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 abundantly 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.

Late Devonian. These were shell-headed amphibians (the obsolete name is stegocephals; now most of these animals are included in the labyrinthodonts). 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.

From the point of view of a progressive classification method - cladistics, which considers the position of organisms in terms of their origin, and not organization features (in particular, the classic "reptilian" signs of crocodiles, such as cold-bloodedness and limbs located on the sides of the body, are secondary), reptiles are all developed amniotes, with the exception of taxa included in the synapsid and possibly anapsid clade.

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 - the Seymouriomorphs (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 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, 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// Zoology of vertebrates. - M.: Higher School, 1979. - S. 272.

transitional form

Transitional form - an organism with an intermediate state that necessarily exists during the 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) features than their later relatives, but at the same time, by the presence of more progressive (in the sense of later) features than their ancestors. As a rule, speaking of intermediate forms, they mean fossil species, although intermediate species should not necessarily 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

Reptiles, or reptiles (lat. Reptilia), are a class of predominantly terrestrial vertebrates, including modern turtles, crocodiles, beakheads and scaly ones. Cladists also include birds as reptiles, since otherwise the former are obtained as a paraphyletic group.

In the XVIII-XIX centuries, together with amphibians, they united in a group of reptiles - cold-blooded terrestrial vertebrates. Traditionally, this group included various vertebrates that, according to their 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 such a classification.

Many authors who adhere to traditional taxonomy believe that archosaurs (crocodiles, pterosaurs, dinosaurs, etc.) should be taken out of 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 inhabit 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 land, sea and air. At the end of the Cretaceous period, most of the reptiles died out. Modern non-avian reptiles are only scattered remnants of that world. However, ancient reptiles gave rise to a currently flourishing group of animals - birds, and many of the adaptations that determined the evolutionary success of this group appeared even in its archosaurian ancestors, which were a specialized group of diapsids (warm-bloodedness, heat-insulating body cover - feathers, a developed brain, and etc).

Terrestrial vertebrates arose in the Devonian. These were armored amphibians, or stegocephalians. They were closely associated with water bodies, since they bred only in water, lived near water bodies, where there was terrestrial vegetation. The development of spaces remote from water bodies required a significant restructuring of the organization: adaptation to protecting the body from drying out, breathing atmospheric oxygen, walking on a solid substrate, the ability to breed out of water, and, of course, improving forms of behavior. These are the basic prerequisites for the emergence of a qualitatively different new group of animals. All these features took shape in reptiles.

To this it must be added that by the end of the Carboniferous, strong changes in the natural situation took place, which led to the emergence of a more diverse climate on the planet, the development of more diverse vegetation, its distribution in territories remote from water bodies, and, in this regard, to the wide distribution of tracheal-breathing arthropods, t .e. possible food items also spread to the watershed areas of the land.

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

adapted to life in the water. Some mastered the air environment. The adaptive divergence of reptiles was striking. With good reason, the Mesozoic is 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 cotilosaurs. According to a number of features, 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, the sacrum had only one vertebra; in the shoulder girdle, a kleytrum was preserved - a skin bone characteristic of fish; 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 the Permian deposits of Eastern Europe, on the Northern Dvina. Among them are three-meter herbivorous pareiasaurs (Pareiasaurus).

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

In the Middle Permian, cotilosaurs flourished. 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 the very diverse living conditions that they encountered during reproduction and settlement. Most of the groups have acquired greater mobility; 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 kleytrum bone 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.

Below we consider the main groups of reptiles, a review of which should show the exceptional diversity of these animals, their adaptive specialization, and their likely relationship with living groups.

In the formation of the appearance of ancient reptiles and in the assessment of their subsequent fate, the characteristic of their skull is essential.

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

The primitiveness of stegocephalians ("whole-cranial") and early reptiles was expressed in the structure of the skull by the absence of any depressions in it, except for the ocular and olfactory ones. This feature is reflected in the name Anapsida. The temporal region of the reptiles of this group was covered with bones. Turtles (now Testudines, or Chelonia) became probable descendants of this direction; they have a continuous bone cover behind their eye sockets. Tortoises known from the Lower Triassic of the Mesozoic reveal similarities with the current forms. Their fossil remains are confined to the territory of Germany. The skull, teeth, shell structure of ancient turtles are extremely close to modern ones. The ancestor of turtles is considered to be the Permian eunotosaurus(Eunotosaurus) - a small lizard-like animal with short and very wide ribs, forming a kind of dorsal shield (Fig. 115). He did not have a ventral shield. There were teeth. Mesozoic tortoises were originally terrestrial and apparently burrowing animals. Only later, some groups switched to an aquatic lifestyle, and in connection with this, many of them partially lost their bone and horn shell.

From the Triassic to the present day, turtles have retained the main features of their organization. They survived all the trials that killed most of the reptiles, and are now flourishing as well as in the Mesozoic.

The current crypto-necked and side-necked tortoises to a greater extent preserve the primary appearance of the Triassic land tortoises. Marine and soft-skinned appeared in the late Mesozoic.

All other reptiles, both ancient and modern, acquired one or two temporal cavities in the structure of the skull. One, lower, temporal cavity had synapsid. One superior temporal cavity is noted in two groups: paranoid and euryantsid. And finally, two depressions had diapsid. The evolutionary fate of these groups is different. The first to depart from the ancestral trunk synapsids(Synapsida) - reptiles with lower temporal cavities, limited by the zygomatic, squamous and postorbital 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 consecutive orders: pelycosaurs(Pelicosauria) and therapsids(Therapsida). They are also called bestial(Theromorpha). Animal-like survived the period of their heyday long before the first dinosaurs appeared, cotilosaurs were their immediate relatives. In particular, pelycosaurs(Pelicosauria) were still very close to cotilosaurs. Their remains have been found in North America and Europe. Outwardly, 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, it was planned, albeit to a small extent, differentiation of teeth.

In the Middle Permian, pelycosaurs were replaced by more highly organized animal-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 the dentary. Position

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

Numerous Permian animal-toothed reptiles were very diverse in appearance and lifestyle. Many were predators. Perhaps this was found by the expedition of V.P. Amalitsky in the deposits of the Permian period on the Northern Dvina foreigners(Inostrancevia alexandrovi, Fig. 116). Others ate vegetable or mixed foods. These unspecialized species are closest to mammals. Among them, one should point out cynognathus(Cynognathus), which had many progressive features of the organization.

Animal-toothed were numerous even in the early Triassic, but with the appearance of predatory dinosaurs, they disappeared. Curious materials given in Table 6 testify to a sharp reduction in the diversity of animal-like animals during the Triassic. Animals are of great interest as a group that gave rise to mammals.

Rice. 116. Animal-toothed:
1 - foreigners, Upper Perm (animal restoration), 2 - cynognathus skull

Table 6

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

Period	bestial	Sauropsids
Upper Triassic Middle Triassic Lower Triassic Upper Perm	17 23 36 170	8 29 20 15

The next group to separate 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 extremely wide adaptive radiation to systematic groups and species, which are found both among extinct forms and among modern reptiles. Among the diapsid, two main groups (infra - classes) have been outlined: infraclass Lepidosauromorphs(Lepidosauromorpha) and infraclass archosauromorphs(Archosauromorpha).

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

Who are lepidosauromorphs? This ancient infraclass includes the living tuatara, lizards, snakes, chameleons and their extinct ancestors.

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

Lizards, snakes and chameleons now make up a wide variety of the squamous order (Squamata). Lizards are one of the oldest advanced groups of reptiles, their remains are known from. upper perm. Scientists discover many similarities between lizards and sphenodons. Their limbs are widely spaced and the body moves, wavy curving the spinal column. It is curious that among the common features of their morphological similarity is the presence of an intertarsal joint. Snakes only appear 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 have ever lived on Earth. Among them - crocodiles, pterosaurs, 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 crocodiles in the absence of a true bony palate. Their internal nostrils opened between the palatine bones. The vertebrae were still amphicoelous. Crocodiles of the modern type with a fully developed secondary bony palate and procoelous vertebrae descended from ancient archosaurs - pseudosuchians. They have been known since the Cretaceous (about 200 million years ago). Most lived in fresh water, but real marine species are also known among the Jurassic forms.

Winged lizards, or pterosaurs(Pterosauria), represent one of the remarkable examples of Mesozoic reptile specialization. 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 in birds; the bones of the skull 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 planning. Other's ( pterodactyls) the tail was very short, and the wings were wide; their flight was often rowing (Fig. 117). Judging by the fact that the remains of pterosaurs were found in the sediments of salty reservoirs, they were inhabitants of the coasts. They fed

fish and behavior, apparently, were close to gulls and terns. Sizes ranged from a few centimeters to a meter or more.

The largest 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 every continent except Antarctica.

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

Dinosaurs(Dinosauria) are known in the fossil record from the middle Triassic. This is the most numerous and diverse group of reptiles that have ever lived on land. Among the dinosaurs 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 their 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, the dinosaurs were divided into two branches, the development of which proceeded in parallel. Their characteristic feature was the structure of the pelvic girdle, in connection with which these groups are called lizard and ornithischian.

lizards(Saurischia) were originally relatively small predatory animals, moving in leaps only on their hind legs, while the front legs served to grasp food. A long tail also served as a 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, apparently, were semi-aquatic animals and fed on succulent aquatic vegetation.

Ornithischians(Ornithischia) got its name in connection with the elongated pelvis, similar to the pelvis of birds. Initially, they moved on one elongated hind legs, but later species had both proportionally developed pairs of limbs and walked on four legs. By the nature of their diet, ornithischians were exclusively herbivores. Among them - iguanodon, walking on its hind legs and reaching a height of 9 m. Triceratops outwardly it was very similar to a rhinoceros, usually had a small horn at the end of the muzzle and two long horns above the eyes. Its length reached 8 m. Stegosaurus 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 almost all over the globe and lived in extremely diverse environments. They inhabited deserts, forests, 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 died out.

Finally, it is necessary to recall another group of reptiles, in the skull of which there was only one upper temporal cavity. This was characteristic of parapsid and euryapsid. It has been suggested that they evolved from the diapsids by the loss of the lower depression. 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 the water turned out to be more profitable in terms of the availability of food sources and a small number of predators.

ichthyosaurs(Ichthyosauria) occupied in the Mesozoic the same place that is now occupied by cetaceans. They swam, wavy bending the body, especially its tail, their fins served to 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, they became extinct at the end of the Cretaceous.

Plesiosaurs(Plesiosauria) had other 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 a swimming tool. Unlike ichthyosaurs,

they had a well-developed neck, bearing a small head. Their appearance resembled pinnipeds. Body sizes from 50 cm to 15 m. The way of life 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.

From the above brief review of the phylogeny of reptiles, it can be seen that the vast majority of large systematic groups (orders) died out before the beginning of the Cenozoic era and modern reptiles are only 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 highly specialized animals. The success of their existence depended on the presence of very peculiar 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 certain groups of reptiles occurred throughout the Mesozoic, this manifested itself at the end of the Cretaceous. At this time, in a relatively short period of time, most of the Mesozoic reptiles died out. If it is fair to call the Mesozoic the age of the 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 huge mountain-building phenomena, known in geology as the Alpine stage of mountain building. It is believed that at that 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 changing the physical state of the Earth and other conditions of 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 are not excluded. Naturally, all this could not but affect the success of the existence of all animals and specialized ones in the first place.

Finally, it must be taken 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, received more and more development.

Figure 120 gives a general outline of the phylogeny of reptiles.

), the forms, apparently possessing a greater terrestrial character, were isolated. Like their ancestors, they were still associated with wet biotopes and water bodies, fed on small aquatic and terrestrial invertebrates, but had greater mobility and somewhat larger brains; perhaps they have already begun keratinization of the integument.

In the Middle Carboniferous, a new branch arises from similar forms - Seymouriomorph-Seymourioraorpha. Their remains have been found in the Upper Carboniferous - Lower Permian. They occupy a transitional position between amphibians and reptiles, having undoubted reptilian features; some paleontologists classify them as amphibians. The structure of their vertebrae provided greater flexibility and at the same time strength of the spine; there has been a transformation of the first two cervical vertebrae into atlas and epistrophy. For land animals, this created important advantages in orientation, hunting for mobile prey, and protection from enemies. The skeleton of the limbs and their girdles was completely ossified; there were long bony ribs, but not yet closed into the chest. Stronger than those of stegocephalians, the limbs lifted the body above the ground. The skull had an occipital condyle (Fig. 3); some forms retained gill arches. Seymuria, kotlassia (found on the Northern Dvina), like other seymuriomorphs, were still associated with water bodies; it is believed that they may have still had aquatic larvae.

Proganosaurs and synaptosaurus became extinct without descendants.

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) was formed, displacing most groups of amphibians. The flowering of reptiles was ensured by a number of aromorphoses that affected all organ systems and provided 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 habitats, but returned to the water and rose into the air. Throughout the entire Mesozoic era - for more than 150 million years - they dominated 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.

Everything about everything. Volume 5 Likum Arkady

When did the first reptiles appear?

The first reptiles roamed the Earth about 300,000,000 years ago. In those days, the largest animals on land were amphibians. But they laid eggs in the water. The first reptiles resembled amphibians, but they already laid their eggs on land. Their offspring had lungs and legs and could breathe air. They roamed the wet ground of the forests and could feed on insects. Later, the reptiles became bigger and stronger. They resembled lizards and turtles in appearance.

There were also reptiles with short tails, thick legs and large heads. One type of early reptile was very important because of its descendants, which also looked like lizards, but moved on their hind legs. From these creatures a new type of reptile developed. Some of them had wings. Others fledged and became warm-blooded. This is how birds were born. From some reptiles, crocodiles and the first dinosaurs developed.

At one time, reptiles were the main animals on Earth. But over the course of millions of years, many of the ancient types of reptiles became extinct. There are many theories explaining why this happened. The main reason is seen in the fact that the changes in conditions and climate that have occurred on Earth have made the existence of these animals impossible. The swamps dried up, and the reptiles could not live on land. Their food is gone. The climate became seasonal, ranging from summer heat to winter frost. Most reptiles were unable to adapt to these changes, so they became extinct.

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