Dolphins are mammals, like whales and porpoises which are adapted to living in the sea. They may live in the sea but they have no gills, so they come to the surface for air to provide the oxygen that their bodies need.
Dolphins are social creatures that seem to have a particular affinity with humans. Many people have found swimming with dolphins to be a life-changing experience and this is often used as therapy for very sick children. Even seen from a boat dolphins seem so…