Friendly, playful marine mammals, dolphins and porpoises are highly intelligent, some say easily on the low end of the human spectrum. Most dolphins can learn to comprehend human, humanoid or demihuman languages. In the wild, the chances of encountering one who does is small. Species of dolphins and porpoises can be found in almost any body of salt water. The major differences between dolphins and porpoises is that dolphins generally have dorsal fins with a greater curve and a larger nose and mouth. Both species, on average, grow from 5 to 8 feet in length.