The modern fauna of amphibians, or amphibians, is not numerous - less than 2 thousand species. Throughout their life, or at least in the larval state, amphibians are necessarily connected with the aquatic environment, since their eggs are devoid of shells that protect them from the drying effect of air. For normal life, adult forms need constant skin hydration, therefore they live only near water bodies or in places with high humidity.

Amphibians, in terms of morphological and biological characteristics, occupy an intermediate position between proper aquatic and proper terrestrial organisms.

The origin of amphibians is associated with a number of aromorphoses, such as the appearance of a five-fingered limb, the development of the lungs, the division of the atrium into two chambers and the appearance of two circles of blood circulation, the progressive development of the central nervous system and sensory organs.

Frog - a typical representative of amphibians

Frog - amphibious (not reptile), a typical representative of the amphibian class, on the example of which the characteristic of the class is usually given. The frog has a short body without a tail, elongated hind limbs with swimming membranes. The forelimbs, unlike the hind limbs, are much smaller; they have four fingers instead of five.

The structure of amphibians

Skeleton and muscles

amphibian body coverings. The skin is naked and always covered with mucus, thanks to a large number mucous multicellular glands. It performs not only a protective function and perceives external irritation, but also participates in gas exchange.

Amphibian skeleton. In the spinal column, in addition to the trunk and tail sections, for the first time in the evolution of animals, the cervical and sacral sections appear.

There is only one annular vertebra in the cervical region. This is followed by 7 trunk vertebrae with lateral processes. In the sacral region, there is also one vertebra, to which the pelvic bones are attached. The caudal region of the frog is represented by the urostyle, a formation consisting of 12 fused caudal vertebrae. Between the vertebral bodies, the remnants of the notochord are preserved, there are upper arches and the spinous process. The ribs and chest are absent in amphibians.

Significant remnants of cartilage have been preserved in the skull, which determines the similarity of amphibians with lobe-finned fish. The skeleton of free limbs is divided into 3 sections. The limbs are connected to the spinal column through the bones of the limb belts. The forelimb belt includes: sternum, two crow bones, two collarbones and two shoulder blades. The girdle of the hind limbs is represented by fused pelvic bones.

Musculature of amphibians. The skeletal muscles of the frog can provide movement of body parts through contraction. Muscles can be divided into groups of antagonists: flexors and extensors, adductors and abductors. Most muscles are attached to bones by tendons.

The internal organs of the frog lie in the body cavity, which is lined with a thin layer of epithelium and contains a small amount of fluid. Most of the body cavity of the frog is occupied by the digestive organs.

Digestive system of amphibians

In the oral cavity of the frog there is a tongue, which is attached with its front end and the animals throw it out when catching prey. On the upper jaw of the frog, as well as on the palatine bones, there are undifferentiated teeth, which is similar to fish. Saliva does not contain enzymes.

The alimentary canal, starting with the oropharyngeal cavity, passes into the pharynx, then into the esophagus and, finally, into the stomach, which passes into the intestines. The duodenum lies under the stomach, and the remaining intestines are folded in loops, then pass into the posterior (rectum) and end in the cloaca. There are digestive glands: salivary, pancreas and liver.

excretory system amphibians. Dissimilation products are excreted through the skin and lungs, but most of them are excreted by the kidneys. Urine is excreted from the kidneys through the ureters into the cloaca. For some time, urine can accumulate in the bladder, which is located at the abdominal surface of the cloaca and has a connection with it.

Respiratory system in amphibians

Amphibians breathe with both lungs and skin.

The lungs are represented by thin-walled bags with a cellular inner surface. Air is pumped into the lungs as a result of pumping movements of the bottom of the oropharyngeal cavity. When a frog dives, its air-filled lungs act as a hydrostatic organ.

There are arytenoid cartilages surrounding the laryngeal fissure and the vocal cords stretched over them, which are available only in males. Amplification of sound is achieved by vocal sacs formed by the mucous membrane of the oral cavity.

The circulatory system of amphibians

The heart is three-chambered, consists of two atria and a ventricle. First, both atria contract, then the ventricle. In the left atrium, the blood is arterial, in the right - venous. In the ventricle, the blood is partially mixed, but the structure of the blood vessels is such that:

• The brain receives arterial blood;
• venous blood enters the lungs and skin;
• Mixed blood enters the whole body.

Amphibians have two circulations.

Venous blood in the lungs and skin is oxidized and enters the left atrium, i.e. pulmonary circulation appeared. From the whole body, venous blood enters the right atrium.

Thus, amphibians have formed two circles of blood circulation. But since mixed blood mainly enters the organs of the body, the metabolic rate remains (as in fish) low and the body temperature differs little from environment.

The second circle of blood circulation arose in amphibians in connection with their adaptation to breathing atmospheric air.

Nervous system

The nervous system of amphibians consists of the same sections as those of fish, but in comparison with them it has a number of progressive features: a greater development of the forebrain, a complete separation of its hemispheres.

There are 10 pairs of nerves coming out of the brain. The appearance of amphibians, accompanied by a change of habitat and exit from the water to land, was associated with significant changes in the structure of the sense organs. A flattened lens and a convex cornea appeared in the eye, adapted to vision at a fairly long distance. The presence of eyelids that protect the eyes from the drying effect of air, and a nictitating membrane indicate a similarity in the structure of the amphibian eye with the eyes of real terrestrial vertebrates.

In the structure of the hearing organs, the development of the middle ear is of interest. The outer cavity of the middle ear is closed by the tympanic membrane, adapted to capture sound waves, and the inner cavity is the Eustachian tube that opens into the pharynx. In the middle ear there is an auditory ossicle - the stirrup. The olfactory organ has external and internal nostrils. The organ of taste is represented by taste buds on the tongue, palate and jaws.

Reproduction of amphibians

Amphibians are dioecious. The sex organs are paired, consisting of slightly yellowish testes in the male and pigmented ovaries in the female. The efferent ducts extend from the testes, penetrating into the anterior part of the kidney. Here they join the urinary tubules and open into the ureter, which functions in the same way as the vas deferens and opens into the cloaca. The eggs from the ovaries enter the body cavity, from where they are brought out through the oviducts, which open into the cloaca.

Frogs are sexually dimorphic. hallmarks males are tubercles on the inner toe of the forelegs and vocal sacs (resonators). Resonators amplify the sound when croaking. The voice first appears in amphibians: this is obviously connected with life on land.

Development in a frog, like in other amphibians, occurs with metamorphosis. Amphibian larvae are typical inhabitants of the water, which is a reflection of the lifestyle of their ancestors.

The features of the morphology of the tadpole, which have an adaptive value in accordance with the conditions of the habitat, include:

• a special apparatus on the underside of the head, which serves to attach the tadpole to underwater objects;
• guts longer than those of an adult frog (compared to body size). This is due to the fact that the tadpole consumes plant food, and not animal (like an adult frog) food.

The features of the organization of the tadpole, repeating the signs of their ancestors, should be recognized as a fish-like shape with a long caudal fin, the absence of five-fingered limbs, external gills, a lateral line and one circle of blood circulation. In the process of metamorphosis, all organ systems are rebuilt:

• Grow limbs;
• gills and tail are resorbed;
• the intestines are shortened;
• the nature of food and the chemistry of digestion, the structure of the jaws and the entire skull, and the skin are changing;
• there is a transition from gill breathing to pulmonary breathing, deep transformations occur in the circulatory system.

The rate of development of tadpoles depends on temperature: the hotter, the faster it is. It usually takes 2-3 months for a tadpole to turn into a frog.

Diversity of amphibians

Currently, 3 orders belong to the class of amphibians:

• Tailed;
• tailless;
• legless.

Tailed amphibians(newts, salamanders, etc.) are characterized by an elongated tail and paired short limbs. These are the least specialized forms. The eyes are small, without eyelids. Some retain gills and gill slits for life.

At tailless amphibians(toads, frogs) the body is short, without a tail, with long hind limbs. Among them there are a number of species that are eaten.

To the squad legless amphibians include worms that live in tropical countries. Their body is worm-like, devoid of limbs. Worms feed on rotting plant debris.

On the territory of Ukraine and the Russian Federation, the largest of the European frogs is found - the lake frog, whose body length reaches 17 cm, and one of the smallest tailless amphibians - the common tree frog, which has a length of 3.5-4.5 cm. Adult tree frogs usually live in trees and have special disks at the ends of their fingers for attaching to branches.

Four species of amphibians are listed in the Red Book: the Carpathian newt, the mountain newt, the rush toad, the fast frog.

Origin of amphibians

Amphibians include forms whose ancestors are about 300 million years old. years ago, they came out of the water onto land and adapted to the new terrestrial conditions of life. They differed from fish in the presence of a five-fingered limb, lungs, and related features of the circulatory system.

They were united with fish by:

• The development of the larva (tadpole) in aquatic environment;
• the presence of gill slits in larvae;
• the presence of external gills;
• the presence of a lateral line;
• absence of germinal membranes during embryonic development.

The ancestors of amphibians among ancient animals are considered to be lobe-finned fish.

Stegocephalus - a transitional form between lobe-finned fish and amphibians

All the data of comparative morphology and biology indicate that the ancestors of amphibians should be sought among the ancient lobe-finned fishes. Transitional forms between them and modern amphibians were fossil forms - stegocephals that existed in the Carboniferous, Permian and Triassic periods. These ancient amphibians, judging by the bones of the skull, were extremely similar to the ancient lobe-finned fish. Their characteristic features are: a shell of skin bones on the head, sides and abdomen; spiral valve of the intestines, as in shark fish, lack of vertebral bodies.

Stegocephalians were nocturnal predators that lived in shallow waters. The emergence of vertebrates on land took place in Devonian characterized by an arid climate. During this period, the advantage was acquired by those animals that could move overland from a drying up reservoir to a neighboring one.

The heyday (period of biological progress) of amphibians falls on the Carboniferous period, the even, humid and warm climate of which was favorable for amphibians. It was only thanks to landfall that vertebrates were able to develop progressively in the future.

Let amphibians be not the most attractive and cute creatures. Not kittens after all, to please everyone. But among them there are also the most interesting rare individuals that are able to conquer anyone with a truly extravagant appearance. Let's get acquainted with this strange class of animals (such as neither on earth nor on water - neither yours nor ours) and learn more about the most prominent representatives.

Signs of amphibians: duplicity as a gift

Amphibians, they are also amphibians (translated from Greek means "the one that lives double life”) are those groups of animals that can live both on land and in water. Therefore, against the background of all other living beings, they stand out and have a number of advantages.

Main outward sign amphibians - "nudity" (they are devoid of wool or any other heat-insulating covers). It is believed that the progenitors of amphibians were lobe-finned fish. But they themselves gave life to reptiles.

Types of amphibians: with or without a tail?

Scientists distinguish three types of amphibians by the presence and development of the tail and paws.

Anurans

They have a short body, a poorly defined neck, developed legs (the hind legs are larger and more massive than the front ones: they serve to move by jumping), of course they do not have a tail. This species includes toads, frogs, tree frogs, spadefoot, toads, and others. This is the largest detachment, which has about five thousand different types.

Tailed amphibians

They have a long body, which ends with a strong developed tail, but their paws are short and weak (although there are exceptions). Among the representatives of this order, the most noticeable newts, salamanders. In total, the group has about five hundred species. And just some species of salamanders stand out for general background They can run fast and even jump.

Legless (they are worms)

They differ in that they have neither a tail nor paws - the animals are unlucky, they seem completely helpless! Moreover, they also look very unattractive - these amphibians look like nasty worms. And from a scientific point of view, they have the most primitive structure of their kind.

Not only hypocrites, but opportunists

Animals belonging to the class of amphibians are surprisingly tenacious - they live on all continents of the globe, except for Antarctica. They are still opportunists: very salty waters, arid territories and serious cold - they have nothing to do with any difficulties! You will climb into the Himalayas - you will meet an amphibian in the mountain heights.

And if you are brought into the desert or beyond the Arctic Circle (you never know what is fanciful for the sake of entertainment), then they are here too, just like underground.

True, these are rather exceptional options. The most fertile environment for amphibians is humid, warm and satisfying (where it is easy for amphibians to find edible prey) tropical countries.

Amphibious Animals: Immortal Snow Queen

One of the rarest amphibians is the Siberian salamander. It has a unique cold resistance, which allows this amphibian to exist, in principle, in conditions uncharacteristic of the class - on harsh north Russia (the territory from the Urals to Kamchatka). And these are temperatures reaching 30-35 degrees below zero, and permafrost ...

It is noteworthy that these creatures can survive even in ice for several years in a row. After such seemingly frozen individuals were found by geologists, they thawed, warmed up and returned to frisky life. How can one return to life after an icy death? The fact is that during frost, the water in the cells of this amphibian turns into glycerin, which protects them from certain death.

Rare amphibians: the frog that doesn't croak

But in the lowlands of the British mountains lives a kind of frog, called chicken. In addition to being one of the most large frogs in the world (reaches 21 centimeters), so its meat still has an exceptional taste.

Actually, for this, a green amphibian of peculiar beauty was called that. True, only criminal wealthy gourmets can now afford such a delicacy, because it is under the protection of the country as a species on the verge of extinction.

The fish that walks

Either a fish or a reptile - a very strange creature! Another unique class of amphibians with awesome names is a water monster, walking fish, and in science, the axolotl. He, too, can boast of unbanal beauty and strange qualities of survival.

The most remarkable of them is that these amphibians reach sexual maturity without passing into the adult stage, but remaining a larva, sometimes even for life. They, as befits amphibians, can live both on land and in water. But often they do not “work” on the development of the lungs, like other amphibians, but live in water spaces, but without the scales that fish rely on.

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The fauna of the planet Earth is diverse. Some representatives of the fauna live in water, others live on land, and still others have adapted to life both there and there. They make up the class of amphibians. A description of the organisms included in this group, as well as their habitats, are presented in this article.

general information

Amphibians are born in water bodies. They breathe with the help of gills. For some time after birth, they experience metamorphosis - the transformation from a tadpole into an adult organism. In this state, amphibians come to land. In total, there are three groups of representatives of this class of organisms.

1. Frogs, toads and tree frogs form the first group, which is considered the most numerous. They live in damp tropical forests, cold swamps in the north of the planet and even in semi-deserts.
2. Longtails: Newts and salamanders, which make up the second group, prefer the cooler climate of the Northern Hemisphere. Their favorite habitats are small shelters under rocks and old trees, protecting the animals' thin skin from drying out.
3. Representatives of the third group are often confused with snakes and worms. Amazing organisms called worms live in the tropics. They live underground.

Tritons

Surely in biology lessons you were told that there are such amphibians as newts. These amphibians have a long body. Their tail is flattened on the sides. Coloration largely depends on the habitat. Tritons have unique ability to tissue regeneration: they can restore the tail and limbs, if for some reason they have lost them.

Tritons feel equally comfortable in water and on land. However, they are looking for places with lush vegetation. In the winter season, they hibernate, and wake up in the spring. At this point, reproduction begins: newts lay their eggs next to aquatic plants. Before the mating season, a special outgrowth forms on the back of males. The diet of these amphibians consists of crustaceans, worms and larvae. Animals that are mostly nocturnal prefer territories with temperate climate.

salamanders

These amphibious animals are known to people as heroes of mythical stories. Since ancient times, they have been endowed with unique traits, such as immortality, the ability to turn into a dragon, or immunity to fire. Some of these "abilities" have a logical basis: for example, due to the presence of poison, salamanders can be dangerous to humans, as well as other animals.

frogs

The list of amphibians continues. Such tailless amphibians as frogs have been living on our planet since the time of the dinosaurs. The structure of their body allows them to live both on land and in water. There are practically no differences between a fish fry and a tadpole, but adult organisms that have passed the stage of metamorphosis are perfectly adapted to life on land. Frogs breathe using their lungs, mouth, and skin. Their circulatory system is called universal, since two sections of their heart work in water, and the left atrium pumps blood on land. Frog activity peaks at dusk, when the weather is cool. AT very coldy these amphibious animals try to find shelter, and if they fail to do this, they hibernate at the bottom of the reservoir. Skin color directly depends on the habitat. There are green, blue, blue frogs.

tree frogs

By appearance tree frogs resemble medium-sized frogs. Their legs are thin and long, which allows them to balance perfectly on smooth vertical surfaces, jump and swim well. The eyes of tree frogs are very large and expressive. At the ends of the fingers there are small suction cups, with the help of which amphibians cling to branches and various surfaces. The skin on the back is very smooth, on the belly it is coarse-grained.

Coloring can be varied. But the common tree frog, which is most common, has a bright green color with a white or black stripe. The average size of the animal is no more than 5 cm, although there are larger individuals, but they belong to other types of tree frogs.

toads

Many people confuse frogs, tree frogs and toads. However, all these representatives of the amphibian class have distinctive features. For example, toads have shorter hind legs than frogs. Because of this, the length of their jump is only 20 cm. Dry skin is generously strewn with a large number of warts. Toads live in water only during the breeding season, they spend the rest of the time on land.

Toads eat insects, worms and molluscs. Therefore, contrary to popular belief, they can benefit a person by destroying slugs in the garden. They are found on all continents, but their population is small in Australia. On the territory of this state, a species of toads lives, whose representatives have teeth and are able to accumulate fluid in the body cavities.

Worms

Legless amphibians are practically unknown to people far from biology. However, it is very interesting to study them. The skin is represented by numerous annular folds, which makes the body look like an earthworm. Some individuals have scales, while others have eyes that shine through the skin. One way or another, the worms look very original.

These amphibians burrow into moist soil and anthills in the expanses of Africa, South America and Asia. To protect themselves from all sorts of dangers, they use poisonous skin. It turns out that these amazing representatives of the fauna are little known. However, once you see them, you will never forget them.

Myths about amphibians

There are a number of myths about amphibians.

• There are amphibious reptiles. Technically, the reptile or reptile class sits between the amphibian and mammal classes. Frogs and salamanders are not reptiles, just like turtles and snakes are amphibians. So, reptiles lay eggs on land, and amphibians spawn in water. There are fundamental differences in the structure of the body and ontogenesis (the process of individual development). The same applies to amphibious mammals.

• Newts are lizards. This belief is wrong for several reasons. First, the newt goes through metamorphosis. Secondly, its body is smooth, while reptiles have scaly skin.
• Toads harm the household, as they drink cow's milk and eat strawberries. In fact, toads feed on insects that are found in vegetable gardens and barns, such as horseflies and slugs. So toads are very, very useful amphibians.

Another myth common among people of all ages is that if you touch a toad or a frog, warts will appear. This is not true, because otherwise all scientists who experiment on these animals would be completely covered with warts.

Amphibians, or amphibians(lat. Amphibia) - a class of vertebrate tetrapods, including newts, salamanders, frogs and worms - in total more than 6700 (according to other sources - about 5000) modern species, which makes this class relatively few in number. In Russia - 28 species, in Madagascar - 247 species.

The group of amphibians belongs to the most primitive terrestrial vertebrates, occupying an intermediate position between terrestrial and aquatic vertebrates: reproduction and development in most species occurs in the aquatic environment, while adults live on land.

general characteristics

Skin

All amphibians have smooth thin skin, relatively easily permeable to liquids and gases. The structure of the skin is characteristic of vertebrates: a multilayered epidermis and the skin itself (corium) stand out. The skin is rich in skin glands that secrete mucus. In some, the mucus may be poisonous or facilitate gas exchange. The skin is an additional organ for gas exchange and is supplied with a dense network of capillaries.

Horny formations are very rare, and ossification of the skin is also rare: in Ephippiger aurantiacus and horned toad species Ceratophrys dorsata there is a bone plate in the skin of the back, in legless amphibians - scales; in toads, sometimes, under old age, lime is deposited in the skin.

Skeleton

The body is divided into head, trunk, tail (for caudates) and five-fingered limbs. The head is movably connected to the body. The skeleton is divided into sections:

• axial skeleton (spine);
• head skeleton (skull);
• paired limb skeleton.

• skin-pulmonary arteries (carry venous blood to the lungs and skin);
• carotid arteries (supply arterial blood to the organs of the head);
• the aortic arches carry mixed blood to the rest of the body.

Small circle - pulmonary, begins with skin-pulmonary arteries that carry blood to the respiratory organs (lungs and skin); From the lungs, oxygenated blood is collected into the paired pulmonary veins that empty into the left atrium.

The systemic circulation begins with the aortic arches and carotid arteries, which branch in organs and tissues. Venous blood flows through the paired anterior vena cava and unpaired posterior vena cava into the right atrium. In addition, oxidized blood from the skin enters the anterior vena cava, and therefore the blood in the right atrium is mixed.

Due to the fact that the organs of the body are supplied with mixed blood, amphibians have a low metabolic rate, and therefore they are cold-blooded animals.

Digestive organs

All amphibians feed only on moving prey. At the bottom of the oropharyngeal cavity is the tongue. In anurans, it is attached to the lower jaws with its front end, when catching insects, the tongue is thrown out of the mouth, prey sticks to it. The jaws have teeth that serve only to hold prey. In frogs, they are located only on the upper jaw.

The ducts of the salivary glands open into the oropharyngeal cavity, the secret of which does not contain digestive enzymes. From the oropharyngeal cavity, food enters the stomach through the esophagus, from there into the duodenum. The ducts of the liver and pancreas open here. Digestion of food occurs in the stomach and in the duodenum. The small intestine passes into the rectum, which forms an extension - the cloaca.

excretory organs

The brain consists of 5 sections:

• the forebrain is relatively large; divided into 2 hemispheres; has large olfactory lobes;
• diencephalon is well developed;
• the cerebellum is poorly developed due to simple, monotonous movements;
• the medulla oblongata is the center of the respiratory, circulatory and digestive systems;
• the midbrain is relatively small, is the center of vision, skeletal muscle tone.

sense organs

In the organ of hearing, a new department is the middle ear. The external auditory opening is closed by the tympanic membrane, connected to the auditory bone - the stirrup. The stirrup rests against the oval window leading to the cavity of the inner ear, transmitting to it the vibrations of the tympanic membrane. To equalize pressure on both sides of the tympanic membrane, the middle ear cavity is connected to the oropharyngeal cavity by the auditory tube.

The organ of touch is the skin, which contains tactile nerve endings. Aquatic representatives and tadpoles have lateral line organs.

Sex organs

All amphibians are dioecious. In most amphibians, fertilization is external (in water).

Amphibians of some species take care of their offspring (toad, tree frogs).

Lifestyle

Most spend their lives in humid places, alternating between land and water, but there are some purely aquatic species, as well as species that spend their lives exclusively on trees. Insufficient adaptability of amphibians to living in a terrestrial environment causes drastic changes in their lifestyle due to seasonal changes conditions of existence. Amphibians are able to hibernate for a long time under adverse conditions (cold, drought, etc.). In some species, activity can change from nocturnal to diurnal as temperatures drop at night. Amphibians are active only in warm conditions. At a temperature of +7 - +8 ° C, most species fall into a stupor, and at -1 ° C they die. But some amphibians are able to endure prolonged freezing, drying out, and also regenerate significant lost parts of the body.

Some amphibians, such as the sea toad Bufo marinus can live in salt water. However, most amphibians are found only in fresh water. Therefore, they are absent on most oceanic islands, where conditions are favorable for them in principle, but which they cannot reach on their own.

Food

All modern amphibians in the adult stage are predators, feed on small animals (mainly insects and invertebrates), and are prone to cannibalism. There are no herbivorous animals among amphibians due to extremely sluggish metabolism. In the diet aquatic species may include juvenile fish, and the largest may prey on chicks of waterfowl and small rodents that have fallen into the water.

The nature of the nutrition of the larvae of tailed amphibians is almost similar to the nutrition of adult animals. Tailless larvae have a fundamental difference, feeding on plant food and detritus, turning to predation only at the end of the larval stage.

reproduction

A common feature of the reproduction of almost all amphibians is their attachment during this period to the water, where they lay their eggs and where the larvae develop. Amphibians breed in shallow, well-warmed areas of water bodies. On warm spring evenings, at the end of April and in May, loud croaking sounds are heard from the ponds. These "concerts" are arranged by male frogs to attract females. The reproductive organs in males are the testes, in females the ovaries. Fertilization is external. Caviar sticks to aquatic plants or rocks.

Virulence

The most poisonous vertebrates on Earth belong to the order of amphibians - these are dart frogs. Poison, which is secreted by the skin glands of amphibians, contains substances that kill bacteria (bactericides). In most amphibians in Russia, the poison is completely harmless to humans. However, many tropical frogs are not so safe.

The absolute "champion" in terms of toxicity among all vertebrates, including snakes, should be recognized as a resident rainforest Columbia - a tiny, only 2-3 cm in size, terrible leaf climber (the locals call it "cocoi"). Her skin mucus contains batrachotoxin. From the skin of cocoa, the Indians prepare poison for arrows. One frog is enough to poison 50 arrows. 2 mg of purified poison is enough to kill a human. However, this frog has a natural enemy - a small snake. Leimadophis epinephelus, which feeds on young leaf climbers.

Amphibians and people: active life

Due to their vitality, amphibians are often used as laboratory animals.

Classification

Modern representatives are represented by three groups:

• Tailless (frogs, toads, tree frogs, etc.) - about 2100 species.
• Tailed (salamanders, newts, etc.) - about 280 species.
• Legless, the only family of caecilians - about 60 species.

Evolution

In evolutionary terms, amphibians descended from ancient lobe-finned fish and gave rise to representatives of the reptile class. The most primitive order of amphibians are caudate. Tailed amphibians are most similar to the most ancient representatives of the class. More specialized groups are the anurans and the legless.

There is still debate about the origin of amphibians, and according to the latest data, amphibians descend from ancient lobe-finned fish, specifically, from the order of ripidistia. In terms of the structure of the limbs and skull, these fish are close to fossil amphibians (stegocephals), which are considered the ancestors of modern amphibians. Ichthyostegids are considered the most archaic group, which retain a number of features characteristic of fish - the caudal fin, rudiments of gill covers, organs corresponding to the organs of the lateral line of fish.

Basic aromorphoses

1. The appearance of a five-fingered limb.
2. Lung development.
3. The presence of a three-chambered heart.
4. Formation of the middle ear.
5. The appearance of two circles of blood circulation

see also

Notes

1. Amphibian Species of the World. Amphibian database. Darrel Frost and The American Museum of Natural History. Archived
2. Class Amphibians, or Amphibians: general characteristics. Biology and medicine. Archived from the original on June 22, 2012. Retrieved March 13, 2012.
3. Classis AMPHIBIA (L. Ya. Borkin, 1992) . Archived from the original on June 22, 2012. Retrieved March 13, 2012.
4. // Encyclopedic Dictionary of Brockhaus and Efron: In 86 volumes (82 volumes and 4 additional). - St. Petersburg. , 1890-1907.
5. Workshop on vertebrate zoology. An autopsy of an amphibian. Archived from the original on August 4, 2012. Retrieved 16 July 2012.
6. Nikitenko, 1969 The brain of amphibians. Biology and medicine. Archived from the original on June 22, 2012. Retrieved March 13, 2012.
7. Why are they ... water? . Zooclub. Archived from the original on June 22, 2012. Retrieved March 13, 2012.
8. Alexander Markov How Amphibians Learned to Transform (January 24, 2008). Archived from the original on June 22, 2012. Retrieved March 13, 2012.
9. Amphibian nutrition. Biologists and medicine. Archived from the original on June 22, 2012. Retrieved March 13, 2012.
10. Digestive system of amphibians. Biology and medicine. Archived from the original on June 22, 2012. Retrieved March 13, 2012.
11. Poisonous evolution. Magazine "Around the World". Archived from the original on June 22, 2012. Retrieved March 13, 2012.

Amphibians are a group of anamnia that have partially switched to a terrestrial way of life, but retained the features of their aquatic ancestors.

Systematics. The world fauna has about 3400 species. Modern amphibians are divided into three groups.

Squad Legless- about 170 species of caecilians leading an underground lifestyle. All are inhabitants of the tropics.

Squad Tailed- about 350 species, distributed mostly in the northern hemisphere. These include newts, salamanders, salamanders, axolotls. About 12 species live in the CIS.

Detachment Tailless- about 2900 species of frogs and toads, distributed on all continents. The fauna of the CIS has about 25 species.

Body dimensions. The smallest amphibians reach a length of 1-2 cm, and the largest - gigantic salamanders exceed 1 m in length.

External building. Amphibians have a naked, slimy body. The head is movably connected to a single cervical vertebra by two condyles. At tailed amphibians the body is elongated, there are four limbs of approximately the same length and a long tail. Limbs can be more or less reduced. There are also completely legless forms (worms). At tailless amphibians the body is short and wide. The hind limbs are jumping and significantly exceed the length of the front ones.

Covers. The skin is devoid of horny formations and is very rich in multicellular glands that secrete mucus. There are extensive lymphatic sacs under the skin, so that the skin is attached to the body only in certain places. The skin is richly supplied with blood vessels and takes an active part in gas exchange (respiratory function). Covers also perform a protective function. Many species have bumps and warts on the skin that secrete a poisonous secret. Many poisonous species are brightly colored (salamanders, poison dart frogs), but basically the coloring of amphibians is patronizing.

Skeleton. The skull is mostly cartilaginous. The spine consists of several sections: cervical (one vertebra), trunk (several vertebrae), sacral (one vertebra) and tail. In tailless amphibians, the rudiments of the caudal vertebrae fuse into a process - urostyle. There are no ribs on the spine.

The skeleton of the forelimb consists of the humerus, two bones of the forearm (radius and ulna), and numerous bones of the hand (wrist, metacarpus, phalanges of the fingers). The forelimb girdle consists of the scapula, coracoid, and clavicle. The sternum is connected to the girdle of the forelimbs.

The hind limb consists respectively of one femur bone, two lower leg bones (tibia and fibula), and foot bones (tarsus, metatarsus and phalanges). The pelvic bones (iliac, ischial and pubic) belong to the hind limb girdle.

In general, the limbs are five-fingered, however, in many amphibians, especially on the forelimbs, there are 4 fingers.

Muscular system more differentiated than in fish. The muscles of the extremities are especially developed. In places, a distinct segmentation of the musculature is preserved.

Digestive system amphibians are well developed. The jawbones contain small teeth. The ducts of the salivary glands open into the oral cavity. Saliva does not contain digestive enzymes and only moistens food. In the mouth is the tongue, which has its own muscles. In frogs, it is attached to the front of the lower jaw. The eyeballs protrude strongly into the oral cavity and take part in pushing food further into the pharynx. The pharynx leads into a relatively short esophagus; the stomach is not sharply isolated. The intestine is clearly differentiated into a thin and thick section. The ducts of the liver and pancreas open into the small intestine. The posterior intestine flows into the cloaca.

Respiratory system. At the end of the muzzle of amphibians there are nostrils, which are equipped with valves and open into the oropharyngeal cavity with choanae. The larynx, consisting of cartilages, of which the most developed pair of arytenoids, forming the laryngeal fissure, opens into the same cavity. Actually, the respiratory organs in amphibians are paired sack-shaped cellular lungs with fairly elastic walls. The lungs are either suspended from the lower part of the laryngeal chamber (in tailless ones), or connected to it by a long tube - the trachea, in the wall of which there are cartilaginous elements that do not allow the tube to subside (in tailed ones). The trachea only opens into the lungs with a hole, but does not branch into them.

The act of breathing due to the absence of the chest occurs in a very peculiar way. The animal opens the valves of the nostrils and lowers the floor of the mouth: air fills the oral cavity. After that, the valves close and the floor of the mouth rises: air is pushed through the laryngeal fissure into the lungs, which are somewhat stretched. Then the animal opens the valves of the nostrils: the elastic walls of the lungs collapse and the air is pushed out of them.

No less important respiratory organ is, as already mentioned, the skin. For example, in a common frog, about 30% of oxygen enters through the skin, and in a pond frog, up to 56%. Most carbon dioxide (up to 90%) is removed through the skin.

In amphibian larvae, the respiratory organs are external or internal gills. For the most part, they subsequently disappear, but in some species (Proteus, axolotl) they can persist throughout life.

Circulatory system. Changes in the circulatory system are also associated with the development of skin-pulmonary respiration. The three-chambered heart consists of two isolated atria and one ventricle. An arterial cone departs from the ventricle, from which, in turn, three pairs of vessels originate: two carotid arteries, carrying arterial blood to the head; two aortic arches with mixed blood, which release vessels into the forelimbs and then merge into an unpaired dorsal aorta; two pulmonary arteries that carry venous blood to the lungs and to the skin for oxidation. This separation of blood flows is provided by the presence of special pockets in the ventricle itself, as well as the work of the muscles of the arterial cone.

The blood returns to the heart through the veins: one posterior and two anterior vena cava with venous blood flow into the right atrium, while the skin veins with arterial blood also flow into the anterior vena cava. Arterial blood from the lungs flows into the left atrium through the pulmonary veins. Blood from the atria is pushed into the ventricle, where it does not completely mix.

Thus, amphibians form small, pulmonary circle circulation, which is not yet completely separated from the systemic circle. Erythrocytes in amphibians are oval in shape and contain a nucleus.

Body temperature. Amphibians are poikilothermic animals, since they are not able to maintain a constant body temperature and are highly dependent on the ambient temperature.

Nervous system. The amphibian brain differs from the fish brain in a number of ways. The main ones are the complete division of the forebrain into hemispheres and the very weak development of the cerebellum. The latter is associated with low mobility and uniformity of animal movements. In the forebrain, the roof (fornix) contains nerve matter, but there are no proper nerve cells on the surface of the brain. The olfactory lobes are poorly differentiated. This formation is called the primary cerebral fornix ( archipallium). Of the peripheral nervous system, the nerves of the hind limbs are especially developed.

sense organs in connection with access to land, they acquire a more complex structure than that of fish.

organs of vision. The eyes are well developed. The lens has the appearance of a biconvex lens, in contrast to the spherical lens of fish. The cornea is also convex. Accommodation is achieved by changing the distance from the lens to the retina. The eyes are protected by movable eyelids. Some species lack eyes (Proteus).

hearing organs. In addition to the inner ear, developed in fish, amphibians have a middle ear, delimited from external environment tympanic membrane. This membrane is connected to the inner ear by the auditory ossicle. stirrup(column), which transmits the vibrations of air, which conducts sound much worse than water. The middle ear cavity is connected to the oral cavity by the Eustachian tubes, which equalize internal and external pressure, protecting the eardrum from rupture.

Balance organ connected with the inner ear and represented by the sac and three semicircular canals.

Olfactory organs located in the nasal passages of amphibians. Unlike fish, the olfactory surface increases due to folding.

Lateral line organ, characteristic of fish, in amphibians is present exclusively in the larval phase. In the process of development, it disappears.

sense organs represented by numerous nerve endings in the skin.

excretory system amphibian performs the function of removing excess fluid from the body, which enters not only through the mouth, but also through the entire surface of the skin. Amphibians have two large trunk ( mesonephric) kidneys. The ureters depart from them, flowing into the posterior part of the intestine - the cloaca. It opens into it bladder in which urine accumulates before being expelled from the body.

reproductive system amphibians are very similar to the reproductive organs of fish.

At male on the front of the kidneys are paired testes, from which numerous seminiferous tubules depart, flowing into the ureters. There are seminal vesicles where spermatozoa are stored.

At females sex glands - ovaries - large, granular. Their size depends on the season. During the breeding season, they occupy most of the body cavity. Mature eggs fall into the body cavity, from where they are brought out through the oviducts into the cloaca, and then out.

Biology of nutrition. Amphibians react only to moving food. All amphibians, without exception, feed on invertebrates - arthropods, molluscs and worms. Large tropical frogs are able to eat small rodents. They all swallow their prey whole.

Biology of reproduction. The breeding season usually occurs in the spring. Mating is preceded by various courtship rituals. During this period, males may change color, and a crest may appear (in newts). In tailless amphibians, fertilization is external, as in fish: the female spawns eggs into the water, and the male immediately fertilizes the laid eggs. In a number of species of tailed amphibians, the male lays the so-called spermatophore- a gelatinous lump containing spermatozoa and attaches it to underwater objects. The female later captures these formations with the edges of the cloaca and places them in the spermatheca. Fertilization takes place inside the body of the female.

Development. In the vast majority of amphibians, eggs are deposited in the water. Each egg is covered with a gelatinous shell, which includes substances that inhibit the development of microorganisms. Fertilized eggs, poor in yolk, undergo complete uneven crushing. Gastrulation occurs through intussusception and epiboly. In the end, a larva is formed from the egg - a tadpole. This larva is in many ways similar to fish: a two-chambered heart, one circle of blood circulation, gills, and a lateral line organ. In the process of metamorphosis, the disappearance or change of larval organs and the formation of an adult animal occur. External gills gradually turn into internal ones, and with the advent of pulmonary respiration, they can disappear altogether. The tail and lateral line are reduced, first the hind limbs appear, and then the forelimbs. A septum appears in the atrium, and the heart becomes three-chambered.

In this way, in the process of individual development (ontogenesis) of amphibians, repetition is clearly visible historical development this group (phylogenesis).

In some species, fertilized eggs are attached to the hind limbs of the male (midwife toad) or to the dorsal part of the female (pipa toad). Sometimes fertilized eggs are swallowed by males, and further development of eggs and the formation of tadpoles and frogs occurs in his stomach. Some species have live birth.

Neoteny. In some tailed amphibians, the final transformation of the larva into an adult animal does not occur. Such larvae have acquired the ability to reproduce sexually. This phenomenon is called neoteny. Neoteny has been studied especially well on the example of axolotls - neotenic larvae of ambistomes. Under artificial conditions, through the action of hormones, it is also possible to obtain adult forms that lack external gills.

Lifespan amphibians is usually calculated in several years. However, some specimens lived in captivity for 10-30 years. Some Siberian species, such as salamanders living in the permafrost zone, are able to fall into running stupor for 80-100 years.

Origin. Ancient lobe-finned fish, which probably also had pulmonary respiration, are considered as the ancestral form of amphibians. Their paired fins gradually evolved into a five-fingered limb. This happened, as expected, in the Devonian period (at least 300 million years ago). Among the paleontological remains of that time, imprints of the most primitive amphibians, stegocephalians and labyrinthodonts, were found, which had many features in common with ancient lobe-finned fish.

It has been proven that lungfish separated from the common trunk much earlier than the lobe-finned ones and could not be among the ancestors of amphibians.

Spreading. The number and species diversity of amphibians are especially high in the tropics, where it is constantly warm and humid. Naturally, the number of amphibian species will decrease towards the poles.

Lifestyle. Amphibians can be divided into two groups according to the nature of their habitat.

The first group includes terrestrial species. They mostly live on land and only return to the water for the breeding season. These include toads, tree frogs and other tree anurans, as well as burrowing species - spadefoot and all legless (worms).

The second group includes water sports. If they leave the reservoirs, then not for long. These include most tailed amphibians (salamanders, proteas) and some anurans (lake frog, pipa).

In the temperate climate zone, amphibians go to winter. Tritons and toads winter in underground shelters (rodent burrows, cellars and cellars). Frogs most often hibernate in the water.

Proteas inhabiting cave reservoirs, where the temperature does not change, remain active throughout the year.

Some amphibians, despite their moisture-loving nature, can sometimes even live in deserts, where they are active only during the rainy season. The rest of the time (about 10 months) they spend in hibernation, digging into the ground.

Meaning. Amphibians make up a significant portion of the vertebrate population in most landscapes. They eat a huge amount of invertebrates. It has more greater value, given that birds, the main competitors of amphibians for food, mostly sleep at night, and amphibians are mostly nocturnal hunters. At the same time, amphibians themselves serve as food for a huge number of animals. This is especially true for tadpoles and young animals, the density of which reaches hundreds, and sometimes thousands of specimens per square meter!

In practical terms, amphibians are useful as exterminators of harmful invertebrates (slugs, Colorado potato beetles), which other animals most often do not eat. Lake frogs sometimes exterminate fish fry, but the harm they cause is very small. Some species of amphibians have become classic test animals. A number of species are edible. Many countries have laws on the protection of amphibians.

Class Reptiles or Reptiles.

Reptiles are true terrestrial animals of the amniote group with unstable body temperature (poikilothermic).

Systematics. The modern fauna of reptiles includes about 8,000 species belonging to several orders.

Turtle Squad- about 250 species, in the CIS - 7 species.

Squamous order- about 7000 species. There are about 80 species of lizards and about 60 species of snakes in the CIS.

Beakhead detachment– 1 species (tuatara)

Squad of crocodiles- 26 types.

External building. The body of reptiles is usually elongated in length. The head is connected to the body by a well-defined cervical region and bears various sense organs. Most reptiles have two pairs of originally five-fingered limbs on the sides of the body. However, in a number of groups, the limbs were completely or partially reduced. The tail section is well developed.

Body dimensions reptiles vary widely. The smallest representatives (geckos) can be only a few centimeters in length. Anaconda snakes are considered the largest, sometimes reaching 10-11 m in length.

Covers. Reptiles are covered with dry skin, in which there are no glands. The skin fits snugly to the body and often fuses with the skull on the head. The whole body is covered with horny scales (lizards, snakes) or horny shields (crocodiles). In snakes, the eyes are covered with transparent shields that replace the eyelids. The body of turtles is enclosed in a shell, covered on the outside with shields. All reptiles periodically shed their old skin. At the same time, in turtles, old shields are erased or peeled off from the shell; in lizards, the old skin flakes off in large pieces, and in snakes, it slips off like a stocking.

Skeleton quite ossified. The skull is connected to the first cervical vertebra ( atlas) with only one condyle, and the atlas, in turn, is “put on” on the process of the second cervical vertebra ( epistrophy); thus the head is connected to the body in a very movable way. At the jaw ends are teeth. The spine is divided into several sections: cervical, thoracic, lumbar, sacral and caudal. The ribs are attached to the thoracic vertebrae, which, connecting with the sternum, form the chest. The ribs of the lumbar and posterior thoracic vertebrae are not connected to the sternum. In snakes, the ribs perform part of the function of movement. In turtles, a number of sections of the spine and ribs grow together with the shell. The skeleton of the fore and hind limbs consists of the same bones and sections as in other terrestrial vertebrates.

In flying dragon lizards, elongated false ribs support the lateral skin folds. Thanks to this, animals have developed the ability for gliding flight.

muscles. Musculature reaches even greater development in comparison with amphibians. Of the features, one should point out the appearance of intercostal muscles, as well as underdeveloped subcutaneous muscles. The muscles of some snakes are very strong.

Digestive system. The salivary glands enter the oral cavity. At poisonous snakes there are special glands that produce toxins. The ducts of these glands open into the so-called poisonous teeth. Snake venoms are complex complexes of biologically active compounds. Based on their effect on warm-blooded animals, poisons are divided into two groups: neurotoxic and hemotoxic.

neurotoxic poison affects the central nervous system causing flaccid paralysis of the respiratory and motor muscles. At the same time, pain and swelling at the site of the bite, as a rule, are not very pronounced. The venom of this group is possessed by asps, cobras and sea snakes.

hemotoxic poison contains proteolytic enzymes that destroy tissues and increase vascular permeability. At the same time, against the background of general intoxication, severe edema develops at the site of the bite, accompanied by pain. These poisons can cause disseminated intravascular coagulation. The poisons of this group are characteristic of vipers and pit vipers (vipers, efa, gyurza, muzzle, rattlesnake).

In addition to snakes, venom is also contained in the saliva of a large Mexican lizard - gila-tooth.

Well developed muscular tongue. In chameleons, the tongue is able to stretch out strongly, and serves to catch insects.

The esophagus is usually able to stretch greatly, especially in snakes that swallow prey whole. The esophagus leads to a well-developed stomach. The intestine is divided into thin and thick sections. The ducts of the liver and pancreas flow into the beginning of the small intestine. The large intestine ends with an expansion - the cloaca, into which the ureters and ducts of the reproductive system flow.

Respiratory system. Gas exchange through the skin in reptiles is completely absent, unlike amphibians. On the front of the head, reptiles have paired nostrils that open with choanae into the oral cavity. In crocodilians, the choanae are pushed far back and open into the pharynx, so that they can breathe while grabbing food. From the choanae, air enters the larynx, which consists of the cricoid and two arytenoid cartilages, and from there into trachea. The trachea is a long tube made up of cartilaginous half-rings that prevent it from collapsing. In the lower part, the trachea divides into two bronchi, which join into the lungs, but do not branch into them. The lungs are bags with a cellular structure on the inner surface. Breathing is carried out by changing the volume of the chest due to the work of the intercostal muscles. Such a mechanism is not possible in turtles; they breathe like amphibians, swallowing air.

Circulatory system. The heart of reptiles is generally three-chambered. However, the stomach has incomplete septum, which partially separates the venous and arterial blood in the heart. In the stomach of crocodilians full baffle. Thus, their heart becomes four-chambered, and venous and arterial blood in the heart is completely separated. Two arches of the aorta depart from the heart: one with arterial, the other with mixed (in crocodiles - with venous) blood. Behind the heart, these vessels merge into a common dorsal aorta. The carotid arteries, which carry blood to the head, and the subclavian arteries, which supply blood to the forelimbs, depart from the arc with arterial blood. The pulmonary artery also departs from the heart, carrying venous blood to the lungs. Oxidized blood returns to the left atrium through the pulmonary vein. Venous blood from all over the body is collected in the right atrium through two anterior and one posterior vena cava.

Nervous system. The brain is relatively larger than that of amphibians. The roof of a well-developed forebrain contains bodies of nerve cells, in contrast to amphibians, in which the fornix contains only processes of nerve cells. The olfactory lobes are differentiated. The medulla oblongata forms a sharp bend, characteristic of all amniotes. The cerebellum is well developed. parietal organ, associated with the diencephalon, is exceptionally well developed and has the structure of an eye.

sense organs reptiles are diverse and well developed.

organs of vision- eyes - differ in structure from the eyes of amphibians in the presence of striated muscles, which, during accommodation, not only moves the lens, but also changes its curvature. The eyes of reptiles are surrounded by eyelids. There is also a third eyelid - the nictitating membrane. The exceptions are snakes and some lizards, whose eyes are covered with transparent shields. The parietal organ is covered with a transparent shield and also functions as a photosensitive organ.

Olfactory organ located in the paired nasal cavity leading through the choanae to the oral cavity or pharynx. In lizards and snakes, the so-called Jacobson's organ opens into the oral cavity. This is a chemical analyzer that receives information from the tip of the tongue, from time to time protruding partly open mouth of reptiles.

hearing organ represented by the inner and middle ear, in which the only auditory bone is located - the stirrup. With the inner ear, as in all terrestrial vertebrates, there is also a pair balance organ, represented by the sac and three semicircular canals.

sense organs represented by nerve endings in the skin. However, due to the development of the cornea, the skin sense of touch is rather poorly developed.

organs of taste located in the oral cavity.

thermosensitive organ located in snakes on the front of the head in the form of small pits. With the help of this organ, reptiles can detect prey (small warm-blooded animals) by thermal radiation.

excretory system reptiles is represented by a pair of compact metanephric kidneys adjacent to the dorsal side in the pelvic region. The ureters depart from them, flowing into the cloaca from the dorsal side. From the ventral side, the bladder flows into the cloaca. Snakes and crocodiles do not have a bladder.

reproductive system. Reptiles are dioecious animals. Many are sexually dimorphic. Usually males are slightly larger than females and more brightly colored.

In males, paired oval testicles lie on the sides of the lumbar spine. Numerous tubules depart from each testicle, uniting in the vas deferens, which flows into the ureter of the corresponding side. Paired copulatory organs of a peculiar structure depart from the posterior section of the cloaca.

In females, paired tuberous ovaries also lie in the lumbar region. Paired thin-walled wide oviducts open at one end into the anterior part of the body cavity, and at the other into the cloaca.

Autotomy. Some lizards are able to drop their tail when threatened. At this moment, the muscles of the tail in a certain place are sharply reduced and, as a result, the vertebrae breaks. The detached tail retains mobility for some time. There is practically no blood at the wound site. After 4-7 weeks, the tail regenerates.

Biology of nutrition. Reptiles are mainly carnivores that feed on vertebrates and invertebrates. Small species mainly catch insects, while large ones also cope with large ungulates. This group includes both ambush species (chameleons, crocodiles) and active hunters (snakes, monitor lizards). Some reptiles swallow food whole (snakes), others can tear their prey apart (crocodiles, monitor lizards). In the diet of some groups of lizards (iguanas) and turtles, plant foods predominate. There are also fish-eating species.

Biology of reproduction. Mating is sometimes preceded by peculiar tournaments between males for the possession of a female. Fertilization is internal. Most reptiles lay eggs rich in yolk and covered with leathery shells. These eggs are usually placed in a substrate - heaps of humus, sun-warmed sand, where incubation takes place. Some reptiles, such as crocodiles, build special nests that are then guarded. And boas even "hatch" their masonry. Already formed animals emerge from the eggs. Development, therefore, in reptiles is direct, without metamorphosis.

Some species are ovoviviparous. These include vipers, viviparous lizards and spindles. In this case, the eggs develop in the mother's body until the formation of young animals, which then are born in the egg shells. Those cubs that could not get out of the shells are often eaten by the mother. Oviparous is characteristic of reptiles living in northern latitudes, where there is not enough solar heat to incubate offspring in any substrate. Therefore, for example, a viviparous lizard in our region gives birth to cubs, and in central Russia and in the Jurassic, it lays eggs.

Reptile fertility is limited to a few dozen eggs or young. Crocodiles, some snakes and lizards take care of their offspring.

Reptile lifestyle. Due to the fact that reptiles are poikilothermic animals (with unstable body temperature), for the most part they are thermophilic. For different species, the optimum ambient temperature ranges from 12 to 45°C. Therefore, temperate reptiles are usually active during the day or at dusk, and in tropical climates there are a lot of nocturnal species.

In addition, in the tropics there is no sharp change in seasons, so reptiles do not have periods of rest there. And in the temperate zone, reptiles are forced to hibernate. Wintering of reptiles occurs most often in underground shelters. Lizards and turtles usually hibernate alone or in small groups. Vipers sometimes accumulate in suitable places in dozens, and common snakes even in hundreds. The wintering of reptiles in our region depends on the weather and begins on average from mid-September and lasts until April-May.

In some species, for example, in the Central Asian tortoise, summer hibernation is also observed. In late May - early June, when vegetation begins to burn out in the deserts, turtles dig holes and fall into a stupor. In places where vegetation does not dry out, turtles are active all summer.

Among reptiles, ecological groups can be distinguished according to their habitats.

living on solid ground (real lizards, monitor lizards, snakes, land turtles).

living in loose sands (round-headed lizards, slender boas, ephs).

underground and burrowing species (skinks, mole rats).

tree and shrub species (chameleons, iguanas, geckos, arrow-snakes, kufii).

aquatic species (crocodiles, anacondas, sea and freshwater turtles, marine iguanas)

Distribution of reptiles. Species diversity and population density certain types naturally increases from north to south. In our latitudes, there are 8 species of reptiles with a density of 1-2 to several dozen individuals per 1 ha. In more southern regions, these same species have a density of up to several hundred individuals per 1 ha.

Origin and history of reptiles. The ancestors of reptiles were primitive amphibians - stegocephals. The most primitive forms of reptiles are Seimuria and cotylosaurus, the fossil remains of which are found in the layers belonging to the Carboniferous and Permian period of the Paleozoic era (300-350 million years ago). The era of reptiles began 225 million years ago - in the Mesozoic era, when they reigned on land, in the sea and in the air. Among them, dinosaurs were the most diverse and numerous group. Their sizes ranged from 30-60 cm to 20-30 m, and the weight of the giants reached 50 tons. In parallel with them, the ancestors of modern groups also developed. In total, there are about a hundred thousand extinct species. However, 65 million years ago, the era of reptiles ended, and most of their species died out. The causes of extinction are catastrophes on a planetary scale, gradual climate change and others.

Skeletons and imprints of extinct reptiles are relatively well preserved in sedimentary rocks, thanks to which science makes it possible to restore the appearance and partly the biology of ancient pangolins.

Meaning. Reptiles play a significant role in the biotic cycle of substances as consumers of various trophic levels. At the same time, they mostly feed on harmful invertebrates, and in some cases even rodents. Reptiles also serve as a source of raw materials for the leather industry (crocodiles). Snake venom is used in medicine. A number of species are used for food. Many species are protected.

Reptiles can also be harmful in places. For example, water snakes can destroy a large number of fry. Reptiles are often hosts for nymphs and adult ixodid ticks and thus can be a reservoir of human and animal diseases (tick-borne typhus, etc.). In some countries, venomous snakes cause serious harm, killing thousands of people every year.