What are the mammals?

Mammals are animals with the highest morphological structure and the most perfect physiological functions in the animal kingdom. Compared with other animals, the most prominent feature of mammals is viviparous, and their young are fed by the milk secreted by their mothers.

Mammals have fur to keep their body temperature constant and adapt to various complex living environments; Mammals have developed brains, so they can produce more complex behaviors than other animals, and can constantly change their behaviors to adapt to changes in the external environment.

There are more than 4000 kinds of mammals in the world. Although they are highly evolved, they still have many characteristics: almost all mammals are warm-blooded, their body temperature is basically constant, and they are covered with hair to protect their bodies from cold and heat.

It is estimated that there are 5400 species of mammals in the industry, which are divided into 29 orders 1200 genera. Mammals are divided into two subclasses: protomammals (including oviparous monotremes) and mammals (including placental mammals and oviparous marsupials). Most mammals (including 6 largest orders) belong to placental mammals. Among them, the largest three orders are rodents, Chiroptera and _ _. Rodents include rodents, Chiroptera includes bats, and orders include _ _, moles and rodents. The other three largest orders are Carnivora (dogs, cats, ferrets, bears, seals, etc. ), cetaceans (ungulates, whales) and primates (including humans).

Mammals are divided into three categories according to their reproductive patterns: monotremes, marsupials and placental mammals.

Mammals are diverse and widely distributed. Mainly according to the appearance, skull, teeth, appendages, reproduction methods, etc. They are customarily divided into three subclasses: protozoa (including the following 1~3), Afterthera (including the following 4~9) and Euthera (including the following 10~28).

Mammals are distributed all over the world, living on land, underground, water and air. There are two kinds of nutrition: herbivores and meat.