The living world around us is very interesting and has many faces. Mammals (or Animals) are the highest class of vertebrate animals, crowning the entire system of the animal world. The structure and appearance of mammals is diverse. Body sizes also vary greatly - from 3.8 cm with a mass of 1.5 g - to 30 m and even more with a mass of about 150 tons.

Mammals are distributed almost throughout the entire Earth: they are not found only on the Antarctic continent, although seals and whales live off its coast. In the area of ​​the North Pole there are polar bears, pinnipeds, and cetaceans (narwhals).

Mammals are widely distributed in living environments. Suffice it to remember that, along with terrestrial species, which are the majority, a number of species are in one way or another associated with the aquatic environment; some fly through the air. A significant number of animals live in the soil, where they spend all or most of their lives. No class of vertebrates has produced such a variety of forms as mammals. My 4th grade students and I will try to tell and give general ideas about those whom we used to call “Beasts” or Mammals.

How did mammals appear on Earth?

Mammals have been living on planet Earth for 200 million years. Scientists agree that they once originated from reptiles. In the Mesozoic era, in the Jurassic period, ancient animals already existed - their descendants live to this day - this is a group that includes the platypus and echidna.

At the same time, the first marsupials appeared; the descendants of these animals inhabit the Earth today - kangaroos, koalas, wombats and possums.

Real animals appeared a little later, in the Cretaceous period (about 100 million years ago). At first they were inconspicuous creatures: the size of a shrew or a mouse, some the size of a rat. Back then they were all insectivores. This means that elephants and monkeys, buffalos and whales, dogs and deer - in short, all modern animals descended from tiny animals, relatives of hedgehogs, shrews and moles. These insectivorous animals developed very rapidly, they populated new and new lands, gradually adapting to new environments and living conditions, and new species appeared. Many of them grew rapidly, some became simply giants, the likes of which the world did not know even in the time of dinosaurs, for example the whale.

Classification of mammals

We will talk later about what allowed the animals to change and spread out so much. And now I would like to tell you what groups all living mammals are divided into.

First animals are the most primitive mammals, very different from all other animals. These are the platypus and the echidna. They, like their ancestors, still lay eggs, covered in shells, but the hatched cubs are already fed with milk, like animals!

Marsupials give birth to underdeveloped tiny cubs, carry them in a pouch, where the babies are fed with mother's milk. Representatives of this group are kangaroos, koalas, and opossums. The first animals and almost all marsupials live in Australia, scientists agree that when one huge continent that existed on Earth began to collapse, small Australia was one of the first to break away, since then it has been quite isolated from other continents, which is why the ancient species have been preserved there.

Real animals carry their young inside the mother's body until the baby is ready to be born. The mother feeds the cubs with milk, the parents take care of their babies until they grow up and are able to eat adult food. This group includes a lot of representatives. For convenience, they were divided into separate orders: bats (bats), lagomorphs (hares and rabbits), pinnipeds (seals and walruses), predators (wolves, foxes, lynxes, tigers, etc.), cetaceans (whales and dolphins), artiodactyls (deer and wild boars), equids (horses and donkeys), primates (monkeys), rodents (mice, squirrels).

What unites mammals?

All mammals have common characteristics. Their body is covered with hair (hair, quills, bristles), which protects them from hypothermia and damage; they have a constant body temperature. Although different animals have their own temperature. For example, whales and dolphins have the same body temperature as humans – 36.6 degrees. And a cat and a dog have a normal temperature of 39 degrees. The animals are moving quite actively. The fastest animal on Earth, the cheetah, can reach speeds of up to 120 km/h. Hound dogs are only slightly inferior to him - 110 km/h. The red deer can make a jump up to 11 meters long. And tigers and lions make jumps 2 times shorter - 5 meters.

All animals have 7 cervical vertebrae in their skeleton. Just think, a mole, a giraffe, and a whale have the same number of cervical vertebrae!

When we read about the anatomical features of the structure of mammals, we immediately remembered that in the first quarter we studied human anatomy. Thus, the structure of the digestive, circulatory, respiratory and other organ systems in the human and animal bodies is very similar. Of course, because humans also belong to the class of mammals! During the lesson, we counted our heart rate per minute (pulse) - approximately 70-80 heart beats. It turned out that animals have different heart rates. For a dolphin this is only 25 heart beats per minute, but for a hare it is as much as 280! We also calculated our breathing rate in 1 minute - this figure is 11-14 inhalations and exhalations. An elephant's breathing rate is only 6 breaths per minute, while a small shrew has 120 breaths per minute. While studying human anatomy, we also learned that teeth are divided into incisors, canines and molars. Animals also have the same division, but depending on what food the animal eats, there are differences, which will be discussed in the next section.

Compared to other animals, animals have a very developed nervous system; the cerebral hemispheres have grooves and convolutions. Therefore, animals have complex behavior; they take care of their babies. Mammals have well-developed senses - vision, touch, smell, taste, hearing. Take, for example, the keen sense of smell and excellent vision of predators. For example, a dog smells some substances that are almost a million times weaker than a human can smell. And bats emit ultrasonic signals that bounce off and return to surrounding objects. Therefore, even in complete darkness, they perfectly “see” all the obstacles and insects they are hunting for. Whales use sound signals to communicate with each other at a distance of many kilometers. The mole is an underground dweller: he sees almost nothing, but he can distinguish smells very well and, with the help of hairs on his muzzle (other animals also have them), he can feel objects.

It is important that animals bear their young inside their bodies, the baby is guaranteed to receive nutrients and protection from the mother, mammals feed their babies with milk, and take care of their offspring until the babies grow up. It is known that a person carries his babies for 9 months. Cats and dogs - about 2 months. And a huge elephant needs about two years for a baby elephant to be ready for birth.

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