Reptiles are true terrestrial animals that breed on land. They live in countries with hot climates, and as they move away from the tropics, their number noticeably decreases. The limiting factor for their spread is temperature, since these cold-blooded animals are active only in warm weather, in cold and hot weather they burrow into holes, hide in shelters or fall into torpor.

In biocenoses, the number of reptiles is small and therefore their role is little noticeable, especially since they are not always active.

Reptiles feed on animal food: lizards - insects, mollusks, amphibians; snakes eat many rodents and insects, but at the same time pose a danger to domestic animals and humans. Herbivorous land turtles cause damage to gardens and vegetable gardens, while aquatic turtles feed on fish and invertebrates.

People use the meat of many reptiles for food (snakes, turtles, large lizards). Crocodiles, turtles and snakes are exterminated for their skin and horny shell, and therefore the numbers of these ancient animals have greatly decreased. There are crocodile breeding farms in the USA and Cuba.

The Red Book of the USSR includes 35 species of reptiles.

There are about 6,300 known species of reptiles, which are much more widespread around the globe than amphibians. Reptiles live mainly on land. Warm and moderately humid areas are most favorable for them; many species live in deserts and semi-deserts, but only very few penetrate into high latitudes.

Reptiles (Reptilia) are the first terrestrial vertebrates, but there are some species that live in water. These are secondary aquatic reptiles, i.e. their ancestors switched from a terrestrial lifestyle to an aquatic one. Among reptiles, poisonous snakes are of medical interest.

Reptiles, together with birds and mammals, form a superclass of higher vertebrates - amniotes. All amniotes are true terrestrial vertebrates. Thanks to the embryonic membranes that have appeared, their development is not associated with water, and as a result of the progressive development of the lungs, adult forms can live on land in any conditions.

The eggs of reptiles are large, rich in yolk and protein, covered with a dense parchment-like shell, and develop on land or in the mother’s oviducts. There is no aquatic larva. A young animal hatched from an egg differs from adults only in size.

Class characteristics

Reptiles are included in the main trunk of vertebrate evolution, since they are the ancestors of birds and mammals. Reptiles appeared at the end of the Carboniferous period, approximately 200 million years BC, when the climate became dry and in some places even hot. This created favorable conditions for the development of reptiles, which turned out to be more adapted to living on land than amphibians.

A number of traits contributed to the advantage of reptiles in competition with amphibians and their biological progress. These include:

• the membrane around the embryo (including the amnion) and a strong shell (shell) around the egg, protecting it from drying out and damage, which made it possible to reproduce and develop on land;
• further development of the five-fingered limb;
• improvement of the structure of the circulatory system;
• progressive development of the respiratory system;
• appearance of the cerebral cortex.

The development of horny scales on the surface of the body, protecting against adverse environmental influences, primarily from the drying effects of air, was also important.

Reptile body divided into head, neck, torso, tail and limbs (absent in snakes). Dry skin is covered with horny scales and scutes.

Skeleton. The spinal column is divided into five sections: cervical, thoracic, lumbar, sacral and caudal. The skull is bony, there is one occipital condyle. In the cervical spine there is an atlas and epistropheus, due to which the head of reptiles is very mobile. The limbs end in 5 fingers with claws.

Musculature. Much better developed than amphibians.

Digestive system . The mouth leads into the oral cavity, equipped with a tongue and teeth, but the teeth are still primitive, of the same type, and serve only to capture and hold prey. The digestive tract consists of the esophagus, stomach and intestines. At the border of the large and small intestines the rudiment of the cecum is located. The intestine ends in the cloaca. Digestive glands (pancreas and liver) are developed.

Respiratory system. In reptiles, the respiratory tract is differentiated. The long trachea branches into two bronchi. The bronchi enter the lungs, which look like cellular thin-walled sacs with a large number of internal partitions. The increase in the respiratory surface of the lungs in reptiles is associated with the lack of cutaneous respiration. Breathing is only pulmonary. The breathing mechanism is of the suction type (breathing occurs by changing the volume of the chest), more advanced than that of amphibians. Conducting airways (larynx, trachea, bronchi) are developed.

Excretory system. It is represented by secondary kidneys and ureters flowing into the cloaca. The bladder also opens into it.

Circulatory system. There are two circles of blood circulation, but they are not completely separated from each other, due to which the blood is partially mixed. The heart is three-chambered (crocodiles have a four-chambered heart), but consists of two atria and one ventricle; the ventricle is divided by an incomplete septum. The systemic and pulmonary circulations are not completely separated, but the venous and arterial flows are more clearly separated, so the reptile body is supplied with more oxygenated blood. The separation of flows occurs due to the septum at the moment of heart contraction. When the ventricle contracts, its incomplete septum, attached to the abdominal wall, reaches the dorsal wall and separates the right and left halves. The right half of the ventricle is venous; the pulmonary artery departs from it, the left aortic arch begins above the septum, carrying mixed blood: the left, part of the ventricle is arterial: the right aortic arch originates from it. Converging under the spine, they unite into the unpaired dorsal aorta.

The right atrium receives venous blood from all organs of the body, and the left atrium receives arterial blood from the lungs. From the left half of the ventricle, arterial blood enters the vessels of the brain and the anterior part of the body, from the right half, venous blood blood is flowing into the pulmonary artery and further into the lungs. The trunk region receives mixed blood from both halves of the ventricle.

Endocrine system. Reptiles have all the endocrine glands typical of higher vertebrates: pituitary gland, adrenal glands, thyroid gland, etc.

Nervous system. The brain of reptiles is different from the brain of amphibians great development hemispheres. The medulla oblongata forms a sharp bend, characteristic of all amniotes. The parietal organ in some reptiles functions as a third eye. The rudiment of the cerebral cortex appears for the first time. There are 12 pairs of cranial nerves leaving the brain.

Sense organs are more complex. The lens in the eyes can not only get mixed up, but also change its curvature. In lizards, the eyelids are movable; in snakes, the transparent eyelids are fused. In the olfactory organs, part of the nasopharyngeal passage is divided into olfactory and respiratory sections. The internal nostrils open closer to the throat, so reptiles can breathe freely when they have food in their mouths.

Reproduction. Reptiles are dioecious. Sexual dimorphism is pronounced. Gonads are paired. Like all amniotes, reptiles are characterized by internal insemination. Some of them are oviparous, others are ovoviviparous (that is, a baby immediately emerges from the laid egg). Body temperature is not constant and depends on the ambient temperature.

Taxonomy. Modern reptiles are divided into four subclasses:

1. proto-lizards (Prosauria). Protolizards are represented by a single species - the hatteria (Sphenodon punctatus), which is one of the most primitive reptiles. The tuateria lives on the islands of New Zealand.
2. scaly (Squamata). This is the only one regarding large group reptiles (about 4000 species). The scaly ones include
   • lizards. Most lizard species are found in the tropics. This order includes agamas, poisonous lizards, monitor lizards, true lizards, etc. Lizards are characterized by well-developed five-fingered limbs, movable eyelids and eardrums [show] .

     The structure and reproduction of a lizard

     Fast lizard. The body, 15-20 cm long, is covered on the outside with dry skin with horny scales, which form quadrangular shields on the abdomen. The hard cover interferes with the uniform growth of the animal; the change of the horny cover occurs through molting. In this case, the animal sheds the upper horny layer of scales and forms a new one. The lizard molts four to five times during the summer. At the ends of the fingers, the horny cover forms claws. The lizard lives mainly in dry, sunny places in steppes, sparse forests, bushes, gardens, on hillsides, railway and highway embankments. Lizards live in pairs in burrows, where they spend the winter. They feed on insects, spiders, mollusks, worms, and eat many crop pests.

     In May-June, the female lays from 6 to 16 eggs in a shallow hole or burrow. The eggs are covered with a soft, fibrous, leathery shell that protects them from drying out. Eggs have a lot of yolk, the white shell is poorly developed. All development of the embryo occurs in the egg; after 50-60 days the young lizard hatches.

     In our latitudes, lizards are often found: quick, viviparous and green. All of them belong to the family of true lizards of the order Squamate. The agama family belongs to the same order (steppe agama and round-headed agama - inhabitants of deserts and semi-deserts of Kazakhstan and Central Asia). Scaly ones also include chameleons that live in the forests of Africa, Madagascar, and India; one species lives in southern Spain.

   • chameleons
   • snakes [show]

     The structure of snakes

     Snakes also belong to the order Scaly. These are legless reptiles (some retain only rudiments of the pelvis and hind limbs), adapted to crawling on their belly. Their neck is not pronounced, the body is divided into head, torso and tail. The spine, which contains up to 400 vertebrae, is highly flexible thanks to additional articulations. It is not divided into departments; almost every vertebra bears a pair of ribs. In this case, the chest is not closed; the sternum of the belt and limbs are atrophied. Only some snakes have preserved a rudimentary pelvis.

     The bones of the facial part of the skull are connected movably, the right and left parts of the lower jaw are connected by very stretchable elastic ligaments, just as the lower jaw is suspended from the skull by stretchable ligaments. Therefore, snakes can swallow large prey, even larger than the snake's head. Many snakes have two sharp, thin, poisonous teeth curved back, sitting on the upper jaws; they serve to bite, capture prey and push it into the esophagus. Poisonous snakes have a longitudinal groove or duct in the tooth through which the venom flows into the wound when bitten. The poison is produced in the modified salivary glands.

     Some snakes have developed special thermal sense organs - thermoreceptors and thermolocators, which allows them to find warm-blooded animals in the dark and in burrows. The tympanic cavity and membrane are atrophied. Eyes without lids, hidden under transparent skin. The snake's skin becomes keratinized on the surface and is periodically shed, i.e., molting occurs.

     Previously, up to 20-30% of victims died from their bites. Thanks to the use of special therapeutic serums, mortality decreased to 1-2%.

3. crocodiles (Crocodilia) are the most highly organized reptiles. They are adapted to an aquatic lifestyle, and therefore have swimming membranes between the toes, valves that close the ears and nostrils, and a velum that closes the pharynx. Crocodiles live in fresh waters and come to land to sleep and lay eggs.
4. turtles (Chelonia). Turtles are covered above and below with a dense shell with horny scutes. Their chest is motionless, so their limbs take part in the act of breathing. When they are drawn in, air leaves the lungs, and when pulled out, it enters again. Several species of turtles live in the USSR. Some species, including the Turkestan tortoise, are eaten.

The meaning of reptiles

Antisnake serums are currently used for medicinal purposes. The process of making them is as follows: horses are successively injected with small but ever-increasing doses of snake venom. Once the horse is sufficiently well immunized, blood is taken from it and a therapeutic serum is prepared. IN Lately Snake venom is used for medicinal purposes. It is used for various bleedings as a hemostatic agent. It turned out that in hemophilia it can increase blood clotting. A drug made from snake venom - vipratox - reduces pain from rheumatism and neuralgia. To obtain snake venom and to study the biology of snakes, they are kept in special nurseries. Several serpentariums operate in Central Asia.

Over 2 thousand species of snakes are non-venomous, many of them feed on harmful rodents and bring significant benefits to the national economy. Non-venomous snakes include snakes, copperheads, snakes, and steppe boas. Water snakes sometimes eat juvenile fish in pond farms.

The meat, eggs and shells of turtles are very valuable and are exported. The meat of monitor lizards, snakes, and some crocodiles is used as food. Valuable skin of crocodiles and monitor lizards is used to make haberdashery and other products. Crocodile breeding farms have been created in Cuba, the USA and other countries.

The meaning of reptiles. Most lizards and snakes, eating insects, rodents and terrestrial mollusks that harm agriculture, benefit humans. In some countries South America In South Asia and Africa, non-venomous snakes are kept instead of cats. In nature, reptiles exist in a common system of food connections: some eat plants, others eat animals (insects, amphibians, reptiles, small animals), and they, in turn, are eaten by other predators - birds of prey and animals.

Sometimes land turtles cause damage to melon fields, and water snakes cause damage to fish farms. Reptiles can spread pathogens to humans and domestic animals.

The bites of poisonous snakes are dangerous. However, studying the effect of snake venoms has made it possible to create valuable medicinal preparations based on them, which are used in the treatment of diseases of the respiratory organs, heart, and joints.

Large snakes and crocodiles are hunted for beautiful and durable leather. Sea turtles are hunted due to delicious meat. Due to overfishing, the numbers of many species have sharply decreased, some are on the verge of extinction. Nature reserves have been created for them. The elephant tortoise, green tortoise, Komodo dragon, Cuban crocodile, and gattperia are listed in the WSOP Red Book.

Among reptiles there are herbivorous and insectivorous species. Most are predators. By eating plants, insects, amphibians, and small animals, reptiles regulate their numbers.

Modern reptiles descended from ancient amphibians - stegocephalians, who lived about 350-400 million years ago. Cotylosaurs, which existed 230-250 million years ago, are considered the most ancient of reptiles. Some features of their organization have been preserved in turtles.

The heyday of reptiles was the period from 250 to 65 million years ago. In those days, numerous reptiles lived on land and in water, and moved in the air (Fig. 153).

Rice. 153. Ancient reptiles: 1 - diplodocus; 2 - pteranodon; 3 - ceratosaurus; 4 - ichthyosaur

Flying lizards - pterodactyls, rhamphorhynchus, pteranodons - looked like giant bats. Their wingspan reached 10-12 m. Lizards resembling dolphins and seals lived in the water - ichthyosaurs, plesiosaurs. These groups of ancient reptiles became extinct, leaving no descendants behind.

Among the ancient lizards there were two more groups that played an important role in the emergence of birds and mammals: dinosaurs and beast-like reptiles (Fig. 154).

Rice. 154. Animal-like beast-toothed reptile

Dinosaurs were a very diverse group: peaceful (herbivorous) and ferocious predators. Some walked on four legs, others only on two hind legs, in an upright position. Very large dinosaurs are known - more than 30 m long, and small ones - the size of a small lizard. Diplodocus (27 m long and weighing about 10 tons), Apatosaurus, Brachiosaurus, and Seismosaurus are also considered the largest. They lived near bodies of water and stood in the water for a long time, eating aquatic and semi-aquatic vegetation. Some dinosaurs had ridges on their backs that they used to capture solar energy. Scientists suggest that birds originated from one of the groups of dinosaurs.

Beast-like reptiles got their name for their resemblance to animals. So, unlike other lizards, their legs were not widely spaced: they were located under the body, and not on the sides. The teeth were divided (differentiated) into incisors, canines and molars. They had fleshy lips, and their skin probably contained glands.

For 200 million years, the fate of dinosaurs and beast-like reptiles was different. Dinosaurs were favored by the warm, mild climate of that era, and they dominated everywhere. The beast-like creatures were few in number and invisible. Approximately 120-130 million years ago, the ratio of the number of species began to change in favor of animal-like ones.

The extinction of dinosaurs occurred as the planet's climate changed. About 130 million years ago, a long warm period was replaced by cooling. The vegetation began to change: angiosperms gradually spread.

There are many scientifically based hypotheses about the causes of the extinction of dinosaurs, for example, active mountain building and associated climate change. Perhaps a large asteroid passed near the Earth, influencing the climate and the natural environment surrounding dinosaurs.

Did the ancient lizards disappear from the face of the planet without a trace, leaving only monuments in the form of skeletons and prints? In the modern fauna of reptiles there is a hatteria, which is called a living fossil. The appearance of this animal has many ancient features: the remains of a shell on the body, the primitive structure of the spine, and an additional parietal eye. This reptile lives on small islands off New Zealand and is strictly protected as a “living natural monument.” Turtles are close to their Mesozoic ancestors. In some organizational features, crocodiles are close to dinosaurs.

Lizards and snakes also have some similarities with dinosaurs. But if lizards - enough ancient group, then snakes appeared only at the end of the warm period on Earth before the cold snap, when their related groups lost their former greatness.

Reptiles descended from ancient amphibians - stegocephalians. The most ancient reptiles are cotylosaurs. A variety of ancient reptiles inhabited land, aquatic environments, and lived in the air and flourished for 200 million years. Modern reptiles, birds and mammals evolved from ancient reptiles.

Exercises based on the material covered

1. What is the importance of reptiles in nature and in human life?
2. What animals did reptiles come from? When did the ancestors of modern reptiles live?
3. Name the animals that belong to the ancient lizards. Which of them gave rise to ancient birds and mammals?
4. What living environments did ancient reptiles master? Why did they go extinct?
5. Why is hatteria called a living fossil?

Reptiles are more adapted to life on land and have a more advanced structure than amphibians. Therefore, in the process of evolution, they occupied more diverse habitats, and this led to the diversity of reptiles.

IN Mesozoic era When dinosaurs lived, the diversity of reptiles was the greatest on Earth. However, even today reptiles are represented in various ecological niches, although not as widely as mammals. Reptiles live not only in warm (including arid) climates, but some of them have returned to aquatic life, although they still go to land and breathe through their lungs to lay eggs.

In the class of reptiles, there are four existing orders. These are squamates, crocodiles, turtles and beaked fish. The total number is more than 8,000 species.

Order Scaly

Representatives of the squamate order form the basis of the diversity of reptiles. This includes all lizards and snakes. Their body is covered with fairly small scales.

A quick lizard lives in our area.

Fast lizard

The spindle is a legless lizard. Unlike snakes, her eyelids do not grow together.

Chameleons are also lizards. They live in trees and are able to change body color. Their eyes move independently of each other. Insects are caught with a long sticky tongue.

In the process of evolution, snakes appeared later than all other groups of reptiles. Their ancestors had limbs. However, in snakes they were reduced due to their special method of movement (they twist their body along the ground). There were also other changes in the internal structure (the sternum and one lung disappeared).

Representatives of the snakes that live in our area are the grass snake and the viper. The latter is poisonous.

The bones in the jaws of snakes are connected movably by ligaments. In addition, ligaments can stretch. Thus, snakes can open their mouths wide and swallow prey whole, crawling onto it.

In venomous snakes, one of the salivary glands is modified into a poisonous gland. Its canal goes into the front tooth. When bitten, venom is injected into the victim's body.

Scaly animals are characterized by frequent molting, since scales impede growth. In snakes, the old skin comes off entirely, like a stocking, and is called a crawl.

Squad Crocodiles

Crocodiles are large reptiles (up to 7 meters) that cannot boast of their diversity (25 species in total). They live in rivers and lakes of tropical countries. The order Crocodiles is divided into alligators, true crocodiles, gharials, and caimans.
True crocodiles have a sharper snout than alligators.

The toes on the hind feet of crocodiles have membranes. The tail is flattened laterally. The nostrils and eyes are on elevations. Thus, a crocodile can sit underwater with only its nostrils and eyes exposed to the surface. This way he remains invisible to the victim. The skin of crocodiles is covered with scutes.

Crocodiles have a four-chambered heart, and not like all reptiles a three-chambered heart. In their heart ventricle, the incomplete septum becomes complete. However, the blood still partially mixes when the aortas leaving the heart join together.

Turtle Squad

The order Turtles are the most ancient of the living variety of reptiles. In the process of evolution, they appeared earlier than other groups. There are currently about 300 species of turtles.

Their shell consists of dorsal and abdominal shields. The dorsal plate is attached to the spine, and the abdominal plate is attached to the sternum. Most turtles can retract their limbs, tail and head into their shell, making them inaccessible to enemies.

Turtles have no teeth. Their jaws are covered with horny plates.

Among turtles there are aquatic species; sea turtles have limbs transformed into flippers.

Order Beakheads

All representatives of this order are extinct, except for two species of tuataria, which live in New Zealand.

A number of primitive features are noted in the structure of the tuateria. For example, she has a so-called third (parietal) eye. Although many lizards have this eye.

Representatives of reptiles (more than 4 thousand species) are true terrestrial vertebrates. Due to the appearance of the embryonic membranes, they are not associated with water in their development. As a result of the progressive development of the lungs, adult forms can live on land in any conditions. Reptiles living in the species are secondary aquatic, i.e. their ancestors switched from a terrestrial lifestyle to an aquatic one.

Remember! Reptiles and reptiles are the same class!

Reptiles, or reptiles, appeared at the end of the Carboniferous period, approximately 200 million years BC. when the climate became dry, and in some places even hot. This created favorable conditions for the development of reptiles, which turned out to be more adapted to living on land than amphibians. A number of traits contributed to the advantage of reptiles in competition with amphibians and their biological progress. These include:

• The membranes around the embryo and a strong shell (shell) around the egg, protecting it from drying out and damage, which made it possible to reproduce and develop on land;
• development of five-fingered limbs;
• improvement of the structure of the circulatory system;
• progressive development of the respiratory system;
• appearance of the cerebral cortex.

The development of horny scales on the surface of the body, protecting against adverse environmental influences, primarily from the drying effects of air, was also important. The prerequisite for the appearance of this device was liberation from skin respiration due to the progressive development of the lungs.

A typical representative of reptiles is the sand lizard. Its length is 15-20cm. It has a well-defined protective coloration: greenish-brown or brown, depending on its habitat. During the day, lizards are easy to see in a sun-warmed area. At night they crawl under stones, into holes and other shelters. They spend the winter in the same shelters. Their food is insects.

On the territory of the CIS, the most widespread are: in the forest zone - the viviparous lizard, in the steppe - the sand lizard. The spindle is a lizard. It reaches 30-40 cm, has no legs, which reminds it of a snake, this often costs it its life. The skin of reptiles is always dry, devoid of glands, and covered with horny scales, scutes or plates.

The structure of reptiles

Skeleton. The spinal column is already divided into cervical, thoracic, lumbar, sacral and caudal sections. The skull is bony, the head is very mobile. The limbs end in five fingers with claws.

The muscles of reptiles are much better developed than those of amphibians.

Digestive system. The mouth leads into the oral cavity, equipped with a tongue and teeth, but the teeth are still primitive, of the same type, and serve only to capture and hold prey. The alimentary canal consists of the esophagus, stomach, and intestines. At the border of the large and small intestines the rudiment of the cecum is located. The intestines end in a cloaca. Digestive glands are developed: pancreas and liver.

Respiratory system. The respiratory tract is much more differentiated than in amphibians. There is a long trachea that branches into two bronchi. The bronchi enter the lungs, which look like cellular, thin-walled sacs with a large number of internal partitions. The increase in the respiratory surfaces of the lungs in reptiles is associated with the lack of cutaneous respiration.

Excretory system represented by the kidneys and ureters flowing into the cloaca. The bladder also opens into it.

Circulatory system. Reptiles have two circles of blood circulation, but they are not completely separated from each other, due to which the blood is partially mixed. The heart has three chambers, but the ventricle is divided by an incomplete septum.

Crocodiles already have a real four-chambered heart. The right half of the ventricle is venous, and the left part is arterial - the right aortic arch originates from it. Converging under the spinal column, they unite into the unpaired dorsal aorta.

Nervous system and sensory organs

The brain of reptiles differs from the brain of amphibians in the greater development of the hemispheres and cerebral vault, as well as the separation of the parietal lobes. Appears for the first time, the cerebral cortex. 12 pairs of cranial nerves arise from the brain. The cerebellum is somewhat more developed than in amphibians, which is associated with more complex coordination of movements.

At the front end of the lizard's head there is a pair of nostrils. The sense of smell in reptiles is better developed than in amphibians.

The eyes have eyelids, upper and lower, in addition, there is a third eyelid - a translucent nictitating membrane that constantly moisturizes the surface of the eye. Behind the eyes is a rounded eardrum. Hearing is well developed. The organ of touch is the tip of the forked tongue, which the lizard constantly sticks out of its mouth.

Reproduction and regeneration

Unlike fish and amphibians, which have external fertilization (in water), reptiles, like all non-amphibious animals, have internal fertilization, in the body of the female. The eggs are surrounded by embryonic membranes that enable development on land.

The female lizard quickly lays 5-15 eggs in a secluded place at the beginning of summer. The eggs contain nutritional material for the developing embryo and are surrounded on the outside by a leathery shell. A young lizard emerges from the egg, looking like an adult. Some reptiles, including some species of lizards, are ovoviviparous (i.e., a baby immediately emerges from a laid egg).

Many species of lizards, when grabbed by the tail, break it off with sharp lateral movements. Throwing back the tail is a reflex response to pain. This should be considered as an adaptation thanks to which lizards escape from enemies. A new one grows in place of the lost tail.

Diversity of modern reptiles

Modern reptiles are divided into four orders:

• Protolizards;
• Scaly;
• Crocodiles;
• Turtles.

Protolizards represented by a single type - tuateria, which is one of the most primitive reptiles. The tuateria lives on the islands of New Zealand.

Lizards and snakes

Scaly animals include lizards, chameleons and snakes. This is the only relatively numerous group of reptiles - about 4 thousand species.

Lizards are characterized by well-developed five-fingered limbs, movable eyelids and the presence of an eardrum. This order includes agamas, poisonous lizards, monitor lizards, true lizards, etc. Most species of lizards are found in the tropics.

Snakes are adapted to crawling on their belly. Their neck is not pronounced, so the body is divided into head, torso and tail. The spinal column, which contains up to 400 vertebrae, is highly flexible thanks to additional articulations. The belts, limbs and sternum are atrophied. Only some snakes have preserved a rudimentary pelvis.

Many snakes have two poisonous teeth on their upper jaws. The tooth has a longitudinal groove or duct through which the poison flows into the wound when bitten. The tympanic cavity and membrane are atrophied. The eyes are hidden under transparent skin, without eyelids. The snake's skin becomes keratinized on the surface and is periodically shed, i.e. moulting occurs.

Snakes have the ability to open their mouths very wide and swallow their prey whole. This is achieved by the fact that a number of skull bones are connected movably, and the lower jaws in front are connected by a very tensile ligament.

The most common snakes in the CIS are snakes, copperheads, snakes. The steppe viper is listed in the Red Book. For its habitat, it avoids agricultural lands, but lives on virgin lands, which are becoming less and less, which threatens it with extinction. The steppe viper (like other snakes) feeds mainly on mouse-like rodents, which is certainly useful. Its bite is poisonous, but not fatal. She can attack a person only by accident, being disturbed by him.

The bites of poisonous snakes - cobra, epha, viper, rattlesnake and others - can be fatal to humans. Among the fauna, the gray cobra and sand efa, which are found in Central Asia, are very dangerous, as well as the viper, found in Central Asia and Transcaucasia, and the Armenian viper, which lives in Transcaucasia. The bites of the common viper and copperhead are very painful, but usually not fatal to humans.

The science that studies reptiles is called herpetology.

Recently, snake venom has been used for medicinal purposes. Snake venom is used for various bleedings as a hemostatic agent. It turned out that some drugs obtained from snake venom reduce pain in rheumatism and diseases of the nervous system. To obtain snake venom for the purpose of studying the biology of snakes, they are kept in special nurseries.

Crocodiles are the most highly organized reptiles, having a four-chambered heart. However, the structure of the partitions in it is such that venous and arterial blood are partially mixed.

Crocodiles are adapted to an aquatic lifestyle, and therefore have swimming membranes between the toes, valves that close the ears and nostrils, and a velum that closes the pharynx. Crocodiles live in fresh waters and come to land to sleep and lay eggs.

Turtles are covered above and below with a dense shell with horny scutes. Their chest is motionless, so their limbs take part in the act of breathing - when they are drawn in, the air leaves the lungs, when they stick out, it enters them. Several species of turtles live in Russia. Some species are eaten, including the Turkestan tortoise, which lives in Central Asia.

Ancient reptiles

It has been established that in the distant past (hundreds of millions of years ago) various types of reptiles were extremely common on Earth. They inhabited land, water, and less often air. Most species of reptiles became extinct due to climate change (cold temperatures) and the rise of birds and mammals, with which they could not compete. Extinct reptiles include orders of dinosaurs, wild-toothed lizards, ichthyosaurs, flying lizards, etc.

Dinosaur Squad

This is the most diverse and numerous group of reptiles that has ever lived on Earth. Among them were both small animals (the size of a cat and smaller) and giants, whose length reached almost 30 m and weight - 40-50 tons.

Large animals had a small head, a long neck and a powerful tail. Some dinosaurs were herbivores, others were carnivores. The skin either had no scales or was covered with a bone shell. Many dinosaurs ran galloping on their hind limbs, leaning on their tail, while others moved on all four legs.

Squad Animal-toothed

Among the ancient land reptiles there were representatives of a progressive group, which resembled animals in the structure of their teeth. Their teeth were differentiated into incisors, canines and molars. The evolution of these animals went in the direction of strengthening their limbs and belts. In the process of evolution, mammals arose from them.

Origin of reptiles

Fossil reptiles are of great importance because they once dominated the globe and from them came not only modern reptiles, but also birds and mammals.

Living conditions at the end of the Paleozoic changed dramatically. Instead of a warm and humid climate, cold winters appeared and a dry and hot climate established. These conditions were unfavorable for the existence of amphibians. However, under such conditions, reptiles began to develop, whose skin was protected from evaporation, a terrestrial method of reproduction, a relatively highly developed brain and other progressive characteristics appeared, which are given in the characteristics of the class.

Based on a study of the structure of amphibians and reptiles, scientists came to the conclusion that there are great similarities between them. This was especially true for ancient reptiles and stegocephalians.

• In very ancient lower reptiles, the vertebral column had the same structure as in stegocephals, and the limbs - like in reptiles;
• the cervical region of reptiles was as short as that of amphibians;
• the chest bone was missing, i.e. they did not yet have a real chest.

All this suggests that reptiles evolved from amphibians.