When a type of animal is extinct, it is impossible to find it anywhere on the planet. For example, dinosaurs have become extinct, as well as the Derfil of the "Baiji" river, which has become extinct a few years ago in China. There are also many familiar animals that have become "very threatened with extinction" and we are afraid that the role in extinction will come to them. In this book, we review about 250 species of these extinct animals, each within the framework of the geological period to which it belongs. There are more than one million animal sex in our world today, but more than 800 sexes of them have become extinct during the past five hundred years only. The extinction is a natural process, but scientists tell us that the rate in which the animals are extinct has become a thousand times faster than the normal rate ... and this is because of humans!