The immense diversity of mammals
In the Mesozoic period, more than 200 million years ago, the first small mammals evolved from reptiles. However, their triumphant progress began only much later, about 65 million years ago. After the dinosaurs had died out at the end of the Cretaceous period, there began a rapid development of very diverse forms of life, which have one characteristic in common: their young are reared by suckling mother's milk.
In Germany, over 100 species of mammals currently live in the wild. They embody incredibly diverse concepts of life. While the European Bison, with a body weight of up to a ton, lies stoically in the grass chewing the cud, the 3-gramme Pygmy Shrew has to hunt day and night through the undergrowth, because several hours without food mean certain death for the tiny creature. The blind Mole digs through the soil in search of earthworms, while in the air above him bats pick insects from leaves. Many species – including the ungulates – are pure vegetarians; others, like members of the canine and feline families, feed only on meat.
The specific development characteristics already begin in the womb, because in most mammals the growing embryo is supplied through the placenta with blood and hence with nutrients and oxygen. After birth, the young are still far from being independent and have to be fed for a long time by the mother. In some species, the so-called altricial animals (e.g. hedgehogs, mice), the young are born blind, naked and helpless. In others, the precocial animals, the young have a fully developed covering of fur and have to get up and run shortly after birth (e.g. horses, deer, antelopes).
A typical feature of mammals is their dense fur with sweat and sebaceous glands. This allows them to keep their body temperature constant in relation to the environment. The scent glands and colour of the fur also serve for communication or camouflage. The long whiskers in the muzzle area fulfil a special function: they are important for orientation in the dark. Mammals also have a very sophisticated sense of smell and hearing.