Mammals treat the most high-organized vertebrate animals. They appeared on Earth about 160-170 million years ago. Ancestors of modern mammals were of the size of a rat and ate generally insects.
Instruction
1. Along with birds, mammals are warm-blooded animals, their body temperature is constant. Existence of indumentum, live birth and feeding of cubs milk is characteristic of them.
2. Milk at females is developed by the mammary glands formed of sweat glands in the course of evolution. Thanks to incubation of children in a womb, to live birth, feeding milk and care of posterity ensures the best safety of young growth in the most various conditions.
3. The sizes and appearance of mammals are very diverse. This class is presented by animals from 4 centimeters to 33 meters (dwarfish belozubka and a blue whale). Mammals have two pairs of five-fingered extremities and various in structure and to the carried-out functions the teeth located on the upper and lower jaws. The cervical department of a backbone consists of seven vertebras and movably connects a trunk and the head.
4. All mammals differ in the high level of the organization of nervous system. They considerably developed bark of big hemispheres and sense organs – sight, hearing, sense of smell, touch, taste. The blood system of mammals closed heart four-chamber, the movement of blood is organized on two circles of blood circulation – big and small.
5. Mammals can live in the most various conditions: on the land and in water (sea and fresh), in the soil and on a surface. Some representatives of a class adapted to flight in air (bats).
6. All mammals there are more than 5.5 thousand types now, and they are widely settled on all globe. The class Mammals includes two subclasses: Yaytsekladushchiye (Pervozveri) and Real animals. To the first duck-bills, pro-echidnas and echidnas, treat the second – all others, for example.