Dolphins are marine mammals that are related to whales and porpoises. A marine mammal is one that lives in the water. Dolphins are found all over the world's oceans as well as in rivers and marshes. Dolphins are carnivores (meat-eaters) and feed on fish, squid and other marine life They often swim together in groups called"pods." They are thought to have powerful eyesight and hearing, but do not have a sense of smell.