Age of Reptiles
In the popular consciousness, the Mesozoic era has long been ingrained as the era of dinosaurs, who reigned supreme over the planet for just under two hundred million years. This is partly true. But this is not the only thing that makes this historical period remarkable from a geological and biological point of view. The Mesozoic era, the periods of which (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 period of time, starting approximately 248 million years ago and ending 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 single-celled algae and protozoa. Falling into zones of collision of lithospheric plates, these carbonate sediments contributed to increased release of carbon dioxide during volcanic eruptions, which significantly changed the composition of water and the atmosphere. Land life in Mesozoic era characterized by the dominance of giant lizards and gymnosperms. In the second half of the Cretaceous period, mammals familiar to us today began to appear on the evolutionary stage, which were then prevented from fully developing by dinosaurs. Significant temperature changes 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 towards the middle of the Cretaceous period.
Triassic. Geology, sea inhabitants, plants
The Mesozoic era began with the Triassic period, which replaced the Permian geological era. Living conditions during this period were practically no different from Permian ones. There were no birds or 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 the Tethys, a giant prehistoric ocean. Due to the absence of corals, the construction of reefs was carried out by green algae, which neither before nor after played a major role in this process. Also characteristic feature life in the Triassic was a combination of old biological species with new ones that had not yet gained strength. The time of conodonts was ending and cephalopods with straight shells; Some species of six-rayed corals have already begun to appear, the flowering of which is yet to come; the first bony fish formed 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 that are very familiar to all of us.
Fauna of the Triassic
Among the animals, amphibians began to appear - the first stegocephals, but dinosaurs, including their flying varieties, began to spread more and more widely. At first they were small creatures, similar to modern lizards, equipped with various biological devices for take-off. Some had dorsal growths that resembled wings. They could not make swings, but they managed to successfully descend with their help, like parachutists. Others were equipped with membranes, which allowed them to glide. These are like 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 lying low, waiting in the wings, hiding in burrows from the owners of the planet. Their time will come. This is how the Mesozoic era began.
Jurassic period
This era gained enormous fame thanks to one Hollywood film in which there is more fiction than reality. There is only one thing true - this is the heyday 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 bivalves, and primitive shells by oysters. It is now difficult to imagine the richness and splendor of the Jurassic forests, especially on the wet coasts. These include giant trees, fantastic ferns, and extremely lush shrub vegetation. And, of course, a huge variety of dinosaurs - the largest creatures that ever lived on the planet.
The Last Dinosaur 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, dominating the flora of the planet to this day. Real thickets of laurels, willows, poplars, plane trees and magnolias have already appeared. In principle, the plant world at that distant time acquired almost modern outlines, which cannot be said about animals. This was the world of ceratopsians, ankylosaurs, tyrannosaurs and the like. It all ended in a grandiose catastrophe - the largest in earthly history. And the era of mammals began. Which over time made it possible for a person to come to the forefront, but that’s another story.
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Mesozoic era(248-65 million years ago) - the fourth era in the evolutionary process of life on our planet. Its duration is 183 million years. The Mesozoic era is divided into 3 periods: Triassic, Jurassic and Cretaceous.
Periods of the Mesozoic era
Triassic period (Triassic). The initial erathema of the Mesozoic era lasts 35 million years. This is the time of formation Atlantic Ocean. The single continent of Pangea again begins to break into two parts - Gondwana and Laurasia. Inland continental reservoirs are beginning to actively dry up. The depressions left from them are gradually filled with rock deposits. New mountain heights and volcanoes are appearing and exhibiting increased activity. A huge part of the land is still occupied by desert zones with weather conditions unsuitable for the life of most species of living beings. The salt level in water bodies is rising. During this time period, representatives of birds, mammals and dinosaurs appear on the planet.
Jurassic period (Jura)- the most famous period of the Mesozoic era. It received its name due to the sedimentary deposits of that time found in the Jura (mountain ranges of Europe). The average period of the Mesozoic era lasts about 69 million years. The formation of modern continents begins - Africa, America, Antarctica, Australia. But they are not yet located in the order to which we are accustomed. Deep bays and small seas appear, separating the continents. Active formation of mountain ranges continues. The Arctic Sea floods the north of Laurasia. As a result, the climate is moistened, and vegetation forms in place of deserts.
Cretaceous period (Cretaceous). The final period of the Mesozoic era occupies a time period of 79 million years. Angiosperms appear. As a result of this, the evolution of fauna representatives begins. The movement of continents continues - Africa, America, India and Australia are moving away from each other. The continents of Laurasia and Gondwana begin to break up into continental blocks. Huge islands are forming in the south of the planet. The Atlantic Ocean is expanding. The Cretaceous period is the heyday of flora and fauna on land. Due to evolution flora, fewer minerals end up in the seas and oceans. The amount of algae and bacteria in water bodies decreases.
In details periods of the Mesozoic era will be discussed in the following lectures.
Climate of the Mesozoic era
Climate of the Mesozoic era at the very beginning there was one on the entire planet. The air temperature at the equator and poles remained at the same level. At the end of the first period of the Mesozoic era most years, drought reigned on Earth, which was briefly replaced by rainy seasons. But, despite the arid conditions, the climate became significantly colder than it was during the Paleozoic period. Some species of reptiles have fully adapted to cold weather. From these species of animals mammals and birds would later develop.
During the Cretaceous period it becomes even colder. All continents have their own climate. Tree-like plants appear, which lose their foliage during the cold season. Snow begins to fall at the North Pole.
Plants of the Mesozoic era
At the beginning of the Mesozoic, the continents were dominated by lycophytes, various ferns, the ancestors of modern palms, conifers and ginkgo trees. In the seas and oceans, the dominance belonged to algae that formed reefs.
The increased humidity of the climate of the Jurassic period led to the rapid formation of plant matter on the planet. The forests consisted of ferns, conifers and cycads. Thujas and araucarias grew near the ponds. In the middle of the Mesozoic era, two vegetation belts formed:
- Northern, which was dominated by herbaceous ferns and gingkovic trees;
- Southern. Tree ferns and cycads reigned here.
In the modern world, ferns, cycads (palm trees reaching 18 meters in size) and cordaites of that time can be found in tropical and subtropical forests. Horsetails, mosses, cypresses and spruce trees had practically no differences from those that are common in our time.
The Cretaceous period is characterized by the appearance of plants with flowers. In this regard, butterflies and bees appeared among insects, thanks to which flowering plants were able to quickly spread across the planet. Also at this time, ginkgo trees with leaves that fall off during the cold season begin to grow. Coniferous forests of this time period are very similar to modern ones. These include yews, firs and cypresses.
The development of higher gymnosperms lasts throughout the Mesozoic era. These representatives of the earth's flora got their name due to the fact that their seeds did not have an outer protective shell. The most widespread are cycads and bennettites. In appearance, cicadas resemble tree ferns or cycads. They have straight stems and massive leaves that look like feathers. Bennettites are trees or shrubs. They are similar in appearance to cycads, but their seeds are covered with a shell. This brings the plants closer to angiosperms.
Angiosperms appeared in the Cretaceous period. From this moment a new stage in the development of plant life begins. Angiosperms (flowering plants) are at the top rung of the evolutionary ladder. They have special reproductive organs - stamens and pistil, which are located in the flower cup. Their seeds, unlike gymnosperms, are hidden by a dense protective shell. These plants of the Mesozoic era quickly adapt to any climatic conditions and actively develop. In a short time, angiosperms began to dominate the entire Earth. Their various types and forms have reached modern world- eucalyptus, magnolia, quince, oleander, walnut trees, oak, birch, willow and beech. Of the gymnosperms of the Mesozoic era, we are now familiar only with coniferous species - fir, pine, sequoia and some others. The evolution of plant life of that period significantly outstripped the development of representatives of the animal world.
Animals of the Mesozoic era
Animals in the Triassic period of the Mesozoic era actively evolved. A huge variety of more developed creatures formed, which gradually replaced the ancient species.
One of these types of reptiles was the animal-like pelycosaurs - sailing lizards. On their backs there was a huge sail, like a fan. They were replaced by therapsids, which were divided into 2 groups - predators and herbivores. Their legs were powerful and their tails were short. Therapsids were much superior to pelycosaurs in speed and endurance, but this did not save their species from extinction at the end of the Mesozoic era.
The evolutionary group of lizards from which mammals would later evolve are the cynodonts (dog teeth). These animals got their name due to their powerful jaw bones and sharp teeth, with which they could easily chew raw meat. Their bodies were covered with thick hair. The females laid eggs, but the newborn cubs fed on their mother's milk.
At the beginning of the Mesozoic era it was formed the new kind lizards - archosaurs (ruling reptiles). They are the ancestors of all dinosaurs, pterosaurs, plesiosaurs, ichthyosaurs, placodonts and crocodylomorphs. Archosaurs, adapted to the climatic conditions on the coast, became predatory thecodonts. They hunted on land near bodies of water. Most thecodonts walked on 4 legs. But there were also individuals that ran on their hind legs. In this way, these animals developed incredible speed. After some time, thecodonts evolved into dinosaurs.
By the end of the Triassic period, 2 species of reptiles predominated. Some are the ancestors of the crocodiles of our time. Others turned into dinosaurs.
Dinosaurs have a body structure that is not similar to other lizards. Their paws are located under the body. This feature allowed dinosaurs to move quickly. Their skin is covered with waterproof scales. Lizards move on 2 or 4 legs, depending on the species. The first representatives were fast coelophysis, powerful herrerasaurs and huge plateosaurs.
Besides dinosaurs, archosaurs gave rise to another species of reptile that was different from the rest. These are pterosaurs - the first lizards that can fly. They lived near bodies of water and ate various insects for food.
The fauna of the deep sea of the Mesozoic era is also characterized by a variety of species - ammonites, bivalves, families of sharks, bony and ray-finned fish. The most prominent predators were the underwater lizards that appeared not so long ago. Dolphin-like ichthyosaurs had high speed. One of the giant representatives of ichthyosaurs is Shonisaurus. Its length reached 23 meters, and its weight did not exceed 40 tons.
Lizard-like nothosaurs had sharp fangs. Placadonts, similar to modern newts, searched for mollusk shells on the seabed, which they bit with their teeth. Tanystrophei lived on land. Long (2-3 times the body size), slender necks allowed them to catch fish while standing on the shore.
Another group of sea lizards of the Triassic period are plesiosaurs. At the beginning of the era, plesiosaurs reached a size of only 2 meters, and by the middle of the Mesozoic they evolved into giants.
The Jurassic period is the time of development of dinosaurs. The evolution of plant life gave rise to the emergence of different types of herbivorous dinosaurs. And this, in turn, led to an increase in the number of predatory individuals. Some dinosaur species were the size of cats, while others were as large as giant whales. The most gigantic individuals are diplodocus and brachiosaurs, reaching a length of 30 meters. Their weight was about 50 tons.
Archeopteryx is the first creature standing on the border between lizards and birds. Archeopteryx did not yet know how to fly long distances. Their beak was replaced by jaws with sharp teeth. The wings ended in fingers. Archeopteryx was the size of a modern crow. They lived mainly in forests and ate insects and various seeds.
In the middle of the Mesozoic era, pterosaurs were divided into 2 groups - pterodactyls and rhamphorhynchus. Pterodactyls lacked a tail and feathers. But there were large wings and a narrow skull with few teeth. These creatures lived in flocks on the coast. During the day they obtained food for themselves, and at night they hid in the trees. Pterodactyls ate fish, shellfish and insects. This group of pterosaurs had to jump from high places to take to the skies. Rhamphorhynchus also lived on the coast. They ate fish and insects. They had long tails with a blade at the end, narrow wings and a massive skull with teeth of different sizes, which were convenient for catching slippery fish.
The most dangerous predator of the deep sea was Liopleurodon, which weighed 25 tons. Huge coral reefs were formed, in which ammonites, belemnites, sponges and sea mats settled. Representatives of the shark family and bony fishes are developing. New species of plesiosaurs and ichthyosaurs, sea turtles and crocodiles appeared. Saltwater crocodiles developed flippers instead of legs. This feature allowed them to increase speed in the aquatic environment.
During the Cretaceous period of the Mesozoic era Bees and butterflies appeared. Insects carried pollen, and flowers gave them food. Thus began a long-term collaboration between insects and plants.
The most famous dinosaurs of the time were the predatory tyrannosaurs and tarbosaurs, the herbivorous bipedal iguanodons, the four-legged rhinoceros-like Triceratops and the small armored ankylosaurs.
Most mammals of that period belong to the subclass Allotheria. These are small animals, similar to mice, weighing no more than 0.5 kg. The only exceptional species is the repenomama. They grew up to 1 meter and weighed 14 kg. At the end of the Mesozoic era, the evolution of mammals occurs - the ancestors of modern animals separate from allotheria. They are divided into 3 species - oviparous, marsupial and placental. It is they who replace the dinosaurs at the beginning of the next era. Rodents and primates emerged from the placental species of mammals. Purgatorius became the first primates. The marsupial species gave rise to modern opossums, and the oviparous species gave rise to platypuses.
The airspace is dominated by early pterodactyls and new species of flying reptiles - Orcheopteryx and Quetzatcoatli. These were the most gigantic flying creatures in the entire history of the development of our planet. Together with representatives of pterosaurs, birds dominate the air. During the Cretaceous period, many ancestors of modern birds appeared - ducks, geese, loons. The length of the birds was 4-150 cm, weight - from 20 grams. up to several kilograms.
The seas were dominated by huge predators reaching 20 meters in length - ichthyosaurs, plesiosaurs and mososaurs. Plesiosaurs had a very long neck and a small head. Their large size did not allow them to develop high speed. The animals ate fish and shellfish. Mososaurs replaced saltwater crocodiles. These are giant predatory lizards with an aggressive character.
At the end of the Mesozoic era, snakes and lizards appeared, the species of which have reached the modern world unchanged. The turtles of this time period were also no different from those we see now. Their weight reached 2 tons, length - from 20 cm to 4 meters.
By the end of the Cretaceous period, most reptiles began to die out en masse.
Minerals of the Mesozoic era
A large number of natural resource deposits are associated with the Mesozoic era. These are sulfur, phosphorites, polymetals, construction and combustible materials, oil and natural gas.
In Asia, due to active volcanic processes, the Pacific belt was formed, which gave the world large deposits of gold, lead, zinc, tin, arsenic and other types of rare metals. In terms of coal reserves, the Mesozoic era is significantly inferior to the Paleozoic era, but even during this period several large deposits of brown and hard coal were formed - the Kansky basin, Bureinsky, Lensky.
Mesozoic oil and gas fields are located in the Urals, Siberia, Yakutia, and the Sahara. Phosphorite deposits have been found in the Volga region and Moscow region.
History and LED
Currently, about 400 species of dinosaurs are known. In the Triassic, the diversity of dinosaurs was not great. The most famous of the Triassic dinosaurs are Coelophysis and Plateosaurus. The Jurassic period is known for the most amazing diversity of dinosaurs that could be found...
Essay
"Mesozoic era"
Prepared by: Savkina Anastasia Sergeevna
Checked by: Glukhareva Ekaterina Sergeevna
2015
- Temporal boundaries
- Climatic conditions
- Development of the plant world, main aromorphoses
- Development of the animal world, main aromorphoses
- conclusions
- Sources
Temporal boundaries
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 period (240 million years ago)
- Jurassic period (195 million years ago)
- Cretaceous period (136 million years ago)
The Triassic and Jurassic periods were much shorter than the Cretaceous, which lasted about 71 million years.
Climatic conditions
The Mesozoic era is the warmest period in the Phanerozoic history of the Earth. It almost completely coincided with the period global warming, which began in the Triassic period and ended in the Cenozoic era with the Little Ice Age, which continues to this day. For 180 million years, even in the subpolar regions there was no stable ice cover. The climate was for the most part warm and even, without significant temperature gradients, although climatic zonation existed in the northern hemisphere. A large number of greenhouse gases in the atmosphere contributed to the uniform distribution of heat. The equatorial regions were characterized by a tropical climate (TethysPanthalassa region) with average annual temperature 2530°С. Up to 4550° N The subtropical region (Peritethys) extended, followed by the warm-temperate boreal zone, and the subpolar regions were characterized by a cool-temperate climate.
The Mesozoic had a warm climate, mostly dry in the first half of the era and humid in the second. Slight cooling in the late Jurassic and the first half of the Cretaceous, strong warming in the middle of the Cretaceous (the so-called Cretaceous temperature maximum), around the same time the equatorial climate zone appeared.
Flora in the Mesozoic era
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. Outwardly, they looked like tree ferns or palm trees. In addition to the cycads, great importance in the mesophyte they acquired bennettites, represented by trees or shrubs. 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 grew on rocks. 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 variety. 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.).
Fauna in the Mesozoic era
Reptiles.
Reptiles became most widespread in the Mesozoic, becoming truly the dominant class of this era. In the course of evolution, the most different genera and types of reptiles, from small ones - the size of a chicken, to giant ones - up to 30 meters long and weighing several tens of tons. They were also the most amazing land animals the earth ever bore.
As has already been said, by anatomical structure The most ancient reptiles were close to labyrinthodonts.
Representative of the reptiles of the early Mesozoic - Anteosaurus
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.
Carnivorous theriodonts 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 shape teeth adapted for crushing shells, and also plesiosaurs that lived in the seas, having 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.
During the Jurassic period, plesiosaurs and ichthyosaurs reached their peak. Both of these groups remained very numerous at the beginning of the Cretaceous period, 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 , and dinosaurs, and flying lizards, and, finally, birds.
Dinosaurs
The most unique group of Mesozoic reptiles were the well-known dinosaurs. They developed from thecodonts and immediately established their leading positions. Even in the Triassic, due to their structural features they had better speed and reaction, dinosaurs very quickly took a dominant position on Earth. 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 are 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. Among the European dinosaurs of this time, the bipedal iguanodons are widely known; in America, the four-legged horned dinosaurs Triceratops, similar to modern rhinoceroses, became widespread. In the Cretaceous period, there were also relatively small armored dinosaurs - ankylosaurs, covered with a massive bony shell. All of these forms were herbivores, as were giant duck-billed dinosaurs such as Anatosaurus and Trachodon, which walked on two legs.
In addition to herbivores, a large group was also represented by carnivorous dinosaurs. All of them belonged to the group of lizards. A group of carnivorous dinosaurs are called terrapods. In the Triassic, this is Coelophysis - one of the first dinosaurs. In the Jurassic period, Allosaurus and Deinonychus reached their peak. In the Cretaceous period, the most remarkable forms were such as Tyrannosaurus rex, whose length exceeded 15 m, Spinosaurus and Tarbosaurus. All these forms, which turned out to be the greatest terrestrial predatory animals in the entire history of the Earth, moved on two legs.
Other reptiles of the Mesozoic era
At the end of the Triassic, the thecodonts also gave rise to the first crocodiles, which became abundant only in the Jurassic period (Steneosaurus and others). In the Jurassic period, flying lizards appeared - pterosaurs (Pterosaurids), also descended from thecodonts. Among the flying dinosaurs of the Jurassic, the most famous are Rhamphorhynchus and Pterodactylus; among the Cretaceous forms, the most interesting is the relatively very large Pteranodon. Flying lizards became extinct by the end of the Cretaceous.
In the Cretaceous seas, giant predatory lizards - mosasaurs, exceeding 10 m in length - became widespread. Among modern lizards, they are closest to monitor lizards, but differ from them, in particular, in their flipper-like limbs. By the end of the Cretaceous, the first snakes (Ophidia) appeared, apparently descended from lizards that led a burrowing lifestyle. Towards the end of the Cretaceous, there was a mass extinction of characteristic Mesozoic groups of reptiles, including dinosaurs, ichthyosaurs, plesiosaurs, pterosaurs and mosasaurs.
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. To the Mesozoic representatives
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 body pulp and a mantle.
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), the colonies of which were active reef builders; the marine reefs they built are now widespread in Pacific Ocean. Some groups of brachiopods still developed in the Mesozoic, such as Terebratulacea and Rhynchonellacea, but the vast majority of them declined. Mesozoic echinoderms were 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); To date, countless species have been described from the Mesozoic. Starfish (Asteroidea) and ophidra were abundant.
Compared to the Paleozoic era, bivalves also became widespread in the Mesozoic. Already in the Triassic, many new genera appeared. 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 one can find curious types of bivalve 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. 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.
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 Mesozoic sedimentary rocks, 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 came to the conclusion that it belongs to the “extinct” group of lobe-finned fish (Coelacanthida). To this day, this species remains the only modern representative of ancient lobe-finned fish. It was named Latimeria chalumnae. Such biological phenomena are called “living fossils.”
The first birds.
Representatives of the class of birds first appear in Jurassic deposits. The remains of Archeopteryx, a well-known and so far only known ancestral bird, were found in lithographic shales of the Upper Jurassic. During the Cretaceous period, the evolution of birds proceeded at a rapid pace; The characteristic genera of this time were Ichthyornis and Hesperornis, which still had serrated jaws.
The first mammals.
The first mammals (Mammalia), modest animals no larger than a mouse, descended from animal-like reptiles in the Late Triassic. Throughout the Mesozoic they remained few in number and by the end of the era the original genera were largely extinct. The most ancient group of mammals were the triconodonts (Triconodonta), to which the most famous of the Triassic mammals, Morganucodon, belongs. During the Jurassic period, a number of new groups of mammals appeared.
Of all these groups, only a few survived the Mesozoic, the last of which died out in the Eocene. The ancestors of the main groups of modern mammals - marsupials (Marsupialia) and placentals (Placentalid) were Eupantotheria. Both marsupials and placentals appeared at the end of the Cretaceous period. The most ancient group of placentals are insectivores (Insectivora), which have survived to this day. Powerful tectonic processes of Alpine folding, which erected new mountain ranges and changed the shape of the continents, radically changed the geographical and climatic conditions. Almost all Mesozoic groups of the animal and plant kingdoms retreat, die out, disappear; on the ruins of the old, a new world arises, the world of the Cenozoic era, in which life receives a new impetus for development and, in the end, living species of organisms are formed.
conclusions
The Mesozoic era was a transitional period in 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 Variscan mountain-building processes; it ended with the beginning of the last powerful tectonic revolution - the Alpine folding.
IN Southern Hemisphere in the Mesozoic, the collapse of the ancient continent of Gondwana was completed, but in general the Mesozoic era here was an era of relative calm, only occasionally and briefly disrupted by light folding. Biologically, the Mesozoic was a time of transition from old, primitive to new, progressive forms. Neither four-rayed corals (rugosas), nor trilobites, nor graptolites crossed the invisible border that lay between the Paleozoic and Mesozoic. The Mesozoic world was much more diverse than the Paleozoic; the fauna and flora appeared in it in a significantly updated composition. The Mesozoic is called the era of reptiles and gymnosperms. Reptiles have reached enormous diversity, populating all land and seas, and some have adapted to flight. Different species of river crocodiles, lizards, and turtles appeared, but dinosaurs were the complete masters of the land. In those distant times, they roamed all over the Earth. Some of them were carnivores, but most were vegetarians. Towards the end of the Mesozoic, a mass extinction of dinosaurs gradually occurred over several million years. The dominance of dinosaurs during an entire geological era and their almost simultaneous extinction at its end represent big mystery paleontology.
Sources
- http://ru.wikipedia.org/wiki/Mesozoic
- http://www.dinozavro.ru/paleontolog/mezozoi.php
- http://sbio.info/page.php?id=11576
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Which lasted from 252.2 ± 0.5 million years ago to 66.0 million years ago (total about 186 million years). This era was first identified by British geologist John Phillips in 1841.
The Mesozoic era is divided into three periods: Triassic, Jurassic and Cretaceous.
The Mesozoic is an era of tectonic, climatic and evolutionary activity. The formation of the main contours of modern continents and mountain building on the periphery of the Pacific, Atlantic and Indian oceans is taking place; the division of land facilitated 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 bulk 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 the Permo-Triassic mass extinction, which resulted in the death of approximately 90-96% of marine fauna and 70% of land vertebrates. The upper limit is set at the Cretaceous-Paleogene boundary, when another very large extinction of many groups of plants and animals occurred, most often attributed to the impact of a giant asteroid (Chicxulub crater on the Yucatan Peninsula) and the subsequent “asteroid winter”. Approximately 50% of all species became extinct, including all flightless dinosaurs.
Tectonics and paleogeography
Compared to the vigorous mountain building of the late Paleozoic, Mesozoic tectonic deformation can be considered relatively mild. The era was characterized primarily by the division of the supercontinent Pangea into a northern continent, Laurasia, and a 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 (for example, the 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 had practically taken on their modern shape. Laurasia was divided into Eurasia and North America, Gondwana into South America, Africa, Australia, Antarctica and the Indian subcontinent, the collision of which with the Asian continental plate caused intense orogenesis with the uplift of the Himalayan mountains.
Africa
At the beginning of the Mesozoic era, Africa was still part of the supercontinent Pangea and had a relatively common fauna with it, which was dominated by theropods, prosauropods and primitive ornithischian dinosaurs (by the end of the Triassic).
Late Triassic fossils are found throughout 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 is marked by a global catastrophe with mass extinction of species (Triassic-Jurassic extinction), but the African layers of this time remain poorly studied today.
Early Jurassic fossil deposits are distributed similarly to Late Triassic deposits, with more frequent exposures in the south of the continent and fewer deposits towards the north. Throughout the Jurassic period, iconic dinosaur groups such as sauropods and ornithopods increasingly spread across Africa. The paleontological layers of the mid-Jurassic period in Africa are poorly represented and also poorly studied.
Late Jurassic strata are also poorly represented here, with the exception of the impressive Tendeguru Jurassic assemblage in Tanzania, whose fossils are very similar to those found in the paleobiotic Morrison Formation of western North America and date to the same period.
In the mid-Mesozoic, about 150-160 million years ago, Madagascar separated from Africa, while remaining connected to India and the rest of Gondwanaland. Abelisaurs and titanosaurs have been discovered among the fossils of Madagascar.
During the Early Cretaceous era, a part of the landmass that made up India and Madagascar separated from Gondwana. In the Late Cretaceous, the divergence of India and Madagascar began, which continued until the achievement of modern outlines.
Unlike Madagascar, mainland Africa was tectonically relatively stable throughout the Mesozoic. And yet, despite its stability, significant changes occurred in its position relative to other continents as Pangea continued to break apart. By the beginning of the Late Cretaceous period, it separated from Africa South America, 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 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 in field work in Malawi, argues that African fossil deposits "need more careful excavation" and are sure to prove "fruitful ... for scientific discoveries."
Climate
Over the past 1.1 billion years, Earth's history has seen three successive ice age-warming cycles, called 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 cyclicity is considered to be the periodic process of connecting continents into a single continent (Pangea) 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 of global warming, which began in the Triassic period and ended in the Cenozoic era with the Little Ice Age, which continues to this day. For 180 million years, even in the subpolar regions there was no stable ice cover. The climate was mostly warm and even, without significant temperature gradients, although climatic zonation existed in the northern hemisphere. The large amount of greenhouse gases in the atmosphere contributed to the uniform distribution of heat. The equatorial regions were characterized by a tropical climate (Tethys-Panthalassa region) with an average annual temperature of 25–30°C. Up to 45-50° N The subtropical region (Peritethys) extended, followed by the warm-temperate boreal zone, and the subpolar regions were characterized by a cool-temperate climate.
During the Mesozoic there was a warm climate, mostly dry in the first half of the era and humid in the second. Slight cooling in the late Jurassic and the first half of the Cretaceous, strong warming in the middle of the Cretaceous (the so-called Cretaceous temperature maximum), around the same time the equatorial climate zone appeared.
Flora and fauna
Giant ferns, tree horsetails, and mosses are dying out. In the Triassic, gymnosperms, especially conifers, flourished. In the Jurassic period, seed ferns died out and the first angiosperms appeared (so far represented only by woody forms), which gradually spread to all continents. This is due to a number of advantages; Angiosperms have a highly developed conducting system, which ensures reliable cross-pollination, the embryo is supplied with food reserves (due to double fertilization, a triploid endosperm develops) and is protected by membranes, etc.
In the animal world, insects and reptiles flourish. Reptiles occupy a dominant position and are represented by a large number of forms. In the Jurassic period, flying lizards appear and conquer air environment. In the Cretaceous period, the specialization of reptiles continued, they reached enormous sizes. The mass of some of the dinosaurs reached 50 tons.
The Mesozoic era began approximately 250 and ended 65 million years ago. It lasted 185 million years. 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.
In the Mesozoic, not only dinosaurs arose, but also other groups of reptiles, which are often mistakenly considered dinosaurs - aquatic reptiles (ichthyosaurs and plesiosaurs), flying reptiles (pterosaurs), lepidosaurs - lizards, among which were aquatic forms - mosasaurs. Snakes evolved from lizards - they also appeared in the Mesozoic - the time of their emergence is generally known, but paleontologists argue about the environment in which this occurred - in water or on land.
Sharks flourished in the seas, and they also lived in freshwater bodies. The Mesozoic is the era of the flourishing of two groups of cephalopods - ammonites and belemnites. But in their shadow, the nautiluses, which arose in the early Paleozoic and still exist, lived well, and the familiar squids and octopuses arose.
In the Mesozoic, modern mammals arose, first marsupials and then placentals. In the Cretaceous period, groups of ungulates, insectivores, predators and primates had already emerged.
Interestingly, modern amphibians - frogs, toads and salamanders - also arose in the Mesozoic, presumably in the Jurassic period. So, despite the antiquity of amphibians in general, modern amphibians are a relatively young group.
Throughout the Mesozoic, vertebrates sought to master a new environment for themselves - the air. The first reptiles were able to take off - first small pterosaurs - rhamphorhynchus, then larger pterodactyls. Somewhere on the border of the Jurassic and Cretaceous, reptiles took to the air - small feathered dinosaurs, capable, if not of flight, then certainly of gliding, and the descendants of reptiles - birds - enantiornis and true fan-tailed birds.
A real revolution in the biosphere occurred with the advent of angiosperms - flowering plants. This resulted in an increase in the diversity of insects that became flower pollinators. The gradual spread of flowering plants has changed the appearance of terrestrial ecosystems.
The Mesozoic ended with the famous mass extinction, better known as the “extinction of the dinosaurs.” The reasons for this extinction are not clear, but the more we learn about the events that took place at the end of the Cretaceous, the less convincing the popular hypothesis of a meteorite catastrophe becomes. The Earth's biosphere was changing and the ecosystems of the Late Cretaceous were very different from the ecosystems of the Jurassic period. A huge number of species became extinct throughout the Cretaceous period, and not at all at its end - they simply did not survive the catastrophe. At the same time, evidence is emerging that in some places the typical Mesozoic fauna still existed at the very beginning of the next era - the Cenozoic. So for now, it is not possible to unequivocally answer the question about the causes of the extinction that occurred at the end of the Mesozoic. It is only clear that if some kind of catastrophe occurred, it only pushed the changes that had already begun in Macroconchs and microconchs? Aalenian Stage - VI
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