Nile crocodile direct or indirect development. How much does a crocodile weigh? The smallest and largest crocodile. How long do crocodiles live. Ridged, or marine

CROCODILE
Squad CROCODILE(Crocodylia) - a family of reptiles. There are three species in Africa. The narrow-nosed crocodile is endemic to Africa. It lives in all major rivers of West Africa, Lake Tanganyika and in the east of the mainland. Blunt (or dwarf) crocodile - in central Africa. Nile crocodile - on the mainland and some islands.

Crocodiles occupy a special position among modern reptiles, being closer relatives of the extinct dinosaurs, which survived almost 60 million years, and modern birds, than other reptiles of our time. A number of features of the organization of crocodiles, and first of all the perfection of the nervous, circulatory and respiratory systems, allows us to consider them the most highly organized of all living reptiles. The evolution of crocodiles, starting from the appearance of this group about 150 million years ago, went in the direction of ever greater adaptation to the aquatic lifestyle and predation. The fact that crocodiles have survived to our time is often explained by their life in various fresh water bodies of the tropical and subtropical zones, that is, in places whose conditions have changed little since the appearance of crocodiles.

The general body shape of a crocodile is lizard-like. They are characterized by a long, laterally compressed, high tail, membranes between the fingers of the hind limbs, a long muzzle and a head flattened in the dorsal-abdominal direction. There are five fingers on the forelimbs, four on the hind limbs (there is no little finger). The nostrils, located at the front end of the muzzle, and the eyes are raised and located on the upper side of the head, which allows crocodiles to stay in the water near its surface, exposing only their eyes and nostrils to the air. External auditory openings are closed with movable valves that protect the eardrums from mechanical damage when immersed in water. The body, tail and limbs of crocodiles are covered with large, regular-shaped horny shields located on the back and abdomen in regular rows. In the inner layer of the skin (corium), under the horny scutes of the outer layer, on the back and in some species on the belly, bone plates (osteoderms) develop that are firmly connected with the horny scutes, forming a shell that protects the body of the crocodile well; on the head, osteoderms fuse with the bones of the skull.

Modern crocodiles inhabit various fresh water bodies. Relatively few species are tolerant of brackish water and are found in river estuaries (African narrow-nosed crocodile, Nile crocodile, American sharp-snouted crocodile). Only the combed crocodile swims far into the open sea and has been observed at a distance of 600 km from the nearest shore. Most of the day crocodiles spend in the water. They come out to the coastal shallows in the morning and in the late afternoon - to warm themselves in the sun.

Crocodiles hunt at night. An essential component in the diet of all crocodiles is fish, but crocodiles devour any prey they can handle. Therefore, the set of feeds changes with age: various invertebrates serve as food for the young - insects, crustaceans, mollusks, worms; larger animals prey on fish, amphibians, reptiles and water birds. Adult crocodiles are able to cope with large mammals. There is a known case of finding the remains of a rhinoceros in the stomach of a Nile crocodile. In many species of crocodiles, cannibalism is noted - devouring larger individuals of smaller ones. Often crocodiles eat carrion; some species hide the uneaten remains of the victim under the overhanging shore and later devour them half-decomposed. Crocodiles move in water with the help of their tail. On land, crocodiles are slow and clumsy, but sometimes they make significant transitions, moving several kilometers away from water bodies. When moving quickly, crocodiles put their legs under the body (usually they are widely spaced), which rises high above the ground. Young Nile crocodiles can run at a gallop at about 12 km per hour. Crocodiles lay eggs the size of chicken or goose, covered with calcareous shells. The number of eggs in a clutch varies from 10 to 100 in different species. Some species bury their eggs in the sand, while others lay them in nests made by the female from rotting vegetation. The female remains close to the clutch, protecting it from enemies. Young crocodiles are still inside the eggs, by the time they hatch, they make croaking sounds, after which the mother digs up the masonry, helping the offspring to get out.

Crocodiles grow rapidly in the first 2-3 years of life, during which they reach crocodiles and gharials. sizes 1-1.5 m. With age, the growth rate decreases, and they add only a few centimeters in length per year. Sexual maturity is reached at the age of 8-10 years. Crocodiles live up to 80 - 100 years. Enemies in adult crocodiles are few, if we exclude humans. Cases of attacks by elephants and lions on crocodiles, making transitions by land from one reservoir to another, have been noted.

Widespread in Africa Nile Crocodile (Crocodylus niloticus). It can be found throughout Africa, except for its northern part, in Madagascar, Comoros and Seychelles. It most often settles outside the forest, but also enters forest water bodies. It reaches a length of 4-6 m. The cubs that have just hatched from eggs are about 28 cm long, by the end of the first year of life they reach 60 cm, by two years - 90 cm, at 5 years old - 1.7 m, at 10 years old - 2, 3 m and at 20 years old - 3.75 m. They spend the night in the water, and by sunrise they go to the shallows and bask in the sun. Midday, the hottest hours are spent in the water, with the exception of cloudy days. In windy, inclement weather, they spend the night on the shore. The maximum duration of stay under water for animals with a length of about 1 m is about 40 minutes; larger crocodiles can stay underwater for much longer. The food of the Nile crocodile is very diverse and changes with age. In cubs up to 30 cm long, 70% of the food is insects. Larger individuals (about 2.5 m long) feed on fish, mollusks, crustaceans, and even larger ones feed on fish, reptiles, birds and mammals. Adult Nile crocodiles can attack large mammals such as buffaloes and even rhinos. Crocodiles lie in wait for animals at watering places, in water or on land in dense grass. In a number of areas, Nile crocodiles are dangerous to humans. Eggs are always laid in the dry season, when the water level is low. Females dig a hole in the sand up to 60 cm deep, where they lay 25-95 (on average 55-60) eggs. Incubation lasts about 90 days, during which the mother remains constantly at the nest, guarding the clutch. Apparently, at this time the animal does not eat. By the time of hatching, young crocodiles inside the eggs begin to make grunting sounds, which serve as a signal for the mother to help the cubs get out from under the sand and accompany them to the water. At this time, the female can attack a person even on land. Hatching from eggs usually occurs after the first rains fall, with a rise in the water level in lakes and rivers, so that young crocodiles immediately find shelter and food in overflowing reservoirs. After the release of young crocodiles from eggs, the mother leads them (according to Kott's observations) to the "nursery" she has chosen - a shallow reservoir protected by vegetation. Here the young crocodiles stay for about six weeks; all this time, the mother stays with the brood, protecting it from attacks of predators. In the absence of a mother, crocodile hatchlings often remain close to the nest, where they are usually exterminated by predators - goliath herons, marabou, and kites. Numerous cases of cannibalism are known (devouring eggs and young individuals), which is usually considered a mechanism for regulating the number of species: it is noted that cannibalism occurs more often, the higher the number of crocodiles. The number of Nile crocodiles has fallen everywhere and continues to fall. In ancient Egypt, crocodiles were revered as sacred animals; now they are almost exterminated. The same fate will befall crocodiles in a number of places in Central and East Africa if measures are not taken to protect the species.

The Nile crocodile is a large reptile that belongs to the family of real crocodiles, lives in Africa and is an integral part of aquatic and semi-aquatic ecosystems there. In size, it exceeds most other crocodiles and is the second largest member of this family after the combed crocodile.

Appearance

The Nile crocodile has a squat body of a strongly stretched format, which turns into a thick and strong tail, tapering towards the end. Moreover, the length of the tail can even exceed the size of the body. The strongly shortened powerful paws of this reptile are widely spaced - on the sides of the body. The head, when viewed from above, has the shape of a cone slightly tapering towards the end of the muzzle, the mouth is large, equipped with many sharp teeth, the total number of which can be 68 pieces.

It is interesting! In crocodile cubs that have just hatched from eggs, one can notice a skin thickening on the front of the muzzle that looks like a tooth. This seal, called the "egg tooth," helps the reptiles preparing to be born to break through the shell and quickly get out of the eggs.

The coloration of Nile crocodiles depends on their age: young individuals are darker - olive-brown in color with a cross-shaped black shading on the body and tail, while their stomach is colored yellowish. With age, the skin of reptiles seems to fade and the color becomes paler - grayish-green with darker, but not too contrasting stripes on the body and tail.

The skin of a crocodile is rough, seated with rows of vertical shields. Unlike most other reptiles, the Nile crocodile does not molt, as its skin tends to stretch and grow with the animal itself.

Lifestyle

The Nile crocodile cannot be called a herd animal, but they live in large groups and often hunt in groups. At the same time, a strict hierarchy is observed in each group, which does not lead to conflicts. Groups are always dominated by the largest individuals.

But group hunting does not take place so often, more often individuals lead a solitary lifestyle. At dawn, the Nile crocodile comes out onto the coastal sand and dries in the sun, while its mouth is usually open at this moment. Having warmed up in the sun, the crocodile returns to the reservoir for hunting closer to noon. Since the Nile crocodile can eat quite a lot, it hunts almost every day, but in those cases when it is not hungry, then at lunchtime it can either simply swim along the perimeter of its site, or remain on the coastal zone half asleep. It is impossible to say that a crocodile ever completely immerses itself in sleep, because thanks to the organs of touch, it always feels everything that happens around.

When a group of crocodiles rests on the same beach, the dominant (i.e. larger) individuals are always in the most convenient places, while the distance between each crocodile is quite respectful. At sunset, the Nile crocodile always returns to the pond for hunting, which continues throughout the night and early morning. Thus, individuals of the Nile crocodile are predominantly nocturnal.

Nile crocodiles hunt most often for fish, but often marsh and water birds, small and large mammals that come to the reservoir where the crocodile lives, to drink, become prey. The Nile crocodile waits for its prey, completely immersed in water and leaving only eyes, nose and ears on the surface. He is able to completely silently and imperceptibly swim up to his prey at a sufficient distance, so that in a sharp jump he grabs the prey by the throat and also quickly drags it under water.

Under water, a crocodile either strangles its prey or waits for it to choke. There have been cases when crocodiles left their prey under water for a while, placing it between the roots of trees, or in crevices, so that the meat softened.

If the prey managed to avoid the attack of the crocodile, then it will not pursue it on land. Extremely rarely, during feeding, crocodiles climbed more than half the exit from the reservoir. Crocodiles will also not hunt on the shore. Crocodiles can eat already dead prey, but they avoid meat in which the process of decay has already begun.

The crocodile most often suppresses the fish with the blows of the tail, after which it swallows it. When hunting in groups, several crocodiles drive fish into schools, where they have the opportunity to stun more prey. At the same time, larger individuals are the first to swallow prey, and their small relatives can only collect the remains after dominant individuals.

Acoustic communication between individuals consists of a rather extensive set of sound signals. Sounds always accompany mating tournaments. In addition, a characteristic dull lowing can be heard during the anxiety of the individual. An angry crocodile makes sounds like a hissing sniff. Young, newly hatched individuals make sonorous croaking sounds.

In general, the behavior of the Nile crocodile can be characterized as individual and social. It can manifest itself both in groups and singly. It even has some semblance of intelligence, and therefore cunning moves are possible during the hunt, as well as the ability to protect and protect offspring, which is not characteristic of most other reptiles.

The Nile crocodile has the glory of a cannibal, because, due to indiscretion, according to information from various sources, several hundred people become victims of crocodiles in their habitats per year. However, there are no official statistics and it is not possible to confirm or deny this information.

Habitat of the Nile crocodile

The Nile crocodile lives on almost the entire African continent.

In ancient times, the Nile crocodile was found in Israel, Palestine, Lebanon, Algeria, Libya, Jordan, Syria and the Comoros.

Now its habitat has been slightly reduced. Most individuals of the Nile crocodile live in Zambia, Ethiopia, Kenya and Somalia in the Nile basin. A smaller number of individuals live in Zanzibar, Morocco, Tanzania, Congo, Senegal, Sierra Leone, Uganda, Rwanda, Kenya, Liberia, Mozambique, Mauritania, Nigeria, Namibia, Malawi, Zaire, Botswana, Cameroon, Angola, Central African Republic, Chad , Burundi, Guinea, Côte d'Ivoire, Swaziland. The Nile crocodile is also found on nearby islands along the coasts of Africa: Madagascar, Socrates Island, the Cape Verde Islands, the archipelago of Sao Tome and Principe.

Nutrition

The daily menu of a crocodile, like most amphibians, is quite diverse. Babies love to eat insects. As they get older, they prefer fish, shellfish and crustaceans. Adult individuals find other prey for themselves - reptiles, birds. Sometimes a large buffalo, rhinoceros, lion or tiger can become their prey. Hiding in the water near the shore, they patiently wait for several hours until the animal approaches the shore. Seeing the prey, the predator quietly approaches it, while she drinks water without suspecting anything, it is not visible, because only the eyes and nostrils of the crocodile are above the water. Suddenly, jumping out of the water, the crocodile grabs its victim by the head with its strong teeth and plunges it under water. A choking animal becomes an easy prey, and the crocodile enjoys it, tearing the victim to pieces with powerful jaws, therefore, its attack is always a win-win.

Easy prey can be a frivolous monkey jumping from branch to branch, or a bird gaping on the shore or resting on large leaves of algae.

The Nile crocodile kills fish with a strong blow of the tail on the water surface and immediately swallows it easily. They eat often, but due to their slow metabolism, they can go without food for several weeks, and even more than one month.

Surprisingly, crocodiles share prey with their brethren, of course, if they took part in the hunt. Having honestly divided the prey into pieces, the alligators calm down and rest, gaining strength before a new hunt.

reproduction

During the mating season, males become especially aggressive. To attract girlfriends, they snort loudly, roar and slap their muzzle on the surface of the water. Females choose their own mate by swimming to the site of the male they like.

The newly-made spouses joyfully sing peculiar trills together and prepare for procreation. Having chosen a dry place, the female digs a hole up to 30-45 cm deep in sand or soft earth. She lays about 50 eggs in it and carefully buries them. All the time of incubation (85-90 days), she keeps close to the masonry, protecting it from uninvited guests. Often in the protection of future offspring she is helped by a nearby spouse.

Ready to hatch, crocodiles squeak plaintively, calling for help from their mother. She carefully digs up the sand and, holding the cubs in her mouth, gently carries them to the pond.

Newborns weigh about 500 g with a body length of 25-30 cm. They spend the first weeks of their lives in shallow water under the close attention of their mother, eating insects. At the age of 8 weeks, they break into small groups and look for shelters in the form of holes, in which they live up to 4-5 years.

By this age, they grow up to 2 m and, no longer fearing enemies, go in search of their own site. They reach sexual maturity at 12-15 years of age.

Nile crocodiles and man

They have few enemies, the greatest danger to crocodiles is man. They are hunted because crocodiles are quite dangerous predators, and besides, their skin has recently become a very valuable product.

As a result of the barbaric destruction on the banks of the reservoirs of the Middle East, they are almost gone. Tropical reservoirs were under the threat of existence, because their orderlies - crocodiles - were gone. They ate sick and weakened animals that came to the water to drink and lived in it, their remains, weedy fish, etc.

Soon, active work began in this direction. Now the situation is under control, and formidable predators are bred on farms specializing in growing crocodile. In addition, other measures are being taken to restore the number of animals.

• The ancient Egyptians worshiped the god of water and the flood of the Nile - Sebek, depicted as a living or mummified crocodile or a man with the head of a crocodile. The cult of the Nile crocodile was widespread among the Egyptians: predators were kept as pets, some individuals were decorated with jewelry during their lifetime, and after death they were mummified and buried with honors in a sarcophagus.
• An amazing fact: hippos and Nile crocodiles quietly coexist in the same reservoir, and female hippos can leave offspring next to reptiles to protect themselves from land-based predators.
• In accordance with the observations of researchers, an interesting hypothesis has emerged, suggesting a symbiosis of the Nile crocodiles with certain types of birds - the clawed lapwing and the Egyptian runner, which is also called the watchman crocodile. The Nile crocodile opens its mouth wide, and the birds pick out the remains of meat and leeches from its teeth. But it has not yet been possible to document the truth of such a symbiosis.
• The peak of the extermination of the Nile crocodiles occurred in the middle of the 20th century, when large aquatic reptiles were killed not only because of the high quality skin, but also for the sake of edible meat and internal organs, supposedly with healing properties. Then the population of the species was on the verge of extinction. Currently, the Nile crocodile is listed in the Red Book of the World Conservation Union (IUCN).

The Nile crocodile (lat. Crocodylus niloticus) is one of three species of crocodiles that live on the African continent. It is smaller but more aggressive. It can live near human settlements and is famous for its cannibalistic inclinations, therefore in ancient Egypt it was revered as a sacred animal of the god Sebek, depicted with a human body and a crocodile head.

Sebek was considered the protector of gods and people, was the deity of reservoirs and the flood of the Nile. In the ancient Egyptian city of Shedit, located on the shores of Lake Merida in the Fayum oasis and better known by the Greek name Crocodilopol, the priests in the temple of Sebek kept a huge Nile crocodile adorned with jewelry made of gold and precious stones. Sometimes human sacrifices were made to him, because the gluttonous reptile was the living embodiment of Sebek with all the ensuing consequences.

Several burials of these reptiles have been found in Egypt. After death, they were mummified and decorated with jewels.

During life, they were intensively fed, cherished in every possible way and carried on special stretchers. The slaves delighted the ears of the reptiles with exquisite music. A respectful attitude towards them has been preserved by almost all the peoples of Africa to this day.

Spreading

Zoologists currently distinguish 7 subspecies of Crocodylus niloticus, living in different regions and having slight external differences. It is found throughout the sub-Saharan continent and Madagascar. Most often observed in slow-flowing rivers or stagnant reservoirs, prefers swampy areas.

Giant reptiles settle in mangrove forests, provided that there is a beach well warmed by the sun and dense reed beds where you can hide in ambush and hide from prying eyes.

Behavior

Nile crocodiles live in loose communities that usually include several groups. Each group consists of animals of the same sex and approximately the same age and size. The dominant role is always occupied by males.

Each male occupies his own area, including part of the coast and part of the water area adjacent to it. Females mostly stay together and even nest in the neighborhood.

Representatives of this species have a very rich language of communication, expressed through a variety of body movements and a rich set of sounds.

A reptile of a lower rank always hides its head in the water in front of a higher one in the hierarchy. The dominant male proudly swims with his body, head and tail above the water. The subordinate exposes only his muzzle.

On land, to scare off rivals, the Nile crocodile rises on all four legs, swells up and lifts its head and tail high. In the case of rare fights, the giants bite each other on the paws and the base of the tail. They lie in wait for their victims at the watering hole and at the crossings.

The toothy monster jumps out of the reservoir with a powerful jerk, grabs the victim by the muzzle or leg, pulls it down and drowns, and then slowly eats it. With sharp teeth, he tears off large pieces of flesh and swallows them without chewing.

Nile crocodiles collectively hunt schooling fish, driving them together in shallow water. They often grab waterfowl, and with their tail they manage to knock down their nests in order to feast on eggs.

After a meal, the predator lays down in the sun to better digest food, and when hungry, hides in the shade, saving energy.

An adult eats about 50 large meals during the year, but can go without food for up to 2 years, limiting energy consumption and using fat reserves, which are located in its tail, along the ridge and body cavities.

The largest specimen weighed more than 1 ton and was about 8 m long.

reproduction

During the mating season, males become especially aggressive. To attract girlfriends, they snort loudly, roar and slap their muzzle on the surface of the water. Females choose their own mate by swimming to the site of the male they like.

The newly-made spouses joyfully sing peculiar trills together and prepare for procreation. Having chosen a dry place, the female digs a hole up to 30-45 cm deep in sand or soft earth. She lays about 50 eggs in it and carefully buries them. All the time of incubation (85-90 days), she keeps close to the masonry, protecting it from uninvited guests. Often in the protection of future offspring she is helped by a nearby spouse.

Ready to hatch, crocodiles squeak plaintively, calling for help from their mother. She carefully digs up the sand and, holding the cubs in her mouth, gently carries them to the pond.

Newborns weigh about 500 g with a body length of 25-30 cm. They spend the first weeks of their lives in shallow water under the close attention of their mother, eating insects. At the age of 8 weeks, they break into small groups and look for shelters in the form of holes, in which they live up to 4-5 years.

By this age, they grow up to 2 m and, no longer fearing enemies, go in search of their own site. They reach sexual maturity at 12-15 years of age.

Description

Adult individuals reach a body length of 3.5-5 m with a weight of about 800 kg. The color is dominated by gray or dark olive color with characteristic dark transverse stripes.

Along the upper side of the tail, two longitudinal ridges stretch from the very base, which merge together in the middle.

The legs are short and very strong. The toes of the hind legs are connected by swimming membranes. All fingers are armed with powerful claws. The tail is long and massive, it serves as a kind of rudder and oar when swimming. The mouth is elongated. Both jaws are equipped with sharp strong teeth.

At the front end of the muzzle are the nostrils. Eyes with vertical pupils are set high on the skull.

The life expectancy of the Nile crocodile in the wild is about 100 years.

The Nile crocodile is a reptile, from the family of crocodiles, the second largest, after the saltwater comb.

Living in the rivers, lakes and swamps of central and southern Africa, this ancient ferocious predator devours almost all living things that come his way.

In terms of size, the Nile crocodile is simply a giant, on average its length is from 5 to 5.5 meters, and its weight often reaches a ton. This is the largest crocodile living in our time in Africa.

Description and lifestyle

The Nile is the most ancient animal in Africa. According to scientists, it has existed on earth for tens of millions of years and is a descendant of a prehistoric archosaurus, a contemporary and relative of the dinosaur and beast lizard. The appearance of this semi-aquatic monster speaks for itself. A huge elongated body, covered with ossified plates, on short curved legs, a powerful vertically flattened tail, a large flat head and a huge mouth with jaws studded with numerous wedge-shaped teeth, betray in it a strong and ruthless predator, which it essentially is.

For a long time, these crocodiles have bred in the waters of almost all of Africa south of the Sahara Desert. This was facilitated by a favorable warm climate, a large amount of water, a lot of vegetation and, as a result, a rich fauna in abundance that provided crocodiles with food. For many years of living in these fertile places, the Nile crocodile has become the largest predator in Africa, which everyone, both animals and people, began to fear.

In ancient times, being helpless against the incredible power of this ferocious monster, people equated it with a deity capable of either benevolent or punishing a person. He was credited with the ability to control the waters of the Nile, Egypt's main waterway. This is how the cult of the god Sebek appeared, a creature with a human body and a crocodile head. This was beneficial to the power of the pharaohs, and they contributed to the creation of a whole system of planting and maintaining this cult. Pharaoh Ptolemy II even built a whole temple of this deity in the city of Shedite, later renamed Crocodilopolis by the Greeks, which was the center of worship for this deity. In this temple, the Nile crocodile was kept in luxury as the earthly incarnation of the god Sebek. This went on for many centuries, and since not a single crocodile could live so long, it was periodically changed, and the bodies of the dead crocodiles were mummified and stored in specially made sarcophagi. All this ended only with the arrival of the Romans in Egypt.

Whatever it was in ancient times, ordinary Nile crocodiles still exist today, and very well. They live in massive colonies in the valleys of large African rivers, where herds of wild animals are still preserved, which always come to the water, which crocodiles need. Crocodiles cannot chase antelopes across the savannah, although juveniles basking in the sun sometimes try to show agility by rushing at a nearby antelope, zebra or young buffalo, but they very rarely succeed. The tactics of adult crocodiles is that they calmly, hiding in the water up to their very nostrils and eyes, wait for a herd of these harmless animals to come to a watering place and start drinking water. Then, almost silently, the crocodile swims up to the intended victim, with a sharp blow of the tail against the bottom, throws its body forward and grabs the animal that did not have time to jump back. There was an antelope and not.

The second option is when herds of animals begin to migrate, changing pasture locations. Then they are simply forced to cross the river, where only agility and speed can save them. Who did not have time, that expects death from crocodile teeth. Although crocodiles are very ferocious, they never hunt for future use. If a crocodile has caught an antelope or a zebra, then he will take care of his meal and he does not care about other animals running nearby. So the animal that died in the teeth of a crocodile, by its death, makes it possible for fellow tribesmen to stay alive. In addition to animals, Nile crocodiles do not disdain birds and turtles, in principle, all that they come across are monkeys, and porcupines, and pigs, and all other living creatures. Among the crocodiles there are also their own, so to speak, "thugs", who rush to animals that are much larger in size, such as hippos or elephants. And, oddly enough, sometimes they succeed, although the crocodile most often cannot cope alone with a multi-ton elephant or hippopotamus. It is not uncommon for a Nile crocodile to attack a person, so in some African countries it was called a cannibal crocodile.

Nile crocodiles are one of the long-livers of the Black Continent. On average, the Nile crocodile lives for about 40 years, but in favorable conditions it can live up to a hundred years, although usually only a few succeed. These large crocodiles have almost no enemies other than lions and humans. Well, if lions are faced mainly by units of the crocodile tribe, then people are a threat to the entire crocodile family. Due to the high demand for the skin of the Nile crocodile, for many years they were ruthlessly killed and in some countries they are under the threat of complete extinction. Now their population is more or less stable in Egypt, Somalia, Ethiopia, Zambia, Kenya, Morocco, and on some islands: Madagascar, Mauritius, Cape Verde, Zanzibar, mainly due to the creation of national parks where hunting for them is prohibited, and for the reproduction of the skin, create special farms for growing crocodiles.

The number of crocodiles is replenished by the peculiarity of their reproduction. During the mating season, the female Nile crocodile lays 50-60 eggs. Of course, not all of them hatch, because there are many people who want crocodile eggs, such as hyenas, baboons, and people too, but the crocodile keeps at least a couple of dozen cubs until next year. And if not for hunting them, they could well be a serious threat to the population of Africa. It seems that this decline somehow also maintains a balance in nature, although now the Nile crocodile is listed in the Red Book.

Crocodiles are vertebrate cold-blooded animals that lead a semi-aquatic lifestyle. Water is their favorite medium, being more constant in terms of temperature. It was thanks to her that the ancestors of crocodiles survived during the global cooling of the climate on Earth. The body shape of crocodile is lizard-shaped. The large head is flattened in the dorsal-abdominal direction, the muzzle is elongated or long, with strong elongated jaws, seated with sharp conical "fangs" up to 5 cm long, which grow throughout the life of the animal, replacing worn and broken ones. The teeth are strengthened in separate bone cells of the jaws, the base of the tooth is hollow inside; The bite of a crocodile is arranged in such a way that opposite the largest teeth of the lateral edge of one jaw are the smallest teeth of the other. This design was able to turn the dental apparatus into a perfect weapon for attack. In narrow-faced fish-eating gharials, the jaws can be compared to the jaws of tweezers, which allow them to grab small moving prey in the water with a lateral movement of the head.

The jaw system is arranged differently in Chinese alligators (Alligator sinensis), common in East China along the lower reaches of the Yangtze River. These are Small reptiles (maximum length 1.5 m), feeding mainly on bivalve mollusks, water snails, crustaceans, as well as frogs and slow-moving fish species. Grind such rough food closely planted posterior teeth with a flat surface of the crown. Rinsing their mouths in the water, the profited alligators get rid of fragments of crushed shells and shells.

At the end of the crocodile muzzle are bulging nostrils, the eyes are also raised and are located on the upper side of the head. This feature of the structure of the skull determines the favorite posture of the aquatic reptile: the body is blissful in the water - only the eyes and nostrils are visible from the outside.

Crocodiles have five fingers on their forelimbs, four on their hind limbs, they are connected by an interdigital swimming membrane. The tail is long, laterally compressed, very powerful and multifunctional: it is a “steering” and “engine” when swimming, a support when moving on land, and when hunting, it is like a stunning mace. During swimming, the limbs of crocodiles are laid back, the front ones are pressed to the sides, and the powerful flattened tail, bending, describes S-shaped movements. Lying in wait for large mammals at a watering hole, a huge combed crocodile (Crocodylus porosus) attacks suddenly, grabbing a zebra or antelope by the head and breaking its neck, or knocking the victim down with a terrible blow of the tail. During the breeding season, females tamp the "building material" brought for the nest with their tail, slap it on the water, spraying the nest with masonry.

The entire surface of the crocodile's body is covered with large, regular-shaped horny scales. The dorsal shields are thicker and bear convex, spiny ridges that merge into barbs on the tail. Each of the scales develops independently and grows at the expense of its underlying layers. Under the large shields of the skin on the back and tail, a real shell of bone plates, the osteoderm, develops. The shields are elastically connected to each other, due to which they do not restrict the movements of the animal. The shape and pattern of the shell surface is individual for each species. On the head, osteoderms fuse with the bones of the skull. Thus, the animal wears a real "armor" that effectively protects vital internal organs and the brain.

The structure of the skull is very unusual. The quadrate and articular bones are pierced by air-bearing outgrowths of the middle ear cavity. Most of the posterior bones of the skull contain cavities of a strongly overgrown and complexly branching system of the Eustachian tubes. The bones of the long muzzle and palate also contain significant voids: blind outgrowths of the nasal passage enter them. Scientists believe that the systems of air cavities and passages, penetrating almost the entire huge crocodile skull, significantly facilitate it, allowing you to keep your head above the surface of the water without significant expenditure of muscle energy (for silent and imperceptible immersion, it is enough for a crocodile to lower the pressure in the chest cavity and direct part of the air from the air cranial passages).

All species of crocodiles have highly organized sense organs. Unlike snakes, they hear perfectly - the range of auditory sensitivity is very large and is 100-4000 Hz. At the same time, crocodiles are deprived of Jacobson's special "snake" organ, which allows creepers to distinguish taste and smell with great accuracy. The eyes of crocodilians are adapted for night vision, but they serve well during the day. The retina of the eye contains mainly rod receptors that capture light photons. The pupil, like a cat's, is able to narrow in the light into a narrow vertical slit, and at night the alligator's eyes have a reddish-pink sheen, which is often taken as invariable evidence of its bloodthirstiness. It should be said that although the hunting instincts of crocodiles are aggravated at night, the ferocious predatory eyes are only a consequence of the anatomical structure of the visual analyzer. In the dark, the vertical pupil expands, and the bloody color is provided by the presence in animals of a special pigment - rhodopsin - on the retina, illuminated by reflected light. Under water, the eyes of crocodiles are protected by a transparent nictitating membrane that closes them when immersed.

Everyone knows the expression "to shed crocodile tears." Indeed, crocodiles cry, but not from grief, pain or the desire to treacherously lull someone's vigilance. Thus, animals are freed from excess organic salts contained in the body. Their cloudy tears are unusually salty, but devoid of emotion. Salt glands are located in representatives of the family of real crocodiles, even under the tongue.

The respiratory system of crocodiles also has its own characteristics. The nostrils, like the external auditory openings, can be tightly closed by muscles - they automatically contract when the animal dives. The lungs have a complex structure compared to the baggy lungs of snakes and are able to accommodate a large supply of air. As a result, for example, a young Nile crocodile only 1 meter long is able to stay under water for about 40 minutes, and without the slightest harm to its own health. As for large adults, the duration of their “diving” can reach 1.5 hours. It should be noted that scaly reptiles are not able to absorb oxygen through rough skin, as thin-skinned amphibians (frogs, newts) do.

The air inhaled through the nostrils passes through the paired nasal passages, separated from the oral cavity by a secondary bony palate, which serves as a kind of protection of the skull from the inside. In the case when a crocodile tries to swallow a large and severely mutilated victim, bone fragments and desperate resistance, jerks and blows of the doomed animal are not able to injure the vault of the oral cavity and damage the brain. In front of the choanas (internal nostrils), a muscular veil descends from above, which is pressed against a similar outgrowth at the base of the tongue and forms a valve that completely separates the oral cavity from the respiratory tract. Thus, due to its anatomical structure, the crocodile is able to drown, tear and swallow prey without the risk of choking itself.

The mechanism of ventilation of the lungs is peculiar and unusual in crocodiles. If for most higher vertebrates a change in the volume of the chest is produced by the movement of the ribs, then the volume of the lungs in crocodiles also changes with the movement of the liver. The latter is moved forward by contraction of the transverse abdominal muscles, causing an increase in pressure in the lungs and exhalation, and then moves backward by the longitudinal diaphragmatic muscles that connect the liver with the pelvis, causing a decrease in pressure in the lungs and, accordingly, inspiration. As researchers K. Hans and B. Clark proved, in crocodiles in water, it is the movements of the liver that play the main role in lung ventilation.

The heart of crocodiles consists of four chambers and is much more perfect than the three-chambered heart of other reptiles: oxygen-enriched arterial blood does not mix with venous blood, which has already given oxygen to organs and tissues. The heart of crocodiles differs from the four-chambered heart of mammals in that the latter retains two aortic arches with an anastomosis (bridge) at the intersection. Thus, despite the fact that the body temperature, metabolic rate, motor activity and appetite of crocodiles significantly depend on the ambient temperature, the process of gas exchange in their cells proceeds more efficiently than in lizards and turtles.

The digestive system of crocodiles is distinguished primarily by the absence of saliva in the oral cavity. In addition, there is another amazing adaptation: in the thick-walled muscular stomach of most adult crocodiles there is a certain amount of stones (the so-called gastroliths), which the animals deliberately swallow. In Nile crocodiles, the weight of stones in the stomach reaches 5 kg. The role of this phenomenon is not entirely clear; it is assumed that the stones play the role of ballast and move the center of gravity of the crocodile down in front, giving greater stability when swimming and facilitating diving, or they contribute to grinding food while contracting the walls of the stomach, as in birds.

Crocodiles do not have a bladder, which is apparently associated with life in the water. Urine is excreted along with feces through a special organ that removes waste products located on the ventral side of the animal (it is called the cloaca). The cloaca has the form of a longitudinal slit, while in lizards and turtles it is of a transverse type. In the back of it, males have an unpaired genital organ. The female lays fertilized eggs, protected from the outside by a dense calcareous shell, and from the inside - by primary reserves of food and moisture sufficient for the development of the embryo.

On the sides of the cloaca, as well as under the lower jaw of crocodiles, there are large paired glands that secrete a brown secret with a strong smell of musk. The secretion of these glands is especially activated during the breeding season, helping sexual partners find each other.

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