Most fishes have fins for swimming, scales for protection and a streamlined body for moving easily through the water. Reptiles are vertebrates that have a backbone with tough, dry skin covered with horny scales. Some of the most widespread living reptiles are turtles, lizards, snakes, crocodiles and alligators. They can live on land and in water. Mammals have entirely different habits and behaviours.
Humans are mammals.
They give birth to their young directly, and don't lay eggs. According to the suitability of their environment, they have different organs for movement, feeding and breathing. Land Animals Land animals have four limbs. Some use all four limbs to walk, run or jump while some use only hind limbs, e.g. kangaroo. Snakes, lizards, crocodile move by crawling, but they do have limbs.