Reptiles are the ancient inhabitants of our planet. They differ in classes and types, each of which has distinguishing characteristic. This article will introduce the reader to the environment in which and how the reptile embryo develops.

General information

Reptiles are those that have adapted to life in land conditions. These first terrestrial are characterized by the following features:

  • Reproduction occurs by eggs and on land.
  • Breathing is done with the lungs. Its mechanism is of a suction type, that is, when the reptile breathes, the volume of the chest changes.
  • The presence of horny scales or scutes on the skin.
  • Skin glands are absent in almost all reptiles.
  • Separation of the ventricle of the heart by partitions is complete and incomplete.
  • The reptile skeleton and musculature received progressive development due to an increase in their mobility: the limb belt became stronger and their position in relation to the body and to each other changed. The spine was divided into different sections, and the head became more mobile.

Reptiles today are represented by scattered remains of reptiles that lived on the planet many thousands of years ago. Now there are six thousand species, almost three times more than amphibians.

Reptiles living today are divided into the following orders of reptiles:

  • beakheads;
  • scaly;
  • crocodiles;
  • turtles.

The first species is represented by the only representative - the hatteria, which has resemblance with a lizard, but its structure is different primitive features. The habitat of the hatteria is New Zealand.

crocodiles

This order includes the following types of reptiles: caiman, gharial, nile crocodile. aquatic lifestyles are characterized by high organization, the presence of a four-chambered heart and a septum that separates the toes of the hind legs. Eyes raised high above the muzzle help crocodiles monitor prey.

Females lay eggs on the shore near water bodies, but in a high, unflooded place. Nests are built from nearby materials. Gharials use the sand where they bury their eggs. Tropical crocodiles mix grass and fallen leaves with earth to build a nest.

The female is able to lay up to 100 eggs, which are fertilized by different partners. Laying occurs at night, a few weeks after the mating process. The eggs are large, similar in size to duck eggs.

And where the embryo develops occurs in the egg, which is in the mother's body. During laying, an embryo is already developing in it. The female is always near the nest, protecting future offspring from predators. Three months later, little crocodiles hatch.

Turtles

Turtles belong to this detachment: red-eared, marsh and steppe. Their body is covered with a bony shell, fused with the vertebrae and ribs. The jaws of turtles do not have teeth. Air enters the lungs in the same way as in amphibians.

Turtles build nests before laying. Aquatic reptiles - in the sand on the shore of reservoirs, and land - on the ground, in a dug hole. They no longer show any concern for their offspring.

Many species of turtles mate in April-early May. Only next spring can be expected from birth adapted to life without parents.

Orders of reptiles: scaly

These include lizards:

  • viviparous;
  • yellowbell;
  • iguana.

Almost all of them, except for the yellowbell, have four limbs for movement and eyes protected by eyelids. The eyelids of the reptiles of this order are mobile.

Egg laying time is May-June. The animal acquires a mink or a hole of small depth and places eggs there. They are from 6 to 16 pieces. Egg large. Inside is the yolk, which contains food reserves for the embryo. In lizards, the egg shell is soft, in crocodiles and turtles it is hard.

Snakes are snakes, vipers, muzzles. They are legless reptiles, when moving, their body bends. The structure of reptiles is distinguished by a long spine of the body and the absence of a chest. Snakes have one lung. The shell of the eyes is formed by fused eyelids.

Reptiles have the ability to swallow large prey. This is achieved by movably connected lower jaws. front teeth poisonous snakes endowed with a channel through which the poison enters the victim.

Snakes reproduce sexually. On this basis, they are viviparous and oviparous. In the natural environment, reproduction is seasonal. The gestation period in time for snakes is different. In snake families - 48 days, in pythons - from 60 to 110.

By the end of pregnancy, snakes begin to build nests. Their locations can be small trees, fallen trunks, rodent minks, anthills. The clutch consists of 3-40 eggs. They have an elongated or oval shape - it depends on the type of reptiles.

Almost all types of snakes do not care about their offspring. The exceptions are the four-lane snake, silt snake and King Cobra. They guard the eggs until the snakes appear.

reproduction

It takes place on dry land. Fertilization in reptiles is internal. Their offspring are born in three ways:

  1. Egg production. This is the case when the question of where the reptile embryo develops can be answered - in the egg. natural environment for him are the genital tract of the mother. It receives nutrition from the egg, after the deposition of which the cub develops from the embryo.
  2. Live birth. It is not inherent in all reptiles, but only certain types sea ​​snakes. Where does the reptile embryo develop? It happens in the mother's body. From it he receives everything necessary for his development.
  3. incubation method. It is used to increase the number of some kind of reptile. From turtles and crocodiles, females will be born if the temperature in the incubator is above 30 ° C, and males - if it is lower.

And where does the embryo of reptiles develop in some vipers and viviparous lizards? Here, the eggs in the mother's oviduct are very long. A cub is formed in them, which is immediately born from the mother's body or hatches from an egg after its laying.

reptile eggs

Reptiles evolved on land. Adapting to the land environment, their eggs were covered with a fibrous shell membrane. Modern lizards and snakes have the most primitive forms of egg shells. And in order for the eggs not to dry out, their development takes place in moist soil.

Dense shells perform not only a protective function. They are the first sign of adaptation of eggs for development on land. The stage of larval formation falls out, due to which the nutrient content increases here. Large reptile eggs.

The second stage in the adaptation of eggs for survival and further development in a land environment is the isolation of the protein shell from the walls of the oviduct. It stores the water supplies needed by the embryo. Crocodiles and turtle eggs are covered with such a shell. They have a fibrous shell replaced by a calcareous one. Water supplies do not pass through it, and with such protection from drying out, embryos can develop under any weather conditions.

Reptiles are dioecious and may differ in secondary sexual characteristics. Often these differences are small or even non-existent. Sometimes males are only larger than females, as is usually the case in species of the genus Lacerta, with the exception of the viviparous lizard (Lacerta vivipara), where the female is larger, which is associated with the development of young in the body. The same is true of viviparous snakes. In males of many species of lizards, snakes and turtles, the tail is swollen at the base. It depends on what is in the contracted state of the double cumulative term. In turtles, the sexes can be distinguished by the appearance of the pectoral shield - in males it is concave, while in females it is flat or convex. In other cases, the meaning of secondary sex differences is unclear; for example, the difference in the number of scutes in many snakes, the great narrowness of the neck. Many female snakes have keeled ridges on their dorsal scales during sexual activity. This sign serves to irritate the female during mating.
The meaning of the difference in coloration seen in some reptiles is unclear. For example, male Cistudo turtles have red eyes, while females have brown eyes. In the bloodsucker (Calotes versicolor), the body color of the male can change at will. Sometimes it is all brilliant red with black spots; in some cases, the color of the skin changes only on the head, in others - on the whole body, not excluding the tail. The female remains monochromatic. However, not always a bright color is associated with the floor. Further, the sexes may differ in the presence of numerous outgrowths on the head, for example, in some species of chameleon, where the male develops horns similar to those of a rhinoceros. This also includes crests on the back of the head and on the back of many iguanas. The so-called femoral pores in male lizards are more strongly developed. In some reptiles, males also differ in voice, and it is possible that it serves to attract females. In geckos and alligators, the voice definitely serves to attract females during the breeding season.
The ratio of the number of individuals of both sexes is not always the same. In snakes, it happens 1:1, 1:3, 1:4, 4:11. Sometimes in the same species, the sex ratio is different in different areas. Thus, the Chinese form of Dinodon septentrionale in the entire habitat gives the figures 3:13, and in South Asia - 0:8. The smaller number of males apparently comes from the greater mortality of the latter.
On the other hand, sometimes there is a temporary predominance of males. Yes, in Central Asia at the end of summer (August), only male snakes are found, females are absent, and it is not known where they are at this time.
During the mating season, there is often a fight between males. Crocodiles ferociously pursue each other at this time and enter into fights. The same is observed in lizards; some of them change color during a fight. During the breeding season, snakes gather in large numbers, coil into balls and hiss until they connect with the female, after which sexual arousal passes.
In reptiles during the mating season, there are often observed love games. Male lizards bite females to force them to mate; the same has sometimes been observed in turtles, where the males emit a whistling tone, crawl after the female, bite her on the head and push until she becomes excited. After mating, the excitement disappears and the individuals disperse. Only rarely is there a long stay of the male and female together. The tortoise Testudo polyphemus has been observed to live in pairs in burrows. There are several more such examples.
Most reptiles lay eggs, others give birth to live young. Eggs are covered with a hard shell or similar to parchment. The first state, typical of tortoises, is apparently the more primitive. Among lizards, eggs in the shell are found only in geckos. But their shell hardens only gradually, taking in carbon dioxide from the air. In snakes, eggs with shells are no longer found. In most snakes, eggs are sticky when laid and stick to objects they come into contact with. They often vary both in size and shape.
The number of eggs is from 2 to 150. Both the number of eggs and the method of reproduction show signs of adaptation to conditions. outside world and is conditioned by them. The largest (up to 400 per year) egg production is observed in sea ​​turtles. This is apparently due to the fact that young turtles are little adapted at first to life in the water: they swim, but do not sink, are washed ashore and serve as prey for fish and birds. Excessive body weight gain from such a mass of eggs and too much nutrient requirement are avoided by egg laying in batches and shell loss. A very small number of eggs can also be seen as an adaptive phenomenon. Turtles that breed in China in cultural areas where animals, their enemies, are almost entirely absent, lay minimal amount eggs (2). Geckos lay more eggs in the south of Asia than in the north, which can be connected with the presence of their enemy, the tree snake - Chrisopelea ornata. Climbing forms lay fewer eggs than ground forms.
Eggs are laid either in specially dug holes, or among moss and foliage, in wet warm places. The US snake Diodophys punctatus lays its face in a variety of places: in the mud thrown out of the quarry, in the dust under a rotten tree, in a stump, under a stone, in the passages of ants with dust - generally in moist, but not wet places exposed to the sun. In 95% of cases, this is a hole in the ground. Usually the female leaves the eggs to their fate. Only some snakes and crocodiles behave differently; some American forms of the latter make real nests for their eggs during wet places. This nest consists of a layer of plants on which eggs are laid, again then covered with plants. Due to the decay of plants in the nest, such heat that the nest is smoking. This heat serves for the speedy development of juveniles.
In Madagascar, the female crocodile guards the nest until the juveniles develop. The female supposedly recognizes this by the special sound that young crocodiles make in the egg, helps them dig out of the sand and immediately leads them to the water. The female caiman behaves in the same way. African crocodiles do not appear to guard their nests. North American alligators lay a nest near the habitat of the female, which rushes at everyone who approaches her, and in this way guards the nest. Here we have an interesting series of gradual complication of instinct, showing how it could arise. As noted in the systematic part, dinosaurs laid their eggs in nests.
Some females large snakes(pythons, for example), after laying their eggs, they lie on them in such a way that they form a flat vault above them, inside which the temperature is 10-12 ° Celsius higher than the ambient, which contributes to the development of eggs. So does the Ancistrodon muzzle. At this time, the female does not take any water or food and protects the eggs from any encroachment on them. This can be seen and care for offspring. A lizard called the teyu (Tupinambis teguixin) digs out termite nests and lays its eggs there. Young lizards emerging from the latter immediately find their food in the form of termites.
Many reptiles give birth to live young and are viviparous. Cubs break through the thin shells of eggs while still in the mother's body or immediately after birth. It is more correct to call them not viviparous, but ovoviviparous. Ovoviviparous forms are known only in crocodiles and turtles. We meet this type of reproduction in many lizards, especially those living in the mountains, in many gigantic American snakes, sea snakes, vipers, in various snakes and others. Only in a few reptiles do we find real viviparity, when the nutrition of the embryo in the mother's body occurs with the help of the blood vessels of the yolk sac, which enter into connection with the vessels of that part of the oviducts that plays the role of the uterus. Fossil ichthyosaurs (Ichtyosauria) were also viviparous. This feature stood in them, as in sea snakes, in connection with the transition to pelagic life in the sea. From the structure of the limbs of ichthyosaurs, it can be judged that ichthyosaurs never went ashore, but led a life similar to that of modern whales.
The primary form of reproduction in reptiles is reproduction by laying eggs. From it a series of transitions leads to ovoviviparity and further to viviparity. This transition is facilitated in reptiles by the circumstance that, in the event of circumstances unfavorable for laying eggs, the latter can be delayed for weeks and the egg remains in the body. The conditions under which viviparity arose in reptiles as an adaptation to them can be named as follows: a) purely aquatic life (Hydrophis); in species of large oviparous genera (Natrix, Elaphe), passing to life in water (Natrix annularis, Elaphe rufodorsata), viviparity develops; b) distribution in cold areas, at the cold borders of their vertical and horizontal range, where night temperatures are too low for eggs and require protection in the mother's body (Phrynocephalus from the Central Asian highlands, Lacerta vivipara, Vipera herus, Ancistrodon in Asia). Living in Tibet at an altitude of 4200 m, but near hot springs, Natrix view lays eggs; c) underground life (Scincus officinalis, Echis carinata, Vipera ammodytes); d) life on trees and shrubs (Dryophis, Boiga). If any group of reptiles from the most ancient geological times lives in conditions that cause viviparity, then the latter is characteristic of all members of the group. So, in Scincidae, skinks, viviparity is a sign of the whole group.
The duration of incubation in reptiles is different. It depends on the conditions in which the eggs develop; on average, snakes are 2 to 3 months old. Hatching from an egg can last many hours, up to a day. Not all eggs hatch at the same time. It takes 2-3 days for snakes to emerge from all eggs in the clutch.
After leaving the egg or being born alive, reptiles grow quickly, but reach sexual maturity very slowly: for example, Chinese snake (Natrix piscator) in the 4th year, tree snake (Dryophis) - at the end of the 2nd year, male pythons - at the end 3rd and female - 4th year. But reptiles reach a deep old age. Regarding turtles, for example, cases are known when they survived in captivity up to 54 years. The giant tortoise (Testudo sunieri) has reached the age of 150 years in captivity. There are cases when turtles lived up to 250 years. Crocodiles also reach a great age. Reptiles, apparently, are not very susceptible to diseases, although parasites from the protozoa type are often found in the blood of reptiles. It must be assumed that in a natural setting, most reptiles die not from old age and disease, but from violent death or from some external unfavorable causes. However, there is a suspicion that lizards are carriers and transmitters of certain diseases (for example, leishmaniasis).

Anatomy, morphology and ecology of reptiles

9. Sex organs and reproduction of reptiles

The sex glands lie in the body cavity on the sides of the spine. testicles - paired oval bodies. Through the appendages, representing the preserved part of the trunk kidney (mesonephros) and containing numerous tubules, the testes are connected to seed tubes , which are the ducts of the mesonephric kidney, i.e., Wolfian channels. The right and left vas deferens open into the corresponding ureters at their confluence with the cloaca.

One of the adaptations for terrestrial existence is internal fertilization. In this regard, the males of all reptiles, except for the tuatara, have special aggregative organs ; in crocodiles and turtles it is unpaired, and in lizards and snakes it is paired outgrowths of the posterior wall of the cloaca, which turn outward during fertilization (Fig. 14).

Rice. 14. Protruding copulatory sacs of a male lizard

Paired ovaries have the appearance of granular oval bodies. Oviducts serve as Mullerian channels. They start shimmering funnels located near the ovaries, and open into the cloaca.

Fertilization occurs in the upper part of the oviduct. The secretions of the secretory glands of the middle part of the oviduct form around eggs(yolk) protein coat , poorly developed in snakes and lizards, and powerful in turtles and crocodiles (Fig. 15).

Rice. 15. Scheme of the development of egg membranes in the Central Asian tortoise during the passage of the egg through the oviduct: 1 - egg, 2 - protein shell, 3 - fibrous shell, 4 - shell shell

From the secret secreted by the cells of the walls of the lower part of the oviduct (uterus), the outer shells are formed.

Embryonic development goes the typical way for amniotes. Are formed germinal membranes - serous and amnion - allantois develops. The water necessary for the formation of amniotic fluid and for the normal development of the embryo in lizards and snakes is obtained due to the oxidation of fats. yolk(metabolic water) and absorption of moisture from the external environment, and in turtles and crocodiles with a dense shell - due to metabolic water and the water supply in a powerful protein shell. The minimum soil moisture at which eggs with a fibrous shell can develop normally is about 2.5%, and in the presence of a shell - even up to 1%. Different types lay eggs in the soil of a certain moisture content that meets the properties of the egg membranes and the needs of the developing embryo.

Most reptiles bury their eggs. into the ground in well-heated places; some species lay their eggs in heaps of plant debris or under rotting stumps, using the heat generated during decay. Some crocodiles dig holes and cover their eggs with plant debris; females stay at the nest and guard the clutch. Guard masonry and some large lizards(lizards, etc.). Python females wrap their bodies around the egg laying, not only protecting it, but also heating it: in such a “nest” the temperature is 6-12 ° C higher than the environment. In crocodiles, the female guarding the nest digs out the masonry when the cubs hatch, making it easier for them to reach the surface; in some species, the females guard the young even during the first period of their independent life. Females of some skinks and spindles also do not leave the clutch, protecting them from enemies.

In a relatively small number of modern squamous species (order Squamata), there is ovoviviparity or less often live birth. The common viper - Vipera berus, viviparous lizard - Lacerta vivipara, spindle - Anguis fragilis fertilized eggs delayed in the genital tract of the female, passing through all stages of development there; the embryos hatch immediately after oviposition.

Oviparous also characteristic of sand boas - Eryx, sea snakes, some snakes and lizards. Oviparous production developed from cases of temporary retention of eggs in the oviducts noted for a number of species of lizards and snakes. So, in ordinary snakes - Natrix natrix, the duration of egg development during external environment may vary between 30-60 days, depending on how long they were in the mother's body. Some species switch to ovoviviparity only under certain conditions. Tibetan roundhead - Phrynocephalus theobaldi at an altitude of 2-3 thousand meters above sea level lays eggs, and above (4-5 thousand meters) - ovoviviparous. The viviparous lizard - Lacerta vivipara in the south of its range (France) lays eggs, and its northern populations are ovoviviparous.

True live birth known in some skinks (Chaleides, Lygosoma, Taliqua). They lack the outer shell of eggs, embryonic shells developing fetus adjoin to the walls of the uterine oviduct; by osmosis and diffusion, oxygen and nutrients from the mother's bloodstream enter the circulatory system of the embryo. Some snakes (already - Thamnophis sirtalis, etc.) and lizards form a real placenta: outgrowths of the serous membrane and allantois of the embryo are introduced into the mucous membrane of the uterine part of the mother's oviduct. Due to the close proximity of the blood vessels of the female and the embryo, the supply of oxygen and nutrients to the embryo is facilitated. Development in the mother's body provides the best temperature conditions for embryogenesis, and therefore both forms of viviparity predominate. in the north and in the mountains. Viviparity is sometimes associated with an arboreal and aquatic lifestyle: some chameleons and water snakes have it.

Puberty occurs at different times: in crocodiles and many turtles at the age of six, ten, in snakes more often in the third or fifth year of life, in large lizards in the second or third year, and in small ones - in the ninth or tenth month of life.

Fertility reptiles are much lower than the fertility of amphibians. Its decrease is associated with a reduction in embryonic mortality due to the sheltered placement of clutches, and in a few species, their protection and ovoviviparity. Important role plays and direct development, without metamorphosis and change of habitats; the latter is always accompanied by high mortality. Reduces the death and high mobility of hatchlings and their secretive way of life. Clutch size rarely exceeds one hundred eggs (some crocodiles, large turtles and snakes); more often it is limited to 20-30 eggs. Small species of lizards lay only 1-2 eggs, but several times a season.

In some lizards (Caucasian rock lizards - Lacerta armenica, Lacerta dahli, Lacerta rostombecovi, North American teiids - Cnemidophorus, possibly in some of the agamas and in the gecko - Hemidaetylus turcicus), it has been established or assumed parthenogenetic reproduction, i.e., the development of laid unfertilized eggs (I. S. Darevsky). Populations of these species are only from females. Parthenogenesis in lizards is usually observed in peripheral populations, i.e., on the borders of the range. In such a situation, the existence of a same-sex population of only females becomes advantage, since it allows the limited food reserves to be spent most efficiently, only on the individuals producing cubs. This can be supported by natural selection, but it represents a dead end of evolution, since it excludes panmixia and the recombination of genes associated with it, which sharply limits variability.

Finally, a surprising case is found in snakes hermaphroditism(bisexuality, or intersexuality). The snake, the island botrops Bothrops insularis, lives only on about. Queimada Grande with an area of ​​​​only 3 km (60 km from Santos in Southern Brazil), most females simultaneously with the ovaries have male copulatory organs and fully developed testes. Apparently, in a small island population, such intersexuality allows you to increase the rate of reproduction without increasing the number of inhabitants. It has been noted that over the past 50 years, the proportion of males in the population has decreased.

Ecological Center "Ecosystem" purchase color identification table " Amphibians and reptiles of central Russia"and a computer determinant of reptiles (reptiles) of Russia and the USSR, as well as others teaching materials on animals and plants of Russia(see below).

On our website you can also find information on anatomy, morphology and ecology of reptiles:

703-01. Are judgments about the signs of reptiles correct?
1. The body of reptiles is covered with thin bare skin that secretes mucus.
2. In snakes and some lizards, the eyelids have grown together and become transparent.
A) only 1 is correct
B) only 2 is true
C) both statements are correct
D) both statements are wrong

Answer

703-02. Reptiles, unlike amphibians, are real land animals, since they
A) have two pairs of lever limbs
B) have a developed nervous system
C) adapted to terrestrial reproduction and development
D) in addition to skin respiration, pulmonary respiration is carried out

Answer

703-03. Fish and reptiles have a similar structure
A) a skeleton
B) circulatory system
B) digestive system
D) respiratory system

Answer

703-04. What feature provides the ability of reptiles to reproduce on land?
A) protection of offspring
B) cold-bloodedness
B) the structure of the egg
D) the number of eggs laid

Answer

703-05. The transition of animals to reproduction on land became possible with the advent of
A) asexual way breeding
B) external fertilization
B) sexual reproduction
D) internal fertilization

Answer

703-06. What respiratory organs are typical for the depicted animal?

A) gills
B) lungs
B) air sacs
D) trachea

Answer

703-07. Ancient reptiles were able to finally switch to a land-air lifestyle because they
A) there was concern for offspring
B) the cells of the body were supplied with mixed blood
B) had an internal bone skeleton
D) internal fertilization appeared

Answer

703-08. What organ system of reptiles is shown in the figure?

A) circulatory
B) respiratory
B) digestive
D) nervous

Answer

703-09. Are the following statements about reptiles correct?
1. Female reptiles lay fertilized eggs with a high yolk content.
2. The development of reptiles occurs with transformation.
A) only 1 is correct
B) only 2 is true
C) both statements are correct
D) both statements are wrong

Answer

703-10. The peculiarity of the structure of the skin in reptiles is
A) total absence skin glands
B) the presence of bone scales
B) the presence of mucous glands
D) the presence of sweat and sebaceous glands

Answer

703-11. Live birth in some species of lizards arose as an adaptation to life in
A) hot climate
B) hollow trees
B) northern latitudes
D) aquatic environment

Answer

703-12. Which of the signs that arose in the ancestors of reptiles allowed reptiles to completely switch to a land way of life?
A) five-fingered limb
B) three-chambered heart
B) the shell of an egg
D) bone skeleton

Answer

703-13. What is characteristic of the animal shown in the picture?

A) gill breathing
B) reproduction in water
B) two-chambered heart
D) fluctuating body temperature

Answer

703-14. In the event of a decrease in air temperature, terrestrial reptiles
A) begin to eat heavily
B) migrate to more favorable areas of the earth
C) do not change their behavior
D) temporarily hibernate

Answer

703-15. Are the judgments about the reproduction of reptiles correct?
1. Fertilization in reptiles is external.
2. Larvae of snakes and lizards do not look like adult animals.
A) only 1 is correct
B) only 2 is true
C) both statements are correct
D) both statements are wrong

Answer

703-16. Indicate what adaptations for reproduction on land arose in reptiles in the process of evolution.
A) external fertilization and a small supply of nutrients in the egg
B) internal fertilization, a large supply of nutrients and dense shells in the egg
C) external fertilization, the absence of a dense shell in the egg
D) a small supply of nutrients in the egg, internal fertilization

Answer

703-17. Are judgments about the life processes of reptiles correct?
1. Breathing of reptiles is carried out with the help of skin and lungs.
2. The organs of reptiles receive blood richer in oxygen than that of amphibians.
A) only 1 is correct
B) only 2 is true
C) both statements are correct
D) both statements are wrong

Yu.Dmitriev

There are still many white spots in the history of reptiles, or reptiles, but we already know the main thing. It is believed that land pioneers - amphibians - appeared at the junction of the Devonian and the Carboniferous period. After leaving the water and acquiring some adaptations for life on land, the first amphibians, apparently, felt good: the climate was even, warm, the air was humid, and there were enough reservoirs. But at the end of the Carboniferous period, significant changes took place on Earth, the climate changed: in a number of places the globe it became hot and dry, at the same time, as evidenced by the annual rings on the trunks of fossil trees, severe and cold winters began. Naturally, the vegetation has also changed. The happy and carefree life of the first amphibians was over. It was necessary to adapt to the new conditions of existence. Part of the amphibians could not adapt and died. Others remained faithful to a semi-terrestrial, semi-aquatic lifestyle and gradually gave rise to modern amphibians. Still others took a decisive and final step on land and remained to master new living conditions.

The most ancient reptiles, extinct, of course, appeared in the middle of the Carboniferous period. And in mesozoic era, which began about 230 million years ago and lasted a little over 160 million years, the ancient reptiles experienced a rapid flowering and reached an unprecedented diversity. Mesozoic means "life in between" in Greek. But it is often called the "age of reptiles", because it was at this time in the history of the Earth that reptiles - the first truly land inhabitants of our planet - finally conquered it, became the full owners of the land. They were no longer so dependent on climatic and weather conditions, they were no longer tied to a specific place of residence - close to a reservoir, they had many advantages over amphibians. And not least due to the fact that they were able to lay eggs that had never been seen before.

Of course, a new miracle of nature - a reptile egg - did not appear immediately, of course, it took millions of years to create and improve it. But in the end, an egg in a dense "package", which was not afraid of drying out, appeared.

We already know that amphibian eggs can only develop in water. In a humid environment, they are protected from drying out. From this environment, the embryos receive the trace elements necessary for successful development. In addition, it is in water or a humid environment that the larval stage of amphibian development takes place. But what if the egg, that is, the egg of an amphibian, is out of water, out of a humid environment? The embryo of an amphibian will not develop in it. What about reptiles? They are all wrong. The egg of reptiles creates all the necessary conditions for the normal and successful development of a new creature. The embryo must be in the aquatic environment for some time. And the egg gives him this opportunity: under the shell there is a tiny "Lake". The fetus must be fed. And the egg gives him everything he needs. In other words, the new egg - the egg of reptiles - was already so perfect and adapted for terrestrial living conditions that for many, many millions of years it did not require significant changes. Even modern birds originating from the ancient winged lizards, it is not much different from the egg of the first reptiles. First of all, this applies to eggs that are shelled with surprisingly perfect material, which both protects the embryo from drying out, and protects against mechanical damage, and allows the embryo to breathe, and so on. In fairness, it must be said that not all reptiles have such eggs. There are also less perfect ones covered not with a shell, but with a leathery substance.

Shelled eggs evaporate up to 10 - 15% of moisture, reptile eggs, dressed with a leathery shell, up to 25%. So reptiles still have to hide their clutches from direct sunlight, looking for a more humid environment.

The independence of reptiles from the presence of water bodies allowed them to spread widely around the planet, to master not only unfavorable for life, but also very harsh areas. Adult animals have learned, adapted to endure harsh conditions. However, eggs, even if they are enclosed in such an ideal "package" as a shell, are less resistant to harsh climatic conditions. So some reptiles "found a way out" in the fact that the eggs linger in the mother's oviducts. (Reptiles, as it were, have expanded and improved this method of preserving eggs, which has already been outlined in some amphibians.) In some reptiles, such a delay is so long that not a “full-fledged” egg with a developed embryo is born, but an almost fully formed cub covered with thin film - the remains of the egg shell. "Newborn" immediately breaks it and immediately begins an independent life.

This phenomenon is called ovoviviparity, and not live birth, as it is sometimes erroneously called. After all, the egg in this case only lingers in the oviduct, the embryo develops autonomously, receiving everything it needs not from the mother, but from the same egg. True, among reptiles there are also real livebearers - their embryos really receive during development nutrients from the mother's body. But such cases are quite rare.

Most reptiles lay eggs. This brings reptiles closer to amphibians. But at the same time, it is the egg that is his fundamental difference- sharply separates reptiles and amphibians. Moreover, it led to further fundamental changes, as it made it possible for reptiles to become completely independent of water, to move away from it at a considerable distance. And this, in turn, could not but affect the structure of the respiratory system.

Amphibians, as we know, get a significant part of their oxygen through their skin. But at the same time, unprotected bare skin leads to a large loss of moisture. For reptiles in a hot dry climate, and even far from water, this could be fatal. And they completely "refused" skin breathing. Their skin glands disappeared, the skin was covered with scales, bone plates or other protective devices. The loss of skin respiration was closely associated with fundamental changes - in comparison with amphibian ancestors - of the respiratory apparatus. Amphibians, as a rule, do not have ribs, and if they do, they are very short and imperfect. In any case, they do not have a chest suitable for breathing. Therefore, when breathing (not skin), they first draw air into the mouth, then, "plugging" the mouth opening, "push" it into the throat.

Reptiles already have ribs rib cage. And this gave them the opportunity not to swallow air, but to inhale it.

The circulatory system has changed, the heart has changed. The skeleton and muscles have changed. First of all, because they have changed - and very much! - limbs of reptiles.

Loop-finned fish to a lesser extent, amphibians to a greater extent, but both of them still took their first steps on earth. Reptiles marched across the planet confidently. For this, appropriate means of transportation were also needed. And the reptiles got them. True, later part of the reptiles lost this great conquest. And because of them, the whole class began to be called reptiles, or reptiles.

The first travelers who saw giant tortoises were amazed not only by their size, but also by their "leggedness". Indeed, the slow-moving giant tortoise seems to be moving on huge pillars. The famous American zoologist Archie Carr told how he was surprised when he first saw a crocodile striving for water. The crocodile suddenly turned out to be not only very agile, but also very long-legged. Many lizards move perfectly on their slender long legs, and there are those that, in case of danger, run - and very quickly - only on their hind legs.

But even the reptiles that lost their legs did not lose the ability to actively move around. Suffice it to recall short-legged lizards and snakes, which are much more agile and generally much better adapted to movement than amphibians.

So, the reptiles firmly set foot on land. They also, like amphibians, lay eggs. But amphibians, even if they live on land all the time, lay their eggs mainly in water or in a humid environment. And reptiles, even if they spend most of their lives in the water and are firmly connected with it, lay their eggs only on land.

Reptiles, although they do not have a constant body temperature, are still less dependent on the environment: their skin is covered with protective devices, air humidity is not so important for them, they are not so afraid of heat, dryness, and direct sunlight. Moreover, moving now to the shade, then to heated places, they to some extent maintain a relatively constant temperature of their body.

Reptiles have many "new acquisitions" that put them among the representatives of the animal world at a higher stage of development compared to amphibians.

However, among the reptiles themselves there are a lot of differences. And in appearance, and in the internal structure, and in behavior, and in the way of life. It `s naturally. After all, they happened in different times and from different ancestors. And in the process of development, changes continued: the loss of legs in some, for example, a change in the lungs of others (in most snakes, only one lung is developed, the other is underdeveloped or absent altogether, the same is true for some lizards).

Some reptiles about 300 million years ago began to return to the water again. Perhaps they were prompted by the same reasons that once forced their ancestors to leave the water: the land was already sufficiently populated, competition appeared, enemies appeared. The sea for such "settlers" was a relatively new and relatively untouched world. 100 million years ago there were already many reptiles in the sea. Of course, they began to differ from terrestrial ones - they regained fins, tails, lost or almost lost their neck. But again they did not turn into fish. They still had lungs, like those of land animals, their blood circulation did not become "fishy", and so on.

Yes, reptiles are very diverse. Nevertheless and common features they have a lot. Therefore, they are combined into one class. And since reptiles are still very different, four orders are distinguished in this class.

The order of beakheads has only one (!) species.

The order of turtles now includes about 250 species.

A detachment of crocodiles is the direct descendants of the inhabitants of the Mesozoic. Crocodiles are now known about 25 species.

And, finally, a detachment of scaly ones. These are the most numerous and most diverse reptiles. They now number about 600 species. Scaly include all snakes, lizards, chameleons.

These are the reptiles that now live on our planet. More precisely, known to us now. Surely there are many still unknown to science.

Bibliography

For the preparation of this work, materials from the site were used.