What are mammals and where do they live. List and description of the main orders of the class Mammals. Significance for a person: positive

Mammals, considered the most developed animals (including humans as a species), are so named because they have mammary glands that allow females to feed their cubs with their own milk.

Mammals have larger and more developed brains than other animals. Some of them are endowed with amazing abilities and a kind of intelligence, such as primates (chimpanzees) and cetaceans (dolphin). In most mammals, the body is covered with hair. With the exception of man, who walks on two legs, mammals usually move with the help of four limbs, which in different zoological species have different shape(hand, hoof, webbed foot, fin), but always with fingers (from one to five). And finally, almost everyone has teeth.

The class of currently existing mammals includes about 4200 species, extremely diverse in appearance and your behavior. Some animals are very tiny, others are real giants. Some are thriving and ubiquitous, while others are endangered. And although most of them, so to speak, are terrestrial creatures, there are also amphibians (beavers, otters, platypuses), and inhabitants of the sea (whales, dolphins), and some can even fly through the air, like birds (bats).

Mammals are divided into three large groups depending on how they produce offspring: cloacal (first animals), marsupials and placental. It is to the latter that man belongs. The most amazing animals are cloacae, or monotremes: they reproduce by laying large eggs, which they then incubate (oviparous reproduction). Egg-laying animals are very few in number. They are represented by only two families living in Australia, Tasmania and New Guinea: echidna and platypus.

In marsupials, the young are born underdeveloped and complete their development in the mother's brood abdominal pouch. They are divided into two groups: one lives in Australia 1 kangaroo), and the other - in South America(opossum). As for placental mammals, whose cubs are born fully developed, they are the most. There are several orders: carnivores, insectivores, rodents, ungulates, edentulous, cetaceans, primates.

interesting similarity

Mammals living on different continents are sometimes strikingly similar. Large South American rodents (capybara, agouti, mara, paca) resemble the pygmy hippopotamus or water deer - the inhabitants of Africa. The American feline, the jaguarundi, is very similar to the giant civet cat from Madagascar. It's about about the so-called phenomenon of convergence: animals belonging to different groups, but living in similar conditions, acquire a certain similarity.

Pangolin - dl. from 80 cm to 1.5 m

Flying monkey - dl. 40 cm

Seal - dl. from 1.5 to 4 m

Platypus - dl. 40 cm, tail - 12 cm

Dolphin - dl. from 2 to 4 m

Gorilla - standing height 1.8 m

Elephant - dl. from 2 to 4 m

Lemur - dl. 50cm tail 50cm

Chimpanzee - standing height 1.4 m

Kangaroo - dl. up to 1.5 m, tail up to 1 m

Dwarf bat - dl. 4.5 cm, tail 3 cm, r.k. 20 cm

Bison - dl. 2.6 m, tail 70 cm, c. 1.2 m

Wild boar - dl. from 1.2 to 1.6 m, c. 60 cm to 1 m

Fox - length 70 cm, tail 45 cm

Hedgehog - length. 25 cm

Giraffe - common c. - 5.5 m, tail 80 cm

Camel - common c. 2 m

Leo - dl. 1.7 m, tail 80 cm

Hippo - dl. 4m, tail 40 cm, c. 1.5 m

Number of species: more than 5 thousand

Habitat: inhabit all seas, oceans and continents, with the exception of Antarctica.

Building features:

The body is covered with skin and is divided into head, neck, trunk, tail and four limbs with five fingers. The skin consists of the epidermis and dermis, it includes glands (sweat, sebaceous). Hair forms a hairline, there are guard hairs (determine the direction of laying fur), downy (participate in thermoregulation), vibrissae (tactile organs). The hair coat may be lost (cetaceans).

Skeleton. The spine is subdivided into the cervical (always 7 vertebrae), thoracic (ribs form the chest), lumbar, sacral (all vertebrae fuse to form the sacrum) and caudal.

The skull is massive, sutures remain between the fused bones. The respiratory tract is separated from the oral cavity by a hard (bony) palate, which allows you to simultaneously breathe and chew food.

Digestive system . The mouth is surrounded by soft lips, necessary when sucking mother's milk. The ducts of four pairs of salivary glands flow into the oral cavity. The teeth are differentiated - they differ in shape and structure. Allocate incisors, canines, premolars and molars involved in food processing. This is followed by the pharynx, esophagus, stomach. In the anterior small intestine duodenum, flow into the ducts of the liver and pancreas. On the border of the small and large intestines is the caecum, which can reach a significant size in herbivores. It develops bacteria that digest fiber. The large intestine ends at the anus.

The internal structure of the dog

Respiratory system represented by paired lungs and airways. The lungs have an alveolar structure - they consist of alveoli - thin-walled bubbles capable of stretching. Due to this, the lungs have a large surface for gas exchange. Inhalation is carried out actively, the intercostal muscles and the diaphragm, a specialized muscular septum, take part in its implementation. Air through the nasal openings, nasal cavity, larynx, trachea and through the two main bronchi enters the lungs. Exhalation occurs passively, the intercostal muscles and the diaphragm relax.

Circulatory system . The heart is four-chambered, consists of two atria and two ventricles, two circles of blood circulation. The heart is located in the pericardial sac called the pericardium. The large circle of blood circulation begins in the left ventricle, the largest artery, the aorta, departs from it. The aorta splits into a series large arteries carrying oxygenated blood to the internal organs. The blood is then collected in the vena cava and returned to the right atrium. The pulmonary circulation begins in the right ventricle, when the pulmonary artery departs from it, carrying blood with a high concentration of carbon dioxide to the lungs. In the lungs, gas exchange occurs, the blood gives off carbon dioxide and is saturated with oxygen, and returns through the pulmonary vein to the left atrium.

Red blood cells (erythrocytes) are different from the erythrocytes of other vertebrates - they lose the nucleus and become biconcave.

excretory system. Paired pelvic kidneys, ureters, bladder, urethra, which in placental mammals opens outwards with its own opening.

Nervous system mammals reaches exceptional development and complexity. Consists of central (brain and spinal cord) and peripheral (nerves) parts. Compared with other groups of animals, the forebrain is the most developed - the large hemispheres, which are covered with a bark. In highly organized mammals, the surface of the cortex is folded, forms furrows and convolutions, which ensures higher nervous activity, complex behavior.

sense organs. The organ of smell is the nose. Olfactory receptors are located in the back of the nasal cavity. The outer ear (pinna and external auditory canal) first appears. In the middle ear there are 3 auditory ossicles - the hammer, anvil and stirrup, which amplify sound vibrations. Eyelids with eyelashes appear to protect the eyes. The organs of touch in the form of numerous nerve endings are located in the internal organs and skin, allow you to feel pain, heat, cold, touch and pressure. Taste organs - taste buds - are located on the tongue.

reproductive system. All representatives are dioecious animals. In males, the paired testes are usually located in the scrotum, the vas deferens open into the urethra. In females in abdominal cavity paired ovaries lie, which are connected by oviducts to the uterus - a specialized muscular organ for bearing offspring.

Fertilization is internal and occurs in upper parts oviduct. The fertilized egg descends into the uterus, attaches to its wall and develops into an embryo. In placental animals, the placenta is formed, through which the exchange of substances between the mother and fetus takes place.

Cubs feed on milk, which is produced in the mammary glands of females.

Taxonomy of Mammals

There are 3 subclasses of mammals:

1. Oviparous (echidna, prochidna, platypus) - live in Australia and New Guinea. The female lays eggs, and feeds the hatched cubs with milk, which is secreted on a special area of ​​​​the skin of her abdomen - the “milky field”. Instead of an anus - a cloaca.
2. Marsupials (kangaroo, koala, wombat, marsupial mice) - have a very short period pregnancy. There is no placenta. A newborn underdeveloped cub is born in a special bag on the stomach.
3. Placental or Higher Mammals are the most numerous subclass. It has 17 orders of animals.

Some squads:

1. bats (bats, fruit bats, flying foxes) are capable of flight. The forelegs are modified into wings. The sternum is keeled.
2. insectivores (hedgehogs, shrews, moles) - small animals, hemispheres almost without convolutions. The teeth are the same.
3. rodents (squirrels, beavers, hamsters, rats) - incisors are highly developed, grow throughout their lives.
4. lagomorphs (hares, rabbits, pikas) - two pairs of upper incisors, one located behind the other.
5. predatory (bears, wolves, lynxes) - fangs are developed. Mostly carnivores.
6. artiodactyls (moose, deer, giraffes, antelopes) - four fingers on the limbs, the second and third are developed. The fingers are covered with horny hooves. There are no keys. Complicated stomach, usually from several departments.
7. equids (horses, donkeys, tapirs, rhinos) - one finger is well developed, usually with a hoof. The stomach is simple.
8. proboscis (elephants) - nose and upper lip grow into a trunk. Paired upper incisors - tusks.
9. primates (lemurs, monkeys, humans) - grasping limbs. The brain is highly developed.

New terms: warm-bloodedness, four-chambered heart, mammary glands, lips, whiskers, alveoli, diaphragm, convolutions of the cerebral cortex, external ear, auditory ossicles (hammer, anvil and stirrup), placenta.

Questions to reinforce:

• Why are mammals considered the most highly organized animals among chordates?
• What are the features of the structure of the brain in mammals?
• Why has no transitional form between birds and mammals been found in paleontological excavations?
• What is the difference between marsupials and placental mammals?
• Which sense organs are most developed in various groups mammals?
• What role do mammals play in human life?

Literature:

1. Bilich G.L., Kryzhanovsky V.A. Biology. Full course. In 3 volumes - M .: LLC Publishing House "Onyx 21st Century", 2002
2. Biology: A Handbook for Applicants to Universities. Volume 1. - M .: New Wave Publishing LLC: ONIKS Publishing House CJSC, 2000.
3. Kamensky, A. A. Biology. Reference manual / A. A. Kamensky, A. S. Maklakova, N. Yu. Sarycheva // Full course of preparation for exams, tests, tests. - M.: CJSC "ROSMEN-PRESS", 2005. - 399s.
4. Konstantinov V.M., Babenko V.G., Kuchmenko V.S. Biology: Animals: A textbook for students of the 7th grade of a comprehensive school / Ed. V.M. Konstantinova, I.N. Ponomareva. – M.: Ventana-Graf, 2001.
5. Konstantinov, V. M. Biology: animals. Proc. for 7 cells. general education schools /V. M. Konstantinov, V. G. Babenko, V. S. Kuchmenko. - M.: Ventana-Graf, 2001. - 304 p.
6. Latyushin, V. V. Biology. Animals: textbook. for 7 cells. general education institutions / V. V. Laktyushin, V. A. Shapkin. - 5th ed., stereotype. - M.: Bustard, 2004. - 304 p.
7. Pimenov A.V., Goncharov O.V. Biology manual for applicants to universities: Electronic textbook. Scientific editor Gorokhovskaya E.A.
8. Pimenov A.V., Pimenova I.N. Zoology of invertebrates. Theory. Tasks. Answers.: Saratov, JSC publishing house "Lyceum", 2005.
9. Taylor D. Biology / D. Taylor, N. Green, W. Stout. - M.: Mir, 2004. - T.1. - 454s.
10. Chebyshev N.V., Kuznetsov S.V., Zaichikova S.G. Biology: a guide for applicants to universities. T.2. - M .: New Wave Publishing LLC, 1998.
11. www.collegemicrob.narod.ru
12. www.deta-elis.prom.ua

In mammals, the spine is divided into five sections: cervical, thoracic, lumbar, sacral, and caudal. Only cetaceans do not have a sacrum. The cervical region almost always consists of seven vertebrae. Thoracic - from 10-24, lumbar from 2-9, sacral from 1-9 vertebrae. Only in the caudal region, their number varies greatly: from 4 (in some monkeys and humans) to 46.

Real ribs articulate only with the thoracic vertebrae (rudimentary may be on other vertebrae). In front, they are connected by the sternum, forming the chest. The shoulder girdle consists of two shoulder blades and two collarbones. Some mammals do not have clavicles (ungulates), in others they are poorly developed or replaced by ligaments (rodents, some carnivores).

The pelvis consists of 3 pairs of bones: iliac, pubic and ischial, which are tightly fused together. Cetaceans do not have a true pelvis.

The forelimbs serve as mammals for movement on the ground, swimming, flight, grasping. The humerus is greatly shortened. The ulna is less developed than the radius and serves to articulate the hand with the shoulder. The hand of the forelimb consists of the wrist, metacarpus and fingers. The wrist consists of 7 bones arranged in two rows. The number of metacarpus bones corresponds to the number of fingers (no more than five). The thumb consists of two joints, the rest - of three. In cetaceans, the number of joints is increased.

In the hind limbs, the femur in most mammals is shorter than the tibia.

The respiratory system of mammals consists of the larynx and lungs. The lungs are distinguished by a large branching of the bronchi. The thinnest of them are the bronchioles. At the ends of the bronchioles are thin-walled vesicles (alveoli), densely braided with capillaries. The diaphragm is a characteristic anatomical feature of mammals. Plays an important role in the process of respiration.

The kidneys in mammals are bean-shaped and located in the lumbar region, on the sides of the spine. In the kidneys, as a result of blood filtration, urine is formed, then it flows down the ureters into the bladder. Urine from it urethra comes out.

In mammals, the forebrain and cerebellum are especially developed. The cerebral cortex is formed by several layers of bodies nerve cells and covers the entire forebrain. It forms folds and folds with deep furrows in most mammalian species. The more folds and convolutions, the more complex and diverse the behavior of the animal. Also, mammals have a well-developed peripheral nervous system, which provides them with the highest speed of reflexes. The sense organs include: organs of vision, organs of hearing, organs of smell. The organs of vision are great importance in the life of mammals. Unlike birds, each eye of which sees objects separately, mammals have binocular vision. The auditory organs contain the external auditory meatus and the auricle. The olfactory organs are located in the anterior and posterior sections of the nasal cavity.

The mammalian digestive system is gastrointestinal tract- a tube connecting the mouth to the anus. The digestive system includes: oral cavity, salivary glands, pharynx, esophagus, stomach, intestines, anus.

Most mammals have teeth (except monotremes, some cetaceans, pangolins and anteaters). They are found in the cells of the jaw bones. There are four types of teeth: incisors, canines, false-rooted and true molars.

After entering the oral cavity, the food is chewed by the teeth. Then the food is moistened with saliva, which flows through the ducts from the salivary glands. This makes it easier to swallow and move down the esophagus. Under the influence of saliva, complex carbohydrates (starch, sugar) contained in food are converted into less complex ones. The salivary glands are highly developed in herbivores. A cow, for example, secretes 60 liters of saliva per day. In most animals, saliva has pronounced antiseptic properties.

The esophagus ensures that the food bolus enters the stomach.

Most mammals have a single chamber stomach. In its walls are glands that secrete digestive juice. But herbivorous mammals, such as deer, cow, goat, sheep, etc., have a multi-chambered stomach. The intestine is divided into thin and large. The small intestine includes the duodenum, jejunum, and ileum. To the thick - the cecum, colon and rectum.

In the small intestine, food is digested under the influence of digestive juices. They are secreted by the glands of the intestinal walls, as well as by the liver and pancreas, which open into the initial section of the small intestine - the duodenum. Nutrients in the small intestine are absorbed into the blood, and the remains of undigested food enter the large intestine.

At the junction of the small and large intestines, there is an ileocecal valve that prevents the forming feces from being thrown back into small intestine. In the caecum, under the influence of bacteria, there is a change in indigestible food substances. Also, in most mammals, in the walls of the caecum there is a large number of lymphatic tissue, making it an important organ immune system. In many animals (for example, rabbits, beavers), the caecum has big sizes. In some animals, it happens with an appendix. In the colon, the feces are dehydrated, accumulate in the rectum, and then are expelled out through the anus.

The ancestors of ancient mammals were animal-toothed reptiles. They are so named because they had a structure of teeth similar to mammals. In the course of evolution, a group of small animals separated from them, outwardly resembling egg-laying ones. In the process of natural selection, these animals developed a more developed brain, and, consequently, they were characterized by more complex behavior. At the end of the Mesozoic, after the extinction of the dinosaurs, ancient mammals mastered various places habitats in terrestrial ecosystems.

Representatives of the class Mammals, or Beasts, are higher vertebrates, warm-blooded animals, whose body is covered with wool. Animals give birth to cubs and feed them with milk. They have a large brain with well-developed forebrain hemispheres. They are characterized by care for offspring and the most complex behavior. In the process of evolution, mammals have reached a huge diversity in connection with the formation of adaptations to different living conditions. About 4,000 are known. modern species.

When determining mammals, one should pay attention to: the color of the fur, the shape of the body and head, the length of the body and tail.

• Animals hunting at night usually have large eyes.
• Some animals have large ears to hear better.
• Wool allows the mammal to keep warm; in addition, coloring helps to hide from the eyes of enemies.
• The tail helps the animal to maintain balance. In different animal species, tails vary in length and thickness.
• Most animals have a great sense of smell.
• The shape of the teeth depends on the food to which the animal is accustomed.
• The mustache helps the animal find its way, especially in a dark note.
• The mammary glands produce milk for offspring.
• Powerful aromatic glands under the tail allow the beast to mark the territory.
• The number of fingers on the paws is different for different species, so the animal is easy to identify by the trail.

The body of mammals consists of a head, neck, trunk, tail and two pairs of limbs. On the head, the facial and cranial regions are distinguished. In front is a mouth surrounded by soft lips. The eyes are protected by movable eyelids. Only mammals have an outer ear - the auricle.

The body of mammals is covered with hair, which reliably protects against sudden changes in temperature. Each hair grows from a hair follicle embedded in the skin. Hair, claws, nails, horns, hooves come from the same skin buds as reptile scales. The skin of mammals is rich in glands. The secretions of the sebaceous glands, located at the base of the hair, lubricate the skin and hair, making them supple and waterproof. The sweat glands are involved in cooling the body and excreting toxic substances. The mammary glands secrete milk.

The limbs of mammals are located not on the sides, as in amphibians and reptiles, but under the body. Therefore, the body is raised above the ground. This makes it easier to move on land.

Musculoskeletal system

The skeleton of mammals, like all terrestrial vertebrates, consists of five sections, but has a number of characteristic features. The skull of the animals is large.

The teeth are differentiated into incisors, canines and molars, they are placed in recesses - alveoli. The cervical spine consists of seven vertebrae. Internal organs protects the chest. sacral department fuses with the bones of the pelvis. The number of vertebrae in the caudal region depends on the length of the tail. The skeleton and the muscles attached to its bones make up a powerful musculoskeletal system that allows the animal to make many complex movements and move actively.

Respiratory system

In mammals, a diaphragm appears - a muscular septum that separates the chest cavity from the abdominal cavity. Due to it, animals can further reduce or increase the volume chest.

When muscles work intensively, the body requires a large amount of oxygen. In this regard, mammals have well-developed lungs.

Circulatory system

The circulatory system of mammals consists of two circles of blood circulation and a four-chambered heart. The movement of arterial and venous blood through the vessels ensures a rapid metabolism, due to which a constant body temperature is maintained.

Digestive system

Digestive system begins oral cavity. Here food is crushed, pounded with the help of teeth and moistened with saliva, secreted by me. salivary glands. In animals that feed on coarse plant foods, the stomach consists of several sections, the intestines are long. Various protozoa that decompose plant fiber live in the stomach and intestines.

In predators, the structure of the stomach is simpler and the intestines are shorter. All mammals have a well-developed liver and pancreas.

excretory system

The excretory organs of mammals are two kidneys. The urine formed in them through the ureters enters the urinary bladder, and from there it is periodically excreted.

Litter

Mammals leave litter in any weather. Litter of predators usually has an oblong shape and contains undigested remains of animals; litter of herbivores is most often rounded, with an admixture of vegetable fibers.

Nervous system

The nervous system, especially the brain, has received a high level of development in mammals. In the forebrain, due to the growth and thickening of the cortex, the large hemispheres developed. In predatory mammals and monkeys, the cortex forms convolutions that increase its area. In this regard, animals have a complex behavior, there is a memory, elements of rational activity. They are able to report their condition, intentions, express emotions. The degree of development of the sense organs depends on the lifestyle and habitat of a particular species.

The cubs of most animals develop in the mother's body and are born fully formed. The mother feeds them with milk. Mothers, and sometimes fathers, look after the growing generation and protect it until the cubs can fend for themselves. Cats, foxes and other predators teach their offspring to hunt. In small mammals, for example, in mice, there are several broods per year; offspring stay with their mother for only a few days, after which they begin an independent life.

breastfeeding

Feeding cubs with milk is a very important feature of mammals. Milk has a high nutritional value and contains all the necessary substances for the growth and development of the cub. The color of milk depends on the amount of fat. Fat is part of the milk in the form of microscopic droplets and therefore is easily digested and absorbed in the baby's body.

Ecological groups of mammals

Adaptation to the environment

Depending on the characteristics of the processes of reproduction and development of mammals, they are divided into two subclasses: First beasts and Beasts.

First beasts

Representatives of the first animals lay eggs, which then incubate ( platypus) or worn in a bag on the belly (echidna). Hatching cubs lick the milk that is secreted on the mother's belly.

Beasts

Animals are divided into infraclasses Inferior, or marsupials, and Higher, or Placental.material from the site

marsupials

Marsupials, distributed mainly in Australia, give birth to small and helpless cubs. They are worn by the female in a bag for several months, attached to the nipple of the mammary gland.

Placental

Placental have for the development of a fertilized egg special body- uterus. The fetus in it is attached to the wall by the placenta and receives nutrients and oxygen from the mother through the umbilical cord.

Among the placental, a special detachment is distinguished Primates. It includes the most developed representatives of the animal world, most of which are monkeys. Humans are also included in this category.

Role in nature

Representatives of mammals differ from each other in their way of life, the type of food they consume, and therefore perform various functions in ecosystems. Herbivorous mammals are the primary consumers organic matter. Predatory beasts contribute to the regulation of the number of herbivorous animals. Many rodents and insectivorous mammals are involved in soil formation. The passages they create in the soil contribute to its enrichment with moisture, air, organic and inorganic substances.

Role in human life

Man began to domesticate mammals and birds about 15 thousand years ago. Probably the first domestic animal was a dog, then a goat, a sheep, and cattle were domesticated. The domestication of animals led to settled life, people began to engage in animal husbandry and agriculture.

Pictures (photos, drawings)

• 4.91. External structure mammal

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  4.92. mammalian skeleton

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  4.93. The circulatory system of a mammal

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  4.94. Digestive, respiratory and excretory system mammal

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  4.95. The mammalian brain

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  4.96. Expression of emotions in a mammal

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  4.97. Representatives of mammals: a) first beasts (echidna); b) lower animals - marsupials (kangaroos)

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  4.98. Supposed appearance ancient mammal

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Class characteristic.mammals- warm-blooded (homeothermic) amniotes; the body is covered with hair; viviparous; babies are fed with milk. Have a large brain; its anterior section (hemisphere) has a "new cortex" - neopallium - from the gray medulla; it provides high level nervous activity and complex adaptive behavior.

The organs of smell, sight, and hearing are well developed. There is an external ear; There are three bones in the middle ear: the hammer, anvil, and stirrup. Bats, dolphins, and some other mammals use ultrasonic echolocation to navigate. Skin with numerous sebaceous and sweat glands, some of which have been converted into lactiferous and odorous glands. The skull is synapsid, articulated with the spine by two condyles; heterodont teeth sit in the alveoli; the lower jaw is only dentary. They breathe with lungs having an alveolar structure. The body cavity is divided by the diaphragm into the thoracic and abdominal departments. The intestinal tube becomes more complicated, sometimes a multi-chambered stomach is formed, the caecum increases. Herbivorous animals develop symbiotic digestion.

African elephant(Loxodonta africana)

The heart is four-chambered, two circles of blood circulation, only the left aortic arch is preserved; erythrocytes are non-nuclear. The kidneys are metanephric. Widespread throughout; inhabit all environments, including soil (soil), water bodies and surface layers of the atmosphere. Very influential members of almost all biocenoses. They are important for humans: farm animals, commercial species, keepers of human and domestic animal diseases, pests of agriculture and forestry, etc.

Origin and evolution of mammals. Mammals descended from theromorphic (animal-like) reptiles that appeared back in the Upper Carboniferous, which had a number of primitive features: amphicoelous vertebrae, movable cervical and lumbar ribs, and small brain sizes. At the same time, their teeth sat in the alveoli and began to differentiate into incisors, canines, and molars. Many animal-like reptiles had a secondary bony palate, and the occipital condyle was two or three-parted; they formed a double articulation of the lower jaw with the skull: through the articular and square and through the dentary and squamous bones. In this regard, the dentary in the lower jaw increased, while the square and articular, on the contrary, decreased; while the latter did not grow to the lower jaw. Theromorphic reptiles differed little from their ancestors - the cotylosaurs that lived in humid biotopes - and retained many features of the organization of amphibians. This may explain the presence of skin with numerous glands and other features in mammals.

For a long time during the Permian and most of the Triassic periods, theromorphic reptiles, having formed a number of groups of herbivorous, predatory and omnivorous species, flourished in land biocenoses and died out only in jurassic, unable to withstand competition with the progressive archosaurs that had appeared by that time (see above the origin of reptiles). Relatively small theromorphs, apparently, were pushed back by competitors and enemies to less favorable biotopes (swamps, thickets, etc.). Life in such conditions required the development of sensory organs and the complication of behavior, the strengthening of communication between individuals. In these groups of medium-sized and less specialized animal-toothed (theriodont) reptiles, a new line of development began. the upper olfactory shell, which provided heating and humidification of the inhaled air; the appearance of three-cusp teeth; an increase in the cerebral hemispheres of the forebrain, the formation of soft lips, which opened up the possibility of sucking milk by the cubs; the emergence of an additional articulation of the lower jaw with the skull, accompanied by a reduction of the quadrate and articular bones, etc. However, the assumptions of G. Simpson (1945, 1969) about the polyphyletic (from different groups of theromorphic reptiles) origin of individual subclasses of mammals were not justified.

Cheetah(Acinonyx jubatus)

It can be considered proven that both subclasses of mammals arose in the Triassic period from one initial group of animal-like reptiles with primitive three-tuberculate teeth - carnivorous cynodonts (Tatarinov, 1975). By this time, they had acquired a secondary palate, which strengthened the jaw apparatus, differentiated dental system and a physique that resembled mammals (in particular, the setting of paired limbs under the body). Apparently, they had a diaphragm separating the body cavity, and other signs of mammals. Known ancient mammal- erythroterium - was small, smaller than a rat. The ways and time of the further formation and evolution of the two subclasses of mammals remain unclear.

Upper Triassic mammals are already divided into two branches (subclasses), in each of which a double articulation of the jaws arose and the formation of the dental system and the formation of "occlusion" - a close closure of the teeth of the upper jaw with the lower one, increasing the possibility of machining food. The first branch - a subclass of the first beasts - Prototheria known from the sediments of the Triassic period by the remains of small animals with three-pointed molars - Triconodontia. From them originated multituberous - Multituberculata(died out at the end of the Cretaceous) and monotremes - Monotremata, currently represented by the platypus and echidnas. The second branch - real animals - Theria- gave rise to the vast majority of modern mammals (infraclasses - marsupials - Metatheria and placental - Eutheria).

It took a long time for the formation of a new class - mammals. Brain development also progressed slowly.

In theromorphic reptiles, the most developed part of the brain was the cerebellum. On this basis, cynodonts (as well as all animal-like reptiles) should be called "metencephalic animals". On the way to mammals, there was a gradual increase in the forebrain. In this, mammals differ sharply from theromorphic reptiles, earning the name telencephalic group.

For two thirds of its geological history mammals remained small creatures that looked like rats and did not play a significant role in nature. Their rapid progress in the Cenozoic, obviously, was associated not only with the successive accumulation of many adaptations that led to the formation of warm-bloodedness and an increase in the energy level (energy of vital activity, according to A. N. Severtsov), live birth and feeding of young with milk, but especially with the development of organs feelings, central nervous system(cerebral cortex) and the hormonal system. Taken together, this led not only to the improvement of the organism as an integral system, but also ensured the complication of behavior. The consequence was the development of connections between individuals and the formation of complex dynamic groupings. Such "socialization" of relationships in mammalian populations (as in birds) has created new opportunities in the struggle for existence and position in biocenoses.

Alpine cycle of mountain building at the end of the Mesozoic and at the beginning cenozoic era changed the face of the earth; high ridges rose, the climate became more continental, its seasonal contrasts increased, and it became colder on a significant part of the Earth's surface. Under these conditions, the modern flora was formed with the dominance of angiosperms, especially dicotyledonous plants, while the flora of cycads and gymnosperms became poorer. All this put large and infertile herbivorous and predatory reptiles in a difficult position, while smaller warm-blooded birds and mammals more easily adapted to change. Switching to a diet of small animals and high-calorie fruits, seeds and vegetative parts angiosperms, they intensively multiplied, successfully competing with reptiles. The result was the extinction of the reptiles discussed above; it completed mesozoic era, and the wide adaptive radiation of mammals and birds opened the Cenozoic era.

bottlenose dolphin or bottlenose dolphin(Tursiops truncatus)

In the Jurassic period, 6 orders of mammals were formed, and in the Paleocene (60 million years ago) there were already at least 16 orders, 9 of which - Monotremata, Marsupialia, Insectivora, Dermoptera, Primates, Edentata, Lagomorpha, Rodentia, Carnivora- have survived to the present day. First marsupials found in Upper Cretaceous deposits North America and Lower Tertiary layers of America and Eurasia; some species live in America and in our time. The preservation of a variety of marsupials in Australia is explained by the fact that it separated from other continents even before the placental settlement. Emerging, apparently, not later than marsupials, placental mammals at first developed slowly. But their main advantage - the birth of more formed cubs, which reduced infant mortality, made it possible to displace marsupials almost everywhere. In our time, they form the core of the mammalian fauna and are represented by a wide variety of life forms that have occupied almost all landscapes of the Earth.

A variety of adaptations of mammals contributed to the development of not only land, but also fresh and marine waters, soil, and air. They ensured an unusually wide use of food resources compared to other vertebrates - the range of nutrition of mammals is more diverse than the composition of the food of other terrestrial and aquatic vertebrates, which increases the importance of mammals in the biosphere and their role in the life of various biocenoses.

Mammal class system and review of modern groups. The class Mammals is divided into two subclasses and includes 19 modern and 12-14 extinct orders. There are 257 families (139 extinct) and about 3000 genera (about 3/4 extinct); about 6,000 species have been described, of which 3,700-4,000 are living. In the modern fauna, there are approximately 2 times less species of mammals than birds (8600). At the same time, a more significant role of mammals (besides humans) in the life of the biosphere is obvious. This can be explained by the fact that the ecological niches of mammalian species are, on average, wider than those of birds.

Accordingly, their biomass (the total mass of all individuals in a given biocenosis) is usually higher than that for birds.

Relationships between orders of placental mammals have not been sufficiently clarified. Undoubtedly, the order of insectivores (remains from the Cretaceous period) is close to the ancestral forms; it has survived to the present day and, in addition, gave rise to woolly wings,