40.
You know, a dolphin mind is fascinating thing! Their brains are bigger than ours and have more neurons in them. Unlike humans and land-based mammals repiration isn't a unconscious mechanism for dolphins, they have to put in the effort to breathe, and because of this dolphins will sleep with only half of their brain at a time, while one side sleeps the other half remains fully awake to keep breathing, alternating between the right portion and the left, in on order to fully rest each part.
They are the closest we have on this planet to telepaths, essentially painting and projecting pictures with sound using echolocation They can instantly map moving surroundings in 3 dimensions, supposedly more accurately than super computers can, identifying the sight, shape and speed of objects from hundreds of yards away, calculating the internal density of things with a sort of xray vision, as they bounce vibrations off objects, conducting feedback along auditory nerves to the brain to analyze the images. Researchers think the holographic acoustics they use with other dolphins could refer not just to people, other marine life and objects around them, but can be used to convey abstract ideas to one another.
In addition to communicating in sonar pictorial form of language, they may might have a vocal language, 5 fundamental units of sounds have been identified in the whistles they make to one another, we know for instance that they use names to refer to one another, and researcher thinks each dolphin chooses their own uniqe one to be greeted and remembered by for the rest of their life.