Animals

When we hear someone talking about animals, we immediately think of the animals we know best and that are evolutively nearer to us, like birds and mammals. Actually, the larger part of the animal kingdom is made up of invertebrates, animals without a skeleton, that account for 95% of the living species. Jellyfish, corals, worms, arachnids, crustaceans, molluscs, echinoderms and, among the most numerous species, insects, are all very different from one another and they populate all the environments on land and in the seas. These are mainly small sized animals, with the exception of the giant squid that is the largest living invertebrate, whose tentacles grow up to twenty meters long. Reptiles exist since millions of years, and their ancestors were amphibian, and lived both on land and in the water. Their size, and their structure varies greatly: tortoises, crocodiles, alligators, lizards and snakes are reptiles. From 230 to 65 million years ago, the Earth was dominated by dinosaurs that became extinct at the end of the period. 150 million years ago, birds evolved from the reptiles and they were characterized by their capacity to fly, that enabled them to spread rapidly to all the environments of the planet. Mammals can survive in almost all the environments and can adapt to various climates: to life in the jungle, in the desert, in the polar regions, in the air, in the oceans, underground, on trees, and they move from one environment to another. In order to live in each environment, mammals have developed different bodies: most of the domestic animals, humans, bats, whales, elephants and beavers, kangaroos, koalas, the duck-billed platypus and bears are mammals!