Triassic period animals and plants. Triassic

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

• Paleozoic;
• Mesozoic;
• Cenozoic.

Periods of the Mesozoic Era

The ending Paleozoic era marked by the extinction of animals. Development of life in mesozoic era characterized by the emergence of new species of creatures. First of all, these are dinosaurs, as well as the first mammals.

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

• Triassic;
• Jurassic;
• chalky.

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

Triassic

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

The climate becomes warm and dry, in connection with which deserts form on the planet, and the level of salt in water bodies rises sharply. However, it is at this unfavorable time that mammals and birds appear. In many respects, this was facilitated by the absence of clearly defined climatic zones and the maintenance of the same temperature throughout the territory. the globe.

Fauna of the Triassic

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

Cynodonts appeared - a group of lizards, which was the ancestor of the first mammals. These lizards were covered with hair and had strongly developed jaws, which helped them eat raw meat. Cynodonts laid eggs, but females fed their young with milk. In the Triassic, the ancestors of dinosaurs, pterosaurs and modern crocodiles, the archosaurs, also originated.

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

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

Plants during the Triassic period

The flora of the first half of the Triassic did not differ significantly from the plants of the end of the Paleozoic era. Grow in abundance in the water different types algae, seed ferns and ancient conifers are widely distributed on land, and lycosid plants are widespread in coastal zones.

By the end of the Triassic, the land was covered with a cover herbaceous plants, which greatly contributed to the emergence of a variety of insects. Also appeared plants of the mesophytic group. Some cycad plants have survived to this day. It is growing in the Malay Archipelago zone. Most plant varieties grew on the coastal areas of the planet, and conifers prevailed on land.

Jurassic period

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

The separation of the two continents of Laurasia and Gondwana that existed until that moment served to form new bays and seas and raise the level of the world's oceans. This had a positive effect on making it more humid. The air temperature on the planet dropped and began to correspond to a temperate and subtropical climate. Such climate change in many ways contributed to the development and improvement of the animal and plant world.

Animals and plants of the Jurassic period

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

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

Climatic changes that occurred during the Jurassic period led to abundant rainfall. This, in turn, gave impetus to the spread of lush vegetation on the surface of the planet. Herbaceous fern and ginkgo plants predominated in the northern zone of the earth. The southern belt was made up of tree ferns and cycads. In addition, the Earth was filled with various coniferous, cordaite and cycad plants.

Age of dinosaurs

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

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

Air space jurassic filled with dinosaurs that could fly. Although for the flight they needed to climb a hill. Pterodactyls and other pterosaurs flocked and hovered above the ground in search of food.

Cretaceous period

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

The formed new continents are moving, and the Earth's tectonics is increasingly acquiring a familiar look. modern man. The climate became noticeably colder, at that time the ice caps of the northern and south pole. There is also a division of the planet into climatic zones. But in general, the climate remained warm enough, which was facilitated by the greenhouse effect.

Cretaceous Biosphere

In reservoirs, belemnites and mollusks continue to evolve and spread, and also develop sea ​​urchins and the first crustaceans.

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

Among the vegetation greatest development got flowers. Spore plants died out due to the characteristics of reproduction, giving way to more progressive ones. At the end of this period, gymnosperms noticeably evolved and began to be replaced by angiosperms.

End of the Mesozoic Era

The history of the Earth has two that served as a mass extinction of the animal world of the planet. The first, Permian catastrophe was the beginning of the Mesozoic era, and the second marked its end. Most of the animal species that actively evolved in the Mesozoic died out. AT aquatic environment ammonites, belemnites, bivalve mollusks ceased to exist. Dinosaurs and many other reptiles disappeared. Many species of birds and insects also disappeared.

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

Which he followed. The Mesozoic era is sometimes referred to as the "era of the dinosaurs" because these animals were the dominant representatives for much of the Mesozoic.

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

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

The first big changes were seen in the type that dominated the Earth. Most of the flora that survived the Permian extinction became plants containing seeds, such as gymnosperms.

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

The last period of the Mesozoic was called the Cretaceous. In the growth of flowering terrestrial plants. They were helped by newly appeared bees and warm climatic conditions. Conifers were still plentiful during the Cretaceous.

As for the marine animals of the Cretaceous period, sharks and rays became commonplace. survivors of the Permian extinction, such as sea ​​stars, were also abundant during the Cretaceous.

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

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

There are different versions as to why it happened. mass extinction. Most scientists agree that it was some kind of catastrophic event that caused this extinction. Various hypotheses include massive volcanic eruptions that sent massive amounts of dust into the atmosphere, reducing the amount of sunlight reaching the Earth's surface and thereby causing the death of photosynthetic organisms such as plants and those who depended on them. Others believe that a meteorite fell to Earth, and the dust covered sunlight. As the plants and animals that fed on them died out, this led to predators such as carnivorous dinosaurs also dying for lack of food.

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Triassic- the first of three periods of the Mesozoic era, originating 252 million years ago after the end of the Permian period (the last of the six periods of the Paleozoic era), and preceding the Jurassic period, which began 201 million years ago. That is, its duration was over 51 million years (according to other sources, the duration of the Triassic: 248 - 213 million years). The Triassic period is significant for the flourishing of new organic species after the mass extinction that occurred at the end of the Permian and the beginning of the disintegration of the supercontinent Pangea.

Subsections of the Triassic period, geographic and climatic changes

Adopted by the International Union of Geological Sciences in December 2016 division of the Triassic as follows. The period is divided into three sections - the Lower, dividing in turn into the Indus and Olenyok stages, the Middle, consisting of the Anzian and Ladin and the Upper, divided into Carnian, Norian and, bordering directly on the first stage of the lower Jurassic period, the Rhettian.

The supercontinent Pangea, formed in the Permian period, began to separate into Laurasia and Gondwana. This was accompanied by violent volcanic activity and the formation in the ocean depths due to stretching earth's crust vast depressions filled with igneous rocks. The continents rose above the water surface, and hot, dry weather set in on large parts of the continents. Most of the inland water bodies have dried up, and salinity levels have risen sharply in the remaining ones. The Atlantic Ocean began to form. Pronounced climatic zones in the Triassic period are not visible, average temperature decreased along the equator in this period, but in general it was warm enough around the globe, so that a uniform Triassic climate in general contributed to the rapid flowering of organic life.

sedimentation

The Triassic period was identified for the first time in Germany. The basis of the Triassic strata in many places are clay shales and red sandstone. Despite the fact that when the total continental mass was raised, many lakes and seas glassed into the world ocean or simply dried up, there were still many water basins. At that time, the whole of Western Europe, up to the islands of England, was occupied by the epicontinental sea, where the above-mentioned stratotypes were deposited. sedimentary rocks. They were also characteristic of the Siberian part of Pangea covered by the sea. Under the Tethys Sea a limestone layer accumulated, which is now found in the layers of the Italian Dolomites. On the territory of the current South America a layer of silts and sands was formed, which became a consequence of the genesis of the continental division.

Animals of the Triassic Period

Despite the mysterious climatic upheavals that occurred at the turn of the Permian and Triassic, which led to the largest extinction of species in the history of organic life, at the beginning of the Mesozoic life again began to seethe in full swing and the vacant ecological and evolutionary niches again began to be rapidly filled with animal diversity. In the depths of the sea, ammonoids began to flourish again, only of much different varieties, belemonoids arose. Also in the Triassic period, bivalves and gastropods multiplied and formed new species. Brachiopods have become an order of magnitude smaller than in the Permian, but despite this they were still an important component of the water kingdom. The ancient extinct genera of sea urchins have been replaced by new ones. Hitherto unknown lilies, bryozoans, radiolarians, foraminifers, etc. appeared. Six-ray corals began to appear.

Changes have also taken place in the world of vertebrates. the lion's share of all land mammals represented reptiles and reptiles. Towards the end of the Triassic, marsupials enter the scene. Many Triassic period animals returned to sea ​​depths and became even more formidable marine predators than sharks, as can be seen in the example. The rise of the continents contributed to the drying up of many fresh inland water bodies, due to which many fish were forced to adapt to life in sea ​​water. Only a small part of the ancient crossopterans found a haven in a few freshwater lakes.

Those few stegocephalians who survived after the great permian extinction, as a result of warming, they were forced to return to the water again, turning into formidable predators like the Mastodonsaurus.

Away from the coastal zones in the sea and ocean depths, highly organized fish have survived and given rise to many varieties. The sharks also survived. The jaws of many fish have acquired such muscles and teeth that they easily gnawed through the shells of any mollusks. But the main water rulers of the Triassic period were still aquatic reptiles. lizard-like notosaurus(Fig. 1) easily hunted any species of fish. His mouth was so toothy that it was not difficult for him to shred both small fish and large sharks with it. And there is no need to talk about the elongated and sharp-toothed jaws of the ichthyosaur. Often, these reptiles simply cut their victims to pieces.

Rice. 1 - Triassic Nothosaurus

Among the variety of Triassic reptiles, there were even those who managed to fish from the shore without being aquatic animals. Such a reptile was tanystropheus. Evolution endowed this animal with a long neck, which he, standing on the shore, lowered with his head into coastal waters and caught from there marine life that fell within its reach.

Due to the fact that in the first half of the Triassic period, climatic conditions were almost the same throughout Laurasia and Gondwana, animal world was almost identical in its diversity in all parts of the continents. Species were evenly distributed throughout the territory of the supercontinent that was beginning to separate. Some populations, such as gregarious leafosaurs(Fig. 2), reached an unprecedented number. They were rightly called Triassic hippos, since they led a lifestyle not far from the current hippos, they also basked in the sun around marshes and other small continental reservoirs, and in the heat of the day they wandered into the water to cool slightly in it. That's just the number of these herds, unlike the current hippos, was simply enormous. The remains of these animals have been found in all corners of the globe. And along with them, inland reservoirs were inhabited by numerous frogs and various turtles that appeared in the Triassic, both land and water. The first crocodiles were also active in such places. Further, both turtles and crocodiles migrated further and further until they reached the World Ocean, from where, along with many other individuals, they settled evenly along the entire perimeter of the continents.

Rice. 2 - Triassic Listosaurus

On land they reigned supreme cynodonts(Fig. 3), or as they are also called "dog-toothed" reptiles - predators, the prey of which often became herds of peaceful leafosaurs. By the beginning of the Triassic period, these animals were the size of a rat, but by the middle of the period they had already reached much impressive sizes. Like the Gorgonopsids in the Permian period, their limbs moved under the body, which made them very fast and agile.

Rice. 3 - Triassic cynodont

Also, in the middle Triassic, another branch of reptiles was formed, according to the structure musculoskeletal system similar to arzosaurs, but with a slightly different structure of the jaws. They were called richosaurs and had massive beaks at the ends of their jaws, for which they were nicknamed "beak-winged". The structure of their jaws, as well as their tooth-beak equipment, allowed these reptiles not only to bite and chew, but also to calmly cut and chop prey. On top of that, when closing, the terminal sharp protrusion of the lower jaw entered a special groove of the upper one, like a penknife that folded into a handle. In this situation, the victim was doomed.

By the end of the Triassic period, many species of reptiles died out, unable to withstand competition with their faster and more agile counterparts, the structure of the musculoskeletal system of which experienced a revolutionary restructuring from the lateral, where the hind limbs were on the sides of the body, to the parasagittal, in which the body is located in an elevated state above the ground, and the hind limbs are located directly below it. These reptiles were called thecodonts(Fig. 4). Previously, they lived in the water, but deciding to get out on land, where there were many times more prey, and many times less threats, they quickly rebuilt their propulsion system in a progressive manner and bred all over the land. These were the most agile and fast reptiles, from which dinosaurs later developed. These reptiles ran excellently on their two overdeveloped hind legs, jumped excellently and showed miracles of maneuverability.

Rice. 4 - Thecodonts of the Triassic period

Also, towards the end of the Triassic period, evolution presented another important surprise. For the first time, reptiles began to make attempts to climb into air space. Wesheltisaurus- lizards of small size, tried to glide through the air due to their incredibly hypertrophied ribs. But they were quickly replaced by pterosaurs, who instead of ribs remade the structure of the limbs for flight, between which a special aeronautical film was formed, with the help of which they could, gliding in air currents, stay in the air for a long time, looking out for their prey from a height.

Also, by the end of the Triassic, the first true mammals began to appear, however, still laying eggs, but already feeding their offspring with milk. In most cases, these were small marsupial animals, like modern platypuses, but they have not yet been given a variety of reptiles to develop, to which they have so far lost both in ferocity and size, and in numbers and agility.

Underwater vegetable world did not change significantly with the onset of the Triassic. Blue-green, brown and other types of algae, characteristic of the Paleozoic, also progressed. Great importance for this period, reef-forming algae, which settled in large numbers on the site of the present Alps, provided. Have not undergone significant changes in comparison with the previous Permian and ground Triassic period plants.

In the tropical zones, varieties of pteridosperms and ancient conifers that have not survived to this day have received the greatest development, temperate zones are more distinguished by the diversity of paleophytic ferns. Although by the middle of the Triassic period, due to the smoothing of critical differences between weather conditions different climatic zones, there is no noticeable division of plant species throughout the territory of the divided Pangea. Some varieties of lycopsids were very common in coastal zones.

The main plants of the second half of the Triassic period are such mesophytic groups of plants as bennettites, cycads, diptheria ferns, mesophytic conifers, various ginkgos. Occasionally there were also cycads, calamites and cordaites. Most of the ferns were seed ferns. Some cycads have survived to our times. They are found in the zone of the Malay Archipelago and are called sago palms. At their core, cycads are an intermediate branch of development between ferns and palms. They, like palm trees, had a powerful trunk, a branched palm pinnate crown at the top, but still reproduced not by seeds, but by micro or macrospores. And since their spores were the worst protected from the cold, these plants of the Triassic period could only survive in those continental zones that never shifted to cold zones and were constantly close to water.

Rice. 5 - Plants of the Triassic period

A large proportion of Triassic ferns grew along coastal areas. Inside the continents, conifers mainly grew. For the most part, these were varieties of voltia. Voltcia had a dense coniferous crown, in which cones grew, in many respects similar in structure to modern spruce ones.

Vast areas of land were covered with grasses and all kinds of flowering plants, on which various hymenoptera constantly worked.

But no matter how the climate contributes to the reproduction and growth vegetation of the Triassic period, more than half of the varieties of all land plants did not live to see its completion.

Minerals of the Triassic period

Due to weak intrusive activity in the Triassic period, a large number of ore deposits were formed. You can also note some Carboniferous horizons, such as the Chelyabinsk basin, the Ural-Tien Shan, South Appalachian, as well as the Australian Cordillera basins.

There are numerous gas fields of this period. These include deposits of the Sahara (Algeria) and the Arctic (Canada). Many Russian deposits also belong to the Triassic. This is mainly the Timan-Pechora province, the Vilyui river basin. Oil and gas deposits related to the Triassic and in Australia have been discovered. The largest oil and gas field of that time is a field discovered in Alaska.

Also, the Triassic period is famous for its uranium deposits (the largest is the USA, the Colorado Plateau). Numerous cobalt, nickel, copper, iron ore, graphite ores (example - Central Siberian Plain). The Australian continent is rich in deposits of silver, gold, zinc, lead, tin and copper, also dated to the Triassic. Yakutia is famous for its diamond-bearing pipes, which also originated in the Triassic period.

The Triassic period began 250 million years ago and ended 200 million years ago. The Permian-Triassic extinction wiped out 90% of the planet's marine species and about 70% of its terrestrial species. However, the planet did not become a desert. The remaining species continued to diversify and fill newly discovered ecological niches. This led to the emergence of many new animal species, including the first dinosaurs and small mammals.

Pangea was a giant supercontinent at the beginning of this period, but tectonic forces began to roll the continent around. By the end of this period, Pangea had split into two separate supercontinents: the supercontinent Laurasia in the northern hemisphere and the supercontinent Gondwana in the southern hemisphere. During these times the climate was dry and hot, and there were probably almost no glaciers. Scientists believe that the polar regions were not covered by ice caps at all, and the climate was temperate and humid, which allowed animals such as reptiles to spread over large areas.

With regard to life during this time, scientists distinguish three different categories: animal species left over from a global extinction event that continued to evolve during this period; new species of life emerged a short time appeared but suddenly died out, and there were those groups of life that not only succeeded, but continued to dominate the rest of the era.

The terrestrial flora included ferns, horsetails, glossopterids, ginkgophytes, lycophytes, and cyclodophytes. In the southern hemisphere, seed ferns called Glossopteris spread, and North hemisphere seized the Bennettitales, coniferous trees and ferns. In the ocean, corals continued to develop and eventually became similar to today's corals - forming massive coral reefs on the ocean floor. Marine reptiles, including nasosaurs, pachyplerosaurs, and sauropterygia flourished. Ichthyosaurs were particularly successful in dispersing throughout the world's oceans and eventually reached gigantic proportions by the end of this period. The fish and ammonites that were able to survive the last extinction event also continued to thrive.

There were also several groups of fauna or flora that arose during the Triassic period and became dominant during this time. One such group was the Temnospondylia. They were one of the most large groups amphibians that appeared during the Carboniferous and were able to survive extinction. These included offshoots: stereospondyls, tupilacosaurs, mastodosaurs, microfoli, and tabanchua. The therapods became another successful group. Therapods appeared during the Triassic and developed well during this period. Etosaurs were another group that developed successfully during this period. Unfortunately, they became extinct during the extinction event that occurred at the end of this period.

At the end of the Triassic, a massive extinction event occurred, known as the Triassic-Jurassic extinction event. This mass extinction killed almost a quarter of all marine families and may have killed off half of all marine genera. Majority marine reptiles ceased to exist - with the exception of plesiosaurs, ichthyosaurs and conodonts. Although molluscs, brachiopods, and gastropods were not completely wiped out, their populations suffered greatly. Several species of reptiles, synapsids, krutrarsans, labyrinthine amphibians and many primitive dinosaurs were destroyed. However, some of the species were able to adapt and continued to dominate during the Jurassic.

These mass extinctions at the end of the Triassic period vacated many ecological niches. This not only allowed dinosaurs to expand their habitat, but also to thrive. Thanks to open ecological niches, dinosaurs increased in size, their population increased, their species became more diverse. Thus began the age of the dinosaurs. Conifers and Cycads will continue to dominate the next period as well.

Scientists are not sure what caused this extinction event in late period, but many believe it is due to massive volcanic eruptions that coincided with the breakup of the supercontinent Pangea. However, not all scientists share this opinion. Other scientists believe that this extinction was caused by an asteroid impact that created the crater that now contains the Manicouagan reservoir in Quebec, Canada.

Mesozoic era.

Triassic.

The Triassic period on Earth lasted about 45 million years. Approximately 220 million years have passed from its beginning to the present day. In the Triassic, land prevailed over the sea. There were two continents. Merged between the North Atlantic and Asian continents formed the Northern land. In the southern hemisphere lay the former Gondwana. Asia joined with Australia and New Zealand. All of Southern Europe, the Caucasus and the Crimea, Iran, the Himalayas and North Africa were flooded by the Tetke ocean. Large mountain ranges did not reappear at this time, but the mountains that had formed in previous periods were still high. There were frequent volcanic eruptions. The climate of the Triassic period was harsh and dry, but warm enough. Deserts in the Triassic are numerous.

Of the plants, gymnosperms noticeably predominated: sago, coniferous and ginkgo. Of the seed ferns, glossopteris continued to exist. At the end of the period, peculiar ferns appeared, especially numerous in the subsequent Jurassic period, the leaves of which, in terms of venation, resembled the leaves of seed plants. Triassic horsetails are much closer to modern horsetails than Paleozoic ones.

Great changes have taken place in the life of the inhabitants of the continents. The predominance of land over the sea, which began in the Permian period, and the progressive drying of many fresh water bodies in the Triassic period, led to the fact that many freshwater fish now moved to the seas, and only lungfish, close to the present, still lived in the surviving freshwater basins. At the end of the Triassic, the stegocephalians became extinct. These were the last representatives of the labyrinth-toothed stegocephalians, so named because the enamel on their teeth had a complex folded structure. All stegocephalians, fleeing from the dry climate and from competition with reptiles, became aquatic, and some even moved to live in the sea. Most of them were very large animals. For example, in Mastodonsaurus, the length of the skull reached 1 m.

At the beginning of the Triassic period, the direct ancestors of modern frogs lived. These protobatrachus are small, 10 cm long, animals, in general structure, they are more like toads than real frogs. Their skin is bumpy, their hind legs are more adapted for swimming than for jumping.

Reptiles have changed especially; whole skulls finally died out. In the second half of the period, the first turtles appeared, which, unlike modern ones, still had teeth in the sky, while the jaws were dressed with a horny beak.

In the Triassic period, they developed intensively, but at the end of it the last animal-like reptiles had already died out. Of these, herbivorous and already completely toothless stahleckers reached the size of a large rhinoceros. The smaller size was a predatory belezodont about 1.5 m.

Particularly interesting are the small animal-like reptiles Ictidosaurs, close to mammals. So, caromis, an animal the size of a rat, is already a real mammal in the structure of its skull, and only additional bones present in its lower jaw indicate that this animal is still a reptile.

Of the other reptiles in the Triassic period, the trunk-headed ones developed, the closest relatives of the modern New Zealand tuatara, which, although similar to ordinary lizards, differ from them in their structure. Tuatara in its structure still retains many ancient features. In her skull there are two temporal (zygomatic) arches, and not one, like in lizards. Her upper jaw hangs down in the form of a small beak. The teeth on the jaws do not sit in separate cells, but in a common groove. In addition to the usual ribs, "abdominal ribs" also develop on the belly. The biconcave vertebrae resemble the vertebrae of fish. Among the trunkheads in the Triassic lived stenaulorhynchuses - large burrowing animals, possibly feeding on roots. In the seas, along the coasts of the continents, there were long-snouted proboscis - fighters of sea mollusks. In a place with them, several resembling sea ​​turtles placodonts, in which real millstones for crushing shells formed in the sky instead of small teeth. Related to placodonts, notosaurs also led an aquatic lifestyle. These long-necked animals could still use their paws (flippers) to walk on the ground. Plesiosaurs, common marine reptiles of the following periods, evolved from notosaurs. In northern waters, the first fish lizards, or ichthyosaurs, appeared. They were not yet as well adapted to swimming in the sea as their descendants, in which the tail became like a fish. The most remarkable thing is that ichthyosaurs did not lay eggs like ordinary reptiles, but gave birth to live young, like mammals. From the Triassic, the flowering of a group of cellular reptiles began. The most ancient forms of them were relatively small carnivores. Instead of the usual movement on four legs, these animals adapted to walking on two legs, and therefore their hind legs became much longer than their front ones. Such was Saltoposuchus, an animal larger than 1 m. By the end of the Triassic, some cellular reptiles switched to an aquatic lifestyle. They again began to walk on four legs and in appearance somewhat resembled crocodiles, which were still absent at that time. The length of such a crocodile-like prestosuchus was at least 5 m. The first dinosaurs, not yet very large in size, appeared mainly on the Northern land. Some of them were not small, up to 1m in length, and led a predatory lifestyle. They walked on their hind legs, which were longer than their front ones. In some ways, dinosaurs resembled birds: the bones of their skeleton were hollow, filled with air, and the first toe on the hind legs was turned back.

Other dinosaurs, such as Plateosaurus, were much larger, reaching 6 m in length. The difference in the structure of the front and hind legs is small, their teeth are blunt. These were the ancestors of the herbivorous giants of the Jurassic period.

It is not surprising that with the abundance of animal-like reptiles in the Triassic, we also find here real mammals. The most ancient mammal known to us, the size of a marmot, is called the tritylodont. It belongs to the group of many tubercular mammals, so called because they had numerous tubercles on their molars in two or three rows. They didn't have fangs. One pair of incisors in the upper jaw and a single pair in the lower were enlarged. Many tuberculate teeth ate plant food. Probably still laid eggs, and did not give birth to live Cubs, as well as modern Australian monotreme mammals: platypus and echidna. Modern egg-laying mammals are toothless, but the embryos of the platypus have the rudiments of teeth of a multi-tubercular type. Therefore, many tuberculates are considered the closest relatives of the Australian monotremes, which still retain many features characteristic of reptiles.

At the bottom of the Triassic sea lived numerous six-ray corals, close to modern ones. Bivalves and gastropods were abundant, replacing brachiopods. Often came across new sea urchins and lilies. But numerous ammonites reached a special diversity in this period. At the same time, the first belemnites appeared - animals close to modern cuttlefish, also related to cephalopods. Under their skin, they had a calcareous skeleton in the form of a plate ending in a sharp spike. This spike is usually preserved as a fossil and is called the "devil's finger".

In the sea, in addition to shark fish, quite a lot of bony fish already lived, whose ancestors moved here from fresh water. met here lobe-finned fish and relatives of modern sturgeon fish, as well as armored pikes and silt fish North America. In terms of the structure of the scales, tail and internal organs, these fish still differed from real ones. bony fish.

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