Palaeozoic(era ancient life) is distinguished by several stages of powerful mountain building, . In this era, the Scandinavian mountains, the Urals, Altai,. At this time, animal organisms with a solid skeleton appeared. Vertebrates first appeared: fish, amphibians, reptiles. Ground vegetation appeared in the Middle Paleozoic. Tree ferns, club mosses, and others served as material for the formation of coal deposits.

Mesozoic era(era average life) is also characterized by intense folding. Mountains formed in areas adjacent to. Reptiles dominated among animals (dinosaurs, proterosaurs, etc.), birds and mammals first appeared. The vegetation consisted of ferns, conifers, angiosperms appeared at the end of the era.

In the Cenozoic era (the era of new life), modern distribution takes shape, intense mountain-building movements occur. Are formed mountain ranges on the banks Pacific Ocean, in the south of Europe and Asia (, Coast Ranges, etc.). At the beginning of the Cenozoic era, the climate was much warmer than today. However, the increase in land area due to the rise of the continents led to a cooling. Extensive covers appeared in the north and. This led to significant changes in the flora and fauna. Many animals have died out. Plants and animals appeared close to modern ones. At the end of this era, man appeared and began to intensively populate the land.

The first three billion years of the development of the Earth led to the formation of land. According to scientists, at first there was one continent on Earth, which subsequently split into two, and then there was another division and, as a result, to today formed five continents.

The last billion years of the Earth's history is associated with the formation of folded regions. At the same time, in geological history During the last billion years, there are several tectonic cycles (epochs): Baikal (end of the Proterozoic), Caledonian (early Paleozoic), Hercynian (late Paleozoic), Mesozoic (Mesozoic), Cenozoic or Alpine cycle (from 100 million years to the present).
As a result of all the above processes, the Earth acquired a modern structure.

The Paleozoic era was a whole revolution in the history of the Earth: a huge glaciation and the death of many animal and plant forms.

IN middle era we no longer meet very many of those organisms that existed hundreds of millions of years before. Huge crayfish - trilobites, which raged in the seas of the Paleozoic, disappear, as if swept away from the face of the Earth. Many echinoderms, whole families of sea urchins, starfish, sea lilies, etc. share their fate. Other echinoderms, it is true, remain in subsequent times, but they change greatly and develop in a completely new direction. Many species of coral are disappearing. Big changes are also taking place with shellfish and fish. Even more changes are experienced by the land population.

The heyday of tree ferns and horsetails is over. Most of them did not survive the Paleozoic. Those species that still existed at the beginning of the Mesozoic era retained faint traces of their former splendor. They are much rarer, do not reach great growth, and often turn out to be completely small. But coniferous and sago trees flourish, and after a while numerous new species of flowering plants join them: palm trees are widespread. By its nature, the Mesozoic forest differs sharply from the forest of the ancient era. There was a monotonous vegetation of gloomy tall trees. Here, coniferous and sago trees, palm trees, and behind them flowering plants give the earth's vegetation cover bright colors and cheerful tones. Flowers bloomed in the fields.

The Mesozoic era is divided into three parts: the initial time - the Triassic period, the middle - the Jurassic period and later - the Cretaceous period.

At the beginning of the Mesozoic time, a dry but warm climate is established, then it became more humid, but continued to remain warm. The Mesozoic era lasted, according to many geologists, about 120 million years, and more than half of this time falls on the share of the last, Cretaceous period.

Already in the first of these periods, a change in the animal world was sharply noticeable. In place of the disappeared inhabitants of the seas, long-tailed crayfish arose in large numbers, similar to those that now live in the seas and rivers. On land, next to the amphibians, many new animals appeared that developed from amphibians and are called reptiles, or reptiles. We know that their amphibian origin is connected with the need to conquer new expanses of land far from water.

In our time, of the reptiles, or scaly reptiles, as they are sometimes called, very few live. We can meet relatively small lizards, turtles, snakes and crocodiles. In Mesozoic time, one could also see large and small lizards everywhere, similar to the inhabitants of our forests and rocks. Lived in those days and turtles; for the most part they were found in the seas. But besides the rather harmless turtles and lizards, there was a terrible, crocodile-like reptile, the distant descendant of which is the present crocodile. There were no snakes at all until the very end of the Mesozoic.

Were in mesozoic times and many other breeds of reptiles, which have now completely disappeared.

Of their remains, strange skeletons are of particular interest to us, in which the signs of reptiles are mixed with the characteristics of mammals, that is, those animals covered with hair, the females of which feed their young with milk (such, for example, cows, pigs, cats, dogs, and in general all predatory , ungulates, rodents, monkeys, etc.). Amazing bones of animal-like reptiles have come down to us, in which the device of legs and teeth is very reminiscent of mammals that did not yet exist on Earth at that time. For the resemblance to animals, this breed was called "animal-like".

Among them is the famous foreigner, which was armed with sharp claws and powerful fangs, similar to the fangs of such predators as the lion and tiger.

Inistrantsevia was found in 1901 during excavations of Permian deposits on the banks of the Northern Dvina.

One can imagine what kind of devastation such predators made among the population of the Mesozoic forests and steppes. They contributed to the death of ancient amphibians, thus clearing the way for the unprecedented development of reptiles, which we see in the Jurassic and Cretaceous.

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The Mesozoic era began 230 million years ago and lasted 163 million years. It is divided into three periods: the Triassic (35 million years), the Jurassic, or Jurassic period (58 million years), and the Cretaceous, or Cretaceous period (70 million years).

In the seas, even in the Permian period, trilobites finally died out. But this was not the sunset of the marine invertebrates. On the contrary: each extinct form was replaced by several new ones. During the Mesozoic era, the Earth's oceans abounded with molluscs: squid-like belemnites (their fossil shells are called "devil's fingers") and ammonites. The shells of some ammonites reached 3m. In diameter. No one else on our planet, either before or later, had such colossal shells!

In the forests of the Mesozoic, conifers and cypresses, as well as cycads, dominated. We are used to seeing insects hovering over flowers. But such a spectacle became possible only from the middle of the Mesozoic, when the first flower bloomed on Earth. By the Cretaceous period, flowering plants had already begun to crowd out conifers and cycads.

The Mesozoic, especially the Jurassic, can be called the kingdom of reptiles. But even at the very beginning of the Mesozoic, when the reptiles were just moving towards their dominance, small, woolly, warm-blooded mammals appeared next to them. For a long 100 million years, they lived next to the dinosaurs, almost invisible against their background, patiently waiting in the wings.

In the Jurassic, dinosaurs also had other warm-blooded rivals - the first birds (Archaeopteryx). They had a lot more in common with reptiles: for example, jaws studded with sharp teeth. In the Cretaceous period, real birds also descended from them.

At the end of the Cretaceous period, the climate on Earth became colder. Nature could no longer feed animals weighing more than ten kilograms. Began mass extinction(stretched, however, for millions of years) dinosaur giants. Now the vacated place could be occupied by animals and birds.

How life arose and developed on Earth Gremyatsky Mikhail Antonovich

XII. Mesozoic ("middle") era

The Paleozoic era ended with a whole upheaval in the history of the Earth: a huge glaciation and the death of many animal and plant forms. In the middle era, we no longer meet very many of those organisms that existed hundreds of millions of years before. Huge crayfish - trilobites, which raged in the seas of the Paleozoic, disappear, as if swept away from the face of the Earth. Many echinoderms, whole families of sea urchins, sea stars, sea lilies, etc. share their fate. Other echinoderms, it is true, remain in subsequent times, but they change greatly and develop in a completely new direction. Many species of coral are disappearing. Big changes are also taking place with shellfish and fish. Even more changes are experienced by the land population.

The heyday of tree ferns and horsetails is over. Most of them did not survive the Paleozoic. Those species that still existed at the beginning of the Mesozoic era retained faint traces of their former splendor. They are much rarer, do not reach great growth, and often turn out to be completely small. But conifers and sago trees flourish, and after a while numerous new species join them. flowering plants: palm trees are widespread. By its nature, the Mesozoic forest differs sharply from the forest of the ancient era. There was a monotonous vegetation of gloomy tall trees. Here, coniferous and sago trees, palm trees, and behind them flowering plants give the earth's vegetation cover bright colors and cheerful tones. Flowers bloomed in the fields.

The Mesozoic era is divided into three parts: the initial time - Triassic period, average - Jurassic period and later chalky period.

At the beginning of the Mesozoic time, a dry but warm climate is established, then it became more humid, but continued to remain warm. The Mesozoic era lasted, according to many geologists, about 120 million years, and more than half of this time falls on the share of the last, Cretaceous period.

Already in the first of these periods, a change in the animal world was sharply noticeable. In place of the disappeared inhabitants of the seas, long-tailed crayfish arose in large numbers, similar to those that now live in the seas and rivers. On land, next to the amphibians, many new animals appeared that developed from amphibians and are called reptiles, or reptiles. We know that their amphibian origin is connected with the need to conquer new expanses of land far from water.

In our time, of the reptiles, or scaly reptiles, as they are sometimes called, very few live. We can meet relatively small lizards, turtles, snakes and crocodiles. In Mesozoic time, one could also see large and small lizards everywhere, similar to the inhabitants of our forests and rocks. Lived in those days and turtles; for the most part they were found in the seas. But besides the rather harmless turtles and lizards, there was a terrible, crocodile-like reptile, the distant descendant of which is the present crocodile. There were no snakes at all until the very end of the Mesozoic.

There were many other breeds of reptiles in Mesozoic times, which have now completely disappeared.

Of their remains, strange skeletons are of particular interest to us, in which the signs of reptiles are mixed with the characteristics of mammals, that is, those animals covered with hair, the females of which feed their young with milk (such, for example, cows, pigs, cats, dogs, and in general all predatory , ungulates, rodents, monkeys, etc.). Amazing bones of animal-like reptiles have come down to us, in which the device of legs and teeth is very reminiscent of mammals that did not yet exist on Earth at that time. For the resemblance to animals, this breed was called "animal-like".

Rice. 31. Pareiasaurus (a reptile close to amphibians) - below and foreigners (a reptile close to mammals) - above

Among them is the famous foreigner, which was armed with sharp claws and powerful fangs, similar to the fangs of such predators as the lion and tiger.

One can imagine what kind of devastation such predators made among the population of the Mesozoic forests and steppes. They contributed to the death of ancient amphibians, thus clearing the way for the unprecedented development of reptiles, which we see in the Jurassic and Cretaceous.

Jurassic period. Changes in the plant world.

Bony fish. reptiles

The Jurassic time brought a lot of new things both to the world of plants and to the development of animals. The Jurassic forests are already very different from the Carboniferous: fern thickets have thinned out, gymnosperms and cycads have greatly multiplied. Cycads are similar in appearance to both ferns and palm trees. These are small trees with straight trunks, decorated at the top with long feathery leaves. They are descendants of seed ferns and in turn reproduced by seeds. Very few of them have survived to this day.

In the Jurassic, another group appeared - close relatives of the cycads, the so-called Bennetites. But their heyday belongs to the Cretaceous period. Bennetites also propagated by seeds that were collected in cones.

Some of the most remarkable Jurassic plants - ginkgo. One species - ginkgo biloba - and now lives on Earth (in China and Japan). The leaves of these plants look like a fan and are collected in beautiful wide domes at the top. Their seeds taste like almonds; wood is very durable. A variety of ginkgo trees were very common on Earth during the Jurassic.

All these numerous plants vigorously assimilated carbon (from the air) and accumulated in themselves stocks of complex organic substances, continuing the work that plants had begun in previous periods. Luxurious development of vegetation has prepared for hitherto unheard-of flourishing of animal life.

With the onset of the Jurassic time, animal life on Earth was enriched with new forms. In the seas, the evolution of fish has led to the emergence of new breeds of fish - teleosts. They were strong rivals of the ancients cartilaginous fish, all these sharks, sturgeons, lobe-finned and lungfish. It is worth watching the movements of fast, nimble bony fish in order to understand what their main advantage is over the inactive and clumsy cartilaginous breeds. From the middle of the Mesozoic, bony fish begin to develop rapidly. They form many families, genera and species that fill the oceans, seas, lakes, and rivers. Even the greatest depths of the sea, in which, it would seem, no life is possible, give shelter to some breeds of bony fish. Not even light can penetrate this vast depth.

The constant calm of the cool water is occasionally disturbed by the appearance of strange, unseen forms of deep-sea creatures. Some of deep sea fish almost devoid of eyes - from these organs they have preserved only small rudiments, like those of a mole; in some, the eyes have completely disappeared, but at the front end of the muzzle there are huge luminous spots. Others have outgrowths with light organs at the ends (Fig. 32). The light emitted by the fish attracts prey to it, which in sea ​​depths irresistibly strives for the light, like night butterflies for a burning candle. In these inaccessible depths reigns brutal war and mutual devouring. There are fish with huge mouths, with a stomach that is stretchable like a rubber bladder, with long sharp teeth. With a deep-sea net, it happened to pull out a voracious predator with a transparent body, in whose huge stomach the luminous fish he had recently swallowed still flickered.

Rice. 32. Sea fish recently found at a depth of 750 meters

The struggle for life has driven some bony fish into these monstrous depths; there, these fish have adapted to conditions in which, it would seem, it is impossible for anyone to live. But the vast majority of fish of a new form - bony - settled in the seas and rivers, displacing almost completely the former inhabitants - sharks and other cartilaginous fish.

Life on land also advanced during this period. Forests, steppes and swamps were enriched with many breeds of reptiles. These animals were even more adapted to life on land than amphibians. Reptiles could already completely break with water. They are true inhabitants of forests, fields, mountains and valleys.

We know that they are descended from amphibians. How did it happen?

We have seen that some fish have developed lungs in the struggle for existence, and these fish, starting from carboniferous period, began to gradually turn into amphibians, then widely settled on the Earth. Being connected with water, amphibians could not settle somewhere in the depths of the country, in any desert area where it bakes during the day. bright sun. Their skin must be constantly moist, they feel good only in damp places. Remember the frog.

Let's go back for a moment to the end of the Paleozoic, when the climate began to change dramatically. Ice has come. At the same time, huge expanses of land were uplifted. The oceans and seas receded. The swamps became incomparably smaller. Extensive dry plains appeared, and in some places deserts. Amphibians had a hard time in the new environment: there was not enough water for the development of caviar, to maintain skin moisture. The adaptations that amphibians possessed were now insufficient for life on land. Some of them, like our toads, have warts on their skin. There were also those covered with scales. This was the easiest way to move to dry places and give rise to new breeds. But they should have happened to them too. big changes. First of all - in the method of reproduction. Spawning became impossible. It has been replaced by a different way of development. First of all, the eggs began to linger longer in the body, where they grew and became covered with a dense shell. But this alone was not enough.

It must also be taken into account that eggs amphibians are very numerous and the larvae hatched from them breathe with gills. They swim for a long time in the water and feed there on the food that they find in the silt and on water plants. With the transition to terrestrial life, such development became impossible. On land, these helpless fish-like larvae are doomed to die. But they survive if the eggs turn into eggs and gill respiration is replaced by pulmonary respiration. Neither reptiles nor their descendants - birds and mammals - ever have gill breathing either in adulthood or in embryonic life. Even if these animals again return to life in the water, such as whales, they rise to the surface of the water to breathe and take air into their lungs. This is an important change, which inevitably followed by others. Thus, the formation of two special embryonic membranes in reptiles, which remained in all birds and mammals, was a huge advantage in the struggle for existence. One of them is called water shell (amnion), the other is respiratory ( allantois, urinary sac). Both of these shells serve to ensure that the developing embryo can use atmospheric air.

The egg of a reptile or bird is very different from the egg of a fish or amphibian. The egg contains a nutritious yolk - a food supply for the embryo, which cannot feed itself, like a frog's tadpole. This food is enough for the embryo for the entire time of its development, until it becomes able to feed on its own (in reptiles).

complex egg reptile is covered with a protective shell - a shell - far from being as hard as that of birds. The eggs are laid on the ground where they develop. As soon as the embryo is formed, a double fold grows from its abdominal wall, which, growing, surrounds the entire embryo. Liquid accumulates between both folds, for which these folds are called " water shell". This shell separates the embryo from the surrounding world with its dangers and surprises. If someone pushes or rolls the egg, the water shell, like good springs, will protect it from shaking. If the air is very hot, the water shell will not allow the egg to overheat or dry out; if it suddenly becomes cold, as happens at night in places with a dry climate, the shell will come to the aid of the embryo here too: the cold will not reach it so soon through a layer of water.

Another germinal membrane is the respiratory, or urinary sac, - arises in a similar way as the water shell, and also consists of two layers. It serves mainly for breathing air. In this regard, the urinary sac lies outside the water sac, i.e., between this latter and the egg shell. This position is quite understandable: after all, it should be as close as possible to the outside air in order to absorb the oxygen necessary for breathing from it and give off the carbon dioxide accumulated in the embryo. On the surface of the urinary sac branches dense network of blood vessels associated with the vessels of the embryo. The blood vessels transport oxygen from the urinary sac to the fetus.

The eggshell is pierced with many small holes that are clearly visible through a magnifying glass. Through these holes, oxygen constantly seeps into the egg, and carbon dioxide leaves it. While the embryo is developing, the egg breathes vigorously. If these holes are covered up, covering, for example, an egg with varnish, then the embryo will soon die from strangulation, like a person whose throat is squeezed. Therefore, the urinary sac serves for breathing and works like lungs, and not like gills. An egg placed in water cannot develop, and the embryo suffocates, like any lung animal submerged in water. Such eggs, equipped with a water shell and a urinary sac, are laid by reptiles in the sand or hidden in a secluded mink warmed by the sun. After a few weeks, they hatch into mobile juveniles. If reptiles sometimes have to live in the water, such as crocodiles or sea turtles, then they still come ashore to breed and lay eggs.

It is clear that reptiles with such habits and adaptations can easily already live in completely dry areas. Indeed, many of them permanently live in deserts. Amphibians, if sometimes they can live as adults in a very dry place, then it is already difficult for them to breed there.

The Jurassic period can rightly be called the age of reptiles. Their prosperity was helped by the warm uniform climate of that time, without sharp changes in heat and cold. It was warm everywhere - both in those countries where the climate is now hot, and in those where we live, i.e. in temperate climate, and even in the cold regions of the far north. All year round stood straight summer weather. In places that are now permanently covered with ice crust, like Greenland, then a mild and warm climate reigned. Device earth's surface in the Jurassic, it also favored the reproduction and resettlement of reptiles. Then there were few mountains and other hills on Earth that would impede the movement of animals. All this prepared an unprecedented flourishing of life on land.

It is difficult for us even to imagine how great the dominance of reptiles was then. In our climate, reptiles are hardly noticeable. Occasionally a green or gray lizard will scurry into the dry grass, even more rarely a snake or a viper will come across, and it is very rare to see a turtle in the wild. We know crocodiles only from zoological gardens and books. True, in warmer climes even now one can come face to face with both a crocodile and terrible snakes - a boa constrictor, a rattlesnake, a spectacle snake; and now you can see huge turtles there, on which a person could ride. But modern monsters are pitiful small fry compared to those that lived in the Jurassic period. Then they were widely distributed throughout the Earth. And most of all there were those who long ago completely disappeared and gave way to new victors in the struggle of life.

During the Jurassic, monstrous reptiles swarmed everywhere. Some of them slowly and noisily wandered through the forests, dumping their heavy body huge trees, gnawing at them and leaving a trail behind them, as if from a windbreak. Others, even larger ones, lived in swamps and devastated entire thickets. Among them were the largest land animals that ever lived. One of these monsters - the brontosaurus - reached a length of almost 20 meters and a height of 5 meters (Fig. 33). And this lizard weighed about 40 tons! And this huge carcass of meat was controlled by a very small brain, sitting in a small head! One must think that the brontosaurus was not distinguished by either intelligence or speed of movement. Well, that's hardly what he needed. Who would dare to attack such a strong man and giant? There were no such brave predators in those days. Yes, and it was difficult to attack him. The brontosaurus spent its time in the water, where it enjoyed chewing soft aquatic plants all day long. In the water, his body was very stable, because his legs were thick, like logs, and heavy, and his fat back, reinforced on empty inside, very light dorsal vertebrae, was not heavy. Where the brontosaurus was up to its neck in water, any predator would have to swim through. This position is not very convenient for attackers.

Rice. 33. Brontosaurus (length about 20 meters) from the Jurassic deposits of North America

The brontosaurus could have been accompanied by other equally huge herbivorous lizards, such as the diplodocus, which was even longer than the brontosaurus (Fig. 34). The huge carcass of diplodocus was kept only on a vegetable diet: vegetable food could then be obtained in plenty, and it was already difficult to get enough animal food to feed this huge body. Both now and in the Jurassic, the largest land animals were herbivores. But no modern elephant can be compared either in height or in weight with the reptiles of that time. They were at least five times more elephants. The structure of the diplodocus teeth directly indicates the vegetable method of nutrition: its teeth are small and weak and could only serve to capture soft plants. The nostrils opened on the upper side of the head; this was very convenient for an animal that breathed air but spent its time in fairly deep water.

Rice. 34. Diplodocus (length about 30 meters) from the Jurassic layers of North America

Next to these huge, but peaceful vegetarians, there also lived ferocious predatory reptiles, recognizing only meat food. With their huge sharp teeth, they inspired no less horror in the then living world than lions and tigers now.

We have already spoken about one of the most ancient predatory reptiles, about foreigners discovered within the limits of our Union. Then the number of predators increased. One of them - Megalosaurus - lived in Western Europe. The huge bones of his legs were empty inside, which made jumping easier; the same was served by the voids in the vertebrae. This animal probably lay in a high thicket waiting for prey or lay in wait for it, hiding under the bushes. Prey were presumably mostly small animals. If any gaping lizard, inadvertently hunting for insects, approached the predator, he instantly jumped to his feet and overtook the victim with one or two jumps. The sharp claws with which his paws were armed pierced the skin of the victim, penetrating the gaps between the scales or tearing the skin. The predator carried his prey away from the battlefield in the same way that a cat carries off its prey. And then he used his saber-like teeth.

His relative was a small lizard known as compsognata. It reached a height of only 35–40 centimeters. Looking at his skeleton, it is easy to imagine that he was jumping or running in a half-upright position on two hind legs, like a bird.

The largest of all predatory lizards was tyrannosaurus rex, really “terrible lizard”, “dinosaur”, as science calls this entire group of extinct reptiles (Fig. 35). It reached 12–14 meters in length and 5–6 meters in height. Now on Earth there is no such huge predator. However, he was not very heavy on the rise. This is evidenced by the voids in his bones, which lightened the weight of the body. He lived, apparently, at the very end of the Jurassic and in the next, Cretaceous, period.

Rice. 35. Tyrannosaurus (had a length of 14 meters)

In the Jurassic time in North America, among the many large and small "saurs", that is, lizards, there lived another monster, which is impossible to remain silent about. When its remains were dug out of the ground, the strangest feature that caught everyone's eye was the huge bone plates sticking out of its back. The plates were of unequal shape and reached a meter in diameter. The skull was amazingly small for such a huge animal and had short, thick jaws. Looking carefully at the structure of the skull, we find that this animal had rather large eyes and, apparently, a good instinct: large eye sockets and a large nasal cavity indicate this. A row of teeth sat in the jaws. When they wear out, new ones grow in their place. They indicate that he ate soft plant foods. But it wasn't the teeth that were the monster's strongest point.

The dorsal vertebrae had huge processes, strong and bifurcated at the end, which supported heavy bone shields, as can be seen in our Fig. 36. The front legs were thick and short, with five fingers, the hind legs were much longer and stronger. If we add to this that a strong tail stretched behind, then it is not difficult to guess that the animal often stood on its hind legs, while leaning on its tail, like on a tripod, like the current kangaroo. On the hind legs there were only three toes, dressed with hooves. The front legs could move quite freely in different directions, like the forelimbs of monkeys, and help grasp food, and, in case of need, the defense of the animal. But for this purpose, a strong tail, armed with powerful sharp spikes, could have served better: with one stroke it could knock down, or even kill, any predator that dared to attack stegosaurus, as the scientists named the described animal. One of the amazing features of the Stegosaurus was the arrangement of its spinal cord. We have already said that his brain was very small. On the other hand, the spinal cord in the region of the sacrum greatly expanded and, as it were, formed an additional brain, which was much larger than the brain. This "brain" apparently served to regulate movements. Such a beast, apparently, really was "strong in hindsight."

Rice. 36. Stegosaurus (6 meters long)

Having mastered the land, the lizards multiplied so strongly, so densely populated the Earth, that they began to experience crowding. Some of them could find more space and food for themselves in the water. Many reptiles that have adapted to life away from water are returning to their native element, to water! But the wheel of history, both human and animal, cannot be turned back. Returning to the water, the reptiles retained all their main acquisitions and adaptations for life on land and did not turn back into amphibians. They remained lung animals, breathing atmospheric air, they did not begin to spawn in water, they retained their well-developed, well-ossified skeleton. At the same time, they also acquired some new features necessary for aquatic existence, and in appearance became more or less like fish.

The most famous aquatic reptile of the Mesozoic time is the fish lizard, or ichthyosaur. He was a strong swimmer, equipped with an excellent motor for moving quickly through the water in search of prey, which he grabbed with his mighty jaws. Its motor was a long, muscular tail; side flippers helped speed and accuracy of movements. The head was pointed at the end, and the whole body was streamlined like a spindle, which reduced the resistance of water during rapid movement. The growth of the ichthyosaur reached 8 meters and was so strong that the most powerful sharks retreated before it. He hunted for fish, although his huge mouth, seated with sharp teeth, could grab any prey. Enormous eyes glittered on the sides of the head, fringed with a ring of bones that protected them. As for the internal structure, the famous Cuvier, the founder of the science of fossil animals, beautifully said about it: “In the ichthyosaur we find the face of a dolphin, the teeth of a crocodile, the head and sternum of a lizard, the flippers of a whale and the vertebrae of a fish!” Such is the strange mixture of features combined in the skeleton of an ichthyosaur (Fig. 37).

Rice. 37. Ichthyosaurus

If this animal has such mixed signs different groups, then what right do we have to assert that it breathed with lungs, like any reptile, and not with gills, like fish? After all, the lungs are not preserved in a fossil form. To resolve this issue, the way is as follows: the gills of fish are always supported by special bones called gill arches. Not the slightest trace of these arcs has been found, although a lot of ichthyosaur skeletons have been excavated. Some museums have long held several dozen of them. In addition, the structure of the nasal cavity and nostrils of an ichthyosaur is exactly the same as that of other reptiles: the nostrils end in holes not at the end of the upper jaw, as in fish, but in front of the eyes, and special passages run from them in the skull through which air from nostril penetrated the windpipe and lungs. Needing air to breathe, ichthyosaurs were forced from time to time to rise to the surface of the water. The caudal fin of ichthyosaurs is arranged similarly to that of a fish; it stands upright and is particularly well adapted to swift and forceful movements in the water. It is interesting to compare the caudal fin of an ichthyosaur with a whale. In a whale, the fin lies transversely - in a horizontal plane and helps the speed of movement in this plane much less. This position of the fin is beneficial for the whale, as it makes it possible to quickly rise from the depth of the water to the surface for breathing with its help. The whale, as a warm-blooded mammal, needs fresh oxygen incomparably more than the ichthyosaur, which, due to its cold blood, has less need for oxygen. If the whale did not have a fin so located, it would not have the means to swim to the surface of the sea with the necessary speed, especially since the whale has only one pair of lateral fins - the front ones. The fish lizard, on the other hand, has both pairs of fins - front and back, and they, of course, helped him swim out of the depths into the upper layers of the water.

Ichthyosaurs swarmed in the seas of the early Jurassic and ate myriads of small and larger fish. We have direct evidence of this; next to their skeletons, fossilized secretions of these animals, the so-called coprolites, are found; these are accumulations of undigested scales of cartilaginous fish, which, as we know, were especially numerous in those days.

The remains of other animals found along with the bones of ichthyosaurs show that these animals swam at a shallow depth, not very far from sea ​​shores. And indeed, could an air-breathing fish lizard descend into a real deep sea? After all, he would have to spend too much time and effort to climb up for breathing.

Did ichthyosaurs ever come ashore? Previously, scientists thought that ichthyosaurs had to do this in order to lay eggs. However, it is difficult to admit that ichthyosaurs with their fins and bare skin dare to get out on land. How did they reproduce? Inside the skeleton of an adult ichthyosaur, small skeletons of ichthyosaurs were sometimes found. These little skeletons were always perfectly intact, even intact. If ichthyosaurs devoured their young, then the bones they swallowed would be torn from one another, crushed, bitten, etc. But it is impossible to assume that ichthyosaurs always swallowed their young as a whole. Therefore, one must think that they were viviparous and that their eggs were not laid in the sand, but developed in the mother's body until the time when the embryo was already able to swim independently in the water and catch fish. That there is nothing impossible in this is proved by the fact that among modern lizards there are also viviparous.

In the life of nature of that time, ichthyosaurs occupied the same place that whales now occupy in it. They are even some external features they looked like whales: they had bare skin, their nostrils sat close to their eyes, like whales, their jaws were very elongated. But this strange resemblance cannot be explained by the fact that ichthyosaurs are related to whales and that whales are descended from ichthyosaurs. This similarity only shows that similar conditions of life lead to similarities in certain characters. In the same way, whales are similar in some features to fish, but, of course, they are not in any close relationship with fish.

No matter how strong, no matter how numerous were the ichthyosaurs, but the time has come when their days began to draw to a close. Reptiles had to give up their place on Earth to other animals better organized than them. At one time, reptiles achieved predominance, but having begun to lag behind in the struggle for life, they almost died out by the end of the Cretaceous period. Major events on Earth led at that time to the extinction of many other ancient breeds of animals and plants.

But how widely these now extinct organisms settled in their time! Their remains have been found in Europe, and in India, and in North America, and in Africa, and in Australia, and even in the Arctic.

The climate in those days in all these places was almost the same and, moreover, mild and warm, semi-tropical. And one can think that it was climate change that was the first strong blow that led to their extinction. The appearance of other marine animals that challenged their prey was another cause of death. The disappearance of ichthyosaurs was, of course, also facilitated by the extinction of the prey itself - some invertebrates and cartilaginous fish.

At this time, there was an increased extinction of two more large groups animals: ammonites and belemnites died out - invertebrate animals belonging to soft-bodied, or molluscs. Both of these groups were very numerous from the first half of the Paleozoic and were found in the seas in a variety of rocks. Their countless shells, preserved in different layers of the Earth, primarily attract the attention of a geologist studying the fossil world.

Usually these shells serve the best leaders in determining the antiquity of one or another layer of the earth's crust. Each layer, each of its subdivisions - layer, or tier - is characterized by its own ammonite rocks with their own features in the structure of the shell, features that are easy to notice and convenient to describe. Both ammonites and belemnites belong to that class of soft-bodied animals called "cephalopods". These are exclusively marine animals. Not many people live in modern seas and oceans. cephalopods: octopuses, cuttlefish and boats with a beautifully twisted shell. The ship (Fig. 38) is a very ancient animal, preserved almost unchanged from the Paleozoic era. He is considered a close relative of the ammonites and belemnites. In most of the ammonites, like in the boat, the shell was twisted spirally in one plane and was divided inside by many partitions into a number of chambers following one after another. The mollusk itself sits in the room closest to the entrance to the shell, in the so-called living chamber, while all the other chambers lying behind the living chamber are filled with gas and are therefore called "air chambers". Passing through the middle of the partitions, a special organ stretches along the entire shell - a siphon, in which there are blood vessels. The mollusk has a complex organization, with well-developed sense organs, a nervous system, gills and a muscular leg. It is assumed that ammonites (Fig. 39) were predatory animals, some of them were good swimmers, others were crawling along the seabed. Belemnites had an inner shell with a long finger-like beak, which is usually the only one preserved. This is the so-called "devil's finger" (Fig. 40).

Rice. 38. The ship, the shell of which is shown opened

Rice. 39. Fossilized shells of two ammonites

Rice. 40. Preserved part of a belemnite shell

Conquest of water and air by reptiles

The fish lizard we have described was not the only reptile that adapted to life in the seas. We must also say a few words about other marine predators that challenged prey with fish lizards. The first place among them belongs to serpentine plesiosaurs.

Looking at the image of a plesiosaur (Fig. 41), we will understand why previous scientists compared it to a turtle through which a snake is threaded. A long, mobile neck and a relatively small head are the first to catch the eye. Plesiosaur fins are very different from ichthyosaur fins. The plesiosaur has flipper-like limbs that retain five fingers, while the ichthyosaur has greatly increased the number of fingers. So, the plesiosaur managed to change less, adapting to aquatic life.

The difference between him and the fish lizard is especially great in the structure of the skull. The head of the ichthyosaur sat on the body without any neck, while the neck of the plesiosaur is the longest part of the body, and the head is small, with long jaws. In the jaws there were numerous cells in which the teeth sat, like in crocodiles (in other reptiles, the teeth sit simply attached to the jaws, without any cells). Those plesiosaurs that lived in the Jurassic period were small, reaching a length of up to two and a half meters; their descendants in the Cretaceous became much larger - sometimes five meters long or more.

Rice. 41. Plesiosaurs from the Jurassic deposits. In the background on the right are ichthyosaurs

How did these animals swim? Ichthyosaurus was helped most of all when swimming by the tail, equipped with a large vertical fin. But the plesiosaur's tail was neither particularly large nor particularly strong. So this swimmer could not count on him. He had most of all to act with flippers. They were the main organs of the movement and, with their size and strength, could successfully play this role. They were like wide oars, two on each side of the body. There was not a trace of claws on them, even as weak as on the paws of turtles; therefore, one might think that the plesiosaurs were at home in the sea, and not on land. It was almost impossible for them to crawl on the ground. Plesiosaurs, like all reptiles, breathed with lungs and therefore had to swim to the surface to stock up on air. Plesiosaurs had many close and distant relatives that filled the seas and lakes. We will not talk about them. Let's just talk about one creature to do away with aquatic reptiles, about the largest and most ferocious predator of the Mesozoic seas - about the mosasaurus.

Mosasaurs appeared and flourished towards the end of the Mesozoic. Especially a lot of them lived in America in the Cretaceous period. Until now, in some places, researchers have found thousands of skeletons of these animals buried in the layers of the earth. Among such a multitude of bones, there are also completely intact skeletons. They reached a length of 14 meters, had an elongated, like a snake, body and a very long tail; their head was large, flattened and pointed towards the end, and their eyes were directed upwards. The body was equipped with two pairs of fins, resembling the flippers of a whale and always containing the bones of five-fingered limbs. With their help, with the assistance of the tail and thanks to the curves of their body, they could swim very quickly. The mouth was seated with several rows of teeth, and the jaws were arranged in a special way to swallow even very large prey whole. If people had lived at that time, then it would not have cost anything for a mosasaurus to swallow a whole person. The bones of the jaws did not grow together, but were connected by tensile ligaments, like rubber, and the mouth could expand as needed, depending on the size of the prey. The same arrangement of jaws is present in the current snakes. Adapting to life in the water, reptiles acquired features that greatly distinguished them from their land counterparts. aquatic life leaves a sharp seal on animals, as seen in whales, seals, and other aquatic mammals.

Rice. 42. Mosasaurus

But reptiles did not stop at the conquest of the earth's surface and waters. They began to take possession of the air. In the Mesozoic era, the great ocean of air was already inhabited by more than just insects, such as dragonflies, grasshoppers, butterflies and moths. Numerous finds of fossil bones show that during the Mesozoic, some reptiles also acquired the ability to fly and, in turn, populated the air. While there were no birds, these flying lizards were masters of the situation in the air; their flocks noisily roamed the sky in all directions, chasing each other or looking for prey. How did reptiles manage to become flyers?

There are two ways to fly in the air. Real flight can be called active: we see such flight in birds and technically carry it out on airplanes. Another flight - passive - consists in gliding through the air, as if on a parachute. During passive flight, the animal only delays, slows down its fall with the help of a flying membrane. With active flight, it can rise into the air and control its movement there. In today's vertebrates, both active and passive flight can be observed.

Some fish of the Earth's hot belt can, with the help of strong blows tail to jump out of the water and rush over its surface for a hundred and a half meters, acting on the front fins, which are greatly enlarged in these fish. Sometimes they rise so high above the water that they happen to fly onto the deck of the ship and fall on it from fatigue. This kind of flying fish lived in earlier times, which we know from their fossil bones and prints.

Rice. 43. Flying frog

From other examples it can be seen that passive flight most often develops in jumping animals. Here in front of you in Fig. 43 flying frog. For big jumps, this tree frog spreads his fingers, between which a particularly wide membrane is stretched. With its help, the frog delays its fall to the ground and glides through the air. Of course, she is not able to take off from the ground. In the same countries where flying frogs live, the so-called "dragon", that is, a flying lizard, is also found. Her flying membrane is reinforced on strongly protruding ribs. This dragon reaches 25 centimeters in length.

Finally, there is also the flying snake; she lives on the island of Borneo (south of the Asian mainland). Unwinding its elastic, like a spiral, body, it rushes obliquely down from the tree, and the concave abdominal surface, representing significant air resistance, protects it from falling to the ground; the snake descends in a smooth motion.

The flying lizards of the Mesozoic were completely different creatures. They appeared with Triassic period, i.e. from the beginning of the Mesozoic era, and existed until the end of the Cretaceous period. They have changed comparatively little over this vast span of time; only their structure was more and more adapted to flight. The size of the flying lizards were very different. Some are as tall as a sparrow, others have a wingspan of up to 8 meters. Some of the earlier ones had long tails and sharp teeth, in the later ones the tail became shorter, and the teeth no longer developed. One cannot help but see the resemblance to birds in this, but this resemblance does not prove a close relationship between birds and flying lizards. The similarity is due to adaptations for flight, which developed quite independently in birds and in flying lizards.

When the fossil bones of flying lizards were first discovered, the opinions of scientists were divided: some said that these were the bones of special birds, others considered them to be mammals similar to bats. Indeed, flying lizards have some similarities with both. Finally, about 130 years ago, the famous French scientist Cuvier took up these wonderful bones. He became convinced that the bones belonged to reptiles that were able to fly. Cuvier investigated how the wings of these animals were arranged. They consisted of a leathery membrane, like those of bats, but were not stretched, like those, between elongated fingers, but went from the hind legs to the forelegs and were attached in front to a very elongated little finger. For such a device of the wings, Cuvier named these animals finger-winged, or pterodactyls. Under this name they are known even now (Fig. 44).

Rice. 44. Jurassic Pterodactyl

Cuvier noticed the huge eye sockets of these animals and decided that they had very large eyes, like those of an owl, and that they probably led a nocturnal life. Later, other pterodactyls were discovered, with small eye sockets. This means that some of them flew more during the day, others - at night. Some of them could, folding their wings, crawl along the ground, clinging to it with sharp claws; others hung from trees or rocks, as the bats; many swooped over the seas and hunted fish, as the sea gulls, albatrosses and other birds do now. Small breeds fed on insects, which they caught with their wide beak. And those that had a wingspan of several meters had huge force and probably could be dragged away in the claws heavy booty. There were some among them who ate fruits, as some of today's bats do. Of course, all pterodactyls often had to sit on the ground to rest, and among them there were no such tireless flyers as are found among birds.

We have not named even a tenth of those monsters that the Earth carried on itself in the Jurassic and Cretaceous periods. We haven't even mentioned some of the biggest ones. The largest of them were the size of a two-story or three-story house. Fossilized skeletons of such lizards are kept in museums, where one such skeleton sometimes occupies two huge floors.

It would seem that reptiles, so large and strong, which gave rise to so many breeds and did not know their rivals for many millions of years, should forever remain masters on Earth. But just when reptiles occupied a dominant position among other animals, the relentlessly continuing struggle for life led to the appearance on Earth of the first small and insignificant mammals, which the huge lizards probably didn't even notice at first. Yet the mammals proved to be the grave-diggers of the lizard giants.

At about the same time, another great event in the history of the Earth was taking place. The first birds. Their remnants have come down to us. According to them, it is possible to some extent to restore the history of the origin of these wonderful creatures.

Origin of birds

In old fairy tales and legends, people are endowed with supernatural powers and are often depicted as flying through the air. But it was only about 150 years ago that science first came close to this issue, and fantasy began to come true. The first flights began balloons . Aeronautics remained at this stage until the end of the 19th century, when a new and major step forward was made in the development of aeronautical technology - the creation of aircraft, raising both the pilot, and the engine, and the fuel supply. But even now, despite the huge achievements of aviation, modern airplanes in some respects, they are still far from the perfection that distinguishes the amazing “flying machine” - the bird. Achieving avian perfection in flight is the task of future technology.

The remains of an ancient representative of birds - firstbirds- miraculously preserved to this day.

It was in the Jurassic period. If a person could travel back in time, he would see a huge shallow sea covered with countless islands and islets in the place of most of modern Europe. IN warm waters this sea flourished a rich life. Motley corals piled up their buildings, and countless fish, crustaceans and worms found shelter in them. There were especially many soft-bodied, with a variety of shells (ammonites, belemnites). From time to time, the crocodile-shaped head of an ichthyosaur protruded from the water and the long swan-like neck of a plesiosaur, those voracious predators of the then seas, rose up from the water.

The bottom of the sea was completely littered with many shells, shells and skeletons of dead animals and was the most delicate and smallest calcareous silt. Gusts of wind often carried seeds from neighboring islands with plant seeds that bordered the calcareous shores with a green frame, and sometimes insects - large dragonflies rushing in the air for prey. Having fallen on soft silt, these animals often left delicate imprints of their structure on it. Ebb and flow waves carried with them the bodies of other animals. They threw the remains of marine rocks onto land, and carried the land ones into the sea. These latter found here a grave for themselves in soft calcareous silt, in which from year to year, from century to century, more and more remains and imprints of living beings accumulated.

The silt of the seabed gradually turned into an underwater museum, preserving countless remains of the then plants and animals. Even those that did not have hard skeletal parts, but consisted entirely of a soft gelatinous substance, sometimes left their marks on it. Their delicate little bodies were enveloped in a soft mass that gradually hardened; when there was nothing left of the animal, at the place of its burial, a kind of death mask was preserved from hardened, often petrified silt.

Millions of years passed slowly. If we could accelerate their course and watch, as in the cinema, the changes that took place where the Central European Plain now stretches, we would notice how the seabed rose and the waves receded, how the Earth's crust how mountains arose and grew, how some plants and animals were replaced by others, until, finally, a picture of modern Europe was formed.

Mesozoic era - the middle ages of the earth Life takes possession of land and air What changes and improves living beings? The collections of fossils collected in the geological and mineralogical museum have already told us a lot: about the depths of the Cambrian Sea, where people similar to