Mesozoic Jurassic period. Brief description of the Mesozoic era and its periods

The Mesozoic era began approximately 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 dinosaurs. These giant reptiles overshadow all other groups of living beings. But you shouldn’t forget about others. After all, it was the Mesozoic - the time when real mammals, birds, and flowering plants appeared - that actually formed the modern biosphere. And if in the first period of the Mesozoic - the Triassic, there were still many animals on Earth from Paleozoic groups that were able to survive the Permian catastrophe, then in the last period - the Cretaceous, almost all those families that flourished in the Cenozoic era had already formed.

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

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

The appearance of gymnosperms was important milestone in the evolution of plants. The fact is that earlier Paleozoic spore-bearing plants needed water or, at least, a humid environment for their reproduction. This made their resettlement quite difficult. The development of seeds allowed plants to lose such close dependence on water. The ovules could now be fertilized by pollen carried by the wind or insects, and water thus did not predetermine more reproduction. In addition, unlike a single-celled spore with its relatively small supply of nutrients, the seed has a multicellular structure and is able to provide food for a young plant in the early stages of development for longer. Under unfavorable conditions, the seed for a long time may remain viable. Having a durable shell, it reliably protects the embryo from external dangers. All these advantages gave seed plants good chances in the struggle for existence. 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. This 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 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 came to the fore. Conifers are spreading quickly, and among them are firs, cypresses, and yews. Among the ginkgos, the genus Baiera has become widespread. The leaves of these plants had the shape of a fan-shaped plate, deeply dissected into narrow lobes. Ferns have taken over damp, shady places along the banks of small bodies of water (Hausmannia and other Dipteraidae). Forms that grow on rocks (Gleicheniacae) are also known among ferns. Horsetails (Equisetites, Phyllotheca, Schizoneura) grew in the swamps, but did not reach the size of their Paleozoic ancestors.
In the middle mesophyte (Jurassic period), the mesophytic flora reached the culmination point of its development. Hot tropical climate in what are today temperate zones was ideal for tree ferns to thrive, while smaller fern species and herbaceous plants were preferred temperate zone. Among the plants of this time, gymnosperms continue to play a dominant role.
(primarily cycads).

The Cretaceous period was 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 at 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 plants (Angiospermae), 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 marked the Cretaceous, they captured more and more new areas on the plains. Quickly adapting to their new environment, they evolved at amazing speed. Fossils of the first true angiosperms are found in the Lower Cretaceous rocks of Western Greenland, and a little later also in Europe and Asia. In a relatively short time, they spread throughout the Earth and reached 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 typical flora temperate zone: oaks, beeches, willows, 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.

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 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 the ammonites at this time, aberrant forms appeared with an incompletely twisted hook-shaped shell (Scaphites), with a shell elongated in a straight line (Baculites) and with a shell irregular shape(Heteroceras). These aberrant forms appeared, apparently, as a result of changes in the course of individual development and narrow specialization. The terminal Upper Cretaceous forms of some branches of ammonites are distinguished by sharply increased shell sizes. In the genus Parapachydiscus, for example, the shell diameter reaches 2.5 m.

Great value in the Mesozoic, the mentioned belemnites also acquired. Some of their genera, for example, Actinocamax and Belenmitella, are important fossils and are successfully used for stratigraphic division and accurate determination of the age of marine sediments.
At the end of the Mesozoic, all ammonites and belemnites 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.
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 freshwater sharks Paleozoic, known from freshwater sediments of the Australian Triassic. sea sharks continued to develop throughout the Mesozoic; Most modern genera were already represented in the Cretaceous seas, in particular, Carcharias, Carcharodon, lsurus, etc.

Ray-finned fish, which arose at the end of the Silurian, initially lived only in freshwater bodies of water, but with the Permian they began to enter the seas, where they multiplied unusually and from the Triassic to the present day they retained a dominant position.
Reptiles became 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 the earth has ever bore. As already mentioned, in terms of anatomical structure, the most ancient reptiles were close to labyrinthodonts. The oldest and most primitive reptiles were the 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 cotylosaurs gave rise to the entire diversity of the reptile world. One of the most interesting groups reptiles that developed from cotylosaurs were animal-like (Synapsida, or Theromorpha), their primitive representatives (pelycosaurs) have been known since the end of the Middle Carboniferous. In the mid-Permian period, pelycosaurs, known mainly from North America, are dying out, but in the Old World they are replaced by more progressive forms that form the order Therapsida.
The predatory theriodonts (Theriodontia) included in it are already very similar to primitive mammals, and it is no coincidence - it was from them that the first mammals developed by the end of the Triassic.

During the Triassic period, many new groups of reptiles appeared. These include turtles, ichthyosaurs ("fish lizards"), 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 that lived in the seas, having a relatively small head, more or a less elongated neck, a wide body, flipper-like paired limbs and a short tail; Plesiosaurs vaguely resemble giant shellless turtles. In the Jurassic, plesiosaurs, like ichthyosaurs, reached their peak. Both of these groups remained very numerous in the Early 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 the most diverse groups - crocodiles, dinosaurs, flying lizards, and, finally, birds.

However, the most remarkable group of Mesozoic reptiles were the well-known dinosaurs. They developed from thecodonts back in the Triassic and took 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, real monsters could be found among dinosaurs, up to 25-30 m long (with tail) and weighing up to 50 tons. Of these giants, the most famous forms are Brontosaurus, Diplodocus and Brachiosaurus. 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, four-legged horned dinosaurs (Triceratops) Styracosaurus, etc.), somewhat reminiscent of modern rhinoceroses, became widespread. Also interesting are the relatively small armored dinosaurs (Ankylosauria), covered with a massive bony shell. All named forms were herbivores, as well as giant duck-billed dinosaurs (Anatosaurus, Trachodon, etc.), which walked on two legs. In the Cretaceous, predatory dinosaurs also flourished, the most remarkable of which were such forms as Tyrannosaurus rex, whose length exceeded 15 m, Gorgosaurus and Tarbosaurus. All of these forms, which turned out to be the greatest land predatory animals in the entire history of the Earth, walked on two legs.

At the end of the Triassic, the thecodonts also gave rise to the first crocodiles, which became abundant only in Jurassic period(Steneosaurus and others). In the Jurassic period, flying lizards appeared - pterosaurs (Pterosauria), 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 mosasaurian lizards, 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.

Representatives of the class of birds (Aves) first appear in Jurassic deposits. The remains of Archaeopteryx, a well-known and so far the 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 (Mattalia), 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. Appears in the Jurassic
a number of new groups of mammals - Symmetrodonta, Docodonta, Multituberculata and Eupantotheria. Of all the named groups, only the Multituberculata survived the Mesozoic, the last representative of which died out in the Eocene. Polytubercles 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 placentals (Placentalia) were Eupantotheria. Both marsupials and placentals appeared in the Late Cretaceous. The most ancient group of placentals are insectivores (insectivora), which have survived to this day.

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 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 facilitated by 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 hair and had highly developed jaws, which helped them feed on 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 arid climate many organisms changed their habitat to aquatic. This is how new species of ammonites, mollusks, as well as bony and ray-finned fish appeared. But the main residents depths of the sea there were predatory ichthyosaurs, which, as they evolved, began to reach gigantic size.

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

The newly formed continents move, and the tectonics of the Earth increasingly takes on a form familiar 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 consumed vegetation 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. Ammonites, belemnites, and bivalves ceased to exist in the aquatic environment. 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 negative impact the greenhouse effect or 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.

Which was followed by . The Mesozoic Era is sometimes called the "Age of the Dinosaurs" because these animals were the dominant species throughout much of the Mesozoic.

After the Permian mass extinction wiped out more than 95% of ocean life and 70% of land species, the new Mesozoic era began about 250 million years ago. It consisted of the following three periods:

Triassic period, or Triassic (252-201 million years ago)

The first big changes were noticed in the type that dominated the Earth. Most of the flora that survived the Permian extinction were seed-bearing plants such as gymnosperms.

Cretaceous period, or Cretaceous (145-66 million years ago)

The last period of the Mesozoic was called the Cretaceous. The growth of flowering land plants occurred. They were helped by newly appeared bees and warm climatic conditions. Coniferous plants were still numerous during the Cretaceous.

In terms of Cretaceous marine animals, sharks and rays became commonplace. Survivors of the Permian extinction, such as starfish, were also abundant during the Cretaceous.

On land, the first small mammals began to develop during the Cretaceous period. First marsupials appeared, and then other mammals. Appeared more birds and it became more reptiles. The dominance of dinosaurs continued, and the number of carnivorous species increased.

At the end of the Cretaceous and Mesozoic, another thing happened. This extinction is commonly called the K-T extinction (Cretaceous-Paleogene extinction). It destroyed all dinosaurs except birds and many other life forms on Earth.

There are different versions as to why the mass disappearance occurred. Most scientists agree that there was some kind of catastrophic event that caused this extinction. Various hypotheses include massive volcanic eruptions that released huge amounts of dust into the atmosphere, reducing the amount of sunlight reaching the Earth's surface and thereby causing the death of photosynthetic organisms such as plants and those that depended on them. Others believe that a meteorite fell to Earth and the dust blocked the sunlight. Because the plants and animals that fed on them died out, this meant that predators such as carnivorous dinosaurs also died due to lack of food.

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
Cretaceous period
The Triassic and Jurassic periods were much shorter than the Cretaceous, which lasted about 71 million years.

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 the 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 earth's 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. In general, the climate was warmer than it is now. However, it was approximately the same throughout the planet. There was never such a temperature difference between the equator and the poles as there is now. Apparently this is due to the location of the continents in the Mesozoic era.
Seas and mountain ranges appeared and disappeared. IN Triassic period the climate is arid. This is due to the location of the land, most of which was desert. Vegetation existed along the ocean shore and along river banks.
During the Jurassic period, when the continent of Gondwana split and its parts began to diverge, the climate became more humid, but remained warm and even. This climate change was the impetus for the development of lush vegetation and rich wildlife.
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 a colder climate.

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 of the 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 for a young plant in the early stages of development for longer. Under unfavorable conditions, the seed can remain viable for a long time. Having a durable shell, it reliably protects the embryo from external dangers. All these advantages gave seed plants good chances in the struggle for existence.
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.
During the Jurassic period, the flora reached the highest point of its development. The hot tropical climate in what is now the temperate zone was ideal for tree ferns to thrive, while smaller fern species and herbaceous plants preferred the temperate zone. Among the plants of this time, gymnosperms (primarily cycads) continue to play a dominant role.

Angiosperms.

At the beginning of the Cretaceous periods, gymnosperms were still widespread, but the first angiosperms, more advanced forms, were already appearing.
The flora of the Lower Cretaceous still resembles in composition the vegetation of the Jurassic period. Gymnosperms are still widespread, but their dominance ends at 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. Which we know now.
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 reached 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 oldest and most primitive reptiles were the clumsy cotylosaurs, which appeared 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 cotylosaurs gave rise to the entire diversity of the reptile world. One of the most interesting groups of reptiles that developed from cotylosaurs were the beast-like animals (Synapsida, or Theromorpha); their primitive representatives (pelycosaurs) have been known since the end of the Middle Carboniferous. In the middle of the Permian period, the pelycosaurs that inhabited the territory of what is now North America die out, but in the European part they are replaced by more developed forms forming the order Therapsida.
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 Albertosaurus

During 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 earliest known dinosaurs were eoraptor And Herrerasaurus. The most famous of the Triassic dinosaurs are coelophysis And 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 And brachiosaurus. Another striking representative of the Jurassic fauna is the bizarre stegosaurus. It can be unmistakably identified among other dinosaurs.
During the Cretaceous period, the evolutionary progress of dinosaurs continued. Of the European dinosaurs of this time, bipeds are widely known iguanodons, four-legged horned dinosaurs became widespread in America Triceratops 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. group carnivorous dinosaurs 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.

Cephalopods.

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 an incompletely 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 of individual development and narrow specialization. The terminal Upper Cretaceous forms of some branches of ammonites are distinguished by sharply increased shell sizes. In one of the species of ammonites, the diameter of the shell reaches 2.5 m. Belemnites acquired great importance in the Mesozoic era. Some of their genera, for example, Actinocamax and Belemnitella, are important fossils and are successfully used for stratigraphic division and accurate determination of the age of marine sediments. At the end of the Mesozoic, all ammonites and belemnites became extinct. Of the cephalopods with an external shell, only nautiluses have survived to this day. More widespread in modern seas are forms with internal shells - octopuses, cuttlefish and squids, distantly related to belemnites.

Other invertebrate animals of the Mesozoic era.

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 evolved in the Mesozoic, such as Terebratulacea and Rhynchonellacea, but the vast majority went into decline. Mesozoic echinoderms were introduced various types sea lilies, 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 from the Mesozoic. Starfish (Asteroidea) and ophidra were abundant.
Compared to 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.
rocks of the Mesozoic, and today they help us establish the age of various layers. The Cretaceous period was also a time of rapid development of new types of sponges and some arthropods, particularly insects and decapods.

The rise of vertebrates. Fishes of the Mesozoic era.

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, concluded that it belongs to the “extinct” group of lobe-fins (Coelacanthida). To
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
- Anura (frogs): Neusibatrachus and Eodiscoglossus in Spain, Notobatrachus and Vieraella in South America. In the Cretaceous, the development of tailless amphibians accelerates, but they reach their greatest diversity in the Tertiary period and today. In the Jurassic, the first tailed amphibians (Urodela) appeared, to which modern newts and salamanders belong. Only in the Cretaceous do their finds become more common, but the group reached its peak only in the Cenozoic.

The first birds.

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; 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.

On land, the diversity of reptiles increased. Their hind limbs have become more developed than their forelimbs. The ancestors of modern lizards and turtles also appeared in the Triassic period. During the Triassic period the climate individual territories It was not only dry, but also cold. As a result of the struggle for existence and natural selection, the first mammals appeared from some predatory reptiles, which were no larger than rats. It is believed that they, like modern platypuses and echidnas, were oviparous.

Repentant in Jurassic period spread not only on land, but also in water and air environment. Flying lizards have become widespread. The Jurassic also saw the appearance of the very first birds, Archeopteryx. As a result of the flourishing of spore and gymnosperm plants, the body size of herbivorous reptiles increased excessively, some of them reaching a length of 20-25 m.

Plants

Thanks to the warm and humid climate During the Jurassic period, tree-like plants flourished. In the forests, as before, gymnosperms and fern-like plants dominated. Some of them, such as sequoia, have survived to this day. The first flowering plants that appeared in the Jurassic period had a primitive structure and were not widespread.

Climate

IN Cretaceous period The climate has changed dramatically. Cloudiness decreased significantly, and the atmosphere became dry and transparent. As a result of this sun rays fell directly on plant leaves. Material from the site

Animals

On land, the reptile class still retained its dominance. Predatory and herbivorous reptiles increased in size. Their bodies were covered with a shell. The birds had teeth, but were otherwise close to modern birds. In the second half of the Cretaceous period, representatives of the subclass of marsupials and placentals appeared.

Plants

Climatic changes in the Cretaceous period had a negative impact on ferns and gymnosperms, and their numbers began to decline. But angiosperms, on the contrary, multiplied. By the mid-Cretaceous, many families of monocotyledonous and dicotyledonous angiosperms had evolved. Due to its diversity and appearance they are in many ways close to modern flora.