The animals or mammals are a separate vertebrate animal’s class. They have descended from the mammal-like reptiles about 230 million years ago. The “pangolin” to “animal” transformation process went gradually and lasted for tens million years.
The first real mammals were as small as a mouse or rat with a thin hair and some of them were oviparas (whose linear descendents were the actual duck moles and the Australian echidna) with the imperfect temperature regulation. There were only a few of them as mostly dinosaurs reined the land at that moment.
These poor, primitive mammals led a life of misery for 150 million years, which is almost two-thirds of the whole class history. And they could probably stay unchanged unless the lucky strike.
Around 65 million years ago the global environmental crisis took over the planet, the causes of which are still argued by the scholars. After a couple of million years, it has destroyed the extremely diverse dinosaur fauna and thus gave the floor to the “life actors”. These actors became the mammals: right after the dinosaurs died out, the Age of Reptiles was replaced by the Cenozoic era, i.e. the Age of Mammals.
Having taken the new lease of life the mammals immediately invaded the whole planet and started reclaiming not only the land, but also the airspace (like bats) and the waters (the cetaceans). Later on, according to the geologists, all the general up-to-date mammal units start appearing. They are as follows: insectivorous, primates, carnivores, ungulates, rodents, etc. Besides this, the animals became not only rich in diversity, but also bigger in size: the cold blooded giants (for instance, diplodocus, brontosaurus, etc.) were made up for the warm blooded giants like elephants, rhinos and whales. All in all, the mammals became number one in the animal kingdom evolution period. In the result of animal evolution some unique creatures started appearing with the only purpose to discover the environmental world, as well as themselves personally. These creatures are the human beings…