Dolphins are mammals like us, as other cetaceans and it's a reason for looking them with especial interest. They have great abilities due to their evolved brain, with demonstrated complex learning skills. Amazing mobility and speed, with a jump of several meters in height, and some of them with a visible curiosity to know other species.
Who studied their live says that they have a social life, with different subtleties and roles although not every species share the same behavior. There are small dolphins with less than a meter in their adult life and others with several meters of length, from a total of around forty species.
They possess a sense that every human maybe would like for him/herself, but as always Nature shows humanity doesn't have that preference assigning the benefit to others, thus we don't have the most amazing senses present in the natural diversity. Echolocation implies the use of sound waves for receiving information about the objects in a near field, and that's a good reason for calling it bio-sonar. They listen up to ten times our frequency range at high pitches, giving them a high range to communicate without being noticed.