The most advanced organisms on Earth are vertebrates. They are the smartest creatures like dolphins, chimpanzees, elephants and humans. But when the fist vertebrates evolved about 525 million years ago, they were simple creatures. Later, reptiles comprised the majority of vertebrates, then dinosaurs, birds and finally mammals. All vertebrates have muscles and skeletons. Also, they usually have tow pairs have wings and legs. Of course, fish do not have limbs, but they use tow sets of fins for steering through the water. All of this means that vertebrates were able to move to a new environment when conditions changed. By being mobile, they could chose where to live more easily than other types of animals.