Cretaceous - the Cretaceous period - the last period of the Mesozoic era, began 145.5 million years ago and ended 65.5 million years ago. It lasted about 80 million years.

In the Cretaceous period, angiosperms appeared - flowering plants. This entailed an increase in the diversity of insects that became pollinators of flowers. So the vegetation cover of the Earth in the Cretaceous period would no longer surprise modern man. What can not be said about the animal world of that time.

Among the land animals reigned a variety of dinosaurs. Dinosaurs are divided into two groups - lizards, among which were both predators and herbivorous forms, and ornithischians, exclusively herbivores. The most famous lizard dinosaurs are tyrannosaurs, tarbosaurus, brontosaurs. Among ornithischian lizards, ceratopsians, iguanodons, and stegosaurus are known. This was the heyday of giant lizards - many dinosaurs reached 5-8 meters in height and 20 meters in length.

Winged reptiles - pterodactyls occupied almost all niches of aerial predators, although real birds had already appeared. Thus, in parallel there were flying lizards - pterosaurs, gliding, and maybe flying lizards such as Archeopteryx, enanciornis birds and real fan-tailed birds.

The Cretaceous period, which is considered the era of dinosaurs, was also the time of the appearance of most contemporary bands mammals. During the Cretaceous, the first placental mammals, and groups of ungulates, insectivores, predators and primates have already stood out.

Modern lizards and snakes evolved, so snakes are a relatively young group. One of the groups of lizards went into the water - so there were mosasaurs, formidable predators of the end Cretaceous sometimes reaching 20 meters in length. There were no mammals in the seas yet, but a niche large predators occupied aquatic reptiles- ichthyosaurs, plesiosaurs, pliosaurs. Sharks were large and numerous, some of them also lived in fresh water.

The variety of marine invertebrates was very great. As in jurassic, ammonites and belemnites, brachiopods, bivalves and sea ​​urchins. Among bivalve mollusks, rudists, which appeared at the end of the Jura, played an important role in marine ecosystems - mollusks that look like single corals, in which one valve looked like a goblet, and the second covered it like a kind of lid.

By the end of the Cretaceous, a lot of heteromorphic forms appeared among ammonites. Heteromorphs arose earlier, in the Triassic, but the end of the Cretaceous became the time of their mass appearance. The shells of heteromorphs were not similar to the classical spiral-twisted shells of monomorphic ammonites. These could be spirals with a hook at the end, various balls, knots, unfolded spirals. Paleontologists have not yet come to a unified explanation of the causes of the emergence of such forms and their way of life.

Almost modern octopuses and squids already lived in the seas; paleontologists believe that they arose as early as the end of the Jurassic, although they were rarely preserved in the fossil record due to the lack of shells. Whether they contributed to the extinction of their relatives - ammonites and belemnites, or simply occupied the vacated niches after the global crisis - we do not yet know.

During the Cretaceous period, the split of the continents continued. Laurasia and Gondwana fell apart. South America and Africa moved away from each other, and Atlantic Ocean became wider and wider. Africa, India and Australia have also begun to diverge in different sides, and giant islands eventually formed south of the equator.

At the end of the Cretaceous period, the most famous and very large extinction of many groups of plants and animals occurred. Many gymnosperms, all dinosaurs, pterosaurs, aquatic reptiles died out. Ammonites disappeared, many brachiopods, almost all belemnites. In the surviving groups, 30-50% of the species became extinct.

The causes of the Cretaceous catastrophe are not fully understood. Now the asteroid theory has become the most popular theory - explaining the extinction of dinosaurs and other organisms by the fall of a giant asteroid and the “asteroid winter” that followed. Apparently, this is not entirely true. This version cannot explain why certain organisms survived when others died. In addition, many groups of animals clearly began to die out long before the end of the Cretaceous. The transition of the same ammonites to heteromorphic forms also clearly indicates some kind of instability. It may very well be that many species have already been undermined by some long-term processes and stood in the way of extinction, and the catastrophe - an asteroid, increased volcanism or climate change due to the movement of the continents - simply accelerated the process.

On July 14, a trip planned last summer to a new chalk location in the Yuryev-Polsky district took place Vladimir region. The prehistory of its discovery is as follows: a few years ago, during a strong flood in a stream near the village of Pavlovskoye, many brilliant fragments of mother-of-pearl shells were washed up, which in large numbers look like countless treasures, this naturally attracted the attention of local residents, from whom an employee of the Museum of Nature, Mr. Vladimir Dudenkov... >>>

Cretaceous period -- geological period, the last period of the Mesozoic era.

Started 145 million years ago and ended 65 million years ago. The Cretaceous period lasted about 80 million years.

In the Cretaceous period, the first angiosperms appeared - flowering plants. This entailed an increase in the diversity of insects that became pollinators of flowers. The evolution of the plant world gave impetus to the rapid development of the animal world, including dinosaurs. The diversity of dinosaur species in the Cretaceous period reached its peak.

Cretaceous tectonics

During the Cretaceous period, the movement of the continents continued. Laurasia and Gondwana fell apart. Africa, India and Australia also began to move apart, and giant islands eventually formed south of the equator. South America and Africa were moving away from each other, and the Atlantic Ocean was getting wider and wider. There were no obvious catastrophes in the Cretaceous period, so the process of evolution proceeded naturally. The earth acquired outlines very close to those known to us.

Cretaceous climate

The climate has changed since the Jurassic. Due to the changing position of the continents, the change of seasons became more and more noticeable. Snow began to fall near the poles, although there were no such ice caps as now on Earth. The climate varied on different continents. This caused differences in the development of flora and fauna in different parts of the world.

Cretaceous flora

The Cretaceous flora was rich and varied. In addition to the plant species transferred from the Jurassic period, a new, revolutionary branch of flowering plants appears

Gradually populating the land, new groups of plants began to form vast forests. There, at the service of land animals, there were a wide variety of leaves and other edible vegetation. Due to the emergence of flowering plants during the Cretaceous period, the amount of plant biomass increased.

The reverse process took place at sea. This was again facilitated by the development of flowering plants. Dense roots prevented soil erosion and therefore fewer minerals entered the sea. The amount of phytoplankton has decreased.

The duration of which is approximately determined at ~80 million years (started ~145 million years ago and ended ~65 million years ago).

Flora and fauna

The fauna of the Cretaceous period had a characteristic appearance for the Mesozoic era, but at the same time it differed sharply from the animal world of the Jurassic period. Among the invertebrates, new forms of belemnites and ammonites appeared in large numbers, and among the latter there are many representatives with an anomalous shell: stick-shaped, tower-shaped, etc. Some groups of lamellar-gills (rudists, inocerams, trigonia) and gastropods (nerineids) developed magnificently. Irregular sea urchins acquired significant development, large foraminifers (orbitolins, orbitoids) appeared. Among the vertebrates, the development of reptiles reached its climax, many of which acquired giant size. There was a heyday bony fish who occupied a dominant position. Of the birds, only toothy ones existed. Mammals still played a modest role and did not reach a large size. Primitive placental forms appeared among them. Reptiles still dominate among fossil vertebrates. Many appeared on land large dinosaurs. Of the aquatic lizards, plesiosaurs, snake-like mosasaurs were widespread, and to a lesser extent, ichthyosaurs, flying lizards, etc. Snakes appeared in the group of terrestrial reptiles. Cretaceous birds are represented by forms that still had teeth in their mouths, but had already lost signs resembling reptiles. The flowering of bony fish has come.

In the Early Cretaceous, the flora resembled the Jurassic: conifers, ginkgos, sagovids, and ferns continued to exist. At the same time, the first angiosperms (flowering) appeared, which rapidly evolved and spread on the Cretaceous land. By the beginning of the Late Cretaceous, angiosperms begin to dominate, while the gymnosperms recede into the background. In the Cretaceous period, angiosperms appeared - flowering plants. This led to an increase in the diversity of insects that became pollinators of flowers. Vegetation, preserving the Mesozoic appearance from the beginning of the period, from the Cenomanian age is characterized by the predominance of angiosperms of flowering plants, the first signs of which are found in the sediments of the Hauterivian or even Valanginian age. All classes of plants of the Cretaceous period continue to exist to this day, but the ratio of angiosperm families has changed significantly.

At the end of the Cretaceous, major changes occurred in the fauna: aquatic reptiles, dinosaurs, flying lizards, toothy birds, ammonites, almost all belemnites and a number of genera and families of invertebrates die out. At this time, the most famous and very large extinction of many groups of plants and animals occurred. Many gymnosperms died out, all dinosaurs, pterosaurs, aquatic reptiles. Ammonites disappeared, many brachiopods, almost all belemnites. In the surviving groups, 30-50% of the species became extinct. Whether the planetary catastrophe was the reason for this, and if so, what were its causes and scale, remains not fully understood.

Tectonics and magmatism

During the Cretaceous period, the Mesozoic tectonic stage of development ends, which manifested itself especially rapidly along the outskirts of the Pacific segment. earth's crust. The result of this was, first of all, the complete formation of the Mesozoic mountain-folded structures (mesozoids) at the site of the Verkhoyansk-Chukotka and Sikhote-Alin geosynclinal regions in the West Pacific geosynclinal belt, almost entirely in the Cordillera geosynclinal region of the East Pacific belt and within the Tibetan geosynclinal region on east of the Mediterranean geosynclinal belt.
The out-of-geosynclinal depressions complete their active tectonic development and platform granitoid magmatism ceases.
On the border of the Pacific geosynclinal belts and the platforms adjacent to them, a structural zone appears in the form of linear large splits, along which the intrusion and outpouring of felsic magma occurs. This volcanic belt was called the Chukchi-Katazia.
The orogenic stage of development of the mesozoids was accompanied by the initiation of large marginal troughs at the boundary with the platforms (Predverkhoyansk trough).
Mountain building processes were accompanied by intensive intrusion of granitoid intrusions.

Intensive tectonic activity in the Cretaceous is not limited to folding and magmatism. New major faults are being laid. They are descending vast territories in Gondwana. As a result, the Gondwana continent breaks up into separate large blocks - the South American, African, Indotan, Australian and Antarctic, and between them the depressions of the Indian and South Atlantic Oceans are completely formed. Similar processes are taking place on Angara, which is splitting into two parts: Eurasian and North American; between them is laid the depression of the northern part of the Atlantic Ocean. Obviously, the formation of the Arctic Ocean depression is associated with the same time.
In African and Hindustan

The Cretaceous period is the last epoch that ends the Mesozoic era. He replaced the Jurassic, according to the calculations of geologists, somewhere around 145 million years ago and lasted about eighty million years, after which the Tertiary period began already another, - the "epoch of new life." This rather long stage of the development of the Earth got its name in connection with the fact that it left us powerful deposits of chalk, marl and sand as a legacy. Although during these eighty million years the Earth did not experience any catastrophes on a planetary scale and, consequently, extinction a large number species of plants and animals, yet the movement of tectonic plates, changes in the level of the world's oceans and climate change have made their own amendments to the process of evolution of living beings.

The Cretaceous period is usually divided into subdivisions: lower and upper Cretaceous. In order to understand how life developed in the seas, on land and in the air space of that time, it is necessary to briefly characterize the tectonic mountain-building processes that took place, starting from the Jurassic stage. During the Lower Cretaceous, Gondwana and Laurasia continued to move away from each other. Exactly the same process took place with Africa and South America. Thus, more and more acquired the outlines familiar to us now. But in the east, Gondwana joined with Laurasia. Australia was where it is today, but only a third of the current territory rose above the water.

The Upper Cretaceous is characterized by the fact that the level of the world's oceans began to rise, and huge areas of Eastern Europe, Western Siberia, all of Arabia and almost all of modern Canada were under water. However, by the end of the Cretaceous period, the Earth began to resemble a modern globe with its outlines.

During the Cretaceous period, the climate also changed. He, of course, was much warmer than modern. The spaces of today's Europe were covered with real tropical jungles. However, in high latitudes, the seasons were already changing, and snow fell in winter. This gave impetus to the fact that, along with spore and gymnosperms, closed-sperm plants appeared. Trees such as beech, birch, ash and walnut, which appeared in the Cretaceous era, have survived to this day unchanged. The earth found the first flowering plants - first magnolias, then roses. The flowering plants had the advantage that their pollen was carried not only by the wind, but also by insects. Fruit plants, hiding the seed in the fruit, spread with the help of animals that ate the fruits. Thus, fruit and flowering plants filled the entire planet.

Changes in flora during the Cretaceous period led to the emergence of new species of fauna. The first butterflies began to flutter in the air and bees began to fly, feeding on the nectar of flowers. The dominance of foraminifera sets in in the sea, the dead and crumbled shells of which gave the name to all this geological time. Along with them, other ammonite molluscs appear. The fish kingdom is dominated by sharks and Animals mesozoic era- first of all, dinosaurs and the first mammals - safely "migrated" from the Jurassic to the Cretaceous. But during the Cretaceous, several dead-end branches of bird-like lizards die out, for example, Archeopteryx. But birds appear - the ancestors of modern geese, plovers, ducks and loons.

(Jurassic period in particular), judging by the famous film, is also known as the era of dinosaurs. In general, the supremacy of the ancient lizards is preserved in the Cretaceous. But during the last period, the stegosaurus disappears from the face of the earth, and the tyrannosaurus rex occupies its niche. Rich vegetable world contributed to the emergence of new species of triceratops, iguanodons, ankylosaurs and others. We can say that in the Cretaceous era, the species diversity of dinosaurs reached its peak. And at this time, hiding from the giants in their minks, the future rulers of the Earth lived - mammals. These rat-like animals rarely reached one meter in length, most species were small oviparous, armored or marsupial animals, up to 500 g in weight. But they were the future.

Department tier Age,
million years ago Paleogene Paleocene Danish less Chalk Upper Maastrichtian 72,1-66,0 Campanian 83,6-72,1 Santonese 86,3-83,6 Cognac 89,8-86,3 Turonian 93,9-89,8 Cenomanian 100,5-93,9 Lower Albian 113,0-100,5 Aptian 125,0-113,0 Barremian 129,4-125,0 Goterivsky 132,9-129,4 Valanginian 139,8-132,9 Berriasian 145,0-139,8 Yura Upper titonian more The division is given in accordance with IUGS
as of December 2016

The Cretaceous period is subdivided into 2 divisions, 2 overstages and 12 stages.

Geology

During the Cretaceous period, the split of the continents continued. Laurasia and Gondwana fell apart. South America and Africa were moving away from each other, and the Atlantic Ocean was getting wider and wider. Africa, India and Australia also began to diverge in different directions, and giant islands eventually formed south of the equator.

Climate

The downward trend in temperature at the end of the Jurassic continued at the beginning of the Cretaceous; the cool climate persisted until the end of the Early Cretaceous (about 100 Ma). In the late Albian, a warming occurred, which intensified in the interval from the late Cenomanian to the early Campanian (95-85 million years ago). This was followed by a cold snap, which especially intensified in last century Cretaceous period - Maastrichtian.

Approximately 120 million years ago, the Aptian anoxic event (Selli Event or OAE 1a) occurred. About 116 million years ago average temperature on the planet fell by 5 ° C, global cooling lasted more than a million years. Then warming began again - volcanoes indian ocean began pumping carbon into the atmosphere. Global warming led to the depletion of oxygen in ocean waters, which 94 million years ago led to an “anoxide catastrophe” and the extinction of ichthyosaurs that did not adapt to climate change.

Approximately 91.5 ± 8.6 million years ago, the Cenomanian-Turonian boundary biotic event occurred, which led to the complete extinction of ichthyosaurs and pliosaurs, families of megalosaurids and stegosaurids, and greatly reduced species diversity other groups of animals.

70 million years ago, the Earth was cooling. Ice caps have formed at the poles. Winters were getting harsher. The temperature dropped in some places below -10 degrees, and in Alaska - up to -45. For dinosaurs of the Cretaceous period, this difference was sharp and very noticeable, more cold-loving species became more widespread. Such fluctuations in temperature were caused by the split of Pangea, and then Gondwana and Laurasia. The sea level rose and fell. The jet streams in the atmosphere have changed, as a result of which the currents in the ocean have also changed.

Vegetation

In the Cretaceous period, angiosperms appeared - flowering plants. This entailed an increase in the diversity of insects that became pollinators of the flowers. As temperatures increased during the late Cretaceous period, plants with more luscious foliage developed.

Animal world

Among terrestrial animals, various large reptiles reigned. This was the heyday of giant lizards - many dinosaurs reached 5-8 meters in height and 20 meters in length. Winged reptiles - pterodactyls - occupied almost all niches of aerial predators, although real birds have already appeared. Thus, in parallel there were flying lizards, lizard-tailed birds of the Archeopteryx type and real fan-tailed birds.

At the end of the period, snakes spread.

There were no mammals in the seas, and the niche of large predators was occupied by reptiles with a comparable level of metabolism - ichthyosaurs, plesiosaurs, mosasaurs, sometimes reaching 20 meters in length.

The diversity of marine invertebrates was very great. As in the Jurassic, ammonites and belemnites, brachiopods, bivalves, and sea urchins were very common. Among bivalve mollusks, rudists, which appeared at the end of the Jura, played a large role in marine ecosystems - mollusks that looked like solitary corals, in which one valve looked like a goblet, and the second covered it like a kind of lid.

By the end of the Cretaceous, a lot of heteromorphs appeared among the ammonites. Heteromorphs arose earlier, in the Triassic, but the end of the Cretaceous became the time of their mass appearance. The shells of heteromorphs were not similar to the classical spiral-twisted shells of monomorphic ammonites. These could be spirals with a hook at the end, various balls, knots, unfolded spirals. Paleontologists have not yet come to a unified explanation of the causes of the emergence of such forms and their way of life.

In the seas, orthoceras were still found - relics of the bygone Paleozoic era. Small shells of these straight-shelled cephalopods are found in the Caucasus.

Cretaceous disaster

At the end of the Cretaceous period, the most famous and very large extinction of many groups of plants and animals occurred. Many gymnosperms, aquatic reptiles, pterosaurs, all dinosaurs died out (but birds survived). Ammonites disappeared, many brachiopods, almost all belemnites. In the surviving groups, 30-50% of the species became extinct. The causes of the Cretaceous catastrophe are not fully understood.

Notes

1. International Chronostratigraphic Chart(English) . International Commission on Stratigraphy (February 2017). Archived from the original on May 15, 2017.
2. N. M. Chumakov. Climate in the epochs of major biospheric changes. M: Nauka, 2004. - 299 p. Ch. 5. Climatic zonality and climate of the Cretaceous.
3. Li, Yong-Xiang; Bralower, Timothy J.; Montañez, Isabel P.; Osleger, David A.; Arthur, Michael A.; Bice, David M.; Herbert, Timothy D.; Erba, Elisabetta; Premoli Silva, Isabella. Toward an orbital chronology for the early Aptian Oceanic Anoxic Event (OAE1a, ~ 120 Ma) (English) // Earth and Planetary Science Letters (English) Russian: journal. - 2008. - July 15 (vol. 271, no. 1-4). - P. 88-100. - DOI:10.1016/j.epsl.2008.03.055 .
4. Mid-Cretaceous 'Global Cooling' Studied , June 18th, 2013
5. The extinction of ichthyosaurs was explained by the slowness of their evolution, March 11, 2016
6. Head J.J. Fossil calibration dates for molecular phylogenetic analysis of snakes 1: Serpentes, Alethinophidia, Boidae, Pythonidae (English) // Palaeontologia Electronica (English) Russian: journal. - 2015.
7. Caldwell M. W., Nydam R. L., Palci A., Apesteguía S.