Message about the Jurassic period. Jurassic period

Jurassic period most famous of all periods mesozoic era. Most likely, such fame Jurassic period acquired thanks to the film "Jurassic Park".

Jurassic period tectonics:

At first jurassic the single supercontinent Pangea began to disintegrate into separate continental blocks. Shallow seas formed between them. Intense tectonic movements at the end Triassic and at the beginning jurassic periods contributed to the deepening of large bays, which gradually separated Africa and Australia from Gondwana. The gulf between Africa and America deepened. Depressions formed in Eurasia: German, Anglo-Paris, West Siberian. The Arctic Sea flooded the northern coast of Laurasia. It is thanks to this that the climate of the Jurassic period became more humid. In the Jurassic the outlines of the continents begin to form: Africa, Australia, Antarctica, North and South America. And although they are located differently than now, they formed precisely in Jurassic period.

This is how the Earth looked at the end of the Triassic - the beginning jurassic
about 205 - 200 million years ago

This is how the Earth looked at the end of the Jurassic period, about 152 million years ago.

Climate and vegetation of the Jurassic period:

Volcanic activity of the end of the Triassic - the beginning jurassic caused the transgression of the sea. The continents separated and the climate in Jurassic period became wetter than in the Triassic. In place of the desert Triassic period, in Jurassic period lush vegetation grew. Huge areas were covered with lush vegetation. The woods jurassic mainly consisted of ferns and gymnosperms.
Warm and humid climate jurassic contributed to the violent development of the plant world of the planet. Ferns, conifers, and cycads formed extensive marshy forests. Araucaria, arborvitae, cicadas grew on the coast. Ferns and horsetails formed extensive woodlands. At the beginning jurassic, about 195 million years ago throughout the northern hemisphere, the vegetation was rather monotonous. But already starting from the middle of the Jurassic, about 170-165 million years ago, two (conditional) plant belts were formed: northern and southern. Ginkgo and herbaceous ferns predominated in the northern vegetation belt. AT Jurassic period Ginkgoaceae were very widespread. Groves of ginkgo trees grew throughout the belt.
In the southern vegetation belt, cycads and tree ferns predominated.
ferns jurassic and today are preserved in some corners of the wild. Horsetails and club mosses almost did not differ from modern ones. Places of growth of ferns and cordaites jurassic now occupied by tropical forests, consisting mainly of cycads. Cycads - a class of gymnosperms that prevailed in the green cover of the Earth jurassic. Now they are found here and there in the tropics and subtropics. Dinosaurs roamed under the canopy of these trees. Outwardly, cycads are so similar to low (up to 10-18 m) palm trees that they were even initially identified as palm trees in the plant system.
AT Jurassic period ginkgo trees are also common - deciduous (which is unusual for gymnosperms) trees with an oak-like crown and small fan-shaped leaves. Only one species has survived to this day - ginkgo biloba. The first cypress and, possibly, spruce trees appear during the Jurassic period. coniferous forests jurassic were similar to modern ones.

land animals Jurassic:

Jurassic period Dawn of the Age of Dinosaurs. It was the violent development of vegetation that contributed to the emergence of many species of herbivorous dinosaurs. The growth in the number of herbivorous dinosaurs gave impetus to the growth in the number of predators. Dinosaurs settled all over the land and lived in forests, lakes, swamps. The range of differences between them is so great that family ties between them are established with great difficulty. Diversity of dinosaur species Jurassic period it was great. They could be the size of a cat or a chicken, or they could reach the size of huge whales.

One of the fossils jurassic combining features of birds and reptiles is archeopteryx, or the first bird. For the first time, his skeleton was discovered in the so-called lithographic slates in Germany. The discovery was made two years after the publication of Charles Darwin's On the Origin of Species and became a strong argument in favor of the theory of evolution. Archeopteryx still flew rather poorly (planned from tree to tree), and was about the size of a crow. Instead of a beak, it had a pair of toothy, albeit weak jaws. It had free fingers on its wings (of modern birds, they were preserved only in hoatzin chicks).

Jurassic Sky Kings:

AT Jurassic period winged lizards - pterosaurs reigned supreme in the air. They appeared as early as the Triassic, but their heyday fell on Jurassic period Pterosaurs were represented by two groups pterodactyls and rhamphorhynchus .

Pterodactyls in most cases were tailless, different in size - from the size of a sparrow to a crow. They had wide wings and a narrow skull extended forward with a small number of teeth in the front. Pterodactyls lived in large flocks on the shores of the lagoons of the late Jurassic sea. During the day they hunted, and at nightfall they hid in trees or in rocks. The skin of pterodactyls was wrinkled and bare. They ate mainly fish or carrion, sometimes sea lilies, mollusks, and insects. In order to take off, pterodactyls had to jump off rocks or trees.

AT Jurassic period the first birds appear, or something in between birds and lizards. Creatures that appeared in Jurassic period and possessing the properties of lizards and modern birds are called Archeopteryx. The first birds are Archeopteryx, the size of a dove. Archeopteryx lived in forests. They fed mainly on insects and seeds.

But Jurassic period is not limited to animals alone. Thanks to climate change and the rapid development of flora jurassic, the evolution of insects accelerated dramatically, and as a result, the Jurassic landscape eventually filled with an endless buzz and crackle, which were emitted by many new types of insects, crawling and flying everywhere. Among them were the predecessors of modern ants, bees, earwigs, flies and wasps..

Masters of the seas of the Jurassic period:

As a result of the split of Pangea, in Jurassic period, new seas and straits were formed, in which new types of animals and algae developed.

Compared to the Triassic, Jurassic period the population of the seabed has changed a lot. Bivalves displace brachiopods from shallow waters. Brachiopod shells are replaced by oysters. Bivalve molluscs fill all the vital niches of the seabed. Many stop collecting food from the ground and move on to pumping water with the help of gills. in warm and shallow seas jurassic other important events took place. AT Jurassic period a new type of reef communities is emerging, approximately the same as that which exists now. It is based on the Triassic six-pointed corals. The resulting giant coral reefs have sheltered numerous ammonites and new varieties of belemnites (old relatives of today's octopuses and squids). Also, many invertebrates settled in them, such as sponges and bryozoans (sea mats). Gradually on seabed accumulated fresh sediments.

On land, in lakes and rivers jurassic There were many different types of crocodiles, widely settled around the globe. There were also saltwater crocodiles with long snouts and sharp teeth for catching fish. Some of their varieties even grew flippers instead of legs to make it easier to swim. Tail fins allowed them to reach greater speed in water than on land. New species of sea turtles have also appeared.

All Jurassic Dinosaurs

Herbivorous dinosaurs:

Jurassic geological period, Jura, Jurassic system, middle period of the Mesozoic. It began 206 million years ago and lasted 64 million years.

For the first time deposits of the Jurassic period were described in the Jura (mountains in Switzerland and France), hence the name of the period. The deposits of that time are quite diverse: limestones, clastic rocks, shales, igneous rocks, clays, sands, conglomerates, formed in a variety of conditions.

190-145 million years ago, during the Jurassic period, the single supercontinent Pangea began to break up into separate continental blocks. Shallow seas formed between them.

Climate

The climate in the Jurassic period was humid and warm (and by the end of the period - arid in the equator).

In the Jurassic period, vast areas were covered with lush vegetation, primarily a variety of forests. They mainly consisted of ferns and gymnosperms.

cycads- a class of gymnosperms that prevailed in the green cover of the Earth. Now they are found here and there in the tropics and subtropics. Dinosaurs roamed under the canopy of these trees. Outwardly, cycads are so similar to low (up to 10-18 m) palm trees that even Carl Linnaeus placed them among palm trees in his plant system.

During the Jurassic period, groves of ginkgo trees grew throughout the then temperate zone. Ginkgoes are deciduous (unusually for gymnosperms) trees with an oak-like crown and small, fan-shaped leaves. Only one species has survived to this day - ginkgo biloba. Very diverse were conifers, similar to modern pines and cypresses, which flourished at that time not only in the tropics, but had already mastered the temperate zone.

marine organisms

Compared with the Triassic, the population of the seabed has changed a lot. Bivalves displace brachiopods from shallow waters. Brachiopod shells are replaced by oysters. Bivalve molluscs fill all the vital niches of the seabed. Many stop collecting food from the ground and move on to pumping water with the help of gills. A new type of reef communities is emerging, approximately the same as it exists now. It is based on six-ray corals that appeared in the Triassic.

land animals

One of the fossil creatures of the Jurassic period, combining the features of birds and reptiles, is Archeopteryx, or the first bird. For the first time, his skeleton was discovered in the so-called lithographic slates in Germany. The discovery was made two years after the publication of Charles Darwin's On the Origin of Species and became a strong argument in favor of the theory of evolution. Archeopteryx still flew rather poorly (planned from tree to tree), and was about the size of a crow. Instead of a beak, it had a pair of toothy, albeit weak jaws. It had free fingers on its wings (of modern birds, they were preserved only in hoatzin chicks).

In the Jurassic period, small, woolly warm-blooded animals - mammals - live on Earth. They live next to dinosaurs and are almost invisible against their background.

Dinosaurs of the Jurassic period ("terrible lizards" from Greek) lived in ancient forests, lakes, swamps. The range of differences between them is so great that family ties between them are established with great difficulty. They could be the size of a cat or a chicken, or they could reach the size of huge whales. Some of them moved on four limbs, while others ran on their hind legs. Among them were clever hunters and bloodthirsty predators, but there were also harmless herbivorous animals. The most important feature common to all their species is that they were land animals.

According to modern ideas of scientists, the geological history of our planet is 4.5-5 billion years. In the process of its development, it is customary to single out geological periods Earth.

general information

The geological periods of the Earth (table below) are a sequence of events that have occurred in the process of the development of the planet since the formation of the earth's crust on it. Over time, various processes take place on the surface, such as the emergence and destruction of submersion of land areas under water and their uplift, glaciation, as well as the appearance and disappearance of various species of plants and animals, etc. Our planet bears obvious traces of its formation. Scientists claim that they are able to fix them with mathematical accuracy in various layers of rocks.

Main sediment groups

Geologists, trying to reconstruct the history of the planet, study rock layers. It is customary to divide these deposits into five main groups, distinguishing the following geological eras of the Earth: the most ancient (Archaean), early (Proterozoic), ancient (Paleozoic), middle (Mesozoic) and new (Cenozoic). It is believed that the boundary between them runs along the largest evolutionary phenomena that have occurred on our planet. The last three eras, in turn, are divided into periods, since the remains of plants and animals are most clearly preserved in these deposits. Each stage is characterized by events that have had a decisive influence on the current relief of the Earth.

oldest stage

The Earth was distinguished by rather violent volcanic processes, as a result of which igneous granite rocks appeared on the surface of the planet - the basis for the formation of continental plates. At that time, only microorganisms existed here that could do without oxygen. It is assumed that deposits of the Archean era cover certain areas of the continents with an almost solid shield, they contain a lot of iron, silver, platinum, gold and ores of other metals.

early stage

It is also characterized by high volcanic activity. During this period, mountain ranges of the so-called Baikal folding were formed. To this day, they have practically not survived, today they are just separate insignificant uplifts on the plains. During this period, the Earth was inhabited by the simplest microorganisms and blue-green algae, the first multicellular organisms appeared. The Proterozoic rock layer is rich in minerals: mica, non-ferrous metal ores and iron ores.

ancient stage

The first period of the Paleozoic era was marked by the formation of mountain ranges. This led to a significant reduction in sea basins, as well as the emergence of huge land areas. Separate ranges of that period have survived to this day: in the Urals, in Arabia, Southeast China and Central Europe. All these mountains are "worn out" and low. The second half of the Paleozoic is also characterized by mountain building processes. Ranges formed here. This era was more powerful, extensive mountain ranges arose in the territories of the Urals and Western Siberia, Manchuria and Mongolia, Central Europe, as well as Australia and North America. Today they are represented by very low blocky massifs. Animals of the Paleozoic era are reptiles and amphibians, the seas and oceans are inhabited by fish. Among the flora, algae predominated. The Paleozoic era is characterized by large deposits of coal and oil, which arose precisely in this era.

middle stage

The beginning of the Mesozoic era is characterized by a period of relative calm and the gradual destruction of the mountain systems created earlier, submersion of flat territories (part of Western Siberia) under water. The second half of this period was marked by the formation of Mesozoic folding ridges. Very vast mountainous countries appeared, which today have the same appearance. As an example, we can cite the mountains of Eastern Siberia, the Cordillera, certain parts of Indochina and Tibet. The ground was densely covered with lush vegetation, which gradually died off and rotted away. Due to the hot and humid climate, peat bogs and marshes were actively formed. It was the era of giant lizards - dinosaurs. The inhabitants of the Mesozoic era (herbivores and predatory animals) spread throughout the entire planet. At the same time, the first mammals appear.

New stage

Cenozoic era, which replaced middle stage, continues to this day. The beginning of this period was marked by an increase in the activity of the internal forces of the planet, which led to a general uplift of huge areas of land. This era is characterized by the emergence of mountain ranges within the Alpine-Himalayan belt. During this period, the Eurasian continent acquired its modern shape. In addition, there was a significant rejuvenation of the ancient massifs of the Urals, Tien Shan, Appalachians and Altai. The climate on Earth changed dramatically, periods of powerful ice cover began. The movements of glacial masses changed the relief of the continents. As a result, hilly plains with a huge number of lakes were formed. Animals of the Cenozoic era are mammals, reptiles and amphibians, many representatives of the initial periods have survived to this day, others have died out (mammoths, woolly rhinos, saber-toothed tigers, cave bears and others) for one reason or another.

What is a geologic period?

The geological stage as a unit of our planet is usually divided into periods. Let's see what the encyclopedia says about this term. Period (geological) is a large interval of geological time during which rocks. In turn, it is subdivided into smaller units, which are commonly called epochs.

The first stages (Archaean and Proterozoic), due to the complete absence or insignificant amount of animal and plant deposits in them, are not usually divided into additional sections. The Paleozoic era includes the Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian periods. This stage is characterized the largest number subintervals, the rest were limited to only three. The Mesozoic era includes the Triassic, Jurassic and Cretaceous stages. The Cenozoic era, the periods of which are most studied, is represented by the Paleogene, Neogene and Quaternary subinterval. Let's take a closer look at some of them.

Triassic

The Triassic period is the first subinterval of the Mesozoic era. Its duration was about 50 million years (beginning - 251-199 million years ago). It is characterized by the renewal of marine and terrestrial fauna. At the same time, a few representatives of the Paleozoic continue to exist, such as spiriferids, tabulata, some laminabranchs, etc. Among the invertebrates, ammonites are very numerous, giving rise to many new forms important for stratigraphy. Among corals, six-rayed forms predominate, among brachiopods - terebratulids and rhynchonelids, in the group of echinoderms - sea ​​urchins. Vertebrate animals are mainly represented by reptiles - large lizard dinosaurs. Thecodonts are widespread land reptiles. In addition, the first large inhabitants of the aquatic environment appear in the Triassic period - ichthyosaurs and plesiosaurs, but they reach their peak only in the Jurassic period. Also at this time, the first mammals arose, which were represented by small forms.

Flora in the Triassic period (geological) loses elements of the Paleozoic and acquires an exclusively Mesozoic composition. Fern species of plants, sago-like, coniferous and ginkgoales predominate here. Climatic conditions characterized by significant warming. This leads to the drying up of many inland seas, and in the remaining seas the level of salinity increases significantly. In addition, the areas of inland water bodies are greatly reduced, resulting in the development of desert landscapes. For example, the Tauride formation of the Crimean peninsula belongs to this period.

Yura

The Jurassic period got its name from the Jura Mountains in Western Europe. It constitutes the middle part of the Mesozoic and most closely reflects the main features of the development of the organics of this era. In turn, it is usually divided into three sections: lower, middle and upper.

The fauna of this period is represented by widely distributed invertebrates - cephalopods (ammonites, represented by numerous species and genera). They sharply differ from representatives of the Triassic in sculpture and character of shells. In addition, in the Jurassic period, another group of mollusks, the belemnites, flourished. At this time, six-ray reef-building corals, lilies and urchins, as well as numerous lamellar gills, reach significant development. On the other hand, species of the Paleozoic brachiopod completely disappear. marine fauna vertebrate species is significantly different from the Triassic, it reaches a huge diversity. In the Jurassic period, fish are widely developed, as well as aquatic reptiles - ichthyosaurs and plesiosaurs. At this time, there is a transition from land and adaptation to marine environment crocodiles and turtles. A huge variety is achieved by various types of terrestrial vertebrates - reptiles. Among them, dinosaurs come to their heyday, which are represented by herbivores, carnivores and other forms. Most of them reach 23 meters in length, for example, diplodocus. In the sediments of this period, a new type of reptile is found - flying lizards, which are called "pterodactyls". At the same time, the first birds appear. The flora of the Jura reaches a luxuriant flowering: gymnosperms, ginkgos, cycads, conifers (araucaria), bennettites, cycads and, of course, ferns, horsetails and club mosses.

Neogene

The Neogene period is the second period of the Cenozoic era. It began 25 million years ago and ended 1.8 million years ago. Significant changes in the composition of the fauna took place at this time. A wide variety of gastropods and bivalves, corals, foraminifers, and coccolithophores emerge. Amphibians have been widely developed sea ​​turtles and bony fish. AT neogene period terrestrial vertebral forms also reach great diversity. For example, rapidly progressing hipparion species appeared: hipparions, horses, rhinos, antelopes, camels, proboscis, deer, hippos, giraffes, rodents, saber-toothed tigers, hyenas, apes and others.

Under the influence of various factors at this time, rapidly evolving organic world: there are forest-steppes, taiga, mountain and plain steppes. In tropical areas - savannahs and wet forests. Climatic conditions are approaching modern ones.

Geology as a science

The geological periods of the Earth are studied by science - geology. It appeared relatively recently - at the beginning of the 20th century. However, despite her youth, she was able to shed light on many controversial issues about the formation of our planet, as well as the origin of the creatures inhabiting it. There are few hypotheses in this science, mainly only the results of observations and facts are used. There is no doubt that the traces of the development of the planet stored in the earth's layers will in any case give a more accurate picture of the past than any written book. However, not everyone is able to read these facts and understand them correctly, therefore, even in this exact science, erroneous interpretations of certain events can occur from time to time. Where traces of fire are present, it is safe to say that there was fire; and where there are traces of water, with the same certainty it can be argued that there was water, and so on. And yet, mistakes also happen. In order not to be unfounded, consider one such example.

"Frost patterns on glass"

In 1973, the journal "Knowledge is Power" published an article by the famous biologist A. A. Lyubimtsev "Frost patterns on glass." In it, the author draws the attention of readers to the striking similarity of ice patterns with plant structures. As an experiment, he photographed a pattern on glass and showed the photo to a botanist he knew. And without slowing down, he recognized the petrified footprint of a thistle in the picture. From the point of view of chemistry, these patterns arise due to the gas-phase crystallization of water vapor. However, something similar occurs in the production of pyrolytic graphite by pyrolysis of methane diluted with hydrogen. Thus, it was found that dendritic forms are formed away from this flow, which are very similar to plant remains. This is explained by the fact that there are general laws that govern the formation of forms in inorganic matter and wildlife.

For a long time, geologists have dated each geologic period based on traces of plant and animal forms found in coal deposits. And just a few years ago, there were statements by some scientists that this method was wrong and that all the fossils found were nothing more than a by-product of the formation of the earth's layers. There is no doubt that everything cannot be measured in the same way, but it is necessary to approach dating issues more carefully.

Was there a global glaciation?

Let's consider one more categorical statement of scientists, and not only geologists. All of us, starting from school, were taught about the global glaciation that covered our planet, as a result of which many animal species became extinct: mammoths, woolly rhinos and many others. And the modern younger generation is brought up on the quadrology "Ice Age". Scientists unanimously argue that geology is an exact science that does not allow theories, but uses only verified facts. However, this is not the case. Here, as in many areas of science (history, archeology, and others), one can observe the rigidity of theories and the steadfastness of authorities. For example, since the end of the nineteenth century, there has been heated debate on the sidelines of science about whether there was a glaciation or not. In the middle of the twentieth century, the famous geologist I. G. Pidoplichko published a four-volume work “On ice age". In this work, the author gradually proves the inconsistency of the version of global glaciation. He relies not on the works of other scientists, but on the geological excavations he personally carried out (moreover, he carried out some of them, being a soldier of the Red Army, participating in battles against the German invaders) throughout the territory Soviet Union and Western Europe. He proves that the glacier could not cover the entire continent, but was only local in nature, and that it did not cause the extinction of many animal species, but completely different factors - these are catastrophic events that led to the pole shift (“Sensational History of the Earth”, A . Sklyarov); and economic activity the person himself.

Mysticism, or Why scientists do not notice the obvious

Despite the irrefutable evidence provided by Pidoplichko, scientists are in no hurry to abandon the accepted version of glaciation. And then even more interesting. The author's works were published in the early 1950s, but with the death of Stalin, all copies of the four-volume edition were confiscated from the libraries and universities of the country, were preserved only in the library's storerooms, and it is not easy to get them from there. AT Soviet time everyone who wanted to borrow this book from the library was registered by the special services. And even today there are certain problems in obtaining this printed edition. However, thanks to the Internet, anyone can get acquainted with the works of the author, who analyzes in detail the periods of the geological history of the planet, explains the origin of certain traces.

Geology - an exact science?

It is believed that geology is an exclusively experimental science, which draws conclusions only from what it sees. If the case is doubtful, then she does not state anything, expresses an opinion that allows for discussion, and postpones the final decision until unambiguous observations are obtained. However, as practice shows, exact sciences are also wrong (for example, physics or mathematics). Nevertheless, mistakes are not a disaster if they are accepted and corrected in time. Often they are not global in nature, but have local significance, you just need to have the courage to accept the obvious, draw the right conclusions and move on towards new discoveries. Modern scientists show a radically opposite behavior, because most of the luminaries of science at one time received titles, awards and recognition for their work, and today they do not want to part with them at all. And such behavior is noticed not only in geology, but also in other fields of activity. Only strong people are not afraid to admit their mistakes, they rejoice at the opportunity to develop further, because the discovery of an error is not a disaster, but, on the contrary, a new opportunity.

160 million years ago rich vegetable world provided food for the giant sauropods that had arisen by this time, and also provided shelter for a huge number of small mammals and pangolins. Conifers, ferns, horsetails, tree ferns and cycads were widespread at this time.

Their fossilized remains are found on all continents (with the exception of Antarctica) in rocks from the early Jurassic to the late Cretaceous, although they were most common in the second half of the Jurassic. At the same time, sauropods reach their most large sizes. They survived until the late Cretaceous, when the huge hadrosaurs ("duck-billed dinosaurs") began to dominate among terrestrial herbivores.

Outwardly, all sauropods looked similar friend on the other: with an extremely long neck, an even longer tail, a massive but relatively short body, four columnar legs and a relatively small head. In different species, only the position of the body and the proportions of individual parts could change. For example, such sauropods of the late Jurassic period as brachiosaurs (Brachiosaurus - “shouldered lizard”) were taller in the shoulder girdle than in the pelvic girdle, while contemporary diplodocus (Diplodocus - “double process”) were significantly lower, and at the same time their hips towered over their shoulders. In some species of sauropods, such as the Camarasaurus (Camarasaurus - "chamber lizard"), the neck was relatively short, only slightly longer than the body, while in others, such as diplodocus, it was more than twice as long as the body.

Teeth and diet

The diplodocus skull has helped paleontologists understand the dinosaur's way of feeding. The abrasion of the teeth indicates that he tore off the leaves either from below or from above himself.

Many books on dinosaurs used to mention "small, thin teeth" of sauropods, but it is now known that the teeth of some of them, such as Camarasaurus, were massive and strong enough to grind even very hard plant foods, while the long and thin ones, the pencil-like teeth of Diplodocus do indeed seem unable to withstand the considerable stress that comes from chewing hard plants.

diplodocus (Diplodocus). The long neck allowed him to "comb" food from the highest coniferous plants. It is believed that diplodocus lived in small herds and fed on tree shoots.

During the study of the teeth of diplodocus, carried out in recent years in England, an unusual deterioration of their lateral surfaces was discovered. This pattern of tooth abrasion gave clues to how these huge animals could have eaten. The side surface of the teeth could wear out only if something moved between them. Apparently, diplodocus used its teeth to tear apart bundles of leaves and shoots, acting as a comb, while its lower jaw could move slightly back and forth. Most likely, when the animal divided into strips of plants captured below, moving its head up and back, the lower jaw was shifted back (upper teeth were located in front of the lower ones), and when it pulled the branches located above tall trees down and back, then pushed the lower jaw forward (the lower teeth were in front of the upper ones).

Brachiosaurus probably used its shorter, slightly pointed teeth to pluck only high-lying leaves and shoots, since its vertical body orientation, due to its longer front legs, made it difficult to feed on plants growing low above the soil.

Narrow specialization

The details of the anatomical structure of sauropods described above show that within the same ecological system (in the forests covering most of the land at that time), sauropods fed on various plant foods, obtaining it in different ways at different levels. This division by feeding strategy and type of food, which can still be seen in herbivore communities today, has been called "tropical sectioning."

Brachiosaurus (Brachiosaurus) reached more than 25 m in length and 13 m in height. Their fossilized remains and fossilized eggs are found in East Africa and North America. They probably lived in herds like modern elephants.

The main difference between today's herbivore ecosystems and the sauropod-dominated ecosystems of the Late Jurassic is only the mass and height of the animals. None of the modern herbivores, including elephants and giraffes, reach a height comparable to that of most large sauropods, and none of the modern land animals requires such a huge amount of food as these giants.

Other end of the scale

Multituberous were the most numerous and most diverse group mammals of the Jurassic and Cretaceous periods. These are the only omnivorous mammals of the Mesozoic era (the rest were specialized insectivores or carnivores). They are known from Late Jurassic deposits, but recent finds show that they are close to a little-known group of extremely ancient mammals of the Late Triassic, the so-called. haramiids.

In the structure of the skull and teeth, the multituberculates were very reminiscent of today's rodents, they had two pairs of protruding incisors, giving them the appearance of a typical rodent. Behind the incisors was a toothless gap, followed by molars to the very end of the small jaws. However, the teeth closest to the incisors had an unusual structure. In fact, these were the first false-rooted (premolar) teeth with curved sawtooth edges.

Such an unusual structure of teeth in the process of evolution re-emerged in some of the modern marsupials, for example, in rat kangaroos in Australia, whose teeth are the same shape and are located in the same place in the jaw as the pseudo-rooted teeth of polytuberculates. When chewing food at the moment of jaw closure, multituberculates could shift the lower jaw back, moving these sharp sawtooth teeth across food fibers, and long incisors could be used to pierce dense plants or hard external skeletons of insects.

Lizard-hipped megalosaurus (Megalosaurus) and its cubs, overtaking the ornithischian Scelidosaurus (Scelidosaurus). Scelidosaurus is an ancient species of dinosaurs of the Jurassic period with unevenly developed limbs, reaching 4 m in length. Its dorsal shell helped protect against predators.

The combination of sharp front incisors, serrated blades, and chewing teeth means that the feeding apparatus of the multituberculates was quite versatile. Today's rodents are also a very successful group of animals, thriving in a wide variety of ecological systems and habitats. Most likely, it was the highly developed dental apparatus, which allows them to eat various foods, that became the reason for the evolutionary success of the multituberous. Their fossilized remains, found on most continents, belong to various species: some of them, apparently, lived in trees, while others, resembling modern gerbils, were probably adapted to existence in an arid desert climate.

Ecosystem change

The ecosystems of small animals of the Jurassic also included small lizards of various species and even their aquatic forms.

Thrinadoxon (cynodont species). Its limbs protruded slightly to the sides, and were not located under the body, as in modern mammals.

They and the rare reptiles of the synapsid group (“animal reptiles”), the tritylodonts, who survived to this time, lived at the same time and in the same ecosystems as the multi-tuberous mammals. Tritylodonts were numerous and widespread throughout the Triassic but, like other cynodonts, suffered greatly during the Late Triassic extinction. This is the only group of cynodonts that survived from the Jurassic. In appearance, they, like multi-tuberous mammals, very much resembled modern rodents. That is, a significant part of the ecosystems of small animals of the Jurassic period consisted of animals resembling rodents: trilodonts and multituberous mammals.

The multitubercular mammals were by far the most numerous and diverse group of mammals of the Jurassic period, but other groups of mammals also existed at this time, including: tinodontids) and docodonts (docodonts). All these small mammals looked like mice or shrews. Docodonts, for example, developed distinctive, wide molars well suited for chewing hard seeds and nuts.

At the end of the Jurassic, significant changes occurred at the other end of the size scale in a group of large bipeds. predatory dinosaurs, theropods, represented at this time by allosaurs (AUosaurus - "strange lizards"). At the end of the Jurassic, a group of theropods became isolated, called spinosaurids (“spiny or spiked lizards”), a distinctive feature of which was a crest of long processes of the trunk vertebrae, which, perhaps, like the dorsal sail in some pelycosaurs, helped them regulate body temperature. Such spinosaurids as Siamosaurus ("lizard from Siam"), whose length reached 12 m, together with other theropods, shared the niche of the largest predators in the ecosystems of that time.

Spinosaurids had non-serrated teeth and elongated, less massive skulls compared to other theropods of that time. These structural features indicate that they differed in their way of feeding from theropods such as allosaurs, Eustreptospondylus ("strongly curved vertebrae") and ceratosaurus (Ceratosaurus - "horned lizard"), and most likely hunted other prey.

bird-like dinosaurs

The very first ornithominid, Elaphrosaums ("light lizard"), from the Late Jurassic of North America, had light, hollow bones and a toothless beak, and its limbs, both hind and fore, were shorter than those of later Cretaceous ornithominids, and, accordingly, it was a slower animal.

Another ecologically important group of dinosaurs that arose in the late Jurassic are the nodosaurs, four-legged dinosaurs with massive, armored bodies, short, relatively thin limbs, a narrow head with an elongated snout (but with massive jaws), small leaf-shaped teeth, and a horny beak. Their name (“knobby lizards”) is associated with bone plates covering the skin, protruding processes of the vertebrae and growths scattered over the skin, which served as protection from predator attacks. Nodosaurs became widespread only in the Cretaceous, and in the Late Jurassic, they, along with huge tree-eating sauropods, were only one element of the herbivorous dinosaur community that served as prey for a number of huge predators.

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Jurassic period- This is the second (middle) period of the Mesozoic era. It begins 201 million years before our times, lasts 56 million years and ends 145 million years ago (according to other sources, the duration of the Jurassic period is 69 million years: 213 - 144 million years). Named after mountains Yura, in which its sedimentary layers were first identified. Significant for the widespread flowering of dinosaurs.

The main subdivisions of the Jurassic period, its geography and climate

According to the classification adopted by the International Union of Geological Sciences, The Jurassic period is divided into three divisions- Lower - Leyas (stages - Gottangsky, Sinemursky, Plinsbakhsky, Toarsky), Middle - Dogger (levels - Aalensky, Bayossky, Batsky, Callovian) and Upper Small (levels - Oxford, Kimmeridgsky, Tithonian).

In this period, the division of Pangea into constituent blocks - the continents - continued. Upper Lawrence, which later became North America and Europe, finally separated from Gondwana, which again began to shift south. As a result, the connection between the global continents was broken, which had an important impact on the further evolution and development of flora and fauna. The differences that originated at that time are sharply expressed to this day.

The Tethys Sea, expanded even more as a result of the separation of the continents, now occupied most of modern Europe. It originated from the Iberian Peninsula and, crossing the south and southeast of Asia diagonally, went into Pacific Ocean. Most of what is now France, Spain and England was under his rule. warm waters. On the left, as a result of the separation of the North American sector of Gondwana, a depression began to emerge, which in the future became the Atlantic Ocean.

With the start of the Jurassic era average temperature on the the globe gradually began to decline, and therefore in the lower section Jurassic climate was close to moderate - subtropical. But closer to the middle, the temperature began to rise again, and by the beginning of the Cretaceous period, the climate became greenhouse.

The ocean level rose and fell slightly throughout the Jurassic, but the average sea level was an order of magnitude higher than in the Triassic. As a result of the divergence of continental blocks, a great many small lakes were formed, in which both plant and animal life began to develop and progress very quickly, so that the quantitative and qualitative level of the flora and fauna of the Jurassic period soon caught up and outstripped the level of the Permian to the point of global mass extinction.

sedimentation

With a drop in temperature, multiple precipitations began to fall abundantly throughout the earth, which contributed to the advancement of vegetation, and then the animal world, into the depths of the continents, which is due to Jurassic sedimentation. But the most intense for this period are the products of the formation of the earth's crust under the influence of continental shifts, and as a result, volcanic and other seismic activity. These are various igneous, clastic rocks. Large deposits of shale, sand, clay, conglomerates, limestone.

The warm and stable climate of the Jurassic period greatly contributed to the rapid development, formation and evolutionary improvement of both old and new life forms. (Fig. 1) have risen to a new level compared to the sluggish, not especially shining varieties, the Triassic.

Rice. 1 - Jurassic Animals

The Jurassic seas were full of various marine invertebrates. Especially numerous were belemnites, ammonites, all kinds of sea lilies. And although there were an order of magnitude fewer ammonites in the Jurassic than in the Triassic, they mostly had a more developed body structure than their ancestors from the previous era, with the exception of the phyloceras, which did not change at all during the millions of years of transition from the Triassic to the Jurassic. It was at that time that many ammonites acquired their indescribable mother-of-pearl coating, which has survived to this day. Ammonites were found in large quantities, both in the distant oceanic depths and in coastal warm and inland seas.

Belemnites in the Jurassic era reached an unprecedented development. They huddled in flocks and plowed the depths of the sea in search of gaping prey. Some of them at that time reached three meters in length. The remains of their shells, nicknamed by scientists "devil's fingers" are found in the sediments of the Jurassic period almost everywhere.

Bivalve mollusks belonging to oyster varieties were also numerous. In that era, they began to form a kind of oyster jars. Numerous sea urchins, which abundantly inhabited reef areas at that time, also received an impetus in development. Some of them have successfully survived to our time. But many, such as elongated hedgehogs irregular shapes, which had a jaw apparatus, became extinct.

Insects have also taken a big step forward. Their visual, flying and other devices improved more and more. More and more varieties appeared among barnacles, decapods, leaf-footed crustaceans, most freshwater sponges, caddisflies multiplied and evolved. Ground jurassic insects replenished with new varieties of dragonflies, beetles, cicadas, bedbugs, etc. Along with the emergence huge amount flowering plants began to appear and a large number of pollinating insects that feed on flower nectar.

But greatest development in the Jurassic era, it was the reptiles that reached - dinosaurs. By the middle of the Jurassic period, they completely took over all the land areas, displacing or destroying their reptilian predecessors, from which they originated, in pursuit of food.

AT sea ​​depths already at the beginning of the Jurassic period reigned supreme dolphin-like ichthyosaurs. Their long heads had strong, oblong jaws studded with rows of sharp teeth, and large, highly developed eyes were framed by bone-plate rings. By the middle of the period, they turned into real giants. The length of the skull of some ichthyosaurs reached 3 meters, and the body length exceeded 12 meters. The limbs of these aquatic reptiles evolved under the influence of underwater life and consisted of simple bone plates. Elbows, metatarsus, hands and fingers ceased to differ from each other, one huge flipper supported more than a hundred bone plates of various sizes. The shoulder girdle, as well as the pelvic girdle, became underdeveloped, but this was not necessary, since additionally grown powerful fins provided them with mobility in the aquatic environment.

Another reptile that seriously and permanently settled in the depths of the sea was plesiosaur. They, like ichthyosaurs, originated in the seas as early as the Triassic period, but in the Jurassic period they branched into two varieties. Some had a long neck and a small head (plesiosaurs), while others had an order of magnitude larger head and a much shorter neck, which made them look more like underdeveloped crocodiles. Both, unlike ichthyosaurs, still needed to rest on land, and therefore often crawled out onto it, becoming the prey of land giants there, such as, for example, a tyrannosaurus rex or herds of smaller predatory reptiles. Very nimble in the water, on land they were the clumsy fur seals of our time. Pliosaurs were much more agile in the water, but what plesiosaurs lacked in agility was made up for by their long necks, thanks to which they instantly grabbed prey, no matter what position their body was in.

In the Jurassic period, all kinds of fish multiplied unusually. water depths literally teemed with a motley variety of coral ray-finned, cartilaginous and ganoid. Sharks with stingrays were also diverse, which, due to their extraordinary agility, speed and agility, developed over hundreds of millions of years of evolution, still constituted Jurassic underwater reptile predators. Also during this period, many new varieties of turtles and toads appeared.

But the terrestrial variety of reptile dinosaurs was truly outstanding. (Fig. 2) were from 10 cm to 30 meters in height. Many of them were simple harmless herbivores, but often came across and ferocious predators.

Rice. 2 - Jurassic Dinosaurs

One of the largest herbivorous dinosaurs was brontosaurus(now Apatosaurus). His body weighed 30 tons, the length from head to tail reached 20 meters. And despite the fact that at the shoulders its height reached only 4.5 meters, with the help of a neck that reached a length of up to 5-6 meters, they perfectly ate tree foliage.

But the largest dinosaur of that era, as well as the absolute champion among all the animals of the Earth of all time, was a 50-ton herbivore. brachiosaurus. With a body length of 26 m, he had such a long neck that when it stretched up, his small head was 13 meters above the ground. To feed, this huge reptile needed to absorb up to 500 kg of green mass daily. It is noteworthy that with such a truly gigantic body size, his brain weighed no more than 450 grams.

It is appropriate to say a few words about predators, of which there were also many in the Jurassic period. the most gigantic and dangerous predator jurassic is considered 12-meter tyrannosaurus rex, but as scientists have proven, this predator was more opportunistic in its views on food. He rarely hunted, often preferring carrion. But they were truly dangerous. allosaurs. With a height of 4 meters and a length of 11 meters, these reptile predators hunted prey many times greater than them in terms of weight and other parameters. Often they, having strayed into a herd, attacked such herbivorous giants of that era, like Camarasaurus (47 tons) and the aforementioned Apatosaurus.

Came across more small predators, for example, such as 3-meter dilophosaurus, weighing only 400 kg, but straying into a flock, attacking even larger predators.

In view of the ever-increasing danger from predatory individuals, evolution has rewarded some herbivorous individuals with formidable elements of protection. For example, such a herbivorous dinosaur as Kentrosaurus was endowed with elements of protection in the form of huge sharp spikes on the tail and sharp plates along the ridge. The spikes were so large that strong blow a Kentrosaurus would go right through a predator like a Velociraptor or even a Dilophosaurus.

With all that animal world Jurassic has been carefully balanced. The herbivorous lizard population was controlled by predatory lizards, predators were kept in check by many smaller predators and aggressive herbivores like stegosaurs. Thus, the natural balance was maintained for many millions of years, and what caused the extinction of dinosaurs in the Cretaceous period is still not known.

By the middle of the Jurassic period, the airspace was filled with many flying dinosaurs, such as pterodactyls and other pterosaurs. They glide quite skillfully in the air, but in order to take to the skies, they need to climb imposing hills. These, for the most part, were not very mobile specimens of ancient mammals, but from the air they could very successfully track down and attack prey in a flocking manner. Smaller representatives of flying dinosaurs preferred to make do with carrion.

In the sediments of the Jurassic period, the remains of a fledged lizard Archeopteryx were found, which for a long time considered by scientists to be the ancestor of birds. But, as recently scientifically proven, this variety of lizards was a dead end. Birds evolved mainly from other varieties of reptiles. Archeopteryx had a long feathered tail, jaws studded with small teeth, and feathered wings had developed fingers, with which the animal grabbed branches. Archeopteryxes flew poorly, mainly gliding from branch to branch. Basically, they preferred to climb tree trunks, digging into their bark and branches with sharp curved claws. It is noteworthy that in our time, fingers on the wings remained only in the chicks of the hoatzin bird.

The first birds, in the form of small dinosaurs, jumped high either in their attempts to reach out for insects fluttering in the sky, or in order to escape from predators. In the process of evolution, they were increasingly overgrown with plumage, their jumps became longer and longer. In the process of jumping, future birds helped themselves more and more intensively, waving their forelimbs. Over time, their now wings, and not just forelimbs, acquired more and more powerful muscles, and the structure of their bones became hollow, as a result of which the overall weight of the birds became much lighter. And all this led to the fact that by the end of the Jurassic period, along with pterosaurs, a large number of all kinds of ancient birds plowed the airspace of the Jura.

In the Jurassic period, small mammals also actively multiplied. But still, they were not allowed to express themselves in breadth, because the ubiquitous power of dinosaurs was too overwhelming.

Since, in the process of climate change, the vast deserts of the Triassic began to be abundantly irrigated with precipitation, this created the prerequisites for the advancement of vegetation even deeper into the continents, and closer to the middle of the Jurassic, almost the entire surface of the continents was covered with lush vegetation.

All low-lying places are abundantly overgrown with ferns, cicadas and coniferous thickets. The coasts of the seas were occupied by araucaria, thuja and, again, cicadas. Also, vast land masses were occupied by ferns and horsetails. Despite the fact that by the beginning of the Jurassic period, the vegetation on the continents of the northern hemisphere was relatively uniform, by the middle of the Jurassic two main belts of plant masses, already established and strengthened, were formed - the northern and southern.

northern belt was notable for the fact that at that time it was formed mainly by ginkgo plants mixed with herbaceous ferns. With all that is half the whole vegetation northern latitudes jurassic consisted of Ginkgo varieties, today only one species of these plants has miraculously survived.

Southern belt were mainly cycads and tree ferns. Generally Jurassic period plants(Fig. 3) more than half still consisted of various ferns. Horsetails and club mosses of those times almost did not differ from the current ones. In those places where cordaite and ferns grew massively during the Jurassic, this moment growing tropical cycad jungle. Of the gymnosperms, cycads were the most common in the Jurassic. Today they can only be found in tropical and subtropical zones. It was them, reminiscent of modern palm trees with their crowns, that most herbivorous dinosaurs ate.

Rice. 3 - Plants of the Jurassic period

In the Jurassic period northern latitudes deciduous Ginkgoaceae began to appear for the first time. And in the second half of the period, the first spruce and cypress trees appeared. The coniferous forests of the Jura looked very much like modern ones.

Minerals of the Jurassic period

The most pronounced minerals related to the Jurassic period are European and North American chromite deposits, Caucasian and Japanese copper-pyrite deposits, Alpine deposits of manganese ores, tungsten ores of the Verkhoyansk-Chukotka region, Transbaikalia, Indonesia, North American Cordilleras. Also to this era can be attributed deposits of tin, molybdenum, gold and other rare metals scattered everywhere, formed in the late Cimmerian era and thrown to the surface due to granitoid mechanisms associated with the separation of the continents that took place at the end of the Jurassic period. Numerous and ubiquitous iron ore deposits. There are deposits of uranium ores on the Colorado Plateau.