Early Mesozoic. Mesozoic era: in the world of fantastic giants

Mesozoic era

The Mesozoic era is the era of middle life. It is named so because the flora and fauna of this era are transitional between the Paleozoic and Cenozoic. During the Mesozoic era, the modern outlines of continents and oceans, modern marine fauna and flora gradually formed. The Andes and Cordillera, the mountain ranges of China and East Asia, were formed. The depressions of the Atlantic and Indian Oceans were formed. The formation of the Pacific Ocean depressions began.

The Mesozoic era is divided into three periods: Triassic, Jurassic and Cretaceous.

Triassic

The Triassic period got its name from the fact that its deposits include three different rock complexes: the lower - continental sandstone, the middle - limestone and the upper - Naper.

The most characteristic deposits of the Triassic period are: continental sandy-clayey rocks (often with lenses of coal); marine limestones, clays, shales; lagoonal anhydrites, salts, gypsum.

During the Triassic period, the northern continent of Laurasia united with the southern one - Gondwana. A large bay that began in the east of Gondwana extended all the way to the northern coast modern Africa, then turned south, almost completely separating Africa from Gondwana. A long bay stretched from the west, separating the western part of Gondwana from Laurasia. Many depressions appeared on Gondwana, which were gradually filled with continental sediments.

During the Middle Triassic, volcanic activity intensified. Inland seas become shallow and numerous depressions form. The formation of the mountain ranges of Southern China and Indonesia begins. In the territory of the modern Mediterranean, the climate was warm and humid. It was cooler and wetter in the Pacific zone. Deserts dominated the territory of Gondwana and Laurasia. The climate of the northern half of Laurasia was cold and dry.

Along with changes in the distribution of sea and land, the formation of new mountain ranges and volcanic areas, there was an intensive replacement of some animal and plant forms by others. Only a few families moved from the Paleozoic era to the Mesozoic. This gave grounds for some researchers to claim about the great catastrophes that occurred at the boundary of the Paleozoic and Mesozoic. However, when studying the deposits of the Triassic period, one can easily verify that there is no sharp line between them and the Permian deposits; therefore, some forms of plants and animals were replaced by others, probably gradually. The main reason was not catastrophes, but the evolutionary process: more perfect forms gradually replaced less perfect ones.

The seasonal temperature changes of the Triassic period began to have a noticeable effect on plants and animals. Individual groups reptiles have adapted to the cold seasons. It was from these groups that mammals originated in the Triassic, and somewhat later, birds. At the end of the Mesozoic era, the climate became even colder. Deciduous woody plants appear, which partially or completely shed their leaves during cold seasons. This feature of plants is an adaptation to a colder climate.

The cooling during the Triassic period was insignificant. It was most pronounced in northern latitudes. The rest of the area was warm. Therefore, reptiles felt quite well in the Triassic period. Their most diverse forms, with which small mammals were not yet able to compete, settled across the entire surface of the Earth. The rich vegetation of the Triassic period also contributed to the extraordinary flourishing of reptiles.

Gigantic forms of cephalopods developed in the seas. The diameter of the shells of some of them was up to 5 m. True, gigantic cephalopods, for example, squids reaching 18 m in length, but in the Mesozoic era there were much more gigantic forms.

The composition of the atmosphere of the Triassic period changed little compared to the Permian. The climate became wetter, but deserts remained in the center of the continent. Some plants and animals of the Triassic period have survived to this day in the region of Central Africa and South Asia. This suggests that the composition of the atmosphere and the climate of individual land areas remained almost unchanged during the Mesozoic and Cenozoic eras.

And yet stegocephalians became extinct. They were replaced by reptiles. More perfect, mobile, well adapted to a variety of living conditions, they ate the same food as stegocephals, settled in the same places, ate the young of stegocephals and ultimately exterminated them.

Among the Triassic flora, calamites, seed ferns and cordaites were also occasionally found. True ferns, ginkgo ferns, bennetite ferns, cycads, and conifers predominated. Cycads still exist in the Malay Archipelago region. They are known as sago palms. In my own way appearance Cycads occupy an intermediate position between palms and ferns. The cycad trunk is quite thick and columnar. The crown consists of hard, feathery leaves arranged in a corolla. Plants reproduce using macro- and microspores.

Triassic ferns were coastal herbaceous plants that had wide, dissected leaves with reticulate venation. Volttsia has been well studied among coniferous plants. It had a thick crown and cones like those of a spruce.

The ginkgos were quite tall trees, their leaves formed dense crowns.

A special place among the Triassic gymnosperms was occupied by bennettites - trees with whorled large compound leaves, reminiscent of the leaves of cycads. The reproductive organs of bennetites occupy an intermediate place between the cones of cycads and the flowers of some flowering plants, in particular magnolias. Thus, it is probably the bennetites that should be considered the ancestors of flowering plants.

Of the invertebrates of the Triassic period, all types of animals that exist in our time are already known. The most characteristic marine invertebrates were reef-building animals and ammonites.

In the Paleozoic, animals already existed that covered the bottom of the sea in colonies, forming reefs, although not very powerful. During the Triassic period, when many colonial six-rayed corals appear instead of tabulates, the formation of reefs up to a thousand meters thick begins. The cups of six-rayed corals had six or twelve calcareous partitions. As a result of the massive development and rapid growth of corals, underwater forests were formed on the seabed, in which numerous representatives of other groups of organisms settled. Some of them took part in reef formation. Bivalves, algae, sea urchins, sea stars, sponges lived between the corals. Destroyed by waves, they formed coarse-grained or fine-grained sand, which filled all the voids of the corals. Washed out of these voids by waves, calcareous silt was deposited in bays and lagoons.

Some bivalves are quite characteristic of the Triassic period. Their paper-thin shells with fragile ribs form in some cases entire layers in the sediments of a given period. Bivalves lived in shallow muddy bays - lagoons, on reefs and between them. In the Upper Triassic period, many thick-shelled bivalves appeared, firmly attached to the limestone deposits of shallow basins.

At the end of the Triassic, due to increased volcanic activity, part of the limestone deposits was covered with ash and lavas. The steam rising from the bowels of the Earth brought with it many compounds from which deposits of non-ferrous metals were formed.

The most common of the gastropods were prosobranchs. Ammonites spread widely in the seas of the Triassic period, the shells of which accumulated in huge quantities in some places. Having appeared in the Silurian period, they did not yet play a major role among other invertebrates throughout the Paleozoic era. Ammonites could not successfully compete with the rather complex nautiloids. Ammonite shells were formed from calcareous plates that were the thickness of tissue paper and therefore did little to protect the soft body of the mollusk. Only when their partitions bent into numerous folds did the shells of ammonites acquire strength and turn into real shelter from predators. With the increasing complexity of the partitions, the shells became even more durable, and the external structure gave them the opportunity to adapt to a wide variety of living conditions.

Representatives of echinoderms were sea urchins, lilies and stars. At the upper end of the body of crinoids there was a flower-like main part. It distinguishes between a corolla and grasping organs - “hands”. Between the “hands” in the corolla there were the oral and anal openings. With its “hands” the sea lily scooped water into its mouth, and with it the sea animals that it fed on. The stem of many Triassic crinoids was spiral.

The Triassic seas were inhabited by calcareous sponges, bryozoans, leaf-footed crayfish, and ostracods.

Fish were represented by sharks that lived in fresh water bodies and molluscoids that inhabited the sea. The first primitive bony fishes appear. Powerful fins, well-developed dental apparatus, perfect shape, strong and light skeleton - all this contributed to the rapid spread of bony fish in the seas of our planet.

Amphibians were represented by stegocephalians from the labyrinthodont group. These were sedentary animals with a small body, small limbs and a large head. They lay in the water waiting for prey, and when the prey approached, they grabbed it. Their teeth had complex labyrinthine folded enamel, which is why they were called labyrinthodonts. The skin was moistened by mucous glands. Other amphibians came onto land to hunt insects. The most characteristic representatives of labyrinthodonts are mastodonosaurs. These animals, whose skulls reached one meter in length, resembled huge frogs in appearance. They hunted fish and therefore rarely left the aquatic environment.

Mastodonosaurus.

The swamps became smaller, and mastodonosaurs were forced to populate deeper and deeper places, often accumulating in large numbers. That is why many of their skeletons are now found in small areas.

Reptiles in the Triassic are characterized by significant diversity. New groups are appearing. Of the cotylosaurs, only procolophons remain - small animals that fed on insects. An extremely interesting group of reptiles was represented by archosaurs, which included thecodonts, crocodiles and dinosaurs. Representatives of thecodonts, ranging in size from a few centimeters to 6 m, were predators. They also differed in a number of primitive features and were similar to the Permian pelycosaurs. Some of them - pseudosuchia - had long limbs, a long tail and led a terrestrial lifestyle. Others, including the crocodyliform phytosaurs, lived in the water.

Crocodiles of the Triassic period - small primitive protosuchian animals - lived in fresh water bodies.

Among the dinosaurs, theropods and prosauropods appear. Theropods moved on well-developed hind limbs, had a heavy tail, powerful jaws, and small and weak forelimbs. These animals ranged in size from a few centimeters to 15 m. All of them were classified as predators.

Prosauropods typically ate plants. Some of them were omnivores. They walked on four legs. Prosauropods had a small head, long neck and tail.

Representatives of the subclass of synaptosaurs led a very diverse lifestyle. Trilophosaurus climbed trees and ate plant foods. In appearance he resembled a cat.

Seal-like reptiles lived near the coast, feeding mainly on mollusks. Plesiosaurs lived in the sea, but sometimes came ashore. They reached 15 m in length. They ate fish.

In some places, quite often they find footprints of a huge animal that walked on four legs. It was called chirotherium. Based on the preserved prints, one can imagine the structure of the foot of this animal. Four gangly toes surrounded a thick, fleshy sole. Three of them had claws. The forelimbs of Chirotherium are almost three times smaller than the hind limbs. The animal left deep footprints on the wet sand. As new layers were deposited, the traces gradually petrified. Later, the land was flooded by the sea, hiding the traces. They turned out to be covered with marine sediments. Consequently, the sea flooded repeatedly during that era. The islands sank below sea level, and the animals living on them were forced to adapt to new conditions. Many reptiles appear in the sea, which undoubtedly descended from continental ancestors. Turtles with a wide bony shell, dolphin-like ichthyosaurs - fish lizards and gigantic plesiosaurs with a small head on a long neck - quickly developed. Their vertebrae are transformed, their limbs change. The cervical vertebrae of an ichthyosaur grow together into one bone, and in turtles they grow to form the upper part of the shell.

The ichthyosaur had a row of uniform teeth; in turtles the teeth disappear. The five-fingered limbs of ichthyosaurs turn into flippers well adapted for swimming, in which it is difficult to distinguish the shoulder, forearm, wrist and finger bones.

Starting from the Triassic period, reptiles, which moved to live in the sea, gradually populated increasingly vast areas of the ocean.

The oldest mammal found in the Triassic sediments of North Carolina is called dromaterium, which means “running beast.” This “beast” was only 12 cm in length. Dromatherium belonged to oviparous mammals. They, like the modern Australian echidna and platypus, did not give birth to young, but laid eggs, from which underdeveloped young hatched. Unlike reptiles, which did not care at all about their offspring, Dromatheriums fed their young with milk.

Deposits of oil, natural gases, brown and hard coal, iron and copper ore, rock salt.

The Triassic period lasted 35 million years.

Jurassic period

For the first time, deposits of this period were found in the Jura (mountains in Switzerland and France), hence the name of the period. The Jurassic period is divided into three divisions: Leyas, Doger and Malm.

The deposits of the Jurassic period are quite diverse: limestones, clastic rocks, shales, igneous rocks, clays, sands, conglomerates, formed in a wide variety of conditions.

Sedimentary rocks containing many representatives of fauna and flora are widespread.

Intense tectonic movements at the end of the Triassic and the beginning of the Jurassic periods contributed to the deepening of large bays, which gradually separated Africa and Australia from Gondwanaland. The gulf between Africa and America has deepened. Depressions formed in Laurasia: German, Anglo-Paris, West Siberian. The Arctic Sea flooded the northern coast of Laurasia.

Intense volcanism and mountain-building processes determined the formation of the Verkhoyansk fold system. The formation of the Andes and Cordillera continued. Warm sea currents reached Arctic latitudes. The climate became warm and humid. This is evidenced by the significant distribution of coral limestones and the remains of thermophilic fauna and flora. Very few deposits of dry climates are found: lagoonal gypsum, anhydrites, salts and red sandstones. The cold season already existed, but it was characterized only by a decrease in temperature. There was no snow or ice.

The climate of the Jurassic period depended not only on sunlight. Many volcanoes and magma outpourings onto the bottom of the oceans heated the water and atmosphere, saturating the air with water vapor, which then rained onto the land and flowed into lakes and oceans in stormy streams. This is evidenced by numerous freshwater deposits: white sandstones alternating with dark loams.

The warm and humid climate favored the flourishing of the plant world. Ferns, cycads, and conifers formed vast swampy forests. Araucarias, thujas, and cycads grew on the coast. Ferns and horsetails formed the undergrowth. In the Lower Jurassic, throughout the northern hemisphere, vegetation was quite monotonous. But starting from the Middle Jurassic, two plant zones can be identified: the northern, in which ginkgo and herbaceous ferns predominated, and the southern with bennetites, cycads, araucarias, and tree ferns.

The characteristic ferns of the Jurassic period were matonia, which are still preserved in the Malay Archipelago. Horsetails and mosses were almost no different from modern ones. The place of extinct seed ferns and cordaites is taken by cycads, which still grow in tropical forests.

Ginkgo plants were also widespread. Their leaves turned edge-on to the sun and resembled huge fans. From North America and New Zealand to Asia and Europe, dense forests of coniferous plants grew - araucaria and bennettites. The first cypress and possibly spruce trees appear.

Representatives of the Jurassic conifers also include sequoia - the modern giant California pine. Currently, redwoods remain only on the Pacific coast of North America. Some forms of even more ancient plants, for example glassopteris, have been preserved. But there are few such plants, since they were replaced by more advanced ones.

The lush vegetation of the Jurassic period contributed to the widespread distribution of reptiles. Dinosaurs have evolved significantly. Among them, lizard-hatched and ornithischian are distinguished. Lizards moved on four legs, had five toes on their feet, and ate plants. Most of them had a long neck, small head and long tail. They had two brains: one small one in the head; the second is much larger in size - at the base of the tail.

The largest of Jurassic dinosaurs there was a brachiosaurus that reached a length of 26 m and weighed about 50 tons. It had columnar legs, a small head, and a thick long neck. Brachiosaurs lived on the shores of Jurassic lakes and fed on aquatic vegetation. Every day, the brachiosaurus needed at least half a ton of green mass.

Brachiosaurus.

Diplodocus is the oldest reptile, its length was 28 m. It had a long thin neck and a long thick tail. Like a brachiosaurus, Diplodocus walked on four legs, the hind legs being longer than the front ones. Diplodocus spent most of its life in swamps and lakes, where it grazed and escaped from predators.

Diplodocus.

Brontosaurus was relatively tall, had a large hump on its back and a thick tail. Its length was 18 m. The vertebrae of the brontosaurus were hollow. Chisel-shaped small teeth were densely located on the jaws of the small head. The brontosaurus lived in swamps and on the shores of lakes.

Brontosaurus.

Ornithischian dinosaurs are divided into bipeds and quadrupeds. Different in size and appearance, they fed mainly on vegetation, but predators are already appearing among them.

Stegosaurs are herbivores. They had two rows of large plates on their backs and paired spikes on their tails that protected them from predators. Many scaly lepidosaurs appear - small predators with beak-like jaws.

Flying lizards first appeared in the Jurassic period. They flew using a leathery shell stretched between the long finger of the hand and the bones of the forearm. Flying lizards were well adapted to flight. They had light tube-shaped bones. The extremely elongated outer fifth digit of the forelimbs consisted of four joints. The first finger looked like a small bone or was completely absent. The second, third and fourth fingers consisted of two, rarely three bones and had claws. The hind limbs were quite developed. There were sharp claws at their ends. The skull of flying lizards was relatively large, usually elongated and pointed. In old lizards, the cranial bones fused and the skulls became similar to the skulls of birds. The premaxillary bone sometimes grew into an elongated toothless beak. Toothed lizards had simple teeth and sat in recesses. The largest teeth were in the front. Sometimes they stuck out to the side. This helped the lizards catch and hold prey. The animals' spine consisted of 8 cervical, 10–15 dorsal, 4–10 sacral and 10–40 caudal vertebrae. The chest was wide and had a high keel. The shoulder blades were long, the pelvic bones were fused. The most typical representatives of flying lizards are pterodactyl and rhamphorhynchus.

Pterodactyl.

Pterodactyls in most cases were tailless, varying in size - from the size of a sparrow to a crow. They had wide wings and a narrow skull elongated forward with a small number of teeth in the front. Pterodactyls lived in large flocks on the shores of the lagoons of the Late Jurassic Sea. During the day they hunted, and at nightfall they hid in trees or rocks. The skin of pterodactyls was wrinkled and bare. They ate mainly fish, sometimes sea lilies, mollusks, and insects. In order to take off, pterodactyls were forced to jump from cliffs or trees.

Rhamphorhynchus had long tails, long narrow wings, and a large skull with numerous teeth. Long teeth of varying sizes curved forward. The lizard's tail ended in a blade that served as a rudder. Rhamphorhynchus could take off from the ground. They settled on the banks of rivers, lakes and seas, feeding on insects and fish.

Rhamphorhynchus.

Flying lizards lived only in the Mesozoic era, and their heyday occurred in the Late Jurassic period. Their ancestors were, apparently, extinct ancient reptiles pseudosuchians. Long-tailed forms appeared earlier than short-tailed ones. At the end of the Jurassic period they became extinct.

It should be noted that flying lizards were not the ancestors of birds and bats. Flying lizards, birds and the bats each originated and developed in its own way, and there are no close family ties between them. The only thing they have in common is the ability to fly. And although they all acquired this ability due to changes in the forelimbs, the differences in the structure of their wings convince us that they had completely different ancestors.

The seas of the Jurassic period were inhabited by dolphin-like reptiles - ichthyosaurs. They had long head, sharp teeth, big eyes surrounded by a ring of bone. The length of the skull of some of them was 3 m, and the length of the body was 12 m. The limbs of ichthyosaurs consisted of bone plates. The elbow, metatarsus, hand and fingers differed little from each other in shape. About a hundred bone plates supported the wide flipper. The shoulder and pelvic girdles were poorly developed. There were several fins on the body. Ichthyosaurs were viviparous animals. Plesiosaurs lived alongside ichthyosaurs. They had a thick body with four flipper-like limbs, a long snake-like neck with a small head.

During the Jurassic period, new genera of fossil turtles appeared, and at the end of the period, modern turtles appeared.

Tailless frog-like amphibians lived in fresh water bodies. There were a lot of fish in the Jurassic seas: bony fish, stingrays, sharks, cartilaginous fish, and ganoid fish. They had an internal skeleton made of flexible cartilage tissue, impregnated with calcium salts: a dense bony scaly covering that protected them well from enemies, and jaws with strong teeth.

Among the invertebrates in the Jurassic seas, there were ammonites, belemnites, and crinoids. However, in the Jurassic period there were much fewer ammonites than in the Triassic. Jurassic ammonites differ from Triassic ammonites in their structure, with the exception of phyloceras, which did not change at all during the transition from the Triassic to the Jurassic. Certain groups of ammonites have preserved mother-of-pearl to this day. Some animals lived in the open sea, others inhabited bays and shallow inland seas.

Cephalopods - belemnites - swam in whole schools in the Jurassic seas. Along with small specimens, there were real giants - up to 3 m long.

Remains of belemnite internal shells, known as “devil's fingers,” are found in Jurassic sediments.

In the seas of the Jurassic period, bivalves also developed significantly, especially those belonging to the oyster family. They begin to form oyster banks.

The sea urchins that settled on the reefs are undergoing significant changes. Along with the round forms that have survived to this day, there lived bilaterally symmetrical irregular shape hedgehogs Their body was stretched in one direction. Some of them had a jaw apparatus.

The Jurassic seas were relatively shallow. The rivers brought them muddy water, delaying gas exchange. The deep bays were filled with rotting debris and silt containing large amounts of hydrogen sulfide. That is why in such places the remains of animals carried by sea currents or waves are well preserved.

Sponges, starfish, and crinoids often overflow the Jurassic sediments. “Five-armed” crinoids became widespread during the Jurassic period. Many crustaceans appear: barnacles, decapods, phyllopods, freshwater sponges, among insects - dragonflies, beetles, cicadas, bugs.

The first birds appeared during the Jurassic period. Their ancestors were the ancient reptiles pseudosuchians, which also gave rise to dinosaurs and crocodiles. Ornithosuchia is most similar to birds. She, like a bird, walked on her hind legs, had a strong pelvis and was covered with feather-like scales. Some pseudosuchians moved to live in trees. Their forelimbs were specialized for grasping branches with their fingers. The pseudosuchian skull had lateral depressions, which significantly reduced the mass of the head. Climbing trees and jumping on branches strengthened the hind limbs. Gradually expanding forelimbs supported the animals in the air and allowed them to glide. An example of such a reptile is Scleromochlusa. His long, thin legs indicate that he was a good jumper. Elongated forearms helped animals climb and cling to branches of trees and bushes. The most important point the process of transforming reptiles into birds involved the transformation of scales into feathers. The animals' hearts had four chambers, which ensured a constant body temperature.

In the Late Jurassic period, the first birds appeared - Archeopteryx, the size of a pigeon. In addition to short feathers, Archeopteryx had seventeen flight feathers on its wings. The tail feathers were located on all tail vertebrae and were directed back and down. Some researchers believe that the bird's feathers were bright, like those of modern tropical birds, others that the feathers were gray or brown, and still others that they were motley. The weight of the bird reached 200 g. Many signs of Archeopteryx indicate its family ties with reptiles: three free fingers on the wings, a head covered with scales, strong conical teeth, a tail consisting of 20 vertebrae. The bird's vertebrae were biconcave, like those of fish. Archeopteryx lived in araucaria and cycad forests. They ate mainly insects and seeds.

Archeopteryx.

Predators appeared among mammals. Small in size, they lived in forests and dense bushes, hunting small lizards and other mammals. Some of them have adapted to life in trees.

Deposits of coal, gypsum, oil, salt, nickel and cobalt are associated with Jurassic deposits.

This period lasted 55 million years.

Cretaceous period

The Cretaceous period received this name because thick chalk deposits are associated with it. It is divided into two sections: lower and upper.

Mountain-building processes at the end of the Jurassic period significantly changed the outlines of continents and oceans. North America, previously separated from the vast Asian continent by a wide strait, connected with Europe. In the east, Asia merged with America. South America was completely separated from Africa. Australia was located where it is today, but was smaller in size. The formation of the Andes and Cordilleras, as well as individual ridges of the Far East, continues.

During the Upper Cretaceous period, the sea flooded vast areas of the northern continents. Were under water Western Siberia and Eastern Europe, most of Canada and Arabia. Thick layers of chalk, sand, and marls accumulate.

At the end of the Cretaceous period, mountain-building processes were again activated, as a result of which the mountain ranges of Siberia, the Andes, the Cordillera and the mountain ranges of Mongolia were formed.

The climate has changed. In the high latitudes in the north during the Cretaceous period there was already real winter with snow. Within the boundaries of the modern temperate zone, some tree species (walnut, ash, beech) were no different from modern ones. The leaves of these trees fell for the winter. However, as before, the climate in general was much warmer than today. Ferns, cycads, ginkgos, bennetites, and conifers, in particular sequoias, yews, pines, cypresses, and spruces, were still common.

In the mid-Cretaceous period, flowering plants flourished. At the same time, they displace representatives of the most ancient flora - spore and gymnosperm plants. It is believed that flowering plants originated and developed in the northern regions, and subsequently they spread throughout the planet. Flowering plants are much younger than conifers, known to us since the Carboniferous period. The dense forests of giant tree ferns and horsetails had no flowers. They adapted well to the living conditions of that time. However, gradually the humid air of the primary forests became increasingly dry. There was very little rain, and the sun was unbearably hot. The soil in the areas of primary swamps dried out. Deserts appeared on the southern continents. Plants moved to areas with cooler, wetter climates in the north. And then the rains came again, saturating the damp soil. Climate ancient Europe became tropical, forests similar to modern jungles appeared on its territory. The sea recedes again, and plants that inhabited the coast in a humid climate found themselves in a drier climate. Many of them died, but some adapted to new living conditions, forming fruits that protected the seeds from drying out. The descendants of such plants gradually populated the entire planet.

The soil also underwent changes. Silt and the remains of plants and animals enriched it with nutrients.

In primary forests, plant pollen was carried only by wind and water. However, the first plants appeared, the pollen of which insects fed on. Some of the pollen stuck to the wings and legs of the insects, and they transferred it from flower to flower, pollinating the plants. In pollinated plants, the seeds ripened. Plants that were not visited by insects did not reproduce. Therefore, only plants with fragrant flowers a variety of shapes and colors.

With the advent of flowers, insects also changed. Among them appear insects that cannot live without flowers at all: butterflies, bees. Fruits with seeds developed from pollinated flowers. Birds and mammals ate these fruits and carried the seeds over long distances, spreading the plants to new areas of the continents. Many herbaceous plants appeared and populated the steppes and meadows. The leaves of the trees fell off in the fall, and in summer heat curled up.

The plants spread to Greenland and the islands of the Arctic Ocean, where it was relatively warm. At the end of the Cretaceous period, with the cooling of the climate, many cold-resistant plants appeared: willow, poplar, birch, oak, viburnum, which are also characteristic of the flora of our time.

With the development of flowering plants, by the end of the Cretaceous period the bennetites became extinct, and the number of cycads, ginkgos, and ferns decreased significantly. Along with the change in vegetation, the fauna also changed.

Foraminifera spread significantly, the shells of which formed thick chalk deposits. The first nummulites appear. Corals formed reefs.

Ammonites of the Cretaceous seas had shells of a peculiar shape. If all the ammonites that existed before the Cretaceous period had shells wrapped in one plane, then the Cretaceous ammonites had elongated shells, bent in the form of a knee, and there were spherical and straight shells. The surface of the shells was covered with spines.

According to some researchers, the bizarre forms of Cretaceous ammonites are a sign of aging of the entire group. Although some representatives of ammonites still continued to reproduce from high speed, their vital energy almost dried up during the Cretaceous period.

According to other scientists, ammonites were exterminated by numerous fish, crustaceans, reptiles, and mammals, and the strange forms of Cretaceous ammonites are not a sign of aging, but mean an attempt to somehow protect themselves from excellent swimmers, which by that time had become bony fish and sharks.

The disappearance of ammonites was also facilitated by a sharp change in physical and geographical conditions in the Cretaceous period.

Belemnites, which appeared much later than ammonites, also completely died out during the Cretaceous period. Among the bivalves there were animals of different shapes and sizes that closed the valves with the help of denticles and pits. In oysters and other mollusks that are attached to the seabed, the valves become different. The lower flap looked like a deep bowl, and the upper one looked like a lid. Among the rudists, the lower valve turned into a large thick-walled glass, inside of which only a small chamber remained for the mollusk itself. The round, lid-like upper flap covered the lower one with strong teeth, with the help of which it could rise and fall. Rudists lived mainly in the southern seas.

In addition to bivalves, whose shells consisted of three layers (outer horny, prismatic and mother-of-pearl), there were mollusks with shells that had only a prismatic layer. These are mollusks of the genus Inoceramus, widely distributed in the seas of the Cretaceous period - animals that reached one meter in diameter.

During the Cretaceous period, many new species of gastropods appeared. Among sea urchins, the number of irregular heart-shaped forms especially increases. And among sea lilies, varieties appear that do not have a stem and float freely in the water with the help of long feathery “arms”.

Great changes have also occurred among fish. In the seas of the Cretaceous period, ganoid fish gradually became extinct. The number of bony fishes is increasing (many of them still exist today). Sharks are gradually acquiring a modern appearance.

Numerous reptiles still lived in the sea. The descendants of the ichthyosaurs that became extinct at the beginning of the Cretaceous period reached 20 m in length and had two pairs of short flippers.

New forms of plesiosaurs and pliosaurs appear. They lived on the open sea. Crocodiles and turtles inhabited freshwater and saltwater basins. On the territory of modern Europe lived large lizards with long spines on the back and huge pythons.

Of the terrestrial reptiles, trachodons and horned lizards were especially characteristic of the Cretaceous period. Trachodons could move on both two and four legs. They had membranes between their fingers that helped them swim. Trachodons' jaws resembled a duck's beak. They had up to two thousand small teeth.

Triceratops had three horns on their heads and a huge bone shield that reliably protected the animals from predators. They lived mainly in dry places. They ate vegetation.

Triceratops.

Styracosaurs had nasal projections - horns and six horny spines on the posterior edge of the bony shield. Their heads reached two meters in length. The spines and horns made Styracosaurus dangerous to many predators.

The most terrible predatory lizard was the Tyrannosaurus. It reached a length of 14 m. Its skull, more than a meter long, had large sharp teeth. The tyrannosaurus moved on powerful hind legs, supported by a thick tail. Its front legs were small and weak. The tyrannosaurs left fossilized footprints 80 cm long. The tyrannosaurus's step was 4 m.

Tyrannosaur.

Ceratosaurus was relatively small, but fast predator. It had a small horn on its head and a bone crest on its back. The ceratosaurus walked on its hind legs, each of which had three toes with large claws.

Torbosaurus was rather clumsy and hunted mainly on sedentary scolosaurs, which resembled modern armadillos in appearance. Thanks to their powerful jaws and strong teeth, torbosaurs easily chewed through the thick bony shell of scolosaurs.

Scolosaurus.

Flying lizards still continued to exist. The huge pteranodon, whose wingspan was 10 m, had a large skull with a long bony crest on the back of its head and a long toothless beak. The animal's body was relatively small. Pteranodons ate fish. Like modern albatrosses, they spent most of their lives in the air. Their colonies were located by the sea. Recently, the remains of another pteranodon were found in the Cretaceous sediments of America. Its wingspan reached 18 m.

Pteranodon.

Birds appeared that could fly well. Archeopteryx became completely extinct. However, some birds had teeth.

In Hesperornis, a waterfowl, the long finger of the hind limbs was connected to three others by a short swimming membrane. All the fingers had claws. All that remained of the forelimbs were slightly bent humerus bones in the form of a thin stick. Hesperornis had 96 teeth. Young teeth grew inside the old ones and replaced them as soon as they fell out. Hesperornis is very similar to the modern loon. It was very difficult for him to move on land. Raising the front part of the body and pushing off the ground with its feet, Hesperornis moved in small jumps. However, he felt free in the water. He dived well, and it was very difficult for fish to avoid his sharp teeth.

Hesperornis.

Ichthyornis, contemporaries of Hesperornis, was the size of a dove. They flew well. Their wings were highly developed, and the chest bone had a high keel, to which powerful pectoral muscles were attached. The beak of Ichthyornis had many small teeth curved back. The small brain of Ichthyornis resembled the brain of reptiles.

Ichthyornis.

In the Late Cretaceous period, toothless birds appeared, whose relatives - flamingos - still exist today.

Amphibians are no longer different from modern ones. And mammals are represented by carnivores and herbivores, marsupials and placentals. They do not yet play a significant role in nature. However, at the end of the Cretaceous period - the beginning of the Cenozoic era, when giant reptiles became extinct, mammals spread widely across the Earth, taking the place of dinosaurs.

There are many hypotheses regarding the reasons for the extinction of dinosaurs. Some researchers believe that the main reason for this was mammals, of which many appeared at the end of the Cretaceous period. Predatory mammals exterminated dinosaurs, and herbivores intercepted plant food from them. A large group of mammals ate dinosaur eggs. According to other researchers, the main reason for the mass death of dinosaurs was a sharp change in physical and geographical conditions at the end of the Cretaceous period. Cold temperatures and droughts led to a sharp decrease in the number of plants on Earth, as a result of which the giant dinosaurs began to feel a lack of food. They were dying. And the predators for whom dinosaurs served as prey also died, since they had nothing to eat. Perhaps the sun's heat was not enough for the embryos to mature in dinosaur eggs. In addition, cold temperatures also had a detrimental effect on adult dinosaurs. Not having a constant body temperature, they depended on the temperature of the environment. Like modern lizards and snakes, they were active in warm weather, but moved sluggishly in cold weather, could fall into winter torpor and became easy prey for predators. Dinosaurs' skin did not protect them from the cold. And they hardly cared about their offspring. Their parental functions were limited to laying eggs. Unlike dinosaurs, mammals had a constant body temperature, and therefore they suffered less from cold snaps. In addition, they were protected by wool. And most importantly, they fed their cubs with milk and took care of them. Thus, mammals had certain advantages over dinosaurs.

Birds that had a constant body temperature and were covered with feathers also survived. They incubated eggs and fed chicks.

Among the reptiles that survived were those that took refuge from the cold in burrows and lived in warm areas. From them came modern lizards, snakes, turtles and crocodiles.

The deposits of the Cretaceous period are associated with large deposits of chalk, coal, oil and gas, marls, sandstones, and bauxites.

The Cretaceous period lasted 70 million years.

From the book Journey to the Past author Golosnitsky Lev Petrovich

Mesozoic era - the Middle Ages of the earth Life takes over 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

From the book Before and After Dinosaurs author Zhuravlev Andrey Yurievich

Mesozoic restructuring Compared to the Paleozoic “immobility” of bottom animals in the Mesozoic, everything literally spread out and spread out in all directions (fish, cuttlefish, snails, crabs, sea urchins). The sea lilies waved their arms and lifted off the bottom. Scallop bivalves

From the book How life arose and developed on Earth author Gremyatsky Mikhail Antonovich

XII. Mesozoic (“middle”) era The Paleozoic era ended with a whole revolution 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 find very many of those organisms that existed hundreds of millions

The history of the Earth goes back four and a half billion years. This huge period of time is divided into four eons, which in turn are divided into eras and periods. The final fourth eon - Phanerozoic - includes three eras:

Paleozoic;
Mesozoic;
Cenozoic

significant for the appearance of dinosaurs, the emergence of the modern biosphere and significant geographical changes.

Periods of the Mesozoic era

The end of the Paleozoic era was marked by the extinction of animals. The development of life in the Mesozoic era is characterized by the emergence of new species of creatures. First of all, these are dinosaurs, as well as the first mammals.

The Mesozoic lasted one hundred eighty-six million years and consisted of three periods, such as:

Triassic;
Jurassic;
chalky.

The Mesozoic period is also characterized as the era of global warming. There have also been significant changes in the tectonics of the Earth. It was at that time that the only existing supercontinent broke into two parts, which were subsequently divided into the continents that exist in the modern world.

Triassic

The Triassic period is the first stage of the Mesozoic era. The Triassic lasted for thirty-five million years. After the catastrophe that occurred at the end of the Paleozoic on Earth, conditions are observed that are little conducive to the flourishing of life. A tectonic fault occurs and active volcanoes and mountain peaks are formed.

The climate becomes warm and dry, as a result of which deserts form on the planet, and the level of salt in water bodies increases sharply. However, it is precisely at this unfavorable time that mammals and birds appear. This was largely due to the absence of clearly defined climatic zones and the maintenance of uniform temperatures throughout the globe.

Fauna of the Triassic

The Triassic period of the Mesozoic is characterized by significant evolution of the animal world. It was during the Triassic period that those organisms arose that subsequently shaped the appearance of the modern biosphere.

Cynodonts appeared - a group of lizards that were the ancestors of the first mammals. These lizards were covered with fur and had strong developed jaws what helped them eat raw meat. Cynodonts laid eggs, but females fed their young with milk. The ancestors of dinosaurs, pterosaurs and modern crocodiles - archosaurs - also arose in the Triassic.

Due to the dry climate, many organisms have changed their habitat to aquatic habitats. This is how new species of ammonites, mollusks, as well as bony and ray-finned fish appeared. But the main inhabitants of the deep sea were predatory ichthyosaurs, which, as they evolved, began to reach gigantic sizes.

By the end of the Triassic, natural selection did not allow all the animals that appeared to survive; many species could not withstand competition with others, stronger and faster. Thus, by the end of the period, thecodonts, the ancestors of dinosaurs, predominated on land.

Plants during the Triassic period

The flora of the first half of the Triassic did not differ significantly from the plants of the end of the Paleozoic era. Various types of algae grew in abundance in the water, seed ferns and ancient conifers were widespread on land, and lycophytes were widespread in coastal zones.

By the end of the Triassic, the land was covered with a cover of herbaceous plants, which greatly contributed to the appearance of a variety of insects. Plants of the mesophytic group also appeared. Some cycad plants have survived to this day. It grows in the Malay Archipelago zone. Most plant species grew on the planet's coastal areas, while conifers predominated on land.

Jurassic period

This period is the most famous in the history of the Mesozoic era. The Jura is the European mountains that give its name to this time. Sedimentary deposits from that era have been found in these mountains. The Jurassic period lasted fifty-five million years. It acquired geographical significance due to the formation of modern continents (America, Africa, Australia, Antarctica).

The separation of the two previously existing continents of Laurasia and Gondwana served to form new bays and seas and raise the level of the world's oceans. This had a beneficial effect on making it more humid. The air temperature on the planet dropped and began to correspond to a temperate and subtropical climate. Such climate changes greatly contributed to the development and improvement of flora and fauna.

Animals and plants of the Jurassic period

The Jurassic period is the era of dinosaurs. Although other forms of life also evolved and took on new forms and species. The seas of that period were filled with many invertebrates, the structure of whose bodies was more developed than in the Triassic. Bivalve mollusks and intrashell belemnites, the length of which reached three meters, became widespread.

The insect world has also received evolutionary growth. The appearance of flowering plants also provoked the appearance of pollinating insects. New species of cicadas, beetles, dragonflies and other terrestrial insects have emerged.

Climatic changes that occurred during the Jurassic period resulted in heavy rainfall. This, in turn, gave impetus to the spread of lush vegetation across the surface of the planet. In the northern belt of the earth, herbaceous ferns and ginkgo plants predominated. The southern zone consisted of tree ferns and cycads. In addition, the Earth was filled with various coniferous, cordaite and cycad plants.

Age of Dinosaurs

During the Jurassic period of the Mesozoic, reptiles reached their evolutionary peak, ushering in the era of dinosaurs. The seas were dominated everywhere by giant dolphin-like ichthyosaurs and plesiosaurs. If ichthyosaurs were inhabitants of an exclusively aquatic environment, then plesiosaurs from time to time needed access to land.

Dinosaurs living on land amazed us with their diversity. Their sizes varied from 10 centimeters to thirty meters, and they weighed up to fifty tons. Herbivores predominated among them, but there were also ferocious predators. A huge number of predatory animals provoked the formation of certain elements of defense in herbivores: sharp plates, spines and others.

The airspace of the Jurassic period was filled with dinosaurs that could fly. Although they needed to climb to higher ground to fly. Pterodactyls and other pterosaurs swarmed and swooped above the surface of the earth in search of food.

Cretaceous period

When choosing the name for the next period, the main role was played by writing chalk, formed in the deposits of dying invertebrate organisms. The period called the Cretaceous was the final period of the Mesozoic era. This time lasted eighty million years.

The newly formed continents move, and the tectonics of the Earth increasingly takes on a familiar appearance. to modern man. The climate became noticeably colder, at which time ice caps formed in the northern and south pole. The planet is also divided into climatic zones. But in general, the climate remained quite warm, helped by the greenhouse effect.

Cretaceous biosphere

Belemnites and mollusks continue to evolve and spread in water bodies, and sea urchins and the first crustaceans also develop.

In addition, fish with hard bones actively develop in reservoirs. Insects and worms have progressed greatly. On land, the number of vertebrates increased, among which the leading positions were occupied by reptiles. They actively absorbed the vegetation of the earth's surface and destroyed each other. During the Cretaceous period, the first snakes arose that lived both in water and on land. Birds, which began to appear at the end of the Jurassic period, became widespread and actively developed during the Cretaceous period.

Among vegetation, flowering plants have received the greatest development. Spore-bearing plants died out due to their reproductive characteristics, giving way to more progressive ones. At the end of this period, gymnosperms evolved noticeably and began to be replaced by angiosperms.

The end of the Mesozoic era

The history of the Earth includes two events that contributed to the mass extinction of the planet's fauna. The first, the Permian catastrophe, marked the beginning of the Mesozoic era, and the second marked its end. Most animal species that actively evolved in the Mesozoic became extinct. IN aquatic environment ammonites, belemnites, and bivalves ceased to exist. Dinosaurs and many other reptiles disappeared. Many species of birds and insects also disappeared.

To date, there is no proven hypothesis about what exactly was the impetus for the mass extinction of fauna in the Cretaceous period. There are versions about the negative impact of the greenhouse effect or about radiation caused by a powerful cosmic explosion. But most scientists are inclined to believe that the cause of the extinction was the fall of a gigantic asteroid, which, when it hit the surface of the Earth, lifted a mass of substances into the atmosphere, blocking the planet from sunlight.

Lesson topic:"The Development of Life in the Mesozoic Era"

The duration of the Mesozoic era is approximately 160 million years. The Mesozoic era includes the Triassic (235-185 million years ago), Jurassic (185-135 million years ago) and Cretaceous (135-65 million years ago) periods. The development of organic life on Earth and the evolution of the biosphere continued against the background of paleogeographical changes characteristic of this stage.

The Triassic is characterized by a general rise of platforms and an increase in land area.

By the end of the Triassic, the destruction of most mountain systems that arose in the Paleozoic had ended. The continents turned into huge plains, which were invaded by the ocean in the next, Jurassic, period. The climate became softer and warmer, covering not only the tropical and subtropical zones, but also modern temperate latitudes. During the Jurassic period the climate was warm and humid. The increased rainfall caused the formation of seas, huge lakes and large rivers. Changes in physical and geographical conditions affected the development of the organic world. The extinction of representatives of marine and terrestrial biota, which began in the arid Permian, continued, which was called the Permian-Triassic crisis. After this crisis and as a result of it, the flora and fauna of land evolved.

Biologically, the Mesozoic was a time of transition from old, primitive to new, progressive forms. The Mesozoic world was much more diverse than the Paleozoic; the fauna and flora appeared in it in a significantly updated composition.

Flora

The vegetation cover of the land at the beginning of the Triassic period was dominated by ancient conifers and seed ferns (pteridosperms). in arid climates, these gymnosperms gravitated towards moist places. On the coasts of drying reservoirs and in disappearing swamps, the last representatives of ancient club mosses and some groups of ferns perished. By the end of the Triassic, a flora was formed in which ferns, cycads, and ginkgos dominated. Gymnosperms reached a special flourishing during this period.

In the Cretaceous, flowering plants appeared and conquered the land.

The putative ancestor of flowering plants, according to most scientists, was closely related to seed ferns and represented one of the branches of this group of plants. Paleontological remains of primary flowering plants and groups of plants intermediate between them and gymnosperm ancestors are, unfortunately, still unknown to science.

The primary type of flowering plant was, according to most botanists, an evergreen tree or low shrub. The herbaceous type of flowering plant appeared later under the influence of limiting environmental factors. The idea of the secondary nature of the herbaceous type of angiosperms was first expressed in 1899 by the Russian botanical geographer A.N. Krasnov and the American anatomist C. Jeffrey.

The evolutionary transformation of woody forms into herbaceous ones occurred as a result of weakening, and then a complete or almost complete decrease in the activity of the cambium. This transformation probably began at the dawn of the development of flowering plants. Over time, it proceeded at a faster pace in the most distant groups of flowering plants and eventually acquired such a wide scale that it covered all the main lines of their development.

Neoteny, the ability to reproduce at an early stage of ontogenesis, was of great importance in the evolution of flowering plants. It is usually associated with limiting environmental factors - low temperature, lack of moisture and a short growing season.

Of the huge variety of woody and herbaceous forms, flowering plants turned out to be the only group of plants capable of forming complex multi-layered communities. The emergence of these communities led to a more complete and intensive use of the natural environment and the successful conquest of new territories, especially unsuitable for gymnosperms.

In the evolution and mass dispersal of flowering plants, the role of pollinating animals is also great. especially insects. By feeding on pollen, insects transferred it from one strobila of the original ancestors of angiosperms to another and were thus the first agents of cross-pollination. Over time, insects have adapted to eat ovules, causing significant harm to plant reproduction. The reaction to such a negative influence of insects was the selection of adaptive forms with closed ovules.

The conquest of land by flowering plants marks one of the decisive, turning-point factors in the evolution of animals. This parallelism in the suddenness and rapidity of the spread of angiosperms and mammals is explained by interdependent processes. The conditions with which the flourishing of angiosperms was associated were also favorable for mammals.

Fauna

Fauna of the seas and oceans: Mesozoic invertebrates were already approaching modern ones in character. A prominent place among them was occupied by cephalopods, to which modern squids and octopuses belong. The Mesozoic representatives of this group included ammonites with a shell twisted into a “ram’s horn”, and belemnites, the inner shell of which was cigar-shaped and overgrown with the flesh of the body - the mantle. Ammonites were found in such numbers in the Mesozoic that their shells are found in almost all marine sediments of this time.

By the end of the Triassic, most of the ancient groups of ammonites died out, but in the Cretaceous they remained numerous, but during the Late Cretaceous the number of species in both groups begins to decline. The diameter of some ammonite shells reaches 2.5 m.

At the end of the Mesozoic, all ammonites became extinct. Of the cephalopods with an external shell, only the genus Nautilus has survived to this day. More widespread in modern seas are forms with internal shells - octopuses, cuttlefish and squids, distantly related to belemnites.

Six-rayed corals began to actively develop(Hexacoralla), whose colonies were active reef-formers. Mesozoic echinoderms were represented by various species of crinoids, or crinoids (Crinoidea), which flourished in the shallow waters of the Jurassic and partly Cretaceous seas. However Sea urchins have made the most progress. Starfish were abundant.

Bivalve mollusks have also become widespread.

During the Jurassic period, foraminifera flourished again, survived the Cretaceous period and reached modern times. In general, single-celled protozoa were an important component in the formation of Mesozoic sedimentary rocks. The Cretaceous period was also a time of rapid development of new types of sponges and some arthropods, particularly insects and decapods.

The Mesozoic era was a time of unstoppable expansion of vertebrates. Of the Paleozoic fish, only a few transitioned into the Mesozoic. Among them were freshwater sharks, sea sharks continued to develop throughout the Mesozoic; Most modern genera were already represented in the Cretaceous seas, in particular.

Almost all lobe-finned fish, from which the first land vertebrates developed, became extinct in the Mesozoic. Paleontologists believed that lobe-finned animals became extinct by the end of the Cretaceous. But in 1938, an event occurred that attracted the attention of all paleontologists. An individual of a species of fish unknown to science was caught off the South African coast. Scientists who studied this unique fish came to the conclusion that it belongs to the “extinct” group of lobe-finned fish ( Coelacanthida). Until now this view remains the only modern representative of ancient lobe-finned fishes. It got the name Latimeria chalumnae. Such biological phenomena are called “living fossils.”

Sushi fauna: New groups of insects, the first dinosaurs and primitive mammals appeared on land. Reptiles became most widespread in the Mesozoic, becoming truly the dominant class of this era.

With the advent of dinosaurs in Early reptiles became completely extinct in the mid-Triassic cotylosaurs and beast-like animals, as well as the last large amphibians, stegocephals. Dinosaurs, which represented the most numerous and diverse superorder of reptiles, became the leading Mesozoic group of terrestrial vertebrates starting from the end of the Triassic. For this reason, the Mesozoic is called the era of dinosaurs. In the Jurassic, real monsters could be found among dinosaurs, up to 25-30 m long (including tail) and weighing up to 50 tons. Of these giants, the best known forms are Brontosaurus, Diplodocus and Brachiosaurus.

The original ancestors of dinosaurs may have been the Upper Permian Eosuchians - a primitive order of small reptiles with a lizard-like physique. From them, in all likelihood, a large branch of reptiles arose - archosaurs, which then split into three main branches - dinosaurs, crocodiles and winged lizards. Representatives of archosaurs were thecodonts. Some of them lived in water and looked like crocodiles. Others, similar to large lizards, lived on open spaces sushi. These land-dwelling thecodonts adapted bipedal walking, which provided them with the ability to observe in search of prey. It was from these thecodonts, which became extinct at the end of the Triassic, that dinosaurs descended, inheriting a bipedal mode of locomotion, although some of them switched to a four-legged mode of locomotion. Representatives of the climbing forms of these animals, which over time moved from jumping to gliding flights, gave rise to pterosaurs (pterodactyls) and birds. Dinosaurs included both herbivores and carnivores.

Towards the end of the Cretaceous, there was a mass extinction of characteristic Mesozoic groups of reptiles, including dinosaurs, ichthyosaurs, plesiosaurs, pterosaurs and mosasaurs.

Representatives of the class of birds (Aves) first appear in Jurassic deposits. The only known first bird was Archeopteryx. The remains of this first bird were found near the Bavarian city of Solnhofen (Germany). During the Cretaceous period, the evolution of birds proceeded at a rapid pace; characteristic of this time, still possessing jagged jaws. The emergence of birds was accompanied by a number of aromorphoses: they acquired a hollow septum between the right and left ventricles of the heart, and lost one of the aortic arches. The complete separation of the arterial and venous blood flows causes birds to be warm-blooded. Everything else, namely the feather cover, wings, horny beak, air sacs and double breathing, as well as shortening of the hindgut, are idioadaptations.

First mammals (Mammalia), modest animals, no larger than a mouse, descended from animal-like reptiles in the Late Triassic. Throughout the Mesozoic they remained few in number and by the end of the era the original genera were largely extinct. Their occurrence is associated with a number of major aromorphoses, developed in representatives of one of the subclasses of reptiles. These aromorphoses include: the formation of hair and a 4-chambered heart, complete separation of arterial and venous blood flows, intrauterine development of the offspring and feeding the baby with milk. Aromorphoses also include development of the cerebral cortex, which determines the predominance of conditioned reflexes over unconditioned ones and the possibility of adaptation to unstable environmental conditions by changing behavior.

Almost all Mesozoic groups of the animal and plant kingdoms retreat, die out, disappear; arises on the ruins of the old new world, the world of the Cenozoic era, in which life receives a new impetus for development and, in the end, living species of organisms are formed.

Speaking about the Mesozoic era, we come to the main topic of our site.
The Mesozoic era is also called the era of middle life. That rich, varied and mysterious life that developed, changed and finally ended around 65 million years ago. Beginning around 250 million years ago.
end about 65 million years ago
The Mesozoic era lasted approximately 185 million years. It is usually divided into three periods:
Triassic
Jurassic period

Georgaphy and tectonics of the planet in the Mesozoic era

At the end of the Paleozoic era, the continents occupied vast spaces. The land prevailed over the sea. All ancient platforms forming the land were raised above sea level and surrounded by folded mountain systems formed as a result of the Variscan folding. The East European and Siberian platforms were connected by newly emerged mountain systems Ural, Kazakhstan, Tien Shan, Altai and Mongolia; The land area increased greatly due to the formation of mountainous areas in Western Europe, as well as along the edges of the ancient platforms of Australia, North America, and South America (Andes). IN Southern Hemisphere there was a huge area
ancient continent
Gondwana.

In the Mesozoic, the collapse of the ancient continent of Gondwana began, but in general the Mesozoic era was an era of relative calm, only occasionally and briefly disturbed by minor geological activity called folding. With the onset of the Mesozoic, the subsidence of the land began, accompanied by the advance (transgression) of the sea. The continent of Gondwana split and broke up into separate continents: Africa, South America, Australia, Antarctica and the Indian Peninsula massif. Within

Southern Europe

and South-West Asia, deep troughs began to form - geosynclines of the Alpine folded region. The same troughs, but on the oceanic crust, arose along the periphery of the Pacific Ocean. Transgression (advance) of the sea, expansion and deepening of geosynclinal troughs continued during the Cretaceous period. Only at the very end of the Mesozoic era did the rise of continents and the reduction of the area of seas begin. Climate in the Mesozoic era Climate in
different periods
changed depending on the movement of continents.
The seasonal temperature changes of the Triassic period began to have a noticeable effect on plants and animals. Certain groups of reptiles have adapted to cold seasons. It was from these groups that mammals arose in the Triassic, and somewhat later, birds. At the end of the Mesozoic era, the climate became even colder. Deciduous woody plants appear, which partially or completely shed their leaves during cold seasons. This feature of plants is an adaptation to colder climates.

Flora in the Mesozoic era

R The first angiosperms, or flowering plants that have survived to this day, spread.
Cretaceous cycad (Cycadeoidea) with a short tuberous stem typical of these gymnosperms Mesozoic era. The height of the plant reached 1 m. Traces of fallen leaves are visible on the tuberous trunk between the flowers. Something similar can be observed in a group of tree-like gymnosperms - Bennettites.
The appearance of gymnosperms was an important step in the evolution of plants.
The ovule (ovum) of the first seed plants was unprotected and developed on special leaves. The seed that emerged from it also did not have an outer shell. Therefore, these plants were called gymnosperms. Earlier, controversial plants of the Paleozoic needed water or, at least, a humid environment for their reproduction. This made their resettlement quite difficult. The development of seeds allowed plants to become less dependent on water. The ovules could now be fertilized by pollen carried by the wind or insects, and water thus no longer determined reproduction. In addition, unlike a single-celled spore, a seed has a multicellular structure and is able to provide food to a young plant in the early stages of development for longer. Under unfavorable conditions, the seed for a long time
Among the most numerous and most curious gymnosperms of the beginning of the Mesozoic era we find the Cycas, or sago. Their stems were straight and columnar, similar to tree trunks, or short and tuberous; they bore large, long, and usually feathery leaves (for example, the genus Pterophyllum, whose name means “feathery leaves”).
Outwardly, they looked like tree ferns or palm trees.
In addition to the cycads, the Bennettitales, represented by trees or shrubs, became of great importance in the mesophyte. They mostly resemble true cycads, but their seed begins to develop a tough shell, which gives Bennettites an angiosperm-like appearance. There are other signs of adaptation of Bennettites to conditions of a drier climate.

In the Triassic, new forms of plants appeared.

Conifers are spreading quickly, and among them are firs, cypresses, and yews.
The leaves of these plants had the shape of a fan-shaped plate, deeply dissected into narrow lobes. The shady places along the banks of small reservoirs are inhabited by ferns. Also known among ferns are forms that grow on rocks (Gleicheniacae). Horsetails grew in the swamps, but did not reach the size of their Paleozoic ancestors.
Angiosperms, or flowering plants, occupy the highest level of the evolutionary ladder of the plant world. Their seeds are enclosed in a durable shell;
there are specialized reproductive organs (stamen and pistil) assembled into a flower with bright petals and a calyx. Flowering plants appear somewhere in the first half of the Cretaceous period, most likely in a cold and dry mountain climate with large temperature differences. With the gradual cooling that began in the Cretaceous period, flowering plants captured more and more areas on the plains. Quickly adapting to the new environment, they developed at great speed.
In a relatively short time, flowering plants spread throughout the Earth and achieved great diversity. From the end of the Early Cretaceous era, the balance of forces began to change in favor of angiosperms, and by the beginning of the Upper Cretaceous their superiority became widespread.

Cretaceous angiosperms belonged to the evergreen, tropical or subtropical types, among them were eucalyptus, magnolia, sassafras, tulip trees, Japanese quince trees, brown laurels, walnut trees, plane trees, and oleanders..

These heat-loving trees coexisted with the typical flora of the temperate zone: oaks, beeches, willows, and birches. This flora also included gymnosperms conifers (sequoias, pines, etc.).

For gymnosperms, this was a time of surrender. Some species have survived to this day, but their total numbers have been declining all these centuries. A definite exception is conifers, which are still found in abundance today. In the Mesozoic, plants made a great leap forward, surpassing animals in terms of development rates. Fauna of the Mesozoic era Reptiles.
The predatory theriodonts (Theriodontia) included in it have some similarities with mammals. By the end of the Triassic period, it was from them that the first mammals developed.
During the Triassic period, many new groups of reptiles appeared.

These include turtles and ichthyosaurs (“fish lizards”), which are well adapted to life in the sea and look like dolphins. Placodonts, sluggish armored animals with powerful flat-shaped teeth adapted for crushing shells, and also plesiosaurs that lived in the seas and had a relatively small head and long neck, a wide body, flipper-like paired limbs and a short tail; Plesiosaurs vaguely resemble giant turtles without a shell.

Mesozoic Crocoile - Deinosuchus attacks AlbertosaurusDuring the Jurassic period, plesiosaurs and ichthyosaurs reached their peak.

Both of these groups remained very numerous at the beginning of the Cretaceous era, being extremely characteristic predators of the Mesozoic seas.

From an evolutionary point of view, one of the most important groups of Mesozoic reptiles were thecodonts, small predatory reptiles of the Triassic period, which gave rise to almost all groups of terrestrial reptiles of the Mesozoic era: crocodiles, dinosaurs, flying lizards, and, finally, birds.
Dinosaurs
In the Triassic, they still competed with animals that survived the Permian catastrophe, but in the Jurassic and Cretaceous periods they confidently led in all ecological niches. Currently, about 400 species of dinosaurs are known. Dinosaurs are represented by two groups, saurischia (Saurischia) and ornithischia (Ornithischia). In the Triassic, the diversity of dinosaurs was not great. The very first famous dinosaurs were eoraptor And Herrerasaurus were . .
The most famous of the Triassic dinosaurs are coelophysis were plateosaurus The Jurassic period is known for the most amazing diversity among dinosaurs; real monsters could be found, up to 25-30 m long (including tail) and weighing up to 50 tons. Of these giants, the most famous diplodocus brachiosaurus
. Another striking representative of the Jurassic fauna is the bizarre stegosaurus . similar to modern rhinoceroses. In the Cretaceous period, there were also relatively small armored dinosaurs - ankylosaurs, covered with a massive bony shell. All of these forms were herbivores, as were giant duck-billed dinosaurs such as Anatosaurus and Trachodon, which walked on two legs.
In addition to herbivores, a large group was also represented by carnivorous dinosaurs. All of them belonged to the group of lizards.

A group of carnivorous dinosaurs are called terrapods. In the Triassic, this is Coelophysis - one of the first dinosaurs. In the Jurassic period, Allosaurus and Deinonychus reached their peak. In the Cretaceous period, the most remarkable forms were such as Tyrannosaurus rex, whose length exceeded 15 m, Spinosaurus and Tarbosaurus. All these forms, which turned out to be the greatest terrestrial predatory animals in the entire history of the Earth, moved on two legs.

Other reptiles of the Mesozoic era
At the end of the Triassic, the thecodonts also gave rise to the first crocodiles, which became abundant only in the Jurassic period (Steneosaurus and others). In the Jurassic period, flying lizards appeared - pterosaurs (Pterosaurids), also descended from thecodonts. Among the flying dinosaurs of the Jurassic, the most famous are Rhamphorhynchus and Pterodactylus; among the Cretaceous forms, the most interesting is the relatively very large Pteranodon. Flying lizards became extinct by the end of the Cretaceous.

In the Cretaceous seas, giant predatory lizards - mosasaurs, exceeding 10 m in length - became widespread. Among modern lizards, they are closest to monitor lizards, but differ from them, in particular, in their flipper-like limbs. By the end of the Cretaceous, the first snakes (Ophidia) appeared, apparently descended from lizards that led a burrowing lifestyle. Towards the end of the Cretaceous, there was a mass extinction of characteristic Mesozoic groups of reptiles, including dinosaurs, ichthyosaurs, plesiosaurs, pterosaurs and mosasaurs.

Belemnite shells are popularly known as “devil’s fingers.” Ammonites were found in such numbers in the Mesozoic that their shells are found in almost all marine sediments of this time. Ammonites appeared in the Silurian, they experienced their first flowering in the Devonian, but reached their highest diversity in the Mesozoic. In the Triassic alone, over 400 new genera of ammonites arose. Particularly characteristic of the Triassic were ceratids, which were widespread in the Upper Triassic marine basin of Central Europe, the deposits of which in Germany are known as shell limestone. By the end of the Triassic, most ancient groups of ammonites died out, but representatives of the Phylloceratida survived in Tethys, the giant Mesozoic Mediterranean Sea. This group developed so rapidly in the Jurassic that the ammonites of this time surpassed the Triassic in the variety of forms. During the Cretaceous, cephalopods, both ammonites and belemnites, remained numerous, but during the Late Cretaceous the number of species in both groups began to decline. Among ammonites at this time, aberrant forms with a not completely twisted hook-shaped shell with a shell elongated in a straight line (Baculites) and with an irregularly shaped shell (Heteroceras) appeared. These aberrant forms appeared, apparently, as a result of changes in the course individual development and narrow specialization. The terminal Upper Cretaceous forms of some branches of ammonites are distinguished by sharply increased shell sizes. In one species of ammonite, the diameter of the shell reaches 2.5 m. Great importance

Belemnites acquired in the Mesozoic era. Some of their genera, for example, Actinocamax and Belemnitella, are important fossils and are successfully used for stratigraphic division and

Tabulates and four-rayed corals were no longer present in the Mesozoic seas. Their place was taken by six-rayed corals (Hexacoralla), whose colonies were active reef builders - the sea reefs they built are now widespread in the Pacific Ocean. Some groups of brachiopods still developed in the Mesozoic, such as Terebratulacea and Rhynchonellacea, but the vast majority of them declined.
Mesozoic echinoderms were represented by various species of crinoids, or crinoids (Crinoidea), which flourished in the shallow waters of the Jurassic and partly Cretaceous seas. However, the greatest progress has been made by sea urchins (Echinoidca); for today
Countless species of them have been described since the Mesozoic. Starfish (Asteroidea) and ophidra were abundant. Compared with Paleozoic era
In the Mesozoic, bivalves also became widespread. Already in the Triassic, many new genera appeared (Pseudomonotis, Pteria, Daonella, etc.). At the beginning of this period we also meet the first oysters, which would later become one of the most common groups of mollusks in the Mesozoic seas. The appearance of new groups of mollusks continued in the Jurassic; the characteristic genera of this time were Trigonia and Gryphaea, classified as oysters. In the Cretaceous formations you can find funny types of bivalves - rudists, the goblet-shaped shells of which had a special cap at the base. These creatures settled in colonies, and in the Late Cretaceous they contributed to the construction of limestone cliffs (for example, the genus Hippurites). The most characteristic bivalves of the Cretaceous were mollusks of the genus Inoceramus; some species of this genus reached 50 cm in length. In some places there are significant accumulations of remains of Mesozoic gastropods (Gastropoda).
During the Jurassic period, foraminifera flourished again, surviving the Cretaceous period and reaching modern times.

In general, single-celled protozoa were an important component in the formation of sediments.

The Mesozoic era was a time of unstoppable expansion of vertebrates. Of the Paleozoic fishes, only a few transitioned into the Mesozoic, as did the genus Xenacanthus, the last representative of the freshwater sharks of the Paleozoic, known from freshwater sediments of the Australian Triassic. Sea sharks continued to evolve throughout the Mesozoic; most modern genera were already represented in the seas of the Cretaceous, in particular Carcharias, Carcharodon, Isurus, etc. Ray-finned fish, which arose at the end of the Silurian, initially lived only in freshwater reservoirs, but with the Permian they begin to enter the seas, where they reproduce unusually and from the Triassic to the present day they retain a dominant position. Earlier we talked about Paleozoic lobe-finned fishes, from which the first land vertebrates developed. Almost all of them became extinct in the Mesozoic; only a few of their genera (Macropoma, Mawsonia) were found in Cretaceous rocks.
Until 1938, paleontologists believed that lobe-finned animals became extinct by the end of the Cretaceous. But in 1938, an event occurred that attracted the attention of all paleontologists. An individual of a species of fish unknown to science was caught off the South African coast. Scientists who studied this unique fish came to the conclusion that it belongs to the “extinct” group of lobe-finned fish (Coelacanthida). Before

Currently, this species remains the only modern representative of ancient lobe-finned fish. It was named Latimeria chalumnae. Such biological phenomena are called “living fossils.”

Amphibians. In some zones of the Triassic, labyrinthodonts (Mastodonsaurus, Trematosaurus, etc.) are still numerous. By the end of the Triassic, these “armored” amphibians disappeared from the face of the earth, but some of them apparently gave rise to the ancestors of modern frogs. It's about
about the genus Triadobatrachus;

To date, only one incomplete skeleton of this animal has been found in the north of Madagascar. True tailless amphibians are already found in the Jurassic

Representatives of the class of birds (Aves) first appear in Jurassic deposits. The remains of Archaeopteryx, the well-known and so far only known first bird, were found in lithographic shales of the Upper Jurassic, near the Bavarian city of Solnhofen (Germany). During the Cretaceous period, the evolution of birds proceeded at a rapid pace; The characteristic genera of this time were Ichthyornis and Hesperornis, which still had serrated jaws.

The first mammals.

The first mammals (Mammalia), modest animals no larger than a mouse, descended from animal-like reptiles in the Late Triassic.
Throughout the Mesozoic they remained few in number and by the end of the era the original genera were largely extinct. The most ancient group of mammals were the triconodonts (Triconodonta), to which the most famous of the Triassic mammals, Morganucodon, belongs. During the Jurassic period, a number of new groups of mammals appeared.

Of all these groups, only a few survived the Mesozoic, the last of which died out in the Eocene. The ancestors of the main groups of modern mammals - marsupials (Marsupialia) and placentals (Placentalid) were Eupantotheria. Both marsupials and placentals appeared at the end of the Cretaceous period. The most ancient group of placentals are insectivores (Insectivora), which have survived to this day. Powerful tectonic processes of Alpine folding, which erected new mountain ranges and changed the shape of the continents, radically changed the geographical and climatic conditions. Almost all Mesozoic groups of the animal and plant kingdoms retreat, die out, disappear; on the ruins of the old, a new world arises, the world of the Cenozoic era, in which life receives a new impetus for development and, in the end, living species of organisms are formed.

The Mesozoic era is divided into the Triassic, Jurassic and Cretaceous periods with a total duration of 173 million years. The deposits of these periods constitute the corresponding systems, which together form the Mesozoic group. The Triassic system is identified in Germany, the Jurassic and Cretaceous - in Switzerland and France. The Triassic and Jurassic systems are divided into three divisions, the Cretaceous - into two.

Organic world

In the Mesozoic seas, cephalopods - ammonites and belemnites - developed exceptionally, the diversity and number of bivalves and gastropods sharply increased, and six-rayed corals appeared and developed. Among the vertebrates, bony fish and swimming reptiles became widespread.

The land was dominated by an extremely diverse range of reptiles (especially dinosaurs). Among terrestrial plants, gymnosperms flourished.

Organic world of the Triassic period. A feature of the organic world of this period was the existence of some archaic Paleozoic groups, although new ones - Mesozoic ones - predominated.

Organic world of the sea. Among the invertebrates, cephalopods and bivalves were widespread. Among the cephalopods, ceratites dominated, which supplanted goniatites. The characteristic genus was ceratites with a typical ceratitic septal line. The first belemnites appeared, but there were still few of them in the Triassic.

Bivalve mollusks inhabited shallow water areas rich in food, where brachiopods lived in the Paleozoic. Bivalves quickly developed and became more diverse in composition. The number of gastropods has increased, six-rayed corals and new sea urchins with durable shells have appeared.

Marine vertebrates continued to develop. Among fish, the number of cartilaginous fish has decreased, and lobe-finned and lungfish have become rare. They were replaced by bony fish. The seas were inhabited by the first turtles, crocodiles and ichthyosaurs - large swimming lizards similar to dolphins.

The organic world of sushi has changed too. Stegocephals died out, and reptiles became the dominant group. The endangered cotylosaurs and bestial lizards were replaced by Mesozoic dinosaurs, which became especially widespread in the Jurassic and Cretaceous. At the end of the Triassic, the first mammals appeared; they were small in size and had a primitive structure.

The flora at the beginning of the Triassic was greatly depleted, due to the influence of the arid climate. In the second half of the Triassic, the climate moistened, and a variety of Mesozoic ferns and gymnosperms (cycads, ginkgos, etc.) appeared. Along with them, conifers were widespread. By the end of the Triassic, the flora acquired a Mesozoic appearance, characterized by the dominance of gymnosperms.

Organic Jurassic World

The organic world of the Jurassic was most typical of the Mesozoic era.

Organic world of the sea. Ammonites dominated among invertebrates; they had a complex septal line and were extremely diverse in shell shape and sculpture. One of the typical Late Jurassic ammonites is the genus Virgatites, with bundles of ribs on its shell that are unique to it. There are many belemnites, their rostra are found in large quantities in Jurassic clays. Characteristic genera are Cylindrotheuthis with a long cylindrical rostrum and Hybolithes with a spindle-shaped rostrum.

Bivalves and gastropods became numerous and diverse. Among the bivalves there were many oysters with thick shells of various shapes. The seas were inhabited by various six-rayed corals, sea urchins and numerous protozoa.

Among marine vertebrates, fish lizards - ichthyosaurs - continued to dominate, and scaly lizards - mesosaurs, similar to giant toothed lizards, appeared. Bony fish developed rapidly.

The organic world of sushi was very peculiar. Giant lizards - dinosaurs - of various shapes and sizes reigned supreme. At first glance, they seem to be aliens from an extraterrestrial world or a figment of the imagination of artists.

The Gobi Desert and neighboring areas of Central Asia are richest in dinosaur remains. For 150 million years before the Jurassic period, this vast territory was in continental conditions favorable for the long-term development of fossil fauna. It is believed that this area was the center of the emergence of dinosaurs, from where they settled all over the world, right up to Australia, Africa, and America.

Dinosaurs were gigantic in size. Modern elephants - the largest of today's land animals (up to 3.5 m tall and weighing up to 4.5 tons) - seem like dwarfs compared to dinosaurs. The largest were herbivorous dinosaurs. “Living mountains” - brachiosaurs, brontosaurs and diplodocus - had a length of up to 30 m and reached 40-50 tons. Huge stegosaurs carried large (up to 1 m) bone plates on their backs, which protected their massive body. There were sharp spines at the end of the stegosaurs' tail. There were many dinosaurs scary predators, which moved much faster than their herbivorous relatives. Dinosaurs reproduced using eggs, burying them in hot sand, as modern turtles do. Ancient clutches of dinosaur eggs are still being found in Mongolia.

The air environment was mastered by flying lizards - pterosaurs with sharp membranous wings. Among them, rhamphorhynchus stood out - toothy lizards that fed on fish and insects. At the end of the Jurassic, the first birds appeared - Archeopteryx - the size of a jackdaw; they retained many of the features of their ancestors - reptiles.

The flora of the land was distinguished by the flourishing of various gymnosperms: cycads, ginkgos, conifers, etc. The Jurassic flora was quite homogeneous on the globe, and only at the end of the Jurassic did floristic provinces begin to emerge.

Organic world of the Cretaceous period

During this period organic world has undergone significant changes. At the beginning of the period it was similar to the Jurassic, and in the Late Cretaceous it began to sharply decline due to the extinction of many Mesozoic groups of animals and plants.

Organic world of the sea. Among invertebrates, the same groups of organisms were common as in the Jurassic period, but their composition had changed.

Ammonites continued to dominate, and many forms with partially or almost completely expanded shells appeared among them. Cretaceous ammonites are known with spiral-conical (like snails) and stick-shaped shells. At the end of the period, all ammonites became extinct.

Belemnites reached their peak; they were numerous and varied. The genus Belemnitella with a cigar-like rostrum was especially widespread. The importance of bivalves and gastropods increased, and they gradually seized a dominant position. Among the bivalves there were many oysters, inoceramus and pectens. In the tropical seas of the Late Cretaceous, peculiar goblet-shaped hippurites lived. The shape of their shells resembles sponges and solitary corals. This is evidence that these bivalves led an attached lifestyle, unlike their relatives. Gastropods reached great diversity, especially towards the end of the period. Among sea urchins, various irregular hedgehogs, one of the representatives of which is the genus Micraster with a heart-shaped shell.

Warm-water Late Cretaceous seas were overcrowded with microfauna, among which small foraminifera-globigerines and ultramicroscopic unicellular calcareous algae - coccolithophores predominated. The accumulation of coccoliths formed a thin calcareous silt, from which writing chalk was subsequently formed. The softest varieties of writing chalk consist almost entirely of coccoliths; the admixture of foraminifera in them is insignificant.

There were many vertebrates in the seas. Bony fish developed rapidly and conquered the marine environment. Until the end of the period, there were swimming lizards - ichthyosaurs, mososaurs.

The organic world of land in the Early Cretaceous differed little from the Jurassic. The air was dominated by flying lizards - pterodactyls, similar to giant bats. Their wingspan reached 7-8 m, and in the USA the skeleton of a giant pterodactyl with a wingspan of 16 m was discovered. Along with such huge flying lizards, there lived pterodactyls no larger than a sparrow. Various dinosaurs continued to dominate the land, but at the end of the Cretaceous period they all went extinct along with their marine relatives.

The terrestrial flora of the Early Cretaceous, as in the Jurassic, was characterized by the dominance of gymnosperms, but starting from the end of the Early Cretaceous, angiosperms appeared and rapidly developed, which, together with conifers, became the dominant group of plants by the end of the Cretaceous. Gymnosperms are sharply declining in number and diversity, many of them are dying out.

Thus, at the end of the Mesozoic era, significant changes occurred in both the animal and plant worlds. All ammonites, most belemnites and brachiopods, all dinosaurs, winged lizards, many aquatic reptiles, ancient birds, and a number of groups disappeared higher plants from gymnosperms.

Among these significant changes, the rapid disappearance of the Mesozoic giants, the dinosaurs, from the face of the Earth is especially striking. What caused the death of such a large and diverse group of animals? This topic has long attracted scientists and is still on the pages of books and scientific journals. There are several dozen hypotheses, and new ones are emerging. One group of hypotheses is based on tectonic reasons - strong orogenesis caused significant changes in paleogeography, climate and food resources. Other hypotheses connect the death of dinosaurs with processes that took place in space, mainly with changes in cosmic radiation. The third group of hypotheses explains the death of giants by various biological reasons: a discrepancy between the volume of the brain and the body weight of animals; the rapid development of predatory mammals that ate small dinosaurs and large eggs; gradual thickening of the eggshell to such an extent that the young could not break through it. There are hypotheses linking the death of dinosaurs with an increase in microelements in the environment, with oxygen starvation, with the leaching of lime from the soil, or with an increase in gravity on Earth to such an extent that the giant dinosaurs were crushed by their own weight.