Diversity of the animal world of the Mesozoic era. mesozoic era mesozoic

26.09.2019 Food and drink

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. IN mesozoic era the modern outlines of continents and oceans, modern marine fauna and flora are gradually formed. The Andes and Cordilleras, mountain ranges of China and East Asia were formed. The basins of the Atlantic and Indian oceans 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 three different rock complexes are considered to be its deposits: the lower one is continental sandstone, the middle one is limestone and the upper one is neiper.

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

During the Triassic period, the northern continent of Laurasia merged with the southern continent - Gondwana. The great bay, which began in the east of Gondwana, stretched all the way to the northern coast of 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 arose on Gondwana, gradually filled with continental deposits.

Volcanic activity intensified in the Middle Triassic. The inland seas become shallow, and numerous depressions are formed. The formation of the mountain ranges of South China and Indonesia begins. On 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 regions, there was an intensive change of some animal and plant forms by others. Only a few families passed from the Paleozoic era to the Mesozoic. This gave grounds to some researchers to assert about the great catastrophes that occurred at the turn of the Paleozoic and Mesozoic. However, when studying the deposits of the Triassic period, one can easily be convinced that there is no sharp boundary 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 change in temperatures of the Triassic period began to have a noticeable effect on plants and animals. Separate groups of 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 the cold seasons. This feature plants is an adaptation to colder climates.

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

Gigantic forms of cephalopods have developed in the seas. The diameter of the shells of some of them was up to 5 m. True, gigantic cephalopod mollusks, such as squid, reaching 18 m in length, still live in the seas, but in the Mesozoic era there were much more gigantic forms.

The composition of the atmosphere of the Triassic period has changed little compared to the Permian. The climate became more humid, but the deserts in the center of the continent remained. 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 have not changed much during the Mesozoic and Cenozoic eras.

And yet the stegocephalians died out. They were replaced by reptiles. More perfect, mobile, well adapted to various living conditions, they ate the same food as stegocephalians, settled in the same places, ate young stegocephalians and eventually exterminated them.

Among the Triassic flora, calamites, seed ferns, and cordaites were occasionally encountered. True ferns predominated, ginkgo, bennetite, cycad, coniferous. Cycads still exist in the area of the Malay Archipelago. They are known as sago palms. In my own way appearance cycads occupy an intermediate position between palms and ferns. The trunk of cycads is rather thick, columnar. The crown consists of stiff pinnate leaves arranged in a corolla. Plants reproduce by means of macro- and microspores.

Triassic ferns were coastal herbaceous plants with broad, dissected leaves with reticulate venation. Of the coniferous plants, volttia has been well studied. She had a dense crown and cones like spruce.

Ginkgoales were quite tall trees, their leaves formed dense crowns.

A special place among the Triassic gymnosperms was occupied by bennetites - trees with whorled large complex leaves resembling 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 magnoliaceae. 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 typical 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. In the Triassic period, when many colonial six-ray corals appear instead of tabulates, the formation of reefs up to a thousand meters thick begins. Cups of six-pointed corals had six or twelve calcareous partitions. As a result of the mass development and rapid growth of corals, underwater forests were formed on the bottom of the sea, in which numerous representatives of other groups of organisms settled. Some of them took part in reef formation. Bivalves, algae, sea urchins, starfish, sponges lived among the corals. Destroyed by waves, they formed coarse-grained or fine-grained sand, which filled all the voids of the corals. Washed out by waves from these voids, calcareous silt was deposited in bays and lagoons.

Some bivalve mollusks are quite characteristic of the Triassic period. Their paper-thin shells with brittle ribs in some cases form whole layers in the deposits of this period. Bivalves lived in shallow muddy bays - lagoons, on reefs and between them. In the Upper Triassic period, many thick-shell bivalve mollusks appeared, firmly attached to the limestone deposits of shallow water basins.

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

The most common of the gastropod molluscs were pronebranchial. Ammonites were widely distributed in the seas of the Triassic period, the shells of which in some places accumulated in huge number. Appearing in Silurian period, they did not yet play a big 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, which had the thickness of tissue paper and therefore almost did not protect the soft body of the mollusk. Only when their partitions were bent into numerous folds, ammonite shells gained strength and turned into a real shelter from predators. With the complication of the partitions, the shells became even more durable, and the external structure made it possible for them to adapt to the most diverse living conditions.

Representatives of echinoderms were sea urchins, lilies and stars. At the upper end of the body of sea lilies, there was a flower-like main body. It distinguishes a corolla and grasping organs - “hands”. Between the "hands" in the corolla were the mouth and anus. With “hands”, the sea lily raked water into the mouth opening, 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-legged crayfish, and ostracods.

The fish were represented by sharks living in fresh water bodies and molluscoids inhabiting the sea. The first primitive bony fish appear. Powerful fins, a well-developed dentition, a perfect shape, a 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 group of labyrinthodonts. They were sedentary animals with a small body, small limbs and a large head. They lay in the water waiting for the 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 with mucous glands. Other amphibians came out on 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 the mastodonosaurs were forced to inhabit ever deeper places, often accumulating in large numbers. That is why many of their skeletons are now being found in small areas.

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

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

Dinosaurs include theropods and prosauropods. Theropods moved on well-developed hind limbs, had a heavy tail, powerful jaws, and small and weak forelimbs. In size, these animals ranged from a few centimeters to 15 m. All of them were predators.

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

Representatives of the synaptosaur subclass led the most diverse lifestyle. Trilophosaurus climbed trees, fed on plant foods. In appearance, he resembled a cat.

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

In some places, footprints of a huge animal walking on four legs are quite often found. They called it the chirotherium. Based on the preserved prints, one can imagine the structure of the foot of this animal. Four clumsy toes surrounded a thick, meaty sole. Three of them had claws. The forelimbs of the chirotherium are almost three times smaller than the hind ones. On the wet sand, the animal left deep footprints. With the deposition of new layers, the traces gradually petrified. Later, the land was flooded with the sea, which hid the traces. They were covered with marine sediments. Consequently, in that era, the sea repeatedly flooded. 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 mainland ancestors. Turtles with a wide bone shell, dolphin-like ichthyosaurs - fish-lizards and gigantic plesiosaurs with a small head on a long neck quickly developed. Their vertebrae are transformed, limbs are changed. The cervical vertebrae of an ichthyosaur fuse into one bone, and in turtles they grow, forming the upper part of the shell.

The ichthyosaur had a row of homogeneous teeth; teeth disappear in turtles. 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.

Since the Triassic period, reptiles that have moved to live in the sea gradually populate more and more vast expanses of the ocean.

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

Deposits of oil, natural gases, brown and hard coal, iron and copper ores, and rock salt are associated with deposits of the Triassic period.

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 subdivided 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 variety of conditions.

Sedimentary rocks containing many representatives of fauna and flora are widely distributed.

Intensive tectonic movements at the end of the Triassic and at the beginning of the Jurassic contributed to the deepening of the large bays that gradually separated Africa and Australia from Gondwana. The gulf between Africa and America 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 led to the formation of the Verkhoyansk fold system. The formation of the Andes and the Cordillera continued. Warm sea currents have reached the 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. There are very few deposits of a dry climate: 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 on more than just sunlight. Many volcanoes, outpourings of magma on the bottom of the oceans heated the water and the atmosphere, saturated the air with water vapor, which then rained on the land, flowing in stormy streams into lakes and oceans. Numerous freshwater deposits testify to this: white sandstones alternating with dark loams.

The warm and humid climate favored the flowering flora. Ferns, cicadas, and conifers formed extensive marshy forests. Araucaria, arborvitae, cicadas grew on the coast. Ferns and horsetails formed the undergrowth. In the Lower Jurassic, the vegetation throughout the northern hemisphere was fairly uniform. But already starting from the Middle Jurassic, two plant belts can be identified: the northern one, in which ginkgo and herbaceous ferns predominated, and the southern one, with bennetites, cicadas, araucaria, and tree ferns.

The characteristic ferns of the Jurassic period were matonii, which have survived to this day in the Malay Archipelago. Horsetails and club mosses almost did not differ from modern ones. The place of extinct seed ferns and cordaites is occupied by cycads, which now grow in tropical forests.

Ginkgoaceae were also widely distributed. Their leaves turned to the sun with an edge and resembled huge fans. From North America and New Zealand to Asia and Europe, dense forests of coniferous plants grew - araucaria and bennetites. The first cypress and, possibly, spruce trees appear.

The representatives of the Jurassic conifers also include sequoia - a modern giant California pine. Currently, sequoias remain only on the Pacific coast of North America. Separate forms of even more ancient plants have been preserved, for example, glassopteris. But there are few such plants, since they were supplanted by more perfect ones.

The lush vegetation of the Jurassic period contributed to the widespread distribution of reptiles. Dinosaurs have greatly evolved. Among them are lizard and ornithischian. Lizards moved on four legs, had five toes on their feet, and ate plants. Most of them had a long neck, a small head and a long tail. They had two brains: one small - 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, reaching a length of 26 m, weighing about 50 tons. It had columnar legs, a small head, and a thick long neck. Brachiosaurs lived on the shores of the Jurassic lakes, 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 moved on four legs, the hind legs were longer than the front ones. Diplodocus spent most of his life in swamps and lakes, where he grazed and escaped from predators.

Diplodocus.

Brontosaurus was comparatively 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 a small head. The brontosaurus lived in swamps, on the shores of lakes.

Brontosaurus.

Ornithischian dinosaurs are divided into bipedal and quadrupedal. 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-shaped jaws.

In the Jurassic period, flying lizards first appear. They flew with the help of 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 tubular bones. The extremely elongated outer fifth finger 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 strongly developed. They had 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 premaxilla sometimes grew into an elongated toothless beak. Toothed lizards had simple teeth and sat in recesses. The largest teeth were in front. Sometimes they stick out to the side. This helped the lizards to catch and hold prey. The animal 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 characteristic representatives of flying lizards are pterodactyl and rhamphorhynchus.

Pterodactyl.

Pterodactyls in most cases were tailless, different in size - from the size of a sparrow to a crow. They had wide wings and a narrow skull extended 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 in rocks. The skin of pterodactyls was wrinkled and bare. They ate mainly fish, sometimes sea lilies, molluscs, and insects. In order to take off, pterodactyls had to jump off rocks or trees.

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

Ramphorhynchus.

Flying lizards lived only in the Mesozoic era, and their heyday falls on the late Jurassic period. Their ancestors were apparently extinct ancient reptiles pseudosuchia. The long-tailed forms appeared before the short-tailed ones. At the end of the Jurassic, they became extinct.

It should be noted that flying lizards were not the ancestors of birds and bats. Flying lizards, birds and bats originated and developed in their own ways, 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 a change 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, large eyes surrounded by a bone ring. The length of the skull of some of them was 3 m, and the body length was 12 m. The limbs of ichthyosaurs consisted of bone plates. Elbow, metatarsus, hand and fingers did not differ much in shape from each other. About a hundred bone plates supported a wide flipper. Shoulder and pelvic girdle were poorly developed. There were several fins on the body. Ichthyosaurs were viviparous animals. Along with ichthyosaurs lived plesiosaurs. They had a thick body with four flipper-like limbs, a long serpentine neck with a small head.

In the Jurassic, new genera of fossil turtles appear, and at the end of the period, modern turtles.

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

Of the invertebrates in the Jurassic seas, ammonites, belemnites, sea lilies were found. However, in the Jurassic period, there were much fewer ammonites than in the Triassic. The Jurassic ammonites also differ from the Triassic in their structure, with the exception of the phyloceras, which did not change at all during the transition from the Triassic to the Jura. Separate groups of ammonites have preserved mother-of-pearl to our time. Some animals lived in the open sea, others inhabited bays and shallow inland seas.

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

The remains of internal shells of belemnites, known as "devil's fingers", are found in Jurassic deposits.

In the seas of the Jurassic period, bivalve mollusks, especially those belonging to the oyster family, also developed significantly. They start to form oyster jars.

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

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

Sponges, starfish, sea lilies often overwhelm Jurassic deposits. In the Jurassic period, "five-armed" sea lilies became widespread. Many crustaceans appear: barnacles, decapods, leaf-legged crayfish, freshwater sponges, among insects - dragonflies, beetles, cicadas, bedbugs.

In the Jurassic period, the first birds appear. Their ancestors were the ancient reptile pseudosuchia, which also gave rise to dinosaurs and crocodiles. Ornithosuchia is most similar to birds. She, like birds, moved on her hind legs, had a strong pelvis and was covered with feather-like scales. Part of pseudosuchia moved to live on trees. Their forelimbs were specialized for grasping branches with their fingers. There were lateral depressions on the skull of Pseudosuchia, 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 scleromochlus. His long thin legs indicate that he jumped well. The elongated forearms helped the animals to climb and cling to the branches of trees and bushes. The most important moment in the process of turning reptiles into birds was the transformation of scales into feathers. The heart of the animals had four chambers, which ensured a constant body temperature.

In the late Jurassic period, the first birds appear - Archeopteryx, the size of a dove. 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 feathers of the bird were bright, like those of modern tropical birds, others that the feathers were gray or Brown, the third - that they were motley. The mass 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, and a tail consisting of 20 vertebrae. The vertebrae of the bird were biconcave, like those of fish. Archeopteryx lived in araucaria and cicada forests. They fed mainly on insects and seeds.

Archeopteryx.

Among mammals, predators appeared. 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 the Jurassic deposits.

This period lasted 55 million years.

Cretaceous period

The Cretaceous period got its name because powerful chalk deposits are associated with it. It is divided into two sections: lower and upper.

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

At the top Cretaceous the sea flooded vast areas of the northern continents. Western Siberia and Eastern Europe, most of Canada and Arabia were under water. Thick strata of chalk, sands, and marls accumulate.

At the end of the Cretaceous period, mountain building processes are 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 a real winter with snow. Within the boundaries of the modern temperate zone, some tree species (walnut, ash, beech) did not differ in any way from modern ones. The leaves of these trees fell for the winter. However, as before, the climate as a whole was much warmer than today. Ferns, cycads, ginkgos, bennetites, conifers, in particular sequoias, yews, pines, cypresses, and spruces were still common.

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

The soil has also changed. Silt, 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 fed on insects. Part of the pollen stuck to the wings and legs of insects, and they carried it from flower to flower, pollinating plants. In pollinated plants, the seeds ripened. Plants that were not visited by insects did not multiply. Therefore, only plants with fragrant flowers of various shapes and colors spread.

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

Plants spread throughout 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, the bennetites died out, and the number of cycads, ginkgos, and ferns significantly decreased. Along with the change in vegetation, the fauna also changed.

Foraminifers spread considerably, the shells of which formed thick deposits of chalk. 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, spherical and straight ones were encountered. The surface of the shells was covered with spikes.

According to some researchers, the bizarre forms of Cretaceous ammonites are a sign of the aging of the entire group. Although some representatives of ammonites still continued to multiply at a high rate, their vital energy in the Cretaceous period almost dried up.

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

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

Belemnites, which appeared much later than ammonites, also completely die out in the Cretaceous period. Among the bivalve mollusks there were animals, different in shape and size, closing the valves with the help of teeth and pits. In oysters and other mollusks attached to the seabed, the valves become different. The lower sash looked like a deep bowl, and the upper one looked like a lid. Among the Rudists, the lower wing turned into a large thick-walled glass, inside of which there was only a small chamber for the mollusk itself. The round, lid-like top flap covered the lower one with strong teeth, with which it could rise and fall. Rudists lived mainly in the southern seas.

In addition to bivalve mollusks, 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 settled in the seas of the Cretaceous period - animals that reached one meter in diameter.

In the Cretaceous period, many new species of gastropods appear. 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 taken place among the fish. In the seas of the Cretaceous period, ganoid fish are gradually dying out. The number of bony fish is increasing (many of them still exist today). Sharks gradually acquire a modern look.

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

New forms of plesiosaurs and pliosaurs appear. They lived on the high seas. Crocodiles and turtles inhabited freshwater and saltwater basins. Large lizards with long spikes on their backs and huge pythons lived on the territory of modern Europe.

Of the terrestrial reptiles for the Cretaceous period, trachodons and horned lizards were especially characteristic. Trachodons could move both on two and on four legs. Between the fingers they had membranes that helped them swim. The jaws of trachodons 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 animals from predators. They lived mostly in dry places. They ate vegetation.

Triceratops.

Styracosaurs had nasal outgrowths - horns and six horny spikes on the posterior edge of the bone shield. Their heads reached two meters in length. The spikes and horns made styracosaurs dangerous to many predators.

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

Tyrannosaur.

Ceratosaurus was a relatively small but fast predator. He had a small horn on his head and a bone crest on his back. Ceratosaurus moved on its hind legs, each of which had three fingers with large claws.

Torbosaurus was rather clumsy and preyed mainly on sedentary scolosaurs, reminiscent of modern armadillos in appearance. Thanks to powerful jaws and strong teeth, Torbosaurs easily gnawed through the thick bone shell of scolosaurs.

Scolosaurus.

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

Pteranodon.

There are birds that could fly well. The Archeopteryx are completely extinct. However, some birds had teeth.

In Hesperornis - waterfowl- the long finger of the hind limbs was connected to the other three by a short swimming membrane. All fingers had claws. From the forelimbs, only slightly bent humerus in the form of a thin stick remained. Hesperornis had 96 teeth. The 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, in the water he felt free. He dived well, and it was very difficult for the fish to avoid his sharp teeth.

Hesperornis.

Ichthyornis, contemporaries of the Hesperornis, were the size of a dove. They flew well. Their wings were strongly developed, and the sternum had a high keel, to which powerful pectoral muscles were attached. The beak of the Ichthyornis had many small, recurved teeth. The small brain of ichthyornis resembled the brain of reptiles.

Ichthyornis.

In the late Cretaceous period, toothless birds appear, whose relatives - flamingos - exist in our time.

Amphibians are no different from modern ones. And mammals are represented by predators 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 cenozoic era When the giant reptiles died out, mammals spread widely across the Earth, taking the place of the dinosaurs.

There are many hypotheses regarding the reasons for the extinction of dinosaurs. Some researchers believe that the main reason for this was mammals, which appeared in abundance at the end of the Cretaceous period. Predatory mammals exterminated dinosaurs, and herbivores intercepted plant food from them. A large group of mammals fed on 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. Cooling and droughts led to a sharp decrease in the number of plants on Earth, as a result of which the dinosaur giants began to feel a lack of food. They perished. And predators, for which dinosaurs served as prey, also died, because they had nothing to eat. Perhaps the heat of the sun was not enough for the embryos to mature in the eggs of dinosaurs. In addition, the cold snap 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 in cold weather they moved sluggishly, could fall into winter stupor and became easy prey for predators. Dinosaur skin did not protect them from the cold. And they almost did not care about their offspring. Their parental functions were limited to laying eggs. Unlike dinosaurs, mammals had a constant body temperature and therefore suffered less from cold snaps. In addition, they were protected by wool. And most importantly, they fed their cubs with milk, took care of them. Thus, mammals had certain advantages over dinosaurs.

Survived and the birds that had constant temperature bodies and were covered with feathers. They incubated the eggs and fed the chicks.

Of the reptiles, those who hid from the cold in burrows that lived in warm areas survived. From them came modern lizards, snakes, turtles and crocodiles.

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

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 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

From the book Before and After Dinosaurs author Zhuravlev Andrey Yurievich

Mesozoic Perestroika In comparison with the Paleozoic "immovability" of bottom animals in the Mesozoic, everything literally spread and spread in all directions (fish, cuttlefish, snails, crabs, sea urchins). The sea lilies waved their arms and broke away from the bottom. Bivalve scallops

From the book How Life Originated 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 meet very many of those organisms that existed for hundreds of millions.

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Mesozoic era(248-65 million years ago) - the fourth epoch in the evolutionary process of the life of our planet. Its duration is 183 million years. The Mesozoic era is divided into 3 periods: Triassic, Jurassic and Cretaceous.

Periods of the Mesozoic Era

Triassic period (Triassic). The initial erathem of the Mesozoic era lasts 35 million years. This is the time of the formation of the Atlantic Ocean. The single continent of Pangea again begins to break into two parts - Gondwana and Laurasia. Inland continental water bodies begin to dry up actively. The depressions remaining from them are gradually filled with rock deposits. New mountain heights and volcanoes appear, which show increased activity. A huge part of the land is also occupied by desert zones with weather conditions unsuitable for the life of most species of living beings. Salt levels in water bodies are rising. During this time period, representatives of birds, mammals and dinosaurs appear on the planet.

Jurassic period (Jura)- the most famous period of the Mesozoic era. It got its name thanks to the sedimentary deposits of that time found in the Jura (mountains of Europe). The average period of the Mesozoic era lasts about 69 million years. The formation of modern continents begins - Africa, America, Antarctica, Australia. But they are not yet in the order to which we are accustomed. Deep bays and small seas appear, separating the continents. The active formation of mountain ranges continues. The Arctic Sea floods the north of Laurasia. As a result, the climate is humidified, and vegetation forms on the site of deserts.

Cretaceous (Cretaceous). The final period of the Mesozoic era takes a time interval of 79 million years. Angiosperms appear. As a result of this, the evolution of representatives of the fauna begins. The movement of the continents continues - Africa, America, India and Australia are moving away from each other. The continents of Laurasia and Gondwana begin to disintegrate into continental blocks. Huge islands are formed in the south of the planet. Expanding Atlantic Ocean. The Cretaceous period is the heyday of flora and fauna on land. Due to the evolution of the plant world, fewer minerals enter the seas and oceans. The number of algae and bacteria in water bodies is reduced.

In details periods of the mesozoic era will be considered in the following lectures.

The climate of the Mesozoic era

The climate of the Mesozoic era at the very beginning there was one on the whole planet. The air temperature at the equator and the poles was kept at the same level. At the end of the first period of the Mesozoic era most drought reigned on Earth, which was briefly replaced by rainy seasons. But, despite the arid conditions, the climate became much colder than it was during the Paleozoic period. Some species of reptiles are fully adapted to cold weather. Mammals and birds would later evolve from these animal species.

In the Cretaceous, it gets even colder. All continents have their own climate. Tree-like plants appear, which lose their foliage during the cold season. Snow begins to fall at the North Pole.

Plants of the Mesozoic Era

At the beginning of the Mesozoic, the continents were dominated by club mosses, various ferns, the ancestors of modern palms, conifers and ginkgo trees. In the seas and oceans, the dominance belonged to the algae that formed the reefs.

The increased humidity of the climate of the Jurassic period led to the rapid formation of the plant mass of the planet. The forests consisted of ferns, conifers and cycads. Tui and araucaria grew near water bodies. In the middle of the Mesozoic era, two belts of vegetation formed:

Northern, dominated by herbaceous ferns and ginkgo trees;
Southern. Tree ferns and cicadas reigned here.

In the modern world, ferns, cycads (palm trees reaching a size of 18 meters) and cordaites of that time can be found in tropical and subtropical forests. Horsetails, club mosses, cypresses and spruce trees practically did not have any differences from those that are common in our time.

The Cretaceous period is characterized by the appearance of plants with flowers. In this regard, butterflies and bees appeared among insects, thanks to which flowering plants could quickly spread across the planet. Also at this time, ginkgo trees begin to grow with foliage falling in the cold season. Coniferous forests of this time period are very similar to modern ones. They include yews, firs and cypresses.

The development of higher gymnosperms lasts throughout the Mesozoic era. These representatives of the terrestrial flora got their name due to the fact that their seeds did not have an outer protective shell. The most widespread are cycads and bennettites. In appearance, cycads resemble tree ferns or cycads. They have straight stems and massive feather-like leaves. Bennettites are trees or shrubs. Outwardly similar to cycads, but their seeds are covered with a shell. This brings plants closer to angiosperms.

In the Cretaceous, angiosperms appear. From this moment begins new stage in the development of plant life. Angiosperms (flowering) are at the top rung of the evolutionary ladder. They have special reproductive organs - stamens and pistil, which are located in the flower bowl. Their seeds, unlike gymnosperms, hide a dense protective shell. These mesozoic era plants quickly adapt to any climatic conditions and actively develop. Behind short term angiosperms began to dominate the entire Earth. Their various kinds and the forms have reached modern world- eucalyptus, magnolias, quince, oleanders, walnut trees, oaks, birches, willows and beeches. Of the gymnosperms of the Mesozoic era, now we are only familiar with coniferous species - fir, pine, sequoia and some others. The evolution of plant life of that period significantly overtook the development of representatives of the animal world.

Animals of the Mesozoic Era

Animals in the Triassic period of the Mesozoic era actively evolved. A huge variety of more developed creatures was formed, which gradually replaced the ancient species.

One of these types of reptiles was pelycosaurs, similar to animals - sailing lizards. On their backs was a huge sail, similar to a fan. They were replaced by therapsids, which were divided into 2 groups - predators and herbivores. Their paws were powerful, their tails were short. In terms of speed and endurance, therapsids far surpassed pelycosaurs, but this did not save their species from extinction at the end of the Mesozoic era.

The evolutionary group of lizards, from which mammals would later emerge, are the cynodonts (dog teeth). These animals got their name due to powerful jaw bones and sharp teeth, with which they could easily chew raw meat. Their bodies were covered with thick fur. Females laid eggs, but newborn cubs fed on mother's milk.

At the beginning of the Mesozoic era, formed the new kind pangolins - archosaurs (ruling reptiles). They are the ancestors of all dinosaurs, pterosaurs, plesiosaurs, ichthyosaurs, placodonts, and crocodylomorphs. Archosaurs, adapted to the climatic conditions on the coast, became predatory thecodonts. They hunted on land near water bodies. Most thecodonts walked on 4 legs. But there were also individuals who ran on their hind legs. In this way, these animals developed incredible speed. Over time, thecodonts evolved into dinosaurs.

By the end of the Triassic period, 2 species of reptiles dominated. Some are the ancestors of the crocodiles of our time. Others have become dinosaurs.

Dinosaurs are not like other lizards in body structure. Their paws are located under the body. This feature allowed the dinosaurs to move quickly. Their skin is covered with waterproof scales. Lizards move on 2 or 4 legs, depending on the species. The first representatives were fast coelophyses, powerful herrerasaurs and huge plateosaurs.

In addition to dinosaurs, archosaurs gave rise to another type of reptile that is different from the rest. These are pterosaurs - the first pangolins that can fly. They lived near water bodies, and ate various insects for food.

Animal world The sea depths of the Mesozoic era are also characterized by a variety of species - ammonites, bivalves, shark families, bony and ray-finned fish. The most outstanding predators were the underwater lizards that appeared not so long ago. Dolphin-like ichthyosaurs had high speed. One of the giant representatives of ichthyosaurs is Shonisaurus. Its length reached 23 meters, and its weight did not exceed 40 tons.

Lizard-like notosaurs had sharp fangs. Plakadonts, similar to modern newts, searched the seabed for the shells of molluscs, which they bit with their teeth. Tanystrophei lived on land. Long (2-3 times the size of the body), slender necks allowed them to catch fish standing on the shore.

Another group of marine dinosaurs of the Triassic period are plesiosaurs. At the beginning of the era, plesiosaurs reached a size of only 2 meters, and by the middle of the Mesozoic evolved into giants.

The Jurassic period is the time of the development of dinosaurs. The evolution of plant life gave impetus to the emergence different types herbivorous dinosaurs. And this, in turn, led to an increase in the number of predatory individuals. Some types of dinosaurs were the size of a cat, while others were as large as giant whales. The most gigantic individuals are diplodocus and brachiosaurus, reaching a length of 30 meters. Their weight was about 50 tons.

Archeopteryx is the first creature to stand on the border between lizards and birds. Archeopteryx did not yet know how to fly long distances. Their beaks were replaced by jaws with sharp teeth. The wings ended in fingers. Archeopteryx were the size of modern crows. They lived mainly in forests, and ate insects and various seeds.

In the middle of the Mesozoic era, pterosaurs are divided into 2 groups - pterodactyls and rhamphorhynchus. Pterodactyls lacked a tail and feathers. But there were large wings and a narrow skull with a few teeth. These creatures lived in flocks on the coast. During the day they hunted for food, and at night they hid in the trees. Pterodactyls ate fish, shellfish and insects. To take to the skies, this group of pterosaurs had to jump from high places. Ramphorhynchus also lived on the coast. They ate fish and insects. They had long tails with a blade at the end, narrow wings and a massive skull with teeth. different sizes, which was convenient to catch slippery fish.

The most dangerous predator of the deep sea was Liopleurodon, which weighed 25 tons. Huge coral reefs were formed, in which ammonites, belemnites, sponges and sea mats settled. Representatives of the shark family and bone fish develop. New species of plesiosaurs and ichthyosaurs, sea turtles and crocodiles appeared. Saltwater crocodiles have flippers instead of legs. This feature allowed them to increase their speed in the aquatic environment.

During the Cretaceous period of the Mesozoic era there were bees and butterflies. Insects carried pollen, and flowers gave them food. Thus began a long-term cooperation between insects and plants.

The most famous dinosaurs of that time were predatory tyrannosaurs and tarbosaurs, herbivorous bipedal iguanodons, quadrupedal rhinoceros-like Triceratops and small armored ankylosaurs.

Most of the mammals of that period belong to the subclass Allotherium. These are small animals, similar to mice, weighing no more than 0.5 kg. The only exceptional species is repenomamas. They grew up to 1 meter and weighed 14 kg. At the end of the Mesozoic era, the evolution of mammals takes place - the ancestors of modern animals are separated from allotheria. They were divided into 3 types - oviparous, marsupial and placental. It is they who at the beginning of the next era replace the dinosaurs. From the placental species of mammals, rodents and primates appeared. Purgatorius became the first primates. From the marsupial species, modern opossums originated, and the egg-laying species gave rise to platypuses.

The air space is dominated by early pterodactyls and new types of flying reptiles - orcheopteryx and quetzatcoatl. These were the most gigantic flying creatures in the entire history of the development of our planet. Together with representatives of pterosaurs, birds dominate the air. In the Cretaceous period, many ancestors of modern birds appeared - ducks, geese, loons. The length of the birds was 4-150 cm, weight - from 20 g. up to several kilograms.

Huge predators reigned in the seas, reaching a length of 20 meters - ichthyosaurs, plesiosaurs and mososaurs. Plesiosaurs had very long necks and small heads. Their large size did not allow them to develop great speed. The animals ate fish and shellfish. Mososaurs replaced saltwater crocodiles. These are giant predatory lizards with an aggressive character.

At the end of the Mesozoic era, snakes and lizards appeared, the species of which have reached the modern world without changing. Turtles of this time period also did not differ from those that we see now. Their weight reached 2 tons, length - from 20 cm to 4 meters.

By the end of the Cretaceous period, most reptiles begin to die out en masse.

Minerals of the Mesozoic era

A large number of deposits of natural resources are associated with the Mesozoic era. These are sulfur, phosphorites, polymetals, building and combustible materials, oil and natural gas.

On the territory of Asia, in connection with active volcanic processes, the Pacific belt was formed, which gave the world large deposits of gold, lead, zinc, tin, arsenic and other types of rare metals. In terms of coal reserves, the Mesozoic era is significantly inferior to Paleozoic era, but even during this period several large deposits of brown and hard coal were formed - the Kansk basin, Bureinsky, Lensky.

Mesozoic oil and gas fields are located in the Urals, Siberia, Yakutia, and the Sahara. Phosphorite deposits have been found in the Volga and Moscow regions.

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 distinguished 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

The organic world of the Mesozoic era is very different from the Paleozoic. The Paleozoic groups that died out in Perm were replaced by new Mesozoic ones.

In the Mesozoic seas, cephalopods - ammonites and belemnites - received exceptional development, the diversity and number of bivalves and gastropods drastically increased, and six-ray corals appeared and developed. Of the vertebrates, bony fish and swimming reptiles are widespread.

Extremely diverse reptiles (especially dinosaurs) dominated on land. Gymnosperms flourished among terrestrial plants.

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

The organic world of the sea. Among the invertebrates, cephalopods and bivalve mollusks were widespread. Among the cephalopods, the ceratites dominated, which replaced the goniatites. The characteristic genus was ceratites with a typical ceratite septal line. The first belemnites appeared, but there were still few of them in the Triassic.

Bivalve mollusks inhabited shallow areas rich in food, where brachiopods lived in the Paleozoic. Bivalves rapidly developed, becoming more diverse in composition. The number of gastropods has increased, six-pointed corals and new sea urchins with a strong shell have appeared.

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

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

The flora at the beginning of the Triassic was severely depleted due to the influence of the arid climate. In the second half of the Triassic, the climate became humid, and various 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 predominance of gymnosperms.

Organic Jurassic World

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

The organic world of the sea. Among the invertebrates, ammonites dominated; they had a complex septal line and were extremely diverse in the shape of the shell and its sculpture. One of the typical Late Jurassic ammonites is the genus Virgatites, with its characteristic tufts of ribs on the shell. There are many belemnites, their rostra are found in mass quantities in Jurassic clays. Characteristic genera are cylindrotheuthis with a long cylindrical rostrum and hyobolites with a fusiform rostrum.

Bivalves and gastropods have become numerous and diverse. Among the bivalves there were many oysters with thick shells of various shapes. Various six-pointed corals, sea urchins and numerous protozoa lived in the seas.

Among marine vertebrates, fish lizards - ichthyosaurs - continued to dominate, scaly lizards - mesosaurs, similar to giant toothed lizards, appeared. The 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 the extraterrestrial world or a figment of the imagination of artists.

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

Dinosaurs had giant size. Modern elephants - the largest land animals today (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 that protected their massive body. Stegosaurs had sharp spikes at the end of their tails. Among the dinosaurs there were many terrible predators that moved much faster than their herbivorous relatives. Dinosaurs reproduced using eggs, burying them in hot sand, as modern turtles do. In Mongolia, ancient dinosaur egg clutches are still being found.

The air environment was mastered by flying lizards - pterosaurs with sharp membranous wings. Rhamphorhynchus stood out among them - toothy lizards that ate fish and insects. At the end of the Jura, the first birds appeared - Archeopteryx - the size of a jackdaw, they retained many 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 Jura did floristic provinces begin to emerge.

Cretaceous Organic World

During this period, the 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 decline sharply 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 distributed as in jurassic but their composition has changed.

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

The 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, they gradually seized the dominant position. Among bivalves there were many oysters, inoceramus and pectenes. Peculiar goblet-shaped hippurites lived in the tropical seas of the Late Cretaceous. In the shape of their shells, they resemble sponges and solitary corals. This is evidence that these bivalve mollusks led an attached lifestyle, unlike their relatives. Gastropod molluscs reached a great diversity, especially towards the end of the period. Among the sea urchins, various irregular urchins dominated, one of the representatives of which is the genus Micraster with a heart-shaped shell.

The warm-water Late Cretaceous seas were overflowing with microfauna, among which small foraminifera-globigerins and ultramicroscopic unicellular calcareous algae - coccolithophorids predominated. The accumulation of coccoliths formed a thin calcareous silt, from which writing chalk was later formed. The softest varieties of writing chalk almost entirely consist of coccoliths, with an insignificant admixture of foraminifers.

There were many vertebrates in the seas. Bony fish developed rapidly, and they conquered marine environment. Until the end of the period, there were floating pangolins - 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, pterodactyls no larger than a sparrow lived. On land, various dinosaurs continued to dominate, but at the end of the Cretaceous they all died out along with their marine relatives.

The terrestrial flora of the Early Cretaceous, as in the Jurassic, was characterized by the predominance of gymnosperms, but starting from the end of the Early Cretaceous, angiosperms appear and rapidly develop, which, together with conifers, become the dominant group of plants by the end of the Cretaceous. Gymnosperms are drastically reduced in number and diversity, many of them are dying out.

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

Among these significant changes, the rapid disappearance from the face of the Earth of the Mesozoic giants - dinosaurs - is especially striking. What was the cause of the death of such a large and diverse group of animals? This topic has long attracted scientists and still does not leave 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 causes - a strong orogeny caused significant changes in paleogeography, climate and food resources. Other hypotheses link 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 brain volume and body weight of animals; the rapid development of predatory mammals that ate small dinosaurs and large eggs; gradual thickening of the egg shell to such an extent that the cubs could not break through it. There are hypotheses linking the death of dinosaurs with an increase in trace elements in the environment, with oxygen starvation, with lime washed out of the soil, or with an increase in gravity on Earth to such an extent that giant dinosaurs were crushed by their own weight.

The Mesozoic era began about 250 and ended 65 million years ago. It lasted 185 million years. 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 Mesozoic is known primarily as the era of the dinosaurs. These giant reptiles obscure all other groups of living beings. But don't forget about others. After all, it was the Mesozoic - the time when real mammals, birds, flowering plants appeared - that the modern biosphere actually formed. And if in the first period of the Mesozoic - the Triassic, there were still many animals from the Paleozoic groups on Earth that could survive the Permian catastrophe, then in last period- Cretaceous, almost all those families that flourished in the Cenozoic era have already formed.

The Mesozoic era was a transitional period in the development of the earth's crust and life. It can be called the geological and biological Middle Ages.
The beginning of the Mesozoic era coincided with the end of the Variscinian mountain-building processes, it ended with the beginning of the last powerful tectonic revolution - Alpine folding. In the Southern Hemisphere in the Mesozoic, the disintegration of the ancient continent of Gondwana ended, but on the whole, the Mesozoic era here was an era of relative calm, only occasionally and briefly disturbed by slight folding.

The progressive flora of gymnosperms (Gymnospermae) has been widespread since the beginning of the Late Permian. The early stage in the development of the plant kingdom, the paleophyte, was characterized by the dominance of algae, psilophytes, and seed ferns. The rapid development of more highly developed gymnosperms, which characterizes the “vegetative Middle Ages” (mesophyte), began in the Late Permian era and ended by the beginning of the Late Cretaceous era, when the first angiosperms, or flowering plants (Angiospermae), began to spread. From the Late Cretaceous, the Cainophyte began - the modern period in the development of the plant kingdom.

The appearance of gymnosperms was an important milestone in the evolution of plants. The fact is that the earlier Paleozoic spore-bearing organisms needed water for their reproduction, or, in any case, in a humid environment. This made it difficult for them to settle. The development of seeds allowed plants to lose such a close dependence on water. The ovules could now be fertilized by pollen carried by the wind or insects, and water thus no longer predetermined reproduction. In addition, in contrast to the unicellular spore with its relatively small supply of nutrients, the seed has a multicellular structure and is able to provide food for a young plant for a longer time in the early stages of development. Under adverse conditions, the seed can remain viable for a long time. Having a strong shell, it reliably protects the embryo from external dangers. All these advantages gave seed plants a good chance in the struggle for existence. The ovule (ovum) of the first seed plants was unprotected and developed on special leaves; the seed that arose from it also did not have an outer shell. That is why these plants were called gymnosperms.

Among the most numerous and most curious gymnosperms of the beginning of the Mesozoic era, we find the cycads (Cycas), or sagos. 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 in translation means "pinnate leaves"). Outwardly, they looked like tree ferns or palm trees.
In addition to cycads, great importance in the mesophyte acquired bennettitales (Bennettitales), represented by trees or shrubs. Basically, they resemble true cycads, but their seed begins to acquire a strong shell, which gives Bennettites a resemblance to angiosperms. There are other signs of adaptation of the bennettites to the conditions of a more arid climate.

In the Triassic, new forms come to the fore. Conifers quickly settle, and among them are firs, cypresses, yews. Of the Ginkgoaceae, the genus Baiera is widespread. The leaves of these plants had the shape of a fan-shaped plate, deeply dissected into narrow lobes. Ferns have captured damp shady places along the banks of small reservoirs (Hausmannia and other Dipteridacea). Known among the ferns and forms that grew on the rocks (Gleicheniacae). Horsetails (Equisetites, Phyllotheca, Schizoneura) grew in swamps, but did not reach the size of their Paleozoic ancestors.
In the middle mesophyte (Jurassic period), the mesophytic flora reached the climax of its development. The hot tropical climate in what is today the temperate zone was ideal for tree ferns to thrive, while smaller ferns and herbaceous plants preferred the temperate zone. Among the plants of this time, gymnosperms continue to play a dominant role.
(primarily cicadas).

The Cretaceous period is marked by rare changes in vegetation. The flora of the Lower Cretaceous still resembles in composition the vegetation of the Jurassic period. Gymnosperms are still widespread, but their dominance ends by the end of this time. Even in the Lower Cretaceous, the most progressive plants suddenly appeared - angiosperms, the predominance of which characterizes the era of new plant life, or cenophyte.

Angiosperms, or flowering (Angiospermae), occupy the highest rung of the evolutionary ladder of the plant world. Their seeds are enclosed in a strong shell; there are specialized reproductive organs (stamen and pistil), collected in a flower with bright petals and a calyx. Flowering plants appear somewhere in the first half of the Cretaceous, most likely in a cold and arid mountain climate with large temperature fluctuations.
With the gradual cooling that marked the chalk, they captured more and more new areas on the plains. Quickly adapting to the new environment, they evolved at an amazing rate. Fossils of the first true angiosperms are found in the Lower Cretaceous rocks of West Greenland, and a little later also in Europe and Asia. Within a relatively short time, they spread throughout the Earth and reached a great diversity.

From the end of the Early Cretaceous, the balance of power began to change in favor of angiosperms, and by the beginning of the Upper Cretaceous, their superiority became widespread. Cretaceous angiosperms belonged to evergreen, tropical or subtropical types, among them were eucalyptus, magnolia, sassafras, tulip trees, Japanese quince trees (quince), brown laurels, walnut trees, plane trees, oleanders. These heat-loving trees coexisted with the typical flora of the temperate zone: oaks, beeches, willows, birches. This flora also included gymnosperms of conifers (sequoias, pines, etc.).

For the gymnosperms, it was a time of surrender. Some species have survived to this day, but their total number has been descending all these centuries. A definite exception is conifers, which are found in abundance today.
In the Mesozoic, plants made a great leap forward, surpassing animals in terms of development.

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. Belemnite shells are popularly known as "devil's fingers". Ammonites were found in the Mesozoic in such quantities that their shells are found in almost all marine sediments of this time. Ammonites appeared as early as the Silurian, they experienced their first heyday in the Devonian, but reached their highest diversity in the Mesozoic. In the Triassic alone, more than 400 new genera of ammonites arose. Particularly characteristic of the Triassic were the ceratids, which were widely distributed in the Upper Triassic marine basin of Central Europe, the deposits of which are known in Germany as shell limestone.

By the end of the Triassic, most ancient groups of ammonites die out, but representatives of phylloceratids (Phylloceratida) have 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. In the Cretaceous, cephalopods, both ammonites and belemnites, are still numerous, but in the course of the Late Cretaceous, the number of species in both groups begins to decline. Among the ammonites at this time, aberrant forms with an incompletely twisted hook-shaped shell (Scaphites), with a shell elongated in a straight line (Baculites) and with an irregularly shaped shell (Heteroceras) appear. These aberrant forms appeared, most likely, as a result of changes in the course of individual development and narrow specialization. The final Upper Cretaceous forms of some ammonite branches are distinguished by sharply increased shell sizes. In the genus Parapachydiscus, for example, the shell diameter reaches 2.5 m.

The mentioned belemnites also acquired great importance in the Mesozoic. Some of their genera, such as Actinocamax and Belenmitella, are important as guide fossils and are successfully used for stratigraphic subdivision and accurate age determination of marine sediments.
At the end of the Mesozoic, all ammonites and belemnites became extinct. Of the cephalopods with an outer shell, only the genus Nautilus has survived to this day. Forms with an internal shell are more widely distributed in modern seas - octopuses, cuttlefish and squids, remotely related to belemnites.
The Mesozoic era was a time of unstoppable expansion of vertebrates. Of the Paleozoic fishes, only a few passed into the Mesozoic, as did the genus Xenacanthus, the last representative of Paleozoic freshwater sharks known from freshwater deposits of the Australian Triassic. Sea sharks continued to evolve throughout the Mesozoic; Most modern genera were already present in the seas of the Cretaceous, in particular, Carcharias, Carcharodon, lsurus, etc.

Ray-finned fish, which arose at the end of the Silurian, originally lived only in freshwater reservoirs, but with the Permian they begin to enter the seas, where they multiply unusually and from the Triassic to the present day retain their dominant position.
Reptiles became the most widespread in the Mesozoic, becoming truly the dominant class of this era. In the course of evolution, a variety of genera and species of reptiles appeared, often of very impressive size. Among them were the largest and most bizarre land animals that the earth had ever worn. As already mentioned, in terms of anatomical structure, the oldest reptiles were close to labyrinthodonts. The most ancient and most primitive reptiles were clumsy cotylosaurs (Cotylosauria), which appeared already at the beginning of the Middle Carboniferous and became extinct by the end of the Triassic. Among cotylosaurs, both small animal-eating and relatively large herbivorous forms (pareiasaurs) are known. The descendants of cotilosaurs gave rise to the whole diversity of the world of reptiles. One of the most interesting groups of reptiles that developed from cotylosaurs were the animal-like ones (Synapsida, or Theromorpha), their primitive representatives (pelycosaurs) have been known since the end of the Middle Carboniferous. In the middle of the Permian period, pelycosaurs, known mainly from North America, die out, but in the Old World they are replaced by more progressive forms that form the Therapsida order.
The carnivorous theriodonts (Theriodontia) included in it are already very similar to primitive mammals, and it is no coincidence that the first mammals developed from them by the end of the Triassic.

During the Triassic period, many new groups of reptiles appeared. These are turtles, and ichthyosaurs ("lizard fish") well adapted to marine life, resembling dolphins in appearance, and placodonts, clumsy armored animals with powerful flattened teeth adapted for crushing shells, and also plesiosaurs living in the seas, which had a relatively small head, more or less elongated neck, broad body, flipper-like paired limbs and short tail; Plesiosaurs vaguely resemble giant shellless tortoises. In the Jurassic, plesiosaurs, like ichthyosaurs, flourished. Both of these groups remained very numerous in the Early Cretaceous, 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, medium-sized predatory reptiles of the Triassic period, which gave rise to the most diverse groups - crocodiles, dinosaurs, flying pangolins, and, finally, birds.

However, the most remarkable group of Mesozoic reptiles were the well-known dinosaurs. They evolved from thecodonts as early as the Triassic and occupied a dominant position on Earth in the Jurassic and Cretaceous. Dinosaurs are represented by two groups, completely separate - saurischia (Saurischia) and ornithischia (Ornithischia). In the Jurassic, among the dinosaurs one could meet real monsters, up to 25-30 m long (with a tail) and weighing up to 50 tons. Of these giants, such forms as the brontosaurus (Brontosaurus), diplodocus (Diplodocus) and brachiosaurus (Brachiosaurus) are best known. And in the Cretaceous period, the evolutionary progress of dinosaurs continued. Of the European dinosaurs of this time, bipedal iguanodonts are widely known; in America, quadrupedal horned dinosaurs (Triceratops) Styracosaurus and others, somewhat reminiscent of modern rhinos, were widely used. Relatively small armored dinosaurs (Ankylosauria), covered with a massive bone shell, are also interesting. All these forms were herbivorous, as were the giant duck-billed dinosaurs (Anatosaurus, Trachodon, etc.), which moved on two legs. Carnivorous dinosaurs also flourished in the Cretaceous, the most remarkable of which were such forms as Tyrannosaurus rex, whose length exceeded 15 m, Gorgosaurus and Tarbosaurus. All these forms, which turned out to be the greatest land predatory animals in the entire history of the Earth, moved on two legs.

At the end of the Triassic, the first crocodiles also originated from thecodonts, which became abundant only in the Jurassic (Steneosaurus and others). In the Jurassic, flying lizards appear - pterosaurs (Pterosauria), also descending from thecodonts.
Among the flying lizards of the Jura, the most famous are the rhamphorhynchus (Rhamphorhynchus) and the pterodactyl (Pterodactylus), of the Cretaceous forms, the relatively very large Pteranodon (Pteranodon) is the most interesting. Flying pangolins become extinct by the end of the Cretaceous.
In the Cretaceous seas, giant predatory mosasaur lizards, exceeding 10 m in length, became widespread. Among modern lizards, they are closest to monitor lizards, but differ from them, in particular, in flipper-like limbs. By the end of the Cretaceous, the first snakes (Ophidia) also appeared, apparently descended from burrowing lizards.
By the end of the Cretaceous, the mass extinction of characteristic Mesozoic groups of reptiles, including dinosaurs, ichthyosaurs, plesiosaurs, pterosaurs and mosasaurs, occurs.

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

The first mammals (Mattalia), modest animals not exceeding the size of 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 had largely died out. The most ancient group of mammals were triconodonts (Triconodonta), to which the most famous of the Triassic mammals Morganucodon belongs. Appears in jura
a number of new groups of mammals - Symmetrodonta, Docodonta, Multituberculata and Eupantotheria. Of all these groups, only the Multituberculata (multi-tubercular) survived the Mesozoic, the last representative of which dies out in the Eocene. Polytuberculates were the most specialized of the Mesozoic mammals, convergently they had some similarities with rodents. The ancestors of the main groups of modern mammals - marsupials (Marsupialia) and placental (Placentalia) were Eupantotheria. Both marsupials and placentals appeared in the Late Cretaceous. The most ancient group of placentals are insectivores (lnsectivora), which have survived to this day.

The Mesozoic era is a period in the geological history of the Earth from 251 million to 65 million years ago. It is at this stage in the history of the Earth that the formation of the main contours of modern continents and mountain building takes place. on the periphery of the Pacific, Atlantic and Indian oceans. Favorable climatic conditions and the division of land contributed to important evolutionary events in the life of the biosphere - by the end of the Mesozoic, the main part of the species diversity of the Earth's life approached its modern state. Today we can judge the natural and climatic conditions, tectonic processes, the composition of the atmosphere, the animal and plant kingdom of the Mesozoic era by a lot of geological evidence. As is known, the closer the events are to the modern period of history, the more interesting and extensive information about the past can be gleaned from the geological record of the Earth.
If for previous epochs the main data were obtained by studying the sediments of rocks of modern continents, then already for the second half of the Mesozoic and beyond, scientists have important indications for the seas and oceans. The Paleozoic era ended with the Hercynian stage of folding. The folded systems formed in the Paleozoic at the site of the North Atlantic, Ural-Tien Shan and Mongolian-Okhotsk geosynclines contributed to the connection of the northern platforms into a huge single massif - Laurasia. This continent stretches from the Rocky Mountains of North America to the Verkhoyansk Range in northeast Asia.

The Southern Hemisphere had its own huge platform - the mainland Gondwana, uniting South America, Antarctica, Africa, Hindustan and Australia. At a certain period in the history of the Earth, Laurasia and Gondwana were one whole - the supercontinent Pangea. But it was in the Mesozoic era that the gradual disintegration of Pangea and the process of formation of modern continents and oceans began. Therefore, the Mesozoic is often called a transitional period in the development of the earth's crust, a real geological Middle Ages.

This era is best remembered as the era of the dinosaurs. It lasted about half as long as Palaeozoic but was eventful. It was a time when plants, fish, mollusks, and especially reptiles, reached enormous sizes, as if everything on Earth was then on megavitamins. Dinosaurs were buried in giant ferns and huge trees, while pterosaurs (flying reptiles) cruised the sky. Climatic conditions were warm everywhere.

While geologists can only guess at what forces caused the breakup of the supercontinent Pangea into Laurasia and Gondwana at this time, the example of Antarctica suggests igneous hotspots causing fractures around the globe. In some areas, dinosaurs and plants became isolated for millions of years and acquired special features, depending on their habitats, as well as local food and temperature conditions. Even small mammals have begun to get under the feet of carnivorous dinosaurs like the Tyrannosaurus Rex as an occasional snack.

During the Mesozoic Era, more modern forms of insects, corals, marine organisms, and flowering plants began to develop. Everything was really wonderful, when suddenly the dinosaurs and many other animals became extinct. Many scientists believe that this was due to a collision with a large asteroid and the resulting atmospheric smoke, volcanic eruptions and mostly inclement weather observed in subsequent years. The sun couldn't break through the ash and smoke, the water was polluted, and Earth certainly wasn't a big resort.