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Characteristic features of mammals

Mammals, like birds, are warm‑blooded animals, which allows them to inhabit in all ecosystems on the earth, from hot deserts, tropical forests to circumpolar areas and Antarctica. They can be found on land, in water and even in the air.

In the mammals’ body structure distinguished are: head, neck, trunk, tail and 2 pairs of usually five‑digit limbs. In most land mammals, the limbs are pulled up under the trunk, lifting it high above the ground, which improves locomotion. The body of mammals is covered with hairhairhair, which can form a thick, compact cover, called fur. Hair protects against mechanical injuries and helps to maintain a constant body temperature. It is the product of the epidermis, as are horns, hooves, claws, nails and scales of reptiles. It's role is also to protect against injuries. In the mammals’ dermis there are numerous glands: sweat glands, sebaceous glands, mammary glandsmammary glandsmammary glands and scent glands. Sweat glandssweat glandsSweat glands produce a special secretion called sweat, the function of which is to cool down the body and to a lesser extent – excrete unnecessary substances. Sebaceous glands secrete sebum, which forms an antibacterial barrier. During the feeding period, the mammary glands secrete milk, while the scent glands are used to mark the territory, attract partners and identify individuals. The innermost part of the skin, the so‑called subcutaneous layer, is composed of fat tissue which has many important functions: it protects against mechanical injuries, loss of heat, it also is the energy reserve for the organism.

Receipt of stimuli from the environment is enabled by a very well‑developed sensory nervous system (mainly the sense of hearing, vision and smell). Mammals are also the only vertebrates to have the auricle that makes it easier to capture sound waves and route them into the auditory meatus.

Mammals’ limbs

Depending on the mode of life and the habitat, limbs of mammals take different forms. Several species of mammals can glide, and bats are the only mammals to fly actively. In bats, the bones of the forelimb are strongly elongated, and between the digits and the side of the body there is a stretched patagiumpatagiumpatagium. Mammals that live in water, such as whales, dolphins and seals, have a streamlined body and limbs that are transformed into fins. Moles spend most of their life underground, which is why their limbs are wide and have their inside sides directed towards the back so that they can dig tunnels. In hoofed animals, the vertically positioned digits are covered with hooves which protect them against mechanical injury and allow them to run quickly. Hares and kangaroos can move as fast as the hoofed animals thanks to their elongated foot bones, which allow them to jump.

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Ilustracja przedstawia 6 schematycznie narysowanych kończyn przednich ssaków z oznaczeniem kości wewnątrz kończyny. Kolory oznaczają różne kości. Ten sam kolor w każdej z kończyn oznacza tę samą kość szkieletu. Kości kończyn pionowo, na tle szarego zarysu kształtu kończyny. Od lewej kończyny: człowieka, psa, delfina, nietoperza, konia i kreta. Podpisane: human; dog; dolphin; bat; horse; mole.

The forelimbs of all mammals are built according to the same plan: the shoulder bone is joined to 2 bones of the forearm, behind them there are several small bones of the wrist, on which 5 metacarpal bones are usually supported. Their extensions are bones forming digit parts. Joints between them have a similar location. This means that they are built according to one structure plan, which indicates the evolutionary relationship of mammals. Depending on the habitat and mode of life, the bones of various mammals’ limbs can be shortened or elongated, sometimes some of them are absent or strongly reduced (as in horses: the bones of the first, second and fifth digit).

Homeothermy

The gas exchange in mammals takes place in the lungs. The mammalian lungs are of alveolar structure. Pulmonary alveoli are thin‑walled bubbles entangled in a network of blood vessels. There are 300‑500 million of them. Thanks to them, the respiratory surface of mammals' lungs (in relation to their body size) is larger than the respiratory surface of other vertebrates. For this reason, the gas exchange is very effective and is one of the adaptations that have made the mammals warm‑blooded animals. They can therefore be very active, even at low temperatures. Mammals need a lot of food from which the energy necessary to carry out life processes and maintain a constant body temperature comes.

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Ilustracja przedstawia schematycznie warunki uzyskania stałocieplności, złożony z siedmiu niebieskich i jednego czerwonego prostokąta. Na samym dole niebieski prostokąt z napisem podpisem thermoregulation mechanisms, powyżej czerwony prostokąt z podpisem homeothermy. Z czerwonego prostokąta wychodzą dwie strzałki – jedna skierowana w dół, druga skierowana w górę. Powyżej niebieski prostokąt z podpisem high demand for energy. Z prostokąta wychodzą dwie strzałki skierowane ku górze. Jedna skierowana do niebieskiego prostokąta po lewej stronie, z podpisem high demand for food, druga – skierowana do niebieskiego prostokąta po prawej stronie, z podpisem high demand for oxygen. Z prostokąta po lewej stronie wychodzą dwie strzałki skierowane ku górze. Jedna do prostokąta z podpisem digestive system capable of absorbing as much nutrients as possible, druga do prostokąta z podpisem efficient blood circulation and a four-chambered heart. Z prostokąta po prawej stronie wychodzą dwie strzałki skierowane ku górze. Jedna do prostokąta z podpisem efficient blood circulation and a four-chambered heart, druga do prostokąta z podpisem large gas exchange area in the lungs.

Vertebrates

Conclusion

• Mammals are warm‑blooded vertebrates that can be found all over the globe – on land, in water or even in the air.

• The body of mammals consists of the head, neck, trunk, tail and 2 pairs of limbs, the structure of which depends on the habitat and the mode of life.

• The body of mammals is covered with skin whose epidermis produces hair, nails, claws, horns and hooves. In the dermis there are numerous glands: sweat glands, sebaceous glands, mammary glands and scent glands.

• Internal fertilisation and viviparity of mammals are the result of adaptation to a terrestrial environment.

• All young mammals are fed with milk.

Keywords

mammals, vertebrates, homeothermy

Glossary