The history of the Earth goes back four and a half billion years. This huge period of time is divided into four eons, which in turn are divided into eras and periods. The final fourth eon - Phanerozoic - includes three eras:
- Paleozoic;
- Mesozoic;
- Cenozoic
Periods of the Mesozoic era
The end of the Paleozoic era was 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 eighty-six million years and consisted of three periods, such as:
- Triassic;
- Jurassic;
- chalky.
The Mesozoic period is also characterized as the era of global warming. There have also been significant changes in the tectonics of the Earth. It was at that time that the only existing supercontinent broke into two parts, which were subsequently divided into the continents that exist in the modern world.
Triassic
The Triassic period is the first stage of the Mesozoic era. The Triassic lasted for thirty-five million years. After the catastrophe that occurred at the end of the Paleozoic on Earth, conditions are observed that are little conducive to the flourishing of life. A tectonic fault occurs and active volcanoes and mountain peaks are formed.
The climate becomes warm and dry, as a result of which deserts form on the planet, and the level of salt in water bodies increases sharply. However, it is precisely at this unfavorable time that mammals and birds appear. This was largely facilitated by the absence of clearly defined climatic zones and the maintenance of uniform temperatures throughout the globe.
Fauna of the Triassic
The Triassic period of the Mesozoic is characterized by significant evolution of the animal world. It was during the Triassic period that those organisms arose that subsequently shaped the appearance of the modern biosphere.
Cynodonts appeared - a group of lizards that were the ancestors of the first mammals. These lizards were covered with hair and had highly developed jaws, which helped them feed raw meat. Cynodonts laid eggs, but females fed their young with milk. The ancestors of dinosaurs, pterosaurs and modern crocodiles - archosaurs - also arose in the Triassic.
Due to the dry climate, many organisms have changed their habitat to aquatic habitats. This is how new species of ammonites, mollusks, as well as bony and ray-finned fish appeared. But the main residents depths of the sea there were predatory ichthyosaurs, which, as they evolved, began to reach gigantic 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 ancestors of dinosaurs, predominated on land.
Plants during the Triassic period
The flora of the first half of the Triassic did not differ significantly from the plants of the end of the Paleozoic era. Various types of algae grew in abundance in the water, seed ferns and ancient conifers were widespread on land, and lycophytes were widespread in coastal zones.
By the end of the Triassic, the land was covered with a cover herbaceous plants, which greatly contributed to the emergence of a variety of insects. Plants of the mesophytic group also appeared. Some cycad plants have survived to this day. It grows in the Malay Archipelago zone. Most plant species grew on the planet's coastal areas, while conifers predominated on land.
Jurassic period
This period is the most famous in the history of the Mesozoic era. The Jura is the European mountains that give its name to this time. Sedimentary deposits from that era have been found in these mountains. The Jurassic period lasted fifty-five million years. It acquired geographical significance due to the formation of modern continents (America, Africa, Australia, Antarctica).
The separation of the two previously existing continents of Laurasia and Gondwana served to form new bays and seas and raise the level of the world's oceans. This had a beneficial effect on making it more humid. The air temperature on the planet dropped and began to correspond to a temperate and subtropical climate. Such climate changes greatly contributed to the development and improvement of flora and fauna.
Animals and plants of the Jurassic period
The Jurassic period is the era of dinosaurs. Although other forms of life also evolved and took on new forms and species. The seas of that period were filled with many invertebrates, the structure of whose bodies was more developed than in the Triassic. Bivalve mollusks and intrashell belemnites, the length of which reached three meters, became widespread.
The insect world has also received evolutionary growth. The appearance of flowering plants also provoked the appearance of pollinating insects. New species of cicadas, beetles, dragonflies and other terrestrial insects have emerged.
Climatic changes that occurred during the Jurassic period resulted in heavy rainfall. This, in turn, gave impetus to the spread of lush vegetation across the surface of the planet. In the northern belt of the earth, herbaceous ferns and ginkgo plants predominated. The southern zone consisted of tree ferns and cycads. In addition, the Earth was filled with various coniferous, cordaite and cycad plants.
Age of Dinosaurs
During the Jurassic period of the Mesozoic, reptiles reached their evolutionary peak, ushering in the era of dinosaurs. The seas were dominated everywhere by giant dolphin-like ichthyosaurs and plesiosaurs. If ichthyosaurs were inhabitants of an exclusively aquatic environment, then plesiosaurs from time to time needed access to land.
Dinosaurs living on land amazed us with their diversity. Their sizes varied from 10 centimeters to thirty meters, and they weighed up to fifty tons. Herbivores predominated among them, but there were also ferocious predators. A huge number of predatory animals provoked the formation of certain elements of defense in herbivores: sharp plates, spines and others.
The airspace of the Jurassic period was filled with dinosaurs that could fly. Although they needed to climb to higher ground to fly. Pterodactyls and other pterosaurs swarmed and swooped above the surface of the earth in search of food.
Cretaceous period
When choosing the name for the next period, the main role was played by writing chalk, formed in the deposits of dying invertebrate organisms. The period called the Cretaceous was the final period of the Mesozoic era. This time lasted eighty million years.
The newly formed continents move, and the tectonics of the Earth increasingly takes on a form familiar to modern man. The climate became noticeably colder, and at this time the ice caps of the north and south poles formed. The planet is also divided into climatic zones. But in general, the climate remained quite warm, helped by the greenhouse effect.
Cretaceous biosphere
Belemnites and mollusks continue to evolve and spread in water bodies; sea urchins and the first crustaceans.
In addition, fish with hard bones actively develop in reservoirs. Insects and worms have progressed greatly. On land, the number of vertebrates increased, among which the leading positions were occupied by reptiles. They actively consumed vegetation earth's surface and destroyed each other. During the Cretaceous period, the first snakes arose that lived both in water and on land. Birds, which began to appear at the end of the Jurassic period, became widespread and actively developed during the Cretaceous period.
Among vegetation, flowering plants have received the greatest development. Spore-bearing plants died out due to their reproductive characteristics, giving way to more progressive ones. At the end of this period, gymnosperms evolved noticeably and began to be replaced by angiosperms.
The end of the Mesozoic era
The history of the Earth includes two events that contributed to the mass extinction of the planet's fauna. The first, the Permian catastrophe, marked the beginning of the Mesozoic era, and the second marked its end. Most animal species that actively evolved in the Mesozoic became extinct. IN aquatic environment ammonites, belemnites, and bivalves 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 was the impetus for the mass extinction of fauna in the Cretaceous period. There are versions about negative impact the greenhouse effect or radiation caused by a powerful cosmic explosion. But most scientists are inclined to believe that the cause of the extinction was the fall of a gigantic asteroid, which, when it hit the surface of the Earth, lifted a mass of substances into the atmosphere, blocking the planet from sunlight.
On land, the diversity of reptiles increased. Their hind limbs have become more developed than their forelimbs. The ancestors of modern lizards and turtles also appeared in the Triassic period. In the Triassic period, the climate of certain 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 larger than rats. It is believed that they, like modern platypuses and echidnas, were oviparous.
Plants
Repentant in Jurassic period spread not only on land, but also in water and air. Flying lizards have become widespread. The Jurassic also saw the appearance of the very first birds, Archeopteryx. As a result of the flourishing of spore and gymnosperm plants, the body size of herbivorous reptiles increased excessively, some of them reaching a length of 20-25 m.
Plants
Thanks to the warm and humid climate During the Jurassic period, tree-like plants flourished. In the forests, as before, gymnosperms and fern-like plants dominated. Some of them, such as sequoia, have survived to this day. The first flowering plants that appeared in the Jurassic period had a primitive structure and were not widespread.
Climate
IN Cretaceous period The climate has changed dramatically. Cloudiness decreased significantly, and the atmosphere became dry and transparent. As a result, the sun's rays fell directly on the leaves of the plants. Material from the site
Animals
On land, the reptile class still retained its dominance. Predatory and herbivorous reptiles increased in size. Their bodies were covered with a shell. The birds had teeth, but were otherwise close to modern birds. In the second half of the Cretaceous period, representatives of the subclass of marsupials and placentals appeared.
Plants
Climatic changes in the Cretaceous period had a negative impact on ferns and gymnosperms, and their numbers began to decline. But angiosperms, on the contrary, multiplied. By the mid-Cretaceous, many families of monocotyledonous and dicotyledonous angiosperms had evolved. Due to its diversity and appearance they are in many ways close to modern flora.
The Mesozoic era is a time of significant changes in the earth's crust and evolutionary progress. Over 200 million years, the main continents and mountain ranges were formed. The development of life in the Mesozoic era was significant. Thanks to warm weather conditions Live nature replenished with new species that became the ancestors of modern representatives.
The Mesozoic era (245–60 million years ago) is divided into the following time periods:
- Triassic;
- Jurassic;
- chalky.
Tectonic movements in the Mesozoic
The beginning of the era coincided with the completion of the formation of Paleozoic mountain folding. Therefore, for millions of years the situation was calm, there were no massive shifts. Only in the Cretaceous period of the Mesozoic did significant tectonic movements and the latest earth changes begin.
At the end of the Paleozoic, the land covered a large area, dominating the area of the world's oceans. The platforms protruded significantly above sea level and were surrounded by old folded formations.
In the Mesozoic, the continent of Gondwana was divided into several separate continents: African, South American, Australian, and Antarctica and the Hindustan Peninsula were also formed.
Already in the Jurassic period, the water rose significantly and flooded a vast area. The flood lasted throughout the Cretaceous period, and only at the end of the era was there a reduction in the area of the seas, and the newly formed Mesozoic folding came to the surface.
Mountains of Mesozoic folding
- Cordillera (North America);
- Himalayas (Asia);
- Verkhoyansk mountain system;
- Kalba Highlands (Asia).
It is believed that the Himalayan mountains of those times were much higher than today, but over time they collapsed. They were formed during the collision of the Indian subcontinent with the Asian plate.
Fauna in the Mesozoic era
The beginning of the Mesozoic era - the Triassic and Jurassic periods - were times of heyday and dominance of reptiles. Some representatives reached gigantic sizes with a body weight of up to 20 tons. Among them were both herbivores and carnivores. But even in the Permian period, beast-toothed reptiles appeared - the ancestors of mammals.
The first mammals are known from the Triassic period. At the same time, reptiles moving on their hind limbs - pseudosuchians - arose. They are considered the ancestors of birds. The first bird - Archeopteryx - appeared in the Jurassic period and continued to exist in the Cretaceous.
The progressive development of the respiratory and circulatory systems in birds and mammals, which provides them with warm-bloodedness, has reduced their dependence on temperature environment and ensured settlement in all geographical latitudes.
The appearance of real birds and higher mammals dates back to the Cretaceous period, and they soon took a dominant position in the phylum chordates. This was also facilitated by the development nervous system, education conditioned reflexes, raising offspring, and in mammals, viviparity and feeding the young with milk.
A progressive feature is the differentiation of teeth in mammals, which was a prerequisite for the use of a variety of foods.
Thanks to divergence and idioadaptations, numerous orders, genera and species of mammals and birds appeared.
Flora in the Mesozoic era
Triassic
On land, gymnosperms are widespread. Ferns, algae, and psilophytes were found everywhere. This was due to the fact that new way fertilization, not associated with water, and the formation of the seed made it possible for plant embryos to survive for a long time in unfavorable conditions.
As a result of the adaptations that arose, seed plants were able to exist not only near wet coasts, but also penetrate deep into the continents. Gymnosperms occupied a dominant place at the beginning of the Mesozoic. The most common species is the cycad. These plants are like trees with straight stems and feathery leaves. They resembled tree ferns or palm trees.
Conifers (Pine, Cypress) began to spread. Small horsetails grew in the swampy area.
Jurassic period
Cretaceous period
Among the angiosperms in the Cretaceous period, the greatest development was achieved by Magnoliaceae (tulip liriodendron), Roseaceae, and Kutrovaceae. Representatives of the Beech and Birch families grew in temperate latitudes.
As a result of divergence in the phylum, angiosperms formed two classes: monocots and dicotyledons, and thanks to idioadaptations, these classes developed numerous diverse adaptations for pollination.
At the end of the Mesozoic, due to the dry climate, the extinction of gymnosperms began, and since they were the main food for many, especially large reptiles, this also led to their extinction.
Features of the development of life in the Mesozoic
- Tectonic movements were less pronounced than in the Paleozoic. An important event- division of the supercontinent Pangea into Laurasia and Gondwana.
- Throughout the era it held on hot weather, temperatures varied between 25-35°C in tropical and 35-45°C in subtropical latitudes. The warmest period on our planet.
- Developed rapidly animal world, the Mesozoic era gave birth to the first lower mammals. Improvements are underway at the system level. The development of cortical structures influenced the behavioral reactions of animals and adaptive capabilities. The spinal column was divided into vertebrae, and two circles of blood circulation were formed.
- The development of life in the Mesozoic era was significantly influenced by climate, so the drought of the first half of the Mesozoic era contributed to the development of seed-bearing plants and reptiles that are resistant to unfavorable conditions, water shortage. In the middle of the second Mesozoic period, humidity increased, which led to the rapid growth of plants and the appearance of flowering plants.
Lesson topic:"The Development of Life in the Mesozoic Era"
The duration of the Mesozoic era is approximately 160 million years. The Mesozoic era includes the Triassic (235-185 million years ago), Jurassic (185-135 million years ago) and Cretaceous (135-65 million years ago) periods. The development of organic life on Earth and the evolution of the biosphere continued against the background of paleogeographical changes characteristic of this stage.
The Triassic is characterized by a general rise of platforms and an increase in land area.
By the end of the Triassic, the destruction of most mountain systems that arose in the Paleozoic. The continents turned into huge plains, which were invaded by the ocean in the next, Jurassic, period. The climate became softer and warmer, covering not only the tropical and subtropical zones, but also modern temperate latitudes. During the Jurassic period the climate was warm and humid. The increased rainfall caused the formation of seas, huge lakes and large rivers. Changes in physical and geographical conditions affected the development of the organic world. The extinction of representatives of marine and terrestrial biota, which began in the arid Permian, continued, which was called the Permian-Triassic crisis. After this crisis and as a result of it, the flora and fauna of land evolved.
Biologically, the Mesozoic was a time of transition from old, primitive to new, progressive forms. The Mesozoic world was much more diverse than the Paleozoic; the fauna and flora appeared in it in a significantly updated composition.
Flora
The vegetation cover of the land at the beginning of the Triassic period was dominated by ancient conifers and seed ferns (pteridosperms). in arid climates, these gymnosperms gravitated towards moist places. On the coasts of drying reservoirs and in disappearing swamps, the last representatives of ancient club mosses and some groups of ferns perished. By the end of the Triassic, a flora was formed in which ferns, cycads, and ginkgos dominated. Gymnosperms reached a special flourishing during this period.
In the Cretaceous, flowering plants appeared and conquered the land.
The putative ancestor of flowering plants, according to most scientists, was closely related to seed ferns and represented one of the branches of this group of plants. Paleontological remains of primary flowering plants and groups of plants intermediate between them and gymnosperm ancestors are, unfortunately, still unknown to science.
The primary type of flowering plant was, according to most botanists, an evergreen tree or low shrub. The herbaceous type of flowering plant appeared later under the influence of limiting environmental factors. The idea of the secondary nature of the herbaceous type of angiosperms was first expressed in 1899 by the Russian botanical geographer A.N. Krasnov and the American anatomist C. Jeffrey.
The evolutionary transformation of woody forms into herbaceous ones occurred as a result of weakening, and then a complete or almost complete decrease in the activity of the cambium. This transformation probably began at the dawn of the development of flowering plants. Over time, it proceeded at a faster pace in the most distant groups of flowering plants and eventually acquired such a wide scale that it covered all the main lines of their development.
Neoteny, the ability to reproduce at an early stage of ontogenesis, was of great importance in the evolution of flowering plants. It is usually associated with limiting environmental factors - low temperature, lack of moisture and a short growing season.
Of the huge variety of woody and herbaceous forms, flowering plants turned out to be the only group of plants capable of forming complex multi-layered communities. The emergence of these communities led to a more complete and intensive use of the natural environment and the successful conquest of new territories, especially unsuitable for gymnosperms.
In the evolution and mass dispersal of flowering plants, the role of pollinating animals is also great. especially insects. By feeding on pollen, insects transferred it from one strobila of the original ancestors of angiosperms to another and were thus the first agents of cross-pollination. Over time, insects have adapted to eat ovules, causing significant harm to plant reproduction. The reaction to such a negative influence of insects was the selection of adaptive forms with closed ovules.
The conquest of land by flowering plants marks one of the decisive, turning-point factors in the evolution of animals. This parallelism in the suddenness and rapidity of the spread of angiosperms and mammals is explained by interdependent processes. The conditions with which the flourishing of angiosperms was associated were also favorable for mammals.
Fauna
Fauna of the seas and oceans: 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. Ammonites were found in such numbers in the Mesozoic that their shells are found in almost all marine sediments of this time.
By the end of the Triassic, most of the ancient groups of ammonites died out, but in the Cretaceous they remained numerous, but during the Late Cretaceous the number of species in both groups begins to decline. The diameter of some ammonite shells reaches 2.5 m.
At the end of the Mesozoic, all ammonites became extinct. Of the cephalopods with an external shell, only the genus Nautilus has survived to this day. More widespread in modern seas are forms with internal shells - octopuses, cuttlefish and squids, distantly related to belemnites.
Six-rayed corals began to actively develop(Hexacoralla), whose colonies were active reef-formers. Mesozoic echinoderms were represented by various species of crinoids, or crinoids (Crinoidea), which flourished in the shallow waters of the Jurassic and partly Cretaceous seas. However Sea urchins have made the most progress. Starfish were abundant.
Bivalve mollusks have also become widespread.
During the Jurassic period, foraminifera flourished again, survived the Cretaceous period and reached modern times. In general, single-celled protozoa were an important component in the formation of Mesozoic sedimentary rocks. The Cretaceous period was also a time of rapid development of new types of sponges and some arthropods, particularly insects and decapods.
The Mesozoic era was a time of unstoppable expansion of vertebrates. Of the Paleozoic fish, only a few transitioned into the Mesozoic. Among them were freshwater sharks, sea sharks continued to develop throughout the Mesozoic; Most modern genera were already represented in the Cretaceous seas, in particular.
Almost all lobe-finned fish, from which the first land vertebrates developed, became extinct in the Mesozoic. 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). Until now this view remains the only modern representative of ancient lobe-finned fishes. It got the name Latimeria chalumnae. Such biological phenomena are called “living fossils.”
Sushi fauna: New groups of insects, the first dinosaurs and primitive mammals appeared on land. Reptiles became most widespread in the Mesozoic, becoming truly the dominant class of this era.
With the advent of dinosaurs in Early reptiles became completely extinct in the mid-Triassic cotylosaurs and beast-like animals, as well as the last large amphibians, stegocephals. Dinosaurs, which represented the most numerous and diverse superorder of reptiles, became the leading Mesozoic group of terrestrial vertebrates starting from the end of the Triassic. For this reason, the Mesozoic is called the era of dinosaurs. In the Jurassic, real monsters could be found among dinosaurs, up to 25-30 m long (including tail) and weighing up to 50 tons. Of these giants, the best known forms are Brontosaurus, Diplodocus and Brachiosaurus.
The original ancestors of dinosaurs may have been the Upper Permian Eosuchians - a primitive order of small reptiles with a lizard-like physique. From them, in all likelihood, a large branch of reptiles arose - archosaurs, which then split into three main branches - dinosaurs, crocodiles and winged lizards. Representatives of archosaurs were thecodonts. Some of them lived in water and looked like crocodiles. Others, similar to large lizards, lived in open areas of land. These land-dwelling thecodonts adapted bipedal walking, which provided them with the ability to observe in search of prey. It was from these thecodonts, which became extinct at the end of the Triassic, that dinosaurs descended, inheriting a bipedal mode of locomotion, although some of them switched to a four-legged mode of locomotion. Representatives of the climbing forms of these animals, which over time moved from jumping to gliding flights, gave rise to pterosaurs (pterodactyls) and birds. Dinosaurs included both herbivores and carnivores.
Towards the end of the Cretaceous, there was a mass extinction of characteristic Mesozoic groups of reptiles, including dinosaurs, ichthyosaurs, plesiosaurs, pterosaurs and mosasaurs.
Representatives of the class of birds (Aves) first appear in Jurassic deposits. The only known first bird was Archeopteryx. The remains of this first bird were found near the Bavarian city of Solnhofen (Germany). During the Cretaceous period, the evolution of birds proceeded at a rapid pace; characteristic of this time, still possessing jagged jaws. The emergence of birds was accompanied by a number of aromorphoses: they acquired a hollow septum between the right and left ventricles of the heart, and lost one of the aortic arches. The complete separation of the arterial and venous blood flows causes birds to be warm-blooded. Everything else, namely the feather cover, wings, horny beak, air sacs and double breathing, as well as shortening of the hindgut, are idioadaptations.
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. Their occurrence is associated with a number of major aromorphoses, developed in representatives of one of the subclasses of reptiles. These aromorphoses include: the formation of hair and a 4-chambered heart, complete separation of arterial and venous blood flows, intrauterine development of the offspring and feeding the baby with milk. Aromorphoses also include development of the cerebral cortex, which determines the predominance of conditioned reflexes over unconditioned ones and the possibility of adaptation to unstable environmental conditions by changing behavior.
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.
