Mammals

Mammals, or mammals (lat. Mammalia), are a class of higher vertebrates; warm-blooded (36-39 °C) vertebrates (cranial). Mammals have a number of unique mechanisms that collectively distinguish them from other vertebrates. Numerous bones and tissues of the embryo are formed even before fertilization: the embryo of oviparous vertebrates (amphibians), reptiles and birds is primitive in mammals. Most mammals lay eggs (marsupials), but there are viviparous (for example, shrews, many bats) and oviparous (sea cows, some cetaceans). Of the eggs of mammals, some species hatch with hair and other characteristics of adult animals (primal animals), while some amphibians hatch without hair, like the eggs of modern crocodiles and turtles, for example. The greatest evolutionary division is observed between the groups of higher primates and placental mammals, although among them there are diversified forms. The main characteristics inherent in this class include warm-bloodedness, viviparity (exceptions - platypus, echidna, monotremes - are born from eggs); mammary glands that produce milk, or a change in the phases of feeding the cubs by the mammary glands and belly of the female; hair or wool; four-chambered heart; alveolar lungs; diaphragm as a separate entity; one half of the brain is represented by gray matter, the second by white matter, the cerebral cortex is characteristic (not typical for other vertebrates); the fetus has a well-developed placenta, the fetus and birth of the fetus are completely separate from the mother's body, with the exception of marsupials, in which birth is more closely associated with the maternal body; ossified skull and differentiated teeth; characteristic teeth marks. About 7 thousand species of mammals are divided into 19 orders. Some primitive groups are already almost extinct. Among the modern ones, the most outstanding are