Each of us, even if only in pictures, has seen frogs and lizards, crocodiles and toads - these animals belong to the classes Amphibians and Reptiles. The example we gave is far from the only one. There really are a lot of such creatures. But how can you tell who is who? How are amphibians and reptiles different and how significant are these differences?

A crocodile and a toad can get along well in the same body of water. Therefore, it is likely that they may appear to be related and share common ancestors. But this is a huge mistake. These animals belong to different systematic classes. There are many fundamental differences between them. And they lie not only in appearance and size. The crocodile and lizard are reptiles, while the frog and toad are amphibians.

But, of course, amphibians and reptiles also have some similarities. They prefer areas with warm climates. True, amphibians choose damp places, preferably near bodies of water. But this is dictated by the fact that they reproduce only in water. Reptiles are not associated with bodies of water. On the contrary, they prefer drier and hotter regions.

Let's look at the structure and physiological characteristics of reptiles and amphibians, and compare how they differ from each other.

Class Reptiles (reptiles)

Class Reptiles, or Reptiles, are terrestrial animals. They got their name due to their method of movement. Reptiles do not walk on the ground, they crawl. It was reptiles who first completely switched from an aquatic to a land way of life. The ancestors of these animals spread widely across the earth. An important feature of reptiles is internal fertilization and the ability to lay eggs rich in nutrients. They are protected by a dense shell, which contains calcium. It was the ability to lay eggs that contributed to the development of reptiles outside the reservoir on land.

The structure of reptiles

The body of reptiles has durable structures - scales. They tightly cover the skin of reptiles. This protects them from moisture loss. Reptile skin is always dry. Evaporation does not occur through it. Therefore, snakes and lizards are able to live in deserts without experiencing discomfort.

Reptiles breathe using fairly well-developed lungs. It is important that intensive breathing in reptiles became possible thanks to the appearance of a fundamentally new part of the skeleton. The rib cage first appears in reptiles. It is formed by ribs extending from the vertebrae. On the ventral side they are already connected to the sternum. Thanks to special muscles, the ribs are mobile. This promotes expansion of the chest during inhalation.

The Reptile class has also undergone changes in the circulatory system. This is due to the complication of the vast majority of reptiles, like amphibians, they have two circles of blood circulation. However, there are some differences. For example, there is a septum in the ventricle. When the heart contracts, it practically divides it into two halves (right - venous, left - arterial). The location of the main blood vessels more clearly distinguishes arterial and venous flows. As a result, the reptile's body is supplied with oxygen-enriched blood much better. At the same time, they have more established processes of intercellular exchange and removal of metabolic products and carbon dioxide from the body. There is an exception in the Reptiles class, an example is the crocodile. His heart is four chambered.

The main large arteries of the pulmonary and systemic circulation are fundamentally the same for all groups of terrestrial vertebrates. Of course, there are some minor differences here too. In reptiles, cutaneous veins and arteries have disappeared. Only the pulmonary vessels remained.

Currently, about 8 thousand species of reptiles are known. They live on all continents, except, of course, Antarctica. There are four orders of reptiles: crocodiles, squamates, turtles and proto-lizards.

Reproduction of reptiles

Unlike fish and amphibians, reproduction in reptiles is internal. They are dioecious. The male has a special organ with which he introduces sperm into the female’s cloaca. They penetrate the eggs, after which fertilization occurs. The eggs develop in the female's body. Then she lays them in a pre-prepared place, usually a dug hole. On the outside, reptile eggs are covered with a dense calcium shell. They contain the embryo and a supply of nutrients. What emerges from the egg is not a larva, as in fish or amphibians, but individuals capable of independent life. Thus, the reproduction of reptiles is fundamentally reaching a new level. The embryo undergoes all stages of development in the egg. After hatching, it does not depend on a body of water and can easily survive on its own. As a rule, adults do not take care of their offspring.

Class Amphibians

Amphibians, or amphibians, include newts. With rare exceptions, they always live near a body of water. But there are species that live in the desert, such as the water-carrying toad. When it rains, it collects fluid in the subcutaneous sacs. Her body swells. Then she buries herself in the sand and, secreting a large amount of mucus, survives a long drought. Currently, about 3,400 species of amphibians are known. They are divided into two orders - tailed and tailless. The former include salamanders and newts, the latter - frogs and toads.

Amphibians are very different from the class Reptiles, for example - the structure of the body and organ systems, as well as the method of reproduction. Like their distant ancestors fish, they spawn in water. To do this, amphibians often look for puddles separated from the main body of water. Both fertilization and larval development occur here. This means that during the breeding season, amphibians have to return to water. This greatly interferes with their settlement and limits their movement. Only a few species were able to adapt to life away from water bodies. They give birth to fully formed offspring. That is why these animals are called semi-aquatic.

Amphibians are the first chordates to develop limbs. Thanks to this, in the distant past they were able to reach land. This, naturally, caused a number of changes in these animals, not only anatomical, but also physiological. Compared to species that remained in the aquatic environment, amphibians have wider chests. This contributed to the development and complexity of the lungs. Amphibians' hearing and vision improved.

Amphibian habitats

Like reptiles, amphibians prefer to live in warm regions. Frogs are usually found in damp places near bodies of water. But you can see them in meadows and forests, especially after heavy rain. Some species thrive even in deserts. For example, the Australian toad. She has adapted very well to survive long droughts. Under such conditions, other types of toads would certainly die quickly. But she learned to accumulate vital moisture in subcutaneous pockets during the rainy season. In addition, during this period it reproduces, laying eggs in puddles. It only takes one month for tadpoles to fully metamorphose. The Australian toad, in extreme conditions for its species, not only found a way to reproduce, but also successfully find food for itself.

Differences between reptiles and amphibians

Although at first glance it seems that amphibians are not much different from reptiles, this is far from the case. In reality there are not that many similarities. Amphibians have less perfect and developed organs than the class Reptiles; for example, the larvae of amphibians have gills, while the offspring of reptiles are already born with formed lungs. To be fair, it should be noted that newts, frogs, turtles, and even snakes may well coexist on the territory of the same body of water. Therefore, some do not see significant differences in these units, often getting confused about who is who. But fundamental differences do not allow these species to be combined into one class. Amphibians always depend on their habitat, that is, a body of water; in most cases they cannot leave it. With reptiles things are different. In case of drought, they may well make a short journey and find a more favorable place.

This is possible largely due to the fact that the skin of reptiles is covered with horny scales, which do not allow moisture to evaporate. The skin of reptiles is devoid of glands that secrete mucus, so it is always dry. Their bodies are protected from drying out, which gives them distinct advantages in dry climates. Reptiles are characterized by molting. For example, a snake's body grows throughout its life. Her skin is “wearing out.” They inhibit growth, so once a year she “resets” them. Amphibians have bare skin. It is rich in glands that secrete mucus. But in extreme heat, the amphibian can get heatstroke.

Ancestors of reptiles and amphibians

7. Amphibians have four sections of the spine, and reptiles have five. This has similarities between mammals and reptiles.

The largest reptiles that ever existed on earth are dinosaurs. They disappeared about 65 million years ago. They inhabited both sea and land. Some species were capable of flight. Currently the most are turtles. They are more than 300 million years old. They existed during the era of dinosaurs. A little later, crocodiles and the first lizard appeared (photos of them can be seen in this article). Snakes are “only” 20 million years old. This is a relatively young species. Although it is their origin that is currently one of the great mysteries of biology.

Reptiles (lat. Reptilia) are typical terrestrial animals whose main method of movement is crawling (i.e., reptiles on the ground). Some important features of their structure, as well as the biology of reptiles, made it possible for their ancestors to emerge from the water and spread widely across our planet. And today we will get acquainted with animals representing the class of reptiles. So, let's get acquainted.

Class reptiles: structural features

Reptiles have interesting features such as internal fertilization, as well as egg laying, which are rich in nutrients and covered with a fairly dense protective shell, which allows them to develop on land.

In all animals belonging to the class of reptiles, the body is covered with protective formations in the form of scales, forming a continuous cover. Their skin is always dry; evaporation of moisture through it is impossible, so they can live in dry places.

Reptile breathing is carried out exclusively by the lungs, which have a more complex structure compared to the lungs of amphibians. Such breathing became possible due to the fact that reptiles had a new section of the skeleton - the chest, formed by a number of ribs, which are connected on the dorsal side to the spine, and on the abdominal side - to the sternum. Thanks to special muscles, the ribs are mobile, which contributes to the expansion of the chest, as well as the lungs during inhalation and their collapse during exhalation.

Changes in the structure of the respiratory system also affected changes in blood circulation in all animals included in the class of reptiles. Most of them have a 3-chamber heart and, like amphibians, 2 circles of blood circulation. And the structure of the heart in reptiles is more complex than in amphibians. Its ventricle has a septum, at the moment of contraction of the heart, almost completely dividing it into the right (or venous) and left (or arterial) halves.

It is this structure of the heart and the different arrangement of the main vessels than in amphibians that contributes to a stronger separation of venous and arterial flows, due to which the body of reptiles is better supplied with more oxygenated blood.

The main vessels included in the systemic and pulmonary circulation are typical for all terrestrial vertebrates. But the main difference between the pulmonary circulation of amphibians and reptiles is that the latter have lost their skin veins and arteries, and the pulmonary circulation includes exclusively pulmonary vessels.

Science knows about 8,000 existing species of reptiles that live on all continents, with the exception of Antarctica. The class of reptiles includes the following orders: proto-lizards, scaly, crocodiles And turtles.

gecko

Reproduction of reptiles

In terrestrial reptiles, fertilization is internal. During the mating process, the male injects sperm into the female's cloaca, then they penetrate into the egg cells, where fertilization occurs. The eggs develop in the female’s body, and then she lays them on land, burying them in holes.

The outside of the egg is covered with a special dense shell. It contains the necessary supply of nutrients, thanks to which the development of the embryo occurs. After a while, from the eggs, not larvae emerge, as in amphibians, but individuals that are capable of independent life.

Turtle lays eggs

This order includes a real “living fossil” called tuateria(lat. Sphenodon punctatus), which is the only species preserved off the coast of New Zealand, on small islands. This lizard-like animal is very sedentary and leads a predominantly nocturnal lifestyle. The structure of the hatteria has features that make reptiles similar to amphibians: the bodies of its vertebrae are biconcave, and a notochord is preserved between them.

Gatteriya

Squad Squamate

Scaly (lat. Squamata) are also one of the orders of the class of reptiles such as chordates. This group includes suborders: lizards, chameleons, snakes and amphisbaenids (two-walkers). The detachment received this name because the bodies of all its representatives are covered with special horny scales or scutes.

A typical representative of scaly ones is quick lizard. Its external structure indicates that it is a terrestrial animal. There are no swimming membranes on her five-fingered limbs, and her fingers are armed with short claws, thanks to which her body crawls along the surface of the earth when moving, in contact with it, i.e. creeping (hence the name).

Xamelon

Squad of crocodiles

Aquatic vertebrate crocodiles (lat. Crocodilia) - are the largest and most highly organized predatory reptiles, adapted to an aquatic lifestyle. These representatives of the reptile class live in the tropics. All crocodiles are semi-aquatic predators, feeding on aquatic, semi-aquatic and watering animals.

Turtle squad

The turtle order includes about 328 modern species, belonging to 14 families and two suborders. They are widespread in both tropical and temperate climate zones, both in water and on land.

Turtles (lat. Testudines) differ from others by a durable, well-developed shell formed from bony plates, which are covered on the outside with a horny substance. It consists of two parts: an upper convex shield and a lower flat shield. The shell of turtles serves as the main protection against enemies.

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 in 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 flows 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 differs from the brain of amphibians by the greater development of the 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 relatively numerous group of 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. Recently, snake venom has been 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.

Amphibians (amphibians). This is a small group of the most primitive terrestrial vertebrates (Fig. 87). Depending on the stage of development, most of them spend part of their lives in water. The ancestors of amphibians were lobe-finned fish that lived in fresh, drying reservoirs.

Rice. 87. Amphibians: 1 - newt; 2 - spotted salamander; 3 - proteus; 4 - axolotl (ambistoma larva); 5 - pond frog; 6 - pipa; 7 - worm

In the larval stage (tadpoles), amphibians are very similar to fish: they retain gill breathing, have fins, a two-chambered heart and one circulation. Adult forms are characterized by a three-chambered heart, two circles of blood circulation, and two pairs of limbs. The lungs appear, but they are poorly developed, so additional gas exchange occurs through the skin (see Fig. 85). Amphibians live in warm, humid places, especially common in the tropics, where climatic conditions are suitable for them.

These are dioecious animals. They are characterized by external fertilization and development in water. From the eggs of a tailless amphibian, such as a frog, a tailed larva emerges - a tadpole with long fins and branched gills. As development progresses, the forelimbs appear, then the hind limbs, and the tail begins to shorten. Branched gills disappear, and gill slits (internal gills) appear. From the anterior section of the digestive tube, the lungs are formed, and as they develop, the gills disappear. Corresponding changes occur in the circulatory, digestive and excretory systems. The tail dissolves and the young frog comes to land. In tailed amphibians, the gills are retained much longer (sometimes throughout life), the tail does not dissolve.

Amphibians feed on animal food (worms, mollusks, insects), but larvae living in water can be herbivorous.

There are three groups of amphibians: caudate(newt, salamander, ambistoma), anurans(toads, frogs), legless, or caecilians(fish snake, worm).

Tailed amphibians most primitive. They live in and near water; their limbs, as a rule, are poorly developed. Some have feathery gills that last their entire lives.

The Ambystoma axolotl larva even begins to reproduce without reaching the adult stage. The most numerous are salamanders.

Worms- a very small family. They have no limbs, their body is elongated, resembling a worm or snake.

The most prosperous group is tailless amphibians. They have a short body and well-developed limbs. During the breeding season, they “sing” - they make various sounds (croak).

Reptiles (reptiles). Reptiles belong to terrestrial vertebrates. They adapted well to life on land and displaced many of their amphibian ancestors. Reptiles have a three-chambered heart. They begin to separate arterial and venous blood due to the appearance of an incomplete septum in the ventricle of the heart; The nervous system is better developed than that of amphibians: the cerebral hemispheres are much larger (see Fig. 85). The behavior of reptiles is much more complex than that of amphibians. In addition to innate unconditioned ones, they also develop conditioned reflexes. The digestive, excretory and circulatory systems open into cloaca- part of the intestine.

The body of reptiles is covered with scales. It is formed in the thickness of the skin - the epidermis - and protects the body from drying out. Some species shed their scales during the molting process (snakes, lizards). The lungs of reptiles are much larger and more voluminous than those of amphibians due to their cellularity.

Reptiles are dioecious animals. Their fertilization is internal. The female lays eggs covered with a leathery shell in the sand or in the soil in small depressions. Even among aquatic inhabitants, egg development occurs on land. Some species are characterized by viviparity.

Reptiles reached their greatest prosperity in the Mesozoic era, about 100-200 million years ago, which is why this era is called the era of reptiles. There was a huge number and variety of them: dinosaurs on land, ichthyosaurs in water, pterosaurs in the air. Among them were species of enormous size, as well as rather small forms, the size of a cat. Almost all of them went extinct about 70 million years ago. The cause of the extinction is still not fully understood. There are several hypotheses: a sudden sharp change in climate, the fall of a giant meteorite, etc. But all of them do not fully explain this mystery.

Currently there are four main groups: turtles, snakes, lizards and crocodiles (Fig. 88).

Rice. 88. Reptiles: 1 - steppe gecko; 2 - agama; 3 - long-eared roundhead; 4 - frilled lizard; 5 - gray monitor lizard; 6 - spectacled snake; 7 - rattlesnake; 8 - already

Characteristic feature turtles is the presence of a shell consisting of bone plates and covered with horny substance. Representatives of this group can live both on land and in water. Giant and elephant turtles (up to 110 cm long) are the largest of those living on land. They are common on the Galopogos Islands of the Pacific Ocean, Madagascar, and the islands of the Indian Ocean.

Sea turtles are much larger (up to 5 m) and have flipper-like legs. They live in water all their lives, but lay eggs on land.

Lizards very diverse. This is the most prosperous group. These include chameleons, geckos, iguanas, agamas, roundheads, monitor lizards and true lizards. Most lizards are characterized by an elongated body, a long tail, and well-developed limbs. Some (yellowbellies) have lost limbs, they resemble snakes.

U snake The main feature is a long, limbless body. These are crawling animals. All snakes are predators; they swallow prey whole or strangle it, squeezing it in the coils of their bodies. Venom glands (modified salivary glands) open through a duct at the base of the poisonous tooth. Snakes include: viper, viper, cobra, python, boa constrictor, as well as snakes - non-venomous representatives of this group.

Crocodiles Of all reptiles, they are closest to mammals. Their heart can be called four-chambered, there is a bony palate, and air enters through the nostrils into the back of the mouth. In terms of the structure of the oral cavity and the position of the tongue, they are closer to mammals than to other reptiles. These are quite large tailed animals that live in water, along river banks. On land they move slowly, but they swim well. Females lay lime-shelled eggs on land in small holes. They are characterized by caring for their offspring: the female protects the clutch and takes care of the cubs.

Reptiles live mainly in warm climates: tropics, subtropics, wet and dry places: deserts, swamps, forests. Their diet is also varied: plants, insects, worms, mollusks, and large individuals eat birds and mammals. All reptiles swallow food whole. Many species, feeding on agricultural pests (insects, rodents), bring great benefits to humans. Snake venom is used to prepare many medicines. Shoes and handbags are made from the skin of snakes and crocodiles, which previously led to the mass extermination of animals. Currently, many species are protected and grown on farms and nurseries.

| |
§ 62. Chordates. Fish§ 64. Birds

The class Reptiles (reptiles) includes about 9,000 living species, which are divided into four orders: Squamate, Crocodiles, Turtles, Beaked. The latter is represented by only one relict species - hatteria. Scaly animals include lizards (including chameleons) and snakes.

The sand lizard is often found in central Russia

General characteristics of reptiles

Reptiles are considered the first true terrestrial animals, since their development is not associated with the aquatic environment. Even if they live in water (aquatic turtles, crocodiles), they breathe with their lungs and come to land to reproduce.

Reptiles are distributed over land much more widely than amphibians and occupy more diverse ecological niches. However, due to their cold-blooded nature, they predominate in warm climates. However, they can live in dry places.

Reptiles appeared from stegocephalians (an extinct group of amphibians) at the end of the Carboniferous period of the Paleozoic era. Turtles appeared earlier, and snakes appeared later than everyone else.

The heyday of reptiles occurred in the Mesozoic era. At this time, various dinosaurs lived on Earth. Among them were not only terrestrial and aquatic species, but also flying ones. Dinosaurs went extinct at the end of the Cretaceous period.

Unlike amphibians, reptiles

improved head mobility due to a larger number of cervical vertebrae and a different principle of their connection to the skull;

the skin is covered with horny scales that protect the body from drying out;

breathing is only pulmonary; the chest is formed, which provides a more advanced breathing mechanism;

although the heart remains three-chambered, the venous and arterial blood flows are better separated than in amphibians;

pelvic kidneys appear as excretory organs (and not the trunk ones as in amphibians); such kidneys retain water in the body better;

the cerebellum is larger than that of amphibians; the volume of the forebrain is increased; the rudiment of the cerebral cortex appears;

internal fertilization; reptiles reproduce on land mainly by laying eggs (some are viviparous or ovoviviparous);

embryonic membranes (amnion and allantois) appear.

Reptile skin

The skin of reptiles consists of a multilayer epidermis and connective tissue dermis. The upper layers of the epidermis become keratinized, forming scales and scutes. The main purpose of scales is to protect the body from water loss. In general, the skin is thicker than that of amphibians.

The scales of reptiles are not homologous to the scales of fish. Horny scales are formed by the epidermis, i.e., they are of ectodermal origin. In fish, scales are formed by the dermis, i.e., they are of mesodermal origin.

Unlike amphibians, there are no mucous glands in the skin of reptiles, which is why their skin is dry. There are only a few scent glands.

In turtles, a bony shell is formed on the surface of the body (top and bottom).

Claws appear on the fingers.

Since keratinized skin inhibits growth, reptiles are characterized by molting. At the same time, the old integument moves away from the body.

The skin of reptiles grows tightly together with the body, without forming lymphatic sacs, like in amphibians.

Reptile skeleton

In comparison with amphibians, the spine of reptiles is no longer divided into four, but five sections, since the trunk section is divided into thoracic and lumbar.

In lizards, the cervical region consists of eight vertebrae (different species have from 7 to 10). The first cervical vertebra (atlas) is like a ring. The odontoid process of the second cervical vertebra (epistrophy) enters it. As a result, the first vertebra can rotate relatively freely around the process of the second vertebra. This gives greater head mobility. In addition, the first cervical vertebra is connected to the skull by one mouse, and not two like in amphibians.

All thoracic and lumbar vertebrae have ribs. In lizards, the ribs of the first five vertebrae are attached to the sternum by cartilage. The chest is formed. The ribs of the posterior thoracic and lumbar vertebrae are not connected to the sternum. However, snakes do not have a sternum and therefore do not form a rib cage. This structure is associated with the characteristics of their movement.

The sacral spine in reptiles consists of two vertebrae (and not one, as in amphibians). The iliac bones of the pelvic girdle are attached to them.

In turtles, the vertebrae of the body are fused with the dorsal shield of the shell.

The position of the limbs relative to the body is on the sides. Snakes and legless lizards have reduced limbs.

Digestive system of reptiles

The digestive system of reptiles is similar to that of amphibians.

The oral cavity contains a movable, muscular tongue, which in many species is forked at the end. Reptiles are able to throw it far.

In herbivorous species, a cecum appears. However, most are predators. For example, lizards eat insects.

The salivary glands contain enzymes.

Respiratory system of reptiles

Reptiles breathe only with their lungs, since due to keratinization the skin cannot take part in respiration.

The lungs are improved, their walls form numerous partitions. This structure increases the inner surface of the lungs. The trachea is long, at the end it is divided into two bronchi. In reptiles, the bronchi in the lungs do not branch.

Snakes have only one lung (the right one, and the left one is reduced).

The mechanism of inhalation and exhalation in reptiles is fundamentally different from that of amphibians. Inhalation occurs when the chest expands due to stretching of the intercostal and abdominal muscles. At the same time, air is sucked into the lungs. When you exhale, the muscles contract and air is pushed out of the lungs.

Circulatory system of reptiles

The heart of the vast majority of reptiles remains three-chambered (two atria, one ventricle), and arterial and venous blood are still partially mixed. But compared to amphibians, in reptiles the venous and arterial blood flows are better separated, and, therefore, the blood mixes less. There is an incomplete septum in the ventricle of the heart.

Reptiles (like amphibians and fish) remain cold-blooded animals.

In crocodiles, the ventricle of the heart has a complete septum, and thus two ventricles are formed (its heart becomes four-chambered). However, blood can still mix through the aortic arch.

Three vessels independently depart from the ventricle of the heart of reptiles:

It departs from the right (venous) part of the ventricle common trunk pulmonary arteries, which further divides into two pulmonary arteries leading to the lungs, where the blood is enriched with oxygen and returns through the pulmonary veins to the left atrium.

Two aortic arches extend from the left (arterial) part of the ventricle. One aortic arch begins to the left (however called right aortic arch, as it bends to the right) and carries almost pure arterial blood. From the right aortic arch originate the carotid arteries leading to the head, as well as the vessels supplying the girdle of the forelimbs with blood. Thus, these parts of the body are supplied with almost pure arterial blood.

The second aortic arch extends not so much from the left side of the ventricle, but from its middle, where the blood is mixed. This arch is located to the right of the right aortic arch, but is called left aortic arch, since at the exit it bends to the left. Both arches of the aorta (right and left) on the dorsal side are connected into a single dorsal aorta, the branches of which supply mixed blood to the organs of the body. Venous blood flowing from the organs of the body enters the right atrium.

Excretory system of reptiles

In reptiles, during embryonic development, the trunk kidneys are replaced by pelvic ones. The pelvic kidneys have long nephron tubules. Their cells are differentiated. Reabsorption of water occurs in the tubules (up to 95%).

The main excretion product of reptiles is uric acid. It is almost insoluble in water, so the urine is mushy.

The ureters extend from the kidneys and empty into the bladder, which opens into the cloaca. In crocodiles and snakes, the bladder is underdeveloped.

Nervous system and sensory organs of reptiles

The brain of reptiles is being improved. In the forebrain, the cerebral cortex appears from the gray medulla.

In a number of species, the diencephalon forms the parietal organ (third eye), which is capable of perceiving light.

The cerebellum in reptiles is better developed than in amphibians. This is due to the more diverse motor activity of reptiles.

Conditioned reflexes are difficult to develop. The basis of behavior is instincts (complexes of unconditioned reflexes).

The eyes are equipped with eyelids. There is a third eyelid - the nictitating membrane. Snakes have transparent eyelids that grow together.

A number of snakes have pits at the front end of their heads that receive thermal radiation. They are good at determining the difference between the temperatures of surrounding objects.

The organ of hearing forms the inner and middle ear.

The sense of smell is well developed. There is a special organ in the oral cavity that distinguishes odors. Therefore, many reptiles stick out their tongue, forked at the end, taking air samples.

Reproduction and development of reptiles

All reptiles are characterized by internal fertilization.

Most lay eggs in the ground. There is a so-called ovoviviparity, when the eggs are retained in the female’s genital tract, and when they emerge from them, the young hatch immediately. In sea snakes, true viviparity is observed, with the embryos developing a placenta similar to the placenta of mammals.

Development is direct, a young animal appears, similar in structure to the adult (but with an underdeveloped reproductive system). This is due to the presence of a large supply of nutrients in the yolk of the egg.

In the eggs of reptiles, two embryonic membranes are formed, which are not present in the eggs of amphibians. This amnion And allantois. The embryo is surrounded by an amnion filled with amniotic fluid. The allantois is formed as an outgrowth of the posterior end of the intestine of the embryo and performs the functions of the bladder and respiratory organ. The outer wall of the allantois is adjacent to the egg shell and contains capillaries through which gas exchange occurs.

Caring for the offspring of reptiles is rare; it consists mainly of protecting the masonry.