When did the first flags appear? What is a flag? It is a symbol or sign made of fabric. It can be carried, it can be waved, it can flutter. And it is believed that people who carry or hang out any flag thus show their belonging to a certain

When did the first pirates appear? Piracy, or sea robbery, has existed for several millennia. Even ancient Greek and Roman ships were attacked by sea robbers in the Aegean and Mediterranean seas. The pirates were so powerful that even

When did the first acrobats appear? Man has always loved to have fun. Since the beginning of civilization, acrobats, jugglers, animal trainers and clowns have existed for such entertainment. So we cannot say exactly when the first acrobats appeared. Today is ours

When did the first stoves appear? At the beginning of the 15th century, stoves began to appear, although the hearth was still the main source of heat in the house. The stove was more efficient than the hearth, since it is located inside the room, and warms it both by radiating heat and by moving hot air.

When did the first fire brigades appear? Man has always known that fire can be a friend and helper, but it can also be a great destroyer. Primitive man, however, did not have the problem of fighting fire, as we do, simply because he did not live in houses,

Where and when did the first dictionaries appear? From the beginning of the 2nd millennium BC, scribes in Akkad (one of the oldest centers of Babylonia) began to compile Sumerian-Akkadian dictionaries - the first dictionaries in human history. In these dictionaries, Sumerian cuneiform characters

Where and when did the first concentration camps appear? The first concentration camps appeared in 1900 during the Boer War (1899–1902) in South Africa. The war got out of the control of the British, the Boers (Afrikaners) gradually switched to partisan methods

When did the first pirates appear? Piracy, or sea robbery, has existed for several millennia. Even ancient Greek and Roman ships were attacked by sea robbers in the Aegean and Mediterranean seas. The pirates were so powerful that even

Late Devonian. These were armored-headed amphibians (the outdated name is stegocephals; now most of these animals are included in the labyrinthodonts). They lived near bodies of water and were closely associated with them, since they reproduced only in water. The development of spaces remote from bodies of water required a significant restructuring of the organization: adaptation to protecting the body from desiccation, breathing atmospheric oxygen, efficient movement on solid substrate, and the ability to reproduce outside of water. These are the main prerequisites for the emergence of a qualitatively different new group of animals - reptiles. These changes were quite complex; for example, it required the development of powerful lungs and a change in the nature of the skin.

From the point of view of a progressive method of classification - cladistics, which considers the position of organisms from the point of view of their origin, and not the characteristics of their organization (in particular, the classic “reptilian” characteristics of crocodiles, such as cold-bloodedness and limbs located on the sides of the body, are secondary), reptiles are all developed amniotes, excluding taxa included in the clade synapsids and possibly anapsids.

Carboniferous period

The remains of the most ancient reptiles are known from the Upper Carboniferous (about 300 million years ago). It is assumed that the separation from amphibian ancestors should have begun, apparently, in the Middle Carboniferous (320 million years), when from anthracosaurs like Diplovertebron, forms became isolated, apparently better adapted to the terrestrial way of life. From such forms a new branch arises - the 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 North America, Western Europe, Russia and China know the remains of cotylosaurs (Cotylosauria). In a number of characteristics they are still very close to stegocephals. Their skull was in the form of a solid bone box with openings only for the eyes, nostrils and parietal organ. cervical region the 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; the cleithrum, a skin bone characteristic of fish, was preserved in the shoulder girdle; 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 became more mobile; their skeleton became lighter, but at the same time stronger. Reptiles consumed a more varied diet than amphibians. The technique of its extraction has changed. In this regard, the structure of the limbs has undergone significant changes, axial skeleton and skulls. For the majority, the limbs became longer, and the pelvis, gaining stability, was attached to two or more sacral vertebrae. The “fishy” bone, the cleithrum, has disappeared from the shoulder girdle. The solid shell of the skull has undergone partial reduction. In connection with the more differentiated muscles of the jaw apparatus, pits and bone bridges separating them appeared in the temporal region of the skull - arches that served to attach a complex system of muscles.

Synapsids

The main ancestral group that gave rise to all the diversity of modern and fossil reptiles was probably cotylosaurs, but the further development of reptiles followed different paths.

Diapsids

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 an extremely broad adaptive radiation to systematic groups and species, which are found both among extinct forms and among living reptiles. Among diapsids, two main groups have emerged: lepidosauromorphs (Lepidosauromorpha) and archosauromorphs (Archosauromorpha). The most primitive diapsids from the group of lepidosaurs - the order Eosuchia - were the ancestors of the order Beaked, from which only one genus is currently preserved - hatteria.

At the end of the Permian, squamate (Squamata) separated from the primitive diapsids, becoming numerous in the Cretaceous period. By the end Cretaceous period Snakes evolved from lizards.

Origin of archosaurs

see also

• Temporal arches

Notes

Literature

• Naumov N. P., Kartashev N. N. Part 2. Reptiles, birds, mammals// Zoology of vertebrates. - M.: graduate School, 1979. - P. 272.

A transitional form is an organism with an intermediate state that necessarily exists during a gradual transition from one biological type of structure to another. Transitional forms are characterized by the presence of more ancient and primitive (in the sense of primary) traits than their later relatives, but, at the same time, the presence of more progressive (in the sense of later) traits than their ancestors. As a rule, when speaking about intermediate forms, they mean fossil species, although intermediate species do not necessarily have to die out. Many transitional forms are known, illustrating the origin of tetrapods from fish, reptiles from amphibians, birds from dinosaurs, mammals from theriodonts, cetaceans from land mammals, horses from a five-toed ancestor, and humans from ancient hominids.

Reptiles, or reptiles (Latin: Reptilia), are a class of predominantly terrestrial vertebrates, including modern turtles, crocodiles, beaked animals and squamates. Cladists are classified as reptiles and birds, since otherwise the former would be a paraphyletic group.

In the 18th-19th centuries, reptiles, cold-blooded terrestrial vertebrates, were grouped together with amphibians. Traditionally, this group included various vertebrates, which, according to initial ideas, were similar in their organization to modern reptiles(for example, some synapsids - the ancestors of modern mammals). However, at present, questions about the physiology of many extinct groups of organisms remain open, and data on their genetic and evolutionary relationships do not support this kind of classification.

Many authors who adhere to traditional taxonomy believe that archosaurs (crocodiles, pterosaurs, dinosaurs, etc.) should be removed from the class of reptiles and combined into one class with birds, since birds are actually a specialized group of dinosaurs. About 10,885 species of non-avian reptiles are known in the world; 77 species live in Russia.

The largest land animals belonged to dinosaurs - representatives of ancient reptiles, currently represented only by birds. Reptiles flourished during the Mesozoic era, when they dominated the land, sea and air. At the end of the Cretaceous period, most reptiles became extinct. Modern non-avian reptiles are only scattered remnants of that world. However, ancient reptiles gave rise to the currently thriving group of animals - birds, and many of the adaptations that determined the evolutionary success of this group appeared in its archosaur ancestors, which were a specialized group of diapsids (warm-blooded, heat-insulating body cover - feathers, a developed brain, and etc).

). They lived near bodies of water and were closely associated with them, since they reproduced only in water. The development of spaces remote from bodies of water required a significant restructuring of the organization: adaptation to protecting the body from desiccation, breathing atmospheric oxygen, efficient movement on solid substrate, and the ability to reproduce outside of water. These are the main prerequisites for the emergence of a qualitatively different new group of animals - reptiles. These changes were quite complex; for example, it required the development of powerful lungs and 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 the separation from amphibian ancestors should have begun, apparently, in the Middle Carboniferous (320 million years), when from anthracosaurs like Diplovertebron, forms became 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 characteristics they are still very close to stegocephals. Their skull was in the form of a solid bone box with openings 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; the cleithrum, a skin bone characteristic of fish, was preserved in the shoulder girdle; 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 became more mobile; their skeleton became lighter, but at the same time stronger. Reptiles consumed a more varied diet than amphibians. The technique of its extraction has changed. In this regard, the structure of the limbs, axial skeleton and skull underwent significant changes. For the majority, the limbs became longer, and the pelvis, gaining stability, was attached to two or more sacral vertebrae. The “fishy” bone, the cleithrum, has disappeared from the shoulder girdle. The solid shell of the skull has undergone partial reduction. In connection with the more differentiated muscles of the jaw apparatus, pits and bone bridges separating them appeared in the temporal region of the skull - arches that served to attach a complex system of muscles.

Synapsids

The main ancestral group that gave rise to all the diversity of modern and fossil reptiles were cotylosaurs, but the further development of reptiles followed different paths.

Diapsids

The next group to split off from the cotylosaurs were the diapsids ( Diapsida). Their skull has two temporal cavities, located above and below the postorbital bone. Diapsids at the end of the Paleozoic (Permian) gave an extremely broad adaptive radiation to systematic groups and species, which are found both among extinct forms and among living reptiles. Among diapsids, two main groups emerged: Lepidosauromorphs ( Lepidosauromorpha) and Archosauromorphs ( Archosauromorpha). The most primitive diapsids from the group of Lepidosaurs are the order Eosuchia ( Eosuchia) - were the ancestors of the Beak-headed order, from which only one genus is currently preserved - hatteria.

At the end of the Permian, squamosids separated from primitive diapsids ( Squamata), which became numerous during the Cretaceous period. By the end of the Cretaceous period, snakes evolved from lizards.

Origin of archosaurs

see also

Write a review of the article "The Origin of Reptiles"

Notes

Literature

• Naumov N. P., Kartashev N. N. Part 2. Reptiles, birds, mammals // Zoology of vertebrates. - M.: Higher School, 1979. - P. 272.

Excerpt characterizing the Origin of Reptiles

Anna Pavlovna smiled and promised to take care of Pierre, who, she knew, was related to Prince Vasily on his father’s side. The elderly lady, who had previously been sitting ma tante, hastily stood up and caught up with Prince Vasily in the hallway. All the previous pretense of interest disappeared from her face. Her kind, tear-stained face expressed only anxiety and fear.
- What will you tell me, prince, about my Boris? – she said, catching up with him in the hallway. (She pronounced the name Boris with special emphasis on the o). – I can’t stay longer in St. Petersburg. Tell me, what news can I bring to my poor boy?
Despite the fact that Prince Vasily listened reluctantly and almost discourteously to the elderly lady and even showed impatience, she smiled tenderly and touchingly at him and, so that he would not leave, took his hand.
“What should you say to the sovereign, and he will be directly transferred to the guard,” she asked.
“Believe me, I will do everything I can, princess,” answered Prince Vasily, “but it’s difficult for me to ask the sovereign; I would advise you to contact 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, had long since left the world and had lost her previous connections. She has now come to secure appointment to her guard only son. Only then, in order to see Prince Vasily, did she introduce herself and come to Anna Pavlovna for the evening, only then did she listen to the Viscount’s story. She was frightened by the words of Prince Vasily; once upon a time Beautiful face she expressed anger, but this lasted only a minute. She smiled again and grabbed Prince Vasily’s hand more tightly.
“Listen, prince,” she said, “I never asked you, I will never ask you, 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 hastily added. - No, you are not angry, but you promise me. I asked Golitsyn, but he refused. Soyez le bon enfant que vous аvez ete, [Be the kind fellow you were,] she said, trying to smile, while there were tears in her eyes.
“Dad, we’ll be late,” said Princess Helen, who was waiting at the door, turning her beautiful head on her antique shoulders.
But influence in the world is capital, which 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 asked 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 they have taken something into their heads, will not leave until their desires are fulfilled, and otherwise are ready for daily every minute harassment and even on stage. This last consideration shook him.
“Here Anna Mikhailovna,” he said with his usual familiarity and boredom in his voice, “it’s almost impossible for me to do what you want; but 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 guard, here is my hand to you. Are you satisfied?
- My dear, you are a benefactor! I didn’t expect anything else from you; I knew how kind you were.
He wanted to leave.
- Wait, two words. Une fois passe aux gardes... [Once he joins the guard...] - She hesitated: - You are good with Mikhail Ilarionovich Kutuzov, recommend Boris to him as an adjutant. Then I would be calm, and then I would...
Prince Vasily smiled.
- I don’t promise that. You don’t know how Kutuzov has been besieged since he was appointed commander-in-chief. He himself told me that all the Moscow ladies agreed to give him all their children as adjutants.
- No, promise me, I won’t let you in, my dear, my benefactor...
- Dad! - the beauty repeated again in the same tone, - we will be late.
- Well, au revoir, [goodbye,] goodbye. Do you see?
- So tomorrow you will report to the sovereign?
- Definitely, but I don’t promise Kutuzov.
“No, promise, promise, Basile, [Vasily],” Anna Mikhailovna said after him, with the smile of a young coquette, which must once have been characteristic of her, but now did not suit her exhausted face.
She apparently forgot her years and, out of habit, used all the old feminine remedies. But as soon as he left, her face again took on the same cold, feigned expression that was on it before. She returned to the circle, in which the Viscount continued to talk, and again pretended to listen, waiting for the time to leave, since her work was done.
– But how do you find all this latest comedy du sacre de Milan? [Milan 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 throne, 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 so new comedy: the people of Genoa and Lucca express their wishes to Mr. Bonaparte. And Mr. Bonaparte sits on the throne and fulfills the wishes of the people. 0! This is amazing! No, this can drive you crazy. You will think that the whole world has lost its head.]
Prince Andrei grinned, looking straight into Anna Pavlovna’s face.
“Dieu me la donne, gare a qui la touche,” he said (the words Bonaparte said when laying on the crown). “On dit qu"il a ete tres beau en prononcant ces paroles, [God gave me the crown. Trouble is the one who touches it. “They say he was very good in saying these words,” he added and repeated these words again in Italian: “Dio mi la dona, guai a chi la tocca.”
“J"espere enfin," Anna Pavlovna continued, "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 this was finally the drop that overflows the glass. The 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. [Sirs! I'm not talking about Russia. Sirs! But what did they do for Louis XVII, for the queen, for Elizabeth? Nothing. And, believe me, they are being punished for their betrayal of the Bourbon cause. Sirs! They send envoys to greet the thief of the throne.]
And he, sighing contemptuously, changed his position again. Prince Hippolyte, who had been looking at the Viscount through his 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 had asked him about it.
- Baton de gueules, engrele de gueules d "azur - maison Conde, [A phrase that is not translated literally, as it consists of conventional heraldic terms that are not used entirely accurately. The general meaning is this: The coat of arms of Conde represents a shield with red and blue narrow jagged stripes ,] - he said.

Land vertebrates arose in the Devonian. These were armored amphibians, or stegocephali. They were closely associated with bodies of water, since they reproduced only in water and lived near bodies of water, where there was terrestrial vegetation. The development of spaces remote from bodies of water required a significant restructuring of the organization: adaptation to protecting the body from desiccation, breathing atmospheric oxygen, walking on solid substrate, the ability to reproduce outside of water and, of course, improving forms of behavior. These are the main prerequisites for the emergence of a qualitatively different new group of animals. All of the above traits took shape in reptiles.

To this we must add that by the end of the Carboniferous there were strong changes in the natural environment, which led to the emergence of a more diverse climate on the planet, the development of more diverse vegetation, its distribution in areas remote from water bodies, and in this regard to the wide spread of tracheal-breathing arthropods, i.e. .e. possible feeding objects also spread to the watershed areas of the land.

The evolution of reptiles proceeded very quickly and violently. Long before the end Permian period Paleozoic they replaced most of the stegocephalians. Having gained the opportunity to exist on land, reptiles in a new environment encountered new and extremely diverse conditions. The versatility of this diversity and the absence of significant competition on land from other animals were the main reasons for the flourishing of reptiles in subsequent times. Mesozoic reptiles are primarily terrestrial animals. Many of them are secondary in one way or another

adapted to life in water. Some have mastered the air. The adaptive divergence of reptiles was astonishing. The Mesozoic is rightly considered the age of reptiles.

Early reptiles. The oldest reptiles are known from the Upper Permian deposits of North America, Western Europe, Russia and China. They are called cotylosaurs. In a number of characteristics they are still very close to stegocephalians. Their skull was in the form of a solid bone box with openings only for the eyes, nostrils and parietal organ, the cervical spine was poorly formed, the sacrum had only one vertebra; the cleithrum, a skin bone characteristic of fish, was preserved in the shoulder girdle; the limbs were short and widely spaced.

Cotylosaurs turned out to be very interesting objects, numerous remains of which were found by V.P. Amalitsky in Permian deposits of Eastern Europe, on Northern Dvina. Among them are the three-meter herbivorous pareiasaurs (Pareiasaurus).

It is possible that cotylosaurs were descendants of Carboniferous stegocephalians - embolomeres.

In the Middle Permian, cotylosaurs reached their peak. But only a few survived until the end of the Permian, and in the Triassic this group disappeared, giving way to more highly organized and specialized groups of reptiles that developed from various orders of cotylosaurs (Fig. 114).

The further evolution of reptiles was determined by their variability due to the influence of very diverse living conditions that they encountered during reproduction and settlement. Most groups acquired greater mobility; their skeleton became lighter, but at the same time stronger. Reptiles consumed a more varied diet than amphibians. The technique of its extraction has changed. In this regard, the structure of the limbs, axial skeleton and skull underwent significant changes. For the majority, the limbs became longer, and the pelvis, gaining stability, was attached to two or more sacral vertebrae. The cleithrum bone has disappeared in the shoulder girdle. The solid shell of the skull has undergone partial reduction. In connection with the more differentiated muscles of the jaw apparatus, pits and bone bridges separating them appeared in the temporal region of the skull - arches that served to attach a complex system of muscles.

The main groups of reptiles are discussed below, a review of which should show the exceptional diversity of these animals, their adaptive specialization and probable relationship with living groups.

In the formation of the appearance of ancient reptiles and in assessing their subsequent fate, the characteristics of their skull are essential.

Rice. 114. Cotylosaurs (1, 2, 3) and pseudosuchia (4):
1 - pareiasaurus (Upper Permian), skeleton; 2 - pareiasaurus, restoration of the animal; 3 - Seymouria; 4 – pseudosuchia

The primitiveness of stegocephalians ("whole-skull") and early reptiles was expressed in the structure of the skull by the absence of any cavities in it, except for the ocular and olfactory ones. This feature is reflected in the name Anapsida. The temporal region of reptiles of this group was covered with bones. Turtles (now Testudines, or Chelonia) became probable descendants of this trend; they retain a continuous bony cover behind their eye sockets. Similarities with current forms are found in turtles known from the Lower Triassic of the Mesozoic. Their fossil remains are confined to the territory of Germany. The skull, teeth, and shell structure of ancient turtles are extremely similar to modern ones. The ancestor of turtles is considered to be the Permian Eunotosaurus(Eunotosaurus) is a small lizard-like animal with short and very wide ribs that form something like a dorsal shield (Fig. 115). He did not have an abdominal shield. There were teeth. Mesozoic turtles were originally land-dwelling and apparently burrowing animals. Only later did some groups switch to an aquatic lifestyle and, as a result, many of them partially lost their bony and horny shells.

From the Triassic to the present day, turtles have retained the main features of their organization. They survived all the trials that killed off most reptiles, and are just as thriving today as they were in the Mesozoic.

Today's hidden-necked and side-necked ones retain their primary appearance to a greater extent. land turtles Triassic Marine and soft-skinned animals appeared in the late Mesozoic.

All other reptiles, both ancient and modern, acquired one or two temporal cavities in the structure of the skull. They had one, lower, temporal cavity synapsid. One superior temporal cavity is noted in two groups: paranoid and euryansid. And finally, two depressions had diapsid. The evolutionary fate of these groups is different. The first to move away from the ancestral trunk synapsids(Synapsida) - reptiles with lower temporal cavities, bounded by the zygomatic, squamosal and post-orbital bones. Already in the Late Carboniferous, this group of the first amniotes became the most numerous. In the fossil record they are represented by two successively existing orders: pelycosaurs(Pelicosauria) and therapsids(Therapsida). They are also called bestial(Theromorpha). Animal-like animals experienced their heyday long before the first dinosaurs appeared; cotylosaurs were their direct relatives. In particular, pelycosaurs(Pelicosauria) were still very close to cotylosaurs. Their remains were found in North America and Europe. In appearance they looked like lizards and were small in size - 1-2 m, had biconcave vertebrae and well-preserved abdominal ribs. However, their teeth sat in the alveoli. In some, teeth differentiation was evident, albeit to a small extent.

In the Middle Permian, pelycosaurs were replaced by more highly organized ones. beast-toothed(Theriodontia). Their teeth were clearly differentiated, and a secondary bony palate appeared. The single occipital condyle split into two. The lower jaw was mainly represented by dentary bone. Position

limbs also changed. The elbow moved back and the knee moved forward, and as a result the limbs began to occupy a position under the body, and not on the sides of it, as in other reptiles. The skeleton appeared to have many features in common with mammals.

Numerous Permian beast-toothed reptiles were very diverse in appearance and lifestyle. Many were predators. Perhaps this was the one found by the expedition of V.P. Amalitsky in the sediments of the Permian period on the Northern Dvina inostranzevia(Inostrancevia alexandrovi, Fig. 116). Others ate a plant-based or mixed diet. These unspecialized species are closest to mammals. Among them it is necessary to point out Cynognathus(Cynognathus), which had many progressive organizational features.

Animal-toothed animals were numerous in the Early Triassic, but with the appearance predatory dinosaurs they disappeared. Interesting materials presented in Table 6 indicate a sharp reduction in the diversity of animal-like animals throughout the Triassic. Animal-like animals are of great interest as the group that gave rise to mammals.

Rice. 116. Animal-toothed:
1 - Inostracevia, Upper Permian (restoration of an animal), 2 - skull of Cynognathus

Table 6

The relationship between the genera of beast-like and sauropsid (lizard-like reptiles) at the end of the Paleozoic - beginning of the Mesozoic
(P Robinson, 1977)

The next group to split off from the anapsid cotylosaurs were diapsid(Diapsida). Their skull has two temporal cavities, located above and below the postorbital bone. Diapsids at the end of the Paleozoic (Permian) gave an extremely broad adaptive radiation to systematic groups and species, which are found both among extinct forms and among living reptiles. Among the diapsids, two main groups (infra-classes) have emerged: infra-class Lepidosauromorphs(Lepidosauromorpha) and infraclass Archosauromorphs(Archosauromorpha).

Paleontologists do not have accurate information to say which of them is older and younger in terms of time of appearance, but their evolutionary fate is different.

Who are lepidosauromorphs? This ancient infraclass unites living hatteria, lizards, snakes, chameleons and their extinct ancestors.

Hatteria, or Sphenodon(Sphenodon punctatus), now living on small islands off the coast of New Zealand, is a descendant of the proto-lizards, or wedge-toothed ones, quite common in the mid-Mesozoic (superorder Prosauria, or Lepidontidae). They are characterized by many wedge-shaped teeth sitting on the jaw bones and on the palate, like amphibians, and amphicoelous vertebrae.

Lizards, snakes and chameleons now make up the wide variety of the order Squamata. Lizards are one of the oldest advanced groups of reptiles, their remains are known from. Upper Permian Scientists have discovered many similarities between lizards and Sphenodon. Their limbs are widely spaced and the body moves, curving the spinal column in waves. Interestingly, among their common morphological similarities is the presence of an intertarsal joint. Snakes appear only in chalk. Chameleons are a specialized group of a later era - the Cenozoic (Paleocene, Miocene).

Now about the fate of archosauromorphs. Archosaurs are considered the most amazing of all reptiles that ever lived on Earth. Among them are crocodiles, pterosaurs, and dinosaurs. Crocodiles are the only archosaurs that have survived to this day.

Crocodiles(Crocodylia) appear at the end of the Triassic. Jurassic crocodiles are significantly different from modern ones in the absence of a true bony palate. Their internal nostrils opened between the palatine bones. The vertebrae were still amphicoelous. Crocodiles modern type with a fully developed secondary bony palate and procoelal vertebrae, they descended from ancient archosaurs - pseudosuchians. They are known from the Cretaceous (about 200 million years ago). Most lived in fresh water bodies, but true marine species are also known among the Jurassic forms.

Winged lizards, or pterosaurs(Pterosauria), represent one of the wonderful examples specializations of Mesozoic reptiles. These were flying animals of a very peculiar structure. Their wings were folds of skin stretched between the sides of the body and the very long fourth finger of the forelimbs. The wide sternum had a well-developed keel, like that of birds; the skull bones fused early; many bones were pneumatic. The jaws extended into a beak bore teeth. The length of the tail and the shape of the wings varied. Some ( Rhamphorhynchus) had long narrow wings and a long tail; they apparently flew in a gliding flight, often gliding. Other's ( pterodactyls) the tail was very short and the wings were wide; their flight was more often rowing (Fig. 117). Judging by the fact that the remains of pterosaurs were found in the sediments of salt water bodies, these were inhabitants of the coasts. They ate

fish and behavior, apparently, were close to gulls and terns. The sizes varied from a few centimeters to a meter or more.

The largest among flying vertebrates belong to the Late Cretaceous winged lizards. These are pteranodons. Their estimated wingspan is 7-12 m, body weight is about 65 kg. They are found on all continents except Antarctica.

Paleontologists suggest a gradual decline in the evolution of this group, which coincided with the appearance of birds.

Dinosaurs(Dinosauria) are known in the fossil record from the mid-Triassic. They are the largest and most diverse group of reptiles ever to live on land. Among the dinosaurs there were small animals, with a body length of less than a meter, and giants up to almost 30 m long. Some of them walked only on hind legs, others - on all four. The general appearance was also very diverse, but in all of them the head was small relative to the body, and the spinal cord in the sacral region formed a local expansion, the volume of which exceeded the volume of the brain (Fig. 118).

At the very beginning of their formation, dinosaurs were divided into two branches, the development of which proceeded in parallel. Characteristic feature their building was pelvic girdle, in connection with which these groups are called lizard and ornithischian.

Lizard-pelvic(Saurischia) were originally relatively small predatory animals that moved in leaps only on their hind legs, while the front legs served for grasping food. The long tail also served for support. Subsequently, large herbivorous forms appeared that walked on all four legs. These included the largest vertebrates that ever lived on land: brontosaurus had a body length of about 20 m, diplodocus- up to 26 m. Most of the giant lizards were apparently semi-aquatic animals and fed on lush aquatic vegetation.

Ornithischian(Ornithischia) got their name due to their elongated pelvis, similar to the pelvis of birds. Initially, they moved on only elongated hind legs, but later species had both proportionately developed pairs of limbs and walked on four legs. By the nature of their diet, ornithischians were exclusively herbivorous animals. Among them - iguanodon, walking on its hind legs and reaching a height of 9 m. Triceratops in appearance it was very similar to a rhinoceros, usually possessing a small horn at the end of its muzzle and two long horns above the eyes. Its length reached 8 m. Stegosaurus was distinguished by a disproportionately small head and two rows of high bone plates located on the back. Its body length was about 5 m.

Rice. 118. Dinosaurs:
1 - iguanodon; 2 - brontosaurus; 3 - diplodocus; 4 - triceratops; 5 - stegosaurus; 6 – ceratosaurus

Dinosaurs were distributed throughout almost the entire globe and lived in extremely diverse environments. They inhabited deserts, forests, and swamps. Some led a semi-aquatic lifestyle. There is no doubt that in the Mesozoic this group of reptiles was dominant on land. Dinosaurs reached their greatest prosperity during the Cretaceous, and by the end of this period they became extinct.

Finally, it is necessary to recall another group of reptiles in whose skull there was only one superior temporal cavity. This was typical for parapsids and euryapsids. It has been suggested that they evolved from diapsids by losing the lower cavity. In the fossil record they were represented by two groups: ichthyosaurs(Ichthyosauria) and plesiosaurs(Plesiosauria). Throughout the Mesozoic, from the Early Triassic to the Cretaceous, they dominated marine biocenoses. As noted by R. Carroll (1993), reptiles became secondary aquatic whenever life in water turned out to be more advantageous in terms of the availability of food sources and a small number of predators.

Ichthyosaurs(Ichthyosauria) occupied in the Mesozoic the same place that cetaceans now occupy. They swam, bending their body in waves, especially its tail part, their fins served for control. Their convergent resemblance to dolphins is striking: a spindle-shaped body, an elongated snout and a large two-lobed fin (Fig. 119). Their paired limbs turned into flippers, while the hind limbs and pelvis were underdeveloped. The phalanges of the fingers were elongated, and the number of fingers in some reached 8. The skin was bare. Body sizes varied from 1 to 14 m. Ichthyosaurs lived only in water and ate fish, partly invertebrates. It was established that they were viviparous. Ichthyosaurs appeared in the Triassic and went extinct at the end of the Cretaceous.

Plesiosaurs(Plesiosauria) had different adaptive features than ichthyosaurs in connection with life in the sea: a wide and flat body with a relatively underdeveloped tail. Powerful flippers served as swimming tools. Unlike ichthyosaurs,

They had a well-developed neck carrying a small head. Their appearance resembled pinnipeds. Body sizes range from 50 cm to 15 m. The lifestyle was also different. In any case, some species inhabited coastal waters. They ate fish and shellfish. Having appeared at the beginning of the Triassic, plesiosaurs, like ichthyosaurs, became extinct at the end of the Cretaceous period.

From the above brief overview phylogeny of reptiles shows that the vast majority of large systematic groups (orders) became extinct before the beginning Cenozoic era and modern reptiles are but miserable remnants of the richest Mesozoic reptile fauna. The reason for this grandiose phenomenon is understandable only in the most general terms. Most Mesozoic reptiles were extremely specialized animals. The success of their existence depended on the presence of very unique living conditions. One must think that one-sided deep specialization was one of the prerequisites for their disappearance.

It has been established that although the extinction of individual groups of reptiles occurred throughout the Mesozoic, this became apparent at the end of the Cretaceous period. At this time, relatively short term Most Mesozoic reptiles became extinct. If it is fair to call the Mesozoic the age of reptiles, then it is no less justified to call the end of this era the age of the great extinction. It should be taken into account that significant changes in climate and landscapes occurred during the Cretaceous. This coincided with significant redistributions of land and sea and movements of the earth's crust, which led to enormous mountain-building phenomena, known in geology as the Alpine stage of mountain building. It is believed that at this time a large cosmic body passed near the Earth. Violations of the existing living conditions in this regard were very significant. However, they consist not only in changes in the physical state of the Earth and other conditions inanimate nature. In the middle of the Cretaceous period, the Mesozoic flora of conifers, cycads and other plants was replaced by representatives of a new type of flora, namely angiosperms. Genetic changes in the nature of the reptiles themselves cannot be ruled out. Naturally, all this could not but affect the success of the existence of all animals and specialized ones in the first place.

Finally, we must take into account that by the end of the Mesozoic, incomparably more highly organized birds and mammals, which played an important role in the struggle for existence between groups of terrestrial animals, were increasingly developing.

Figure 120 gives general scheme phylogeny of reptiles.

Origin of reptiles

Origin of reptiles- one of important issues in the theory of evolution, the process as a result of which the first animals belonging to the class Reptilia appeared.

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 characteristics they are still very close to stegocephals. Their skull was in the form of a solid bone box with openings 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; the cleithrum, a skin bone characteristic of fish, was preserved in the shoulder girdle; 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 became more mobile; their skeleton became lighter, but at the same time stronger. Reptiles consumed a more varied diet than amphibians. The technique of its extraction has changed. In this regard, the structure of the limbs, axial skeleton and skull underwent significant changes. For the majority, the limbs became longer, and the pelvis, gaining stability, was attached to two or more sacral vertebrae. The “fishy” bone, the cleithrum, has disappeared from the shoulder girdle. The solid shell of the skull has undergone partial reduction. In connection with the more differentiated muscles of the jaw apparatus, pits and bone bridges separating them appeared in the temporal region of the skull - arches that served to attach a complex system of muscles.

Synapsids

The main ancestral group that gave rise to all the diversity of modern and fossil reptiles were cotylosaurs, but the further development of reptiles followed different paths.

Diapsids

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 an extremely broad adaptive radiation to systematic groups and species, which are found both among extinct forms and among living reptiles. Among diapsids, two main groups emerged: Lepidosauromorpha and Archosauromorpha. The most primitive diapsids from the group of Lepidosaurs are the order Eosuchia ( Eosuchia) - were the ancestors of the Beak-headed order, from which only one genus is currently preserved - hatteria.

At the end of the Permian, squamate (Squamata) separated from the primitive diapsids, becoming numerous in the Cretaceous period. By the end of the Cretaceous period, snakes evolved from lizards.

Origin of archosaurs

see also

• Temporal arches

Notes

Literature

• Naumov N.P., Kartashev N.N. Part 2. Reptiles, birds, mammals // Zoology of vertebrates. - M.: Higher School, 1979. - P. 272.

Wikimedia Foundation. 2010.