What happened in the Mesozoic era briefly. Fauna and flora in the Mesozoic

Age of Reptiles

In the mass consciousness, the Mesozoic era has long been rooted as the era of dinosaurs, who reigned supreme on the planet for a little less than two hundred million years. In part, this is true. But this historical period is not only remarkable from a geological and biological point of view. The Mesozoic era, whose periods (Triassic, Cretaceous and Jurassic) have their own characteristics, is a time division of the geochronological scale, lasting about one hundred and sixty million years.

General characteristics of the Mesozoic

During this huge time span, which started about 248 million years ago and ended 65 million years ago, the last supercontinent Pangea broke up. And the Atlantic Ocean was born. During this period, chalk deposits on the ocean floor were formed by unicellular algae and protozoa. Getting into the zones of collision of lithospheric plates, these carbonate sediments contributed to an increased release of carbon dioxide during volcanic eruptions, which significantly changed the composition of water and the atmosphere. Land life in the Mesozoic era was characterized by the dominance of giant lizards and gymnosperms. In the second half of the Cretaceous period, the mammals familiar to us today began to enter the evolutionary scene, which were then prevented from fully developing by dinosaurs. Significant temperature fluctuations associated with the introduction of angiosperms into the terrestrial ecosystem, and new classes of unicellular algae into the marine environment, disrupted the structure of biological communities. The Mesozoic era is also characterized by a significant restructuring of food chains, which began closer to the middle of the Cretaceous.

Triassic. Geology, sea creatures, plants

The Mesozoic era began with the Triassic period, which replaced the Permian geological era. Living conditions during this period practically did not differ from those in Perm. There were no birds and grass on Earth at that time. Some part of the modern North American continent and Siberia was at that time the seabed, and the territory of the Alps was hidden under the waters of Tethys - a giant prehistoric ocean. Due to the absence of corals, green algae were engaged in the construction of reefs, which neither before nor after did not play the first role in this process. Also a characteristic feature of life in the Triassic was the combination of old species with new ones that have not yet gained strength. The time of conodonts and cephalopods with straight shells was coming to an end; some types of six-pointed corals have already begun to appear, the flowering of which is yet to come; the first bony fish and sea ​​urchins, having a solid shell that does not decompose after death. Among the terrestrial species, lepidodendrons, cordaites and tree-like horsetails lived out their long lives. They were replaced by coniferous plants, well known to all of us.

Fauna of the Triassic

Among the animals, amphibians began to appear - the first stegocephals, but dinosaurs began to spread more and more widely, including their flying varieties. At first, they were small creatures similar to modern lizards, equipped with various biological devices for taking off. Some had dorsal growths resembling wings. They could not swing, but they managed to successfully descend with their help, like paratroopers. Others were equipped with membranes, which allowed them to plan. Such a prehistoric hang gliders. And Sharovipteryx had a full arsenal of such flight membranes. Its wings can be considered hind limbs, the length of which significantly exceeded the linear dimensions of the rest of the body. During this period, small mammals were already hiding in anticipation of their time, hiding in holes from the owners of the planet. Their time will come. Thus began the Mesozoic era.

Jurassic period

This era has become hugely famous thanks to one Hollywood movie, which is more fiction than reality. True, only one thing is the flowering of the power of dinosaurs, which simply suppressed other forms of animal life. In addition, the Jurassic period is notable for the complete collapse of Pangea into separate continental blocks, which significantly changed the geography of the planet. The population of the ocean floor has undergone extremely strong changes. Brachiopods were replaced by bivalve molluscs, and primitive shells by oysters. Now it is difficult to imagine the richness and splendor of the Jurassic forests, especially on the wet coasts. These are giant trees, and fantastic ferns, extremely lush shrub vegetation. And, of course, a huge variety of dinosaurs - the largest creatures that have ever lived on the planet.

Dinosaur's Last Ball

The largest events of this era in the plant world occurred in the middle of the Cretaceous period. The first flowers bloomed, therefore, angiosperms appeared, which still dominate the flora of the planet. Real thickets of laurels, willows, poplars, plane trees and magnolias have already appeared. Basically, vegetable world in that distant time, it acquired almost modern outlines, which cannot be said about animals. It was the world of ceratopsians, ankylosaurs, tyrannosaurs and the like. It all ended in a grand catastrophe - the largest in earth's history. And the age of mammals has come. Which eventually made it possible for a person to come to the fore, but that's another story.

Mesozoic - an era of tectonic, climatic and evolutionary activity. There is a formation of the main contours of modern continents and mountain building on the periphery of the Pacific, Atlantic and Indian oceans; the division of the landmass contributed to speciation and other important evolutionary events. The climate was warm throughout the entire time period, which also played an important role in the evolution and formation of new animal species. By the end of the era, the main part of the species diversity of life approached its modern state.

Geological periods

• Triassic period (252.2 ± 0.5 - 201.3 ± 0.2)
• Jurassic (201.3 ± 0.2 - 145.0 ± 0.8)
• Cretaceous period (145.0 ± 0.8 - 66.0).

The lower (between the Permian and Triassic periods, that is, between the Paleozoic and Mesozoic) boundary is marked by a massive Permian-Triassic extinction, as a result of which approximately 90-96% of marine fauna and 70% of land vertebrates died. The upper limit was set at the turn of the Cretaceous and Paleogene, when another very major extinction many groups of plants and animals, most often due to the fall of a giant asteroid (the Chicxulub crater on the Yucatan Peninsula) and the “asteroid winter” that followed. Approximately 50% of all species died out, including all flightless dinosaurs.

Tectonics and paleogeography

Compared to the vigorous mountain building of the Late Paleozoic, Mesozoic tectonic deformations can be considered relatively mild. The era is characterized primarily by the division of the supercontinent Pangea into a northern continent, Laurasia, and southern continent, Gondwana . This process led to the formation of the Atlantic Ocean and passive continental margins, in particular most of the modern Atlantic coast(e.g. east coast North America). Extensive transgressions that prevailed in the Mesozoic led to the emergence of numerous inland seas.

By the end of the Mesozoic, the continents practically took on their modern shape. Laurasia split into Eurasia and North America, Gondwana split into South America, Africa, Australia, Antarctica, and the Indian subcontinent, whose collision with the Asian continental plate caused intense orogeny with the uplift of the Himalayan mountains.

Africa

At the beginning of the Mesozoic era, Africa was still part of the Pangea supercontinent and had a relatively common fauna with it, dominated by theropods, prosauropods and primitive ornithischian dinosaurs (by the end of the Triassic).

Late Triassic fossils are found everywhere in Africa, but are more common in the south than in the north of the continent. As is known, the time line separating the Triassic from the Jurassic period was drawn according to the global catastrophe with the mass extinction of species (Triassic-Jurassic extinction), but the African layers of this time remain poorly understood today.

Early Jurassic fossil deposits are distributed similarly to those of the Late Triassic, with more frequent outcrops in the south of the continent and fewer deposits towards the north. During the Jurassic period, such iconic groups of dinosaurs as sauropods and ornithopods increasingly spread across Africa. Paleontological layers of the middle Jurassic in Africa are poorly represented and also poorly studied.

Late Jurassic strata are also poorly represented here, with the exception of the impressive collection of Jurassic Tendeguru fauna in Tanzania, whose fossils are very similar to those found in the paleobiotic Morrison Formation in western North America and date from the same period.

In the middle of the Mesozoic, about 150-160 million years ago, Madagascar separated from Africa, while remaining connected to India and the rest of Gondwana. Fossils from Madagascar have included abelisaurs and titanosaurs.

In the early Cretaceous, a part of the land that made up India and Madagascar separated from Gondwana. In the Late Cretaceous, the divergence of India and Madagascar began, which continued until the modern outlines were reached.

Unlike Madagascar, mainland Africa was tectonically relatively stable throughout the Mesozoic. And yet, despite the stability, significant changes occurred in its position relative to other continents as Pangea continued to fall apart. By the beginning of the Late Cretaceous period, South America separated from Africa, thereby completing the formation of the Atlantic Ocean in its southern part. This event had a huge impact on the global climate by changing ocean currents.

During the Cretaceous, Africa was inhabited by allosauroids and spinosaurids. The African theropod Spinosaurus turned out to be one of the largest carnivores that lived on Earth. Among the herbivores in the ancient ecosystems of those times, titanosaurs occupied an important place.

Cretaceous fossil deposits are more common than Jurassic deposits, but often cannot be radiometrically dated, making it difficult to determine their exact age. Paleontologist Louis Jacobs, who has spent considerable time fieldwork in Malawi, argues that African fossil deposits "need more careful excavation" and are bound to prove "fertile ... for scientific discoveries."

Climate

During the last 1.1 billion years in the history of the Earth, there have been three successive ice age-warm cycles, called the Wilson cycles. Longer warm periods were characterized by a uniform climate, a greater diversity of flora and fauna, and a predominance of carbonate sediments and evaporites. Cold periods with glaciations at the poles were accompanied by a decrease in biodiversity, terrigenous and glacial sediments. The reason for the cyclicity is considered to be the periodic process of connecting the continents into a single continent (Pangaea) and its subsequent disintegration.

The Mesozoic era is the warmest period in the Phanerozoic history of the Earth. It almost completely coincided with the period global warming which started in Triassic period and ended already in the Cenozoic era with a small ice age which continues to this day. For 180 million years, even in the polar regions there was no stable ice cover. The climate was mostly warm and even, without significant temperature gradients, although there was climatic zoning in the northern hemisphere. A large amount of greenhouse gases in the atmosphere contributed to the even distribution of heat. The equatorial regions were characterized by a tropical climate (the Tethys-Pantalassa region) with average annual temperature 25–30°С. Up to 45-50°N the subtropical region (Peritethys) extended, then the moderately warm boreal belt lay further, and the polar regions were characterized by a moderately cool climate.

During the Mesozoic, the climate was warm, mostly dry in the first half of the era and wet in the second. Slight cooling in the late Jurassic and the first half of the Cretaceous, a strong warming in the middle of the Cretaceous (the so-called Cretaceous temperature maximum), at about the same time the equatorial climatic zone appears.

Flora and fauna

Giant ferns, tree horsetails, and club mosses are dying out. Gymnosperms, especially conifers, flourish in the Triassic. In the Jurassic, seed ferns die out and the first angiosperms appear (so far represented only by tree forms), which gradually spread to all continents. This is due to a number of advantages; angiosperms have a highly developed conducting system, which ensures the reliability of cross-pollination, the embryo is supplied with food reserves (due to double fertilization, a triploid endosperm develops) and is protected by shells, etc.

In the animal kingdom, insects and reptiles flourish. Reptiles occupy a dominant position and are represented by a large number of forms. In the Jurassic, flying lizards appear and conquer the air. In the Cretaceous period, the specialization of reptiles continues, they reach enormous sizes. Some of the dinosaurs weighed up to 50 tons.

The parallel evolution of flowering plants and pollinating insects begins. At the end of the Cretaceous, cooling sets in, and the area of ​​near-water vegetation is reduced. Herbivores die out, followed by carnivorous dinosaurs. Large reptiles are preserved only in the tropical zone (crocodiles). Due to the extinction of many reptiles, a rapid adaptive radiation of birds and mammals begins, occupying the vacant ecological niches. In the seas, many forms of invertebrates and sea lizards are dying out.

Birds, according to most paleontologists, evolved from one of the groups of dinosaurs. The complete separation of arterial and venous blood flow determined their warm-bloodedness. They spread widely over land and gave rise to many forms, including flightless giants.

The emergence of mammals is associated with a number of large aromorphoses that arose in one of the subclasses of reptiles. Aromorphoses: a highly developed nervous system, especially the cerebral cortex, which provided adaptation to the conditions of existence by changing behavior, moving limbs from the sides under the body, the emergence of organs that ensure the development of the embryo in the mother's body and subsequent feeding with milk, the appearance of a coat, complete separation of circulatory circles, the emergence of alveolar lungs, which increased the intensity of gas exchange and, as a result, the overall level of metabolism.

Mammals appeared in the Triassic, but could not compete with dinosaurs and for 100 million years occupied a subordinate position in the ecological systems of that time.

Scheme of the evolution of flora and fauna in the Mesozoic era.

Literature

• Jordan N. N. development of life on earth. - M .: Enlightenment, 1981.
• Koronovsky N.V., Khain V.E., Yasamanov N.A. Historical Geology: Textbook. - M .: Academy, 2006.
• Ushakov S.A., Yasamanov N.A. Continental drift and climates of the Earth. - M .: Thought, 1984.
• Yasamanov N.A. Ancient climates of the Earth. - L.: Gidrometeoizdat, 1985.
• Yasamanov N.A. Popular paleogeography. - M .: Thought, 1985.

Links

	Portal "Mesozoic"
	Mesozoic at Wikimedia Commons

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Mesozoic… Spelling Dictionary

The Mesozoic era was a transitional period in the development 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 Mesozoic era lasted approximately 160 million years. It is usually divided into three periods: Triassic, Jurassic and Cretaceous; the first two periods were much shorter than the third, which lasted 71 million years.

In biological terms, the Mesozoic was a time of transition from old, primitive to new, progressive forms. Neither four-beam corals (rugoses), nor trilobites, nor graptolites crossed that invisible boundary that lay between the Paleozoic and Mesozoic. Mesozoic world was much more diverse than the Paleozoic, fauna and flora appeared in it in a significantly updated composition.

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. Cenophyte began from the Late Cretaceous - modern period 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, unlike the unicellular spore with its relatively small supply of nutrients, the seed has a multicellular structure and is able to provide food for longer. young plant in the early stages of development. Under adverse conditions, the seed for a long time may remain viable. 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 (such as the genus Pterophyllum, whose name means "pinnate leaves"). Outwardly, they looked like tree ferns or palm trees. In addition to cycads, bennettitales (Bennettitales), represented by trees or shrubs, have become of great importance in the mesophyte. 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. 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 (primarily cycads) continue to play the dominant role.

Angiosperms.

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 the new plant life, or cenophyte.

Angiosperms, or flowering (Angiospermae), occupy the highest level evolutionary ladder of the plant world. Their seeds are enclosed in a strong shell; there are specialized bodies reproduction (stamen and pistil), collected in a flower with bright petals and a calyx. Flowering plants appear somewhere in the first half of the Cretaceous period, most likely in cold and arid conditions. mountain climate with large temperature differences. 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 typical flora 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.

Animal world of the Mesozoic. Cephalopods.

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 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 Belemnitella, are important as guide fossils and are successfully used for stratigraphic subdivision and exact definition age 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.

Other invertebrates.

Tabulata and four-beam corals were no longer in the Mesozoic seas. Their place was taken by six-ray corals (Hexacoralla), whose colonies were active reef-formers - the marine reefs built by them are now widespread in pacific ocean. Some groups of brachiopods still evolved in the Mesozoic, such as the Terebratulacea and Rhynchonellelacea, but the vast majority of them declined. Mesozoic echinoderms were represented by various types of crinoids, or crinoids (Crinoidea), which flourished in the shallow waters of the Jurassic and partly Cretaceous seas. However, sea urchins (Echinoidca) have made the most progress; to date, countless species have been described from the Mesozoic. Sea stars (Asteroidea) and ophidras were abundant.

Compared with Paleozoic era in the Mesozoic, bivalve mollusks also became widespread. Already in the Triassic, many of their new genera appeared (Pseudomonotis, Pteria, Daonella, etc.). At the beginning of this period, we also meet the first oysters, which later become one of the most common groups of molluscs in the Mesozoic seas. The appearance of new groups of molluscs continues into the Jurassic, the characteristic genera of this time being Trigonia and Gryphaea, classified as oysters. In the Cretaceous formations one can find funny types of bivalves - rudists, whose cup-shaped shells had a special cap at the base. These creatures settled in colonies, and in Late Cretaceous they contributed to the construction of limestone cliffs (for example, the genus Hippurites). The most characteristic bivalves of the Cretaceous were molluscs 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, the foraminifera flourished again, surviving the Cretaceous period and reaching modern times. In general, unicellular protozoa were an important component in the formation sedimentary rocks Mesozoic, and today they help us to establish the age of various layers. The Cretaceous period was also a time of rapid development of new types of sponges and some arthropods, in particular insects and decapods.

The rise of vertebrates. Fish.

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, Isurus, 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.

Earlier we talked about the Paleozoic lobe-finned fish ah, from which the first terrestrial vertebrates evolved. Almost all of them died out in the Mesozoic; only a few of their genera (Macropoma, Mawsonia) were found in the Cretaceous rocks. Up until 1938, paleontologists believed that the crossopterygians had become extinct by the end of the Cretaceous. But in 1938, an event occurred that attracted the attention of all paleontologists. An individual of a fish species unknown to science was caught off the South African coast. Scientists who studied this unique fish came to the conclusion that it belongs to the “extinct” group of lobe-finned fish (Coelacanthida). Until now, this species remains the only modern representative of the ancient lobe-finned fish. It received the name Latimeria chalumnae. Such biological phenomena are referred to as "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 disappear from the face of the earth, but some of them, apparently, gave rise to the ancestors of modern frogs. We are talking about the genus Triadobatrachus; to date, only one incomplete skeleton of this animal has been found in the north of Madagascar. In the Jurassic, real tailless amphibians are already found - Anura (frogs):

Neusibatrachus and Eodiscoglossus in Spain, Notobatrachus and Vieraella in South America. In the Cretaceous, the development of tailless amphibians accelerates, but greatest variety they reach in the Tertiary period and now. In the Jurassic, the first tailed amphibians (Urodela) also appear, to which modern newts and salamanders belong. Only in the Cretaceous did their finds become more common, while the group reached its peak only in the Cenozoic.

Reptiles.

The reptiles, which became truly the dominant class of this era, were most widespread in the Mesozoic. 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 oldest 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 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 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 forming 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 well adapted to marine life ichthyosaurs (“lizard fish”), outwardly resembling dolphins, 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, wide body, flipper-shaped pairs 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 wonderful group Mesozoic reptiles were all 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, real monsters could be found, up to 25-30 m long (with a 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 rhinos, became widespread. Relatively small armored dinosaurs (Ankylosaurid), 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 (Pterosaurid), also descended 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.

First birds.

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

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 had largely died out. most ancient group mammals were triconodonts (Triconodonta), to which the most famous of Triassic mammals Morganucodon. A number of new groups of mammals appeared in the Jurassic - Symmetrodonta, Docodonta, Multituberculata and Eupamotheria. 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 (Placentalid) 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.

Powerful tectonic processes of Alpine folding, which erected new mountain ranges and changed the outlines of continents, radically changed the geographical and climatic situation. Almost all Mesozoic groups of the animal and plant kingdoms retreat, die out, disappear; on the ruins of the old, a new world arises, the world of the Cenozoic era, in which life receives a new impetus to development and, in the end, the living species of organisms are formed.

On land, the variety of reptiles increased. Their hind limbs have become more developed than the front ones. The ancestors of modern lizards and turtles also appeared in the Triassic period. In the Triassic period, the climate of individual territories 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 more than rats. It is assumed that they, like modern platypuses and echidnas, were oviparous.

Plants

Reptiles penitent in jurassic spread not only on land, but also in the water and air environment. Flying lizards are widespread. In the Jurassic period, the very first birds, Archeopteryx, also appeared. As a result of the flowering of spore and gymnosperms, the size of the body of herbivorous reptiles increased excessively, some of them reached a length of 20-25 m.

Plants

Thanks to warm and humid climate in the Jurassic, 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 had a primitive structure and were not widespread.

Climate

AT Cretaceous the climate has changed dramatically. Cloudiness has significantly decreased, and the atmosphere has become dry and transparent. As a result Sun rays fell directly on the leaves of plants. material from the site

Animals

On land, the class of reptiles still maintained its dominance. Predatory and herbivorous reptiles increased in size. Their bodies were covered with armor. The birds had teeth, but otherwise they were close to modern birds. In the second half of the Cretaceous, representatives of the marsupial and placental subclass appeared.

Plants

The climatic changes of the Cretaceous period had a negative impact on ferns and gymnosperms, and their numbers began to decrease. But angiosperms, on the contrary, multiplied. By the middle of the Cretaceous, many families of monocots and dicots of angiosperms had developed. In their diversity and appearance, they are in many respects close to modern flora.

The Mesozoic consists of three periods: Triassic, Jurassic, Cretaceous.

in the triassic most of the land was above sea level, the climate was dry and warm. Due to the very dry climate in the Triassic, almost all amphibians disappeared. Therefore, the flowering of reptiles began, which were adapted to drought (Fig. 44). Among plants in the Triassic, strong development reached gymnosperms.

Rice. 44. Various types of reptiles of the Mesozoic era

Of the Triassic reptiles, turtles and tuatara have survived to this day.

The tuatara, preserved on the islands of New Zealand, is a real "living fossil". Over the past 200 million years, the tuatara has not changed much and has retained, like its Triassic ancestors, a third eye located in the roof of the skull.

Of reptiles, the rudiment of the third eye is preserved in lizards agamas and batbats.

Along with undoubted progressive features in the organization of reptiles, there was one very significant imperfect feature - unstable body temperature. In the Triassic period, the first representatives of warm-blooded animals appeared - small primitive mammals - tricodonts. They originated from ancient animal-toothed lizards. But tricodonts the size of a rat could not compete with reptiles, so they did not spread widely.

Yura named after a French city located on the border with Switzerland. In this period, the planet is "conquered" by dinosaurs. They mastered not only land, water, but also air. Currently, 250 species of dinosaurs are known. One of the most characteristic representatives of dinosaurs was a giant brachiosaurus. It reached a length of 30 m, weight 50 tons, had a small head, a long tail and neck.

In the Jurassic period, various types of insects and the first bird appear - archeopteryx. Archeopteryx is about the size of a crow. His wings were poorly developed, there were teeth, a long tail covered with feathers. In the Jurassic period of the Mesozoic, there were many reptiles. Some of their representatives began to adapt to life in the water.

The rather mild climate favored the development of angiosperms.

Chalk- the name is given because of the powerful Cretaceous deposits formed from the remains of the shells of small marine animals. In this period, angiosperms arise and spread extremely rapidly, gymnosperms are forced out.

The development of angiosperms during this period was associated with the simultaneous development of pollinating insects and insect-eating birds. In angiosperms, a new reproductive organ arose - a flower that attracts insects with color, smell and nectar reserves.

At the end of the Cretaceous, the climate became colder, and the vegetation of the coastal lowlands perished. Together with the vegetation, herbivorous, predatory dinosaurs died. Large reptiles (crocodile) survived only in the tropical zone.

In conditions of sharp continental climate and general cooling, warm-blooded birds and mammals received exceptional advantages. The acquisition of live birth and warm-bloodedness were those aromorphoses that ensured the progress of mammals.

During the Mesozoic period, the evolution of reptiles developed in six directions:

1st direction - turtles (appeared in the Permian period, have a complex shell, fused with ribs and breast bones);

5th direction - plesiosaurs (sea lizards with a very long neck, making up more than half of the body and reaching a length of 13-14 m);

6th direction - ichthyosaurs (lizard fish). Appearance similar to fish and whale, short neck, fins, swim with the help of the tail, legs control the movement. Intrauterine development - live birth of offspring.

At the end of the Cretaceous period, during the formation of the Alps, climate change led to the death of many reptiles. During the excavations, the remains of a bird the size of a dove, with the teeth of a lizard, which had lost the ability to fly, were discovered.

Aromorphoses that contributed to the appearance of mammals.

1. The complication of the nervous system, the development of the cerebral cortex had an impact on the change in the behavior of animals, adaptation to the living environment.

2. The spine is divided into vertebrae, the limbs are located from the abdominal part closer to the back.

3. For intrauterine bearing of cubs, the female has developed a special organ. The babies were fed with milk.

4. Hair appeared to preserve body heat.

5. There was a division into a large and small circle of blood circulation, warm-bloodedness appeared.

6. Lungs have developed with numerous bubbles that enhance gas exchange.

1. Periods of the Mesozoic era. Triassic. Yura. Bor. Tricodonts. Dinosaurs. Archosaurs. Plesiosaurs. Ichthyosaurs. Archeopteryx.

2. Aromorphoses of the Mesozoic.

1. What plants were widespread in the Mesozoic? Explain the main reasons.

2. Tell us about the animals that developed in the Triassic.

1. Why is the Jurassic period called the period of the dinosaurs?

2. Disassemble the aromorphosis, which is the cause of the appearance of mammals.

1. In what period of the Mesozoic did the first mammals appear? Why weren't they widespread?

2. Name the types of plants and animals that developed in the Cretaceous period.

In what period of the Mesozoic did these plants and animals develop? Opposite the corresponding plants and animals, put the capital letter of the period (T - Triassic, Yu - Jurassic, M - Cretaceous).

1. Angiosperms.

2. Tricodonts.

4. Eucalyptus.

5. Archeopteryx.

6. Turtles.

7. Butterflies.

8 Brachiosaurs

9. Tuataria.

11. Dinosaurs.