Mammals owe their name to the fact that females have nipples (lactic glands) and feed their young with milk. Among vertebrates, they are most developed. To the class that includes many species, including man.
In addition to typical lactic glands for them, all mammals have skin covered with hair, that consists mostly of protein (keratin). This often makes the hair coat can also turn into spines (in hedgehogs), horns (in rhinoceros) or scales (in battleships).
Mammals, in addition to birds, are virtually the only animals possessing the ability of self-regulation of body temperature. Evolved from a reptile ssakokształtnych and first appeared on Earth at the same time as dinosaurs, and thus about 200 million years ago during the Mesozoic Era. The transition from reptiles to mammals is expressed primarily changes in the skull and jaw, as well as the major development of the brain. More than 100 million years when dinosaurs dominated the earth, primitive mammals were small and conducted secretive lifestyles.
When the dinosaurs went extinct about 65 million years ago, mammals proliferated and diversified, covering all habitats and all parts of the world.
Today we distinguish 4600 species of mammals. All reproduce by mating male and female of the same species and the fertilized eggs of a female by the male sperm. Way to develop young people can distinguish 3 groups of very unequal quantity: monotremes, marsupials and placentals.
Marsupials and monotremes
Monotremes: dziobaki and echidnas
Najprymitywniejszymi Monotremes are mammals. After his fathers, reptiles, these animals have survived a particular characteristic of egg laying. Young after leaving the eggs are fed mother's milk like mammals. Currently monotremes live only in Australia and New Guinea, and are represented only by 3 species and 2 species of platypus kolczatek.
Platypus has a duck-shaped jaws of the bow, without płetwowate teeth and paws. Półwodnym is an animal lives in rivers, and sleeping on the ground, in the hole, which opened quietly on the shore. It feeds on insect larvae and crustaceans, which collects at the bottom of the water, sediments rozgrzebując.
Large spikes resemble hedgehogs. Their body is covered with hair and spikes, they are tubular snout. Feed on small invertebrates (termites, ants, earthworms). pozdrawiam