour Louis XVII, pour la reine, pour madame Elisabeth? Rien," he continued animatedly. - Et croyez moi, ils subissent la punition pour leur trahison de la cause des Bourbons. Les souverains? Ils envoient des ambassadeurs complimenter l "usurpateur. [Sovereigns! I'm not talking about Russia. Sovereigns! But what did they do for Louis XVII, for the Queen, for Elisabeth? Nothing. And believe me, they are punished for their betrayal of the Bourbon cause. Sovereigns! They send envoys to greet the stealer of the throne.]
And he, with a contemptuous sigh, changed his position again. Prince Hippolyte, who had been looking at the viscount through a lorgnette for a long time, suddenly, at these words, turned his whole body to the little princess and, asking her for a needle, began to show her, drawing with a needle on the table, the coat of arms of Condé. He explained this coat of arms to her with such a significant air, as if the princess asked him about it.
- Baton de gueules, engrele de gueules d "azur - maison Conde, [A phrase that cannot be translated literally, as it consists of conditional heraldic terms that are not quite accurately used. The general meaning is this: The coat of arms of Conde represents a shield with red and blue narrow jagged stripes ,] he said.
Origin of reptiles
Origin of reptiles- one of the important questions in the theory of evolution, the process as a result of which the first animals belonging to the class Reptiles (Reptilia) appeared.
Varanus niloticus ornatus at London ZooPermian period
From the upper Permian deposits of North America, Western Europe, Russia, and China, remains of cotylosaurs are known ( Cotylosauria). In a number of ways, they are still very close to stegocephals. Their skull was in the form of a solid bone box with holes only for the eyes, nostrils and parietal organ, the cervical spine was poorly formed (although there is a structure of the first two vertebrae characteristic of modern reptiles - atlanta and epistrophy), the sacrum had from 2 to 5 vertebrae; in the shoulder girdle, a kleytrum was preserved - a skin bone characteristic of fish; the limbs were short and widely spaced.
The further evolution of reptiles was determined by their variability due to the influence of various living conditions that they encountered during reproduction and settlement. Most groups have become more mobile; their skeleton became lighter, but at the same time stronger. Reptiles used a more varied diet than amphibians. The technique of obtaining it has changed. In this regard, the structure of the limbs, the axial skeleton and the skull underwent significant changes. Most of the limbs became longer, the pelvis, acquiring stability, was attached to two or more sacral vertebrae. In the shoulder girdle, the "fish" bone of the kleytrum disappeared. The solid shell of the skull has undergone a partial reduction. In connection with the more differentiated muscles of the jaw apparatus in the temporal region of the skull, pits and bone bridges separating them appeared - arcs that served to attach a complex system of muscles.
synapsids
The main ancestral group that gave all the variety of modern and fossil reptiles were cotylosaurs, however, the further development of reptiles went in different ways.
Diapsides
The next group to separate from the cotylosaurs were the Diapsida. Their skull has two temporal cavities located above and below the postorbital bone. Diapsids at the end of the Paleozoic (Permian) gave extremely wide adaptive radiation to systematic groups and species, which are found both among extinct forms and among modern reptiles. Among the diapsids, there are two main groups of Lepidosauromorphs (Lepidosauromorpha) and Archosauromorphs (Archosauromorpha). The most primitive diapsids from the Lepidosaur group are the Eosuchia order ( Eosuchia) - were the ancestors of the order Beakheads, of which only one genus is currently preserved - tuatara.
At the end of the Permian, scaly ones (Squamata) separated from primitive diapsids, which became numerous in the Cretaceous period. Towards the end of the Cretaceous, snakes evolved from lizards.
Origin of archosaurs
see also
- Temporal arches
Notes
Literature
- Naumov N.P., Kartashev N.N. Part 2. Reptiles, birds, mammals // Vertebrate Zoology. - M .: Higher School, 1979. - S. 272.
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