Mammalian animals: a brief description

To date, mammalian animals are considered one of the most developed classes. This group is characterized by a number of important features. According to well-known studies, in the modern world there are more than five thousand representatives of the class. Although it is worth noting that this figure is very approximate, since scientists are still looking for new species.

Mammalian animals and their distribution

Mammalian animals are considered to be completely unique fauna. They are distributed throughout the planet.

Representatives of this class can be found in almost all major biotopes of the Earth. These animals perfectly exist in the hot dry desert climate, in high-altitude regions. They can be seen in the polar regions and tropical forests. They are common even in aquatic environments.

Perhaps the only territories that are not inhabited by mammals are the internal territories of Antarctica and the deep-water part of the world's oceans.

It is interesting that the area of distribution of single-pass animals (for example, the platypus) is clearly limited to the territories of New Guinea and Australia. Marsupial representatives are common on the islands of Oceania, as well as in Australia and on the territory of the American continents. It is also interesting that on the Australian continent only some placental mammals lived before the first settlers arrived there.

Mammalian animals: the main features of the class

As already mentioned, this group of animals has a number of unique characteristics that attest to the high level of organization:

• Practically mammals are viviparous.
• Females feed their young with milk, produced in specific glands (by the way, it is thanks to this fact that mammals have their name).
• Representatives of the class have a specific hairline, active sebaceous and sweat glands.
• For mammals, the so-called homeothermia, or warm-bloodedness is characteristic - the temperature of their body does not depend on the conditions and temperature of the external environment.
• A particularly important feature of this group of animals is a perfectly developed brain, in particular, its final part. It is here that the center is located, thanks to which representatives are inclined to very complicated forms of behavior.
• Mammals form an auricle, an external ear passage, and also all three auditory ossicles, which, by the way, are modified bones of the lower jaw.
• For the representatives of the class is characterized by the presence of a developed four-chambered heart and left arch of the aorta, which ensure the separation of blood into the venous and arterial (for example, in reptiles venous and arterial blood is mixed in the heart).
• A distinctive feature is the alveolar structure of the lungs.
• In addition, there are differences in the structure of blood cells - the erythrocytes of these animals do not contain a nucleus, only a respiratory pigment.
• Mammalian animals have seven vertebrae in the cervical region.
• For representatives of this class, a variety of teeth (presence of incisors, canines, molars) is characteristic . In this case, the teeth are immersed in the bone tissue of the jaw with the help of roots.

Origin of mammals

Scientists believe that the ancestors of modern mammalian animals were reptiles that appeared in the Paleozoic. These animals still retain some similarity with amphibians, in particular, the presence of skin glands and, possibly, the double occipital condyle.

Particularly close relatives of modern species are the beetles. Representatives of this group were characterized by the presence of different teeth (molars, incisors and canines). The upper and lower jaws were joined by a special bone, which in mammals turned into an auditory ossicle. But the representatives of the beetles died out in the Upper Triassic.

Already in the Jurassic period, a branch of viviparous species arose from those representatives who still lay eggs.

In fact, it is impossible to clearly formulate the theory of the origin of mammals, because, to this day, paleontologists and other scientists are active in this field.