A Bottlenose Dolphin
The bottlenose dolphin (Tursiops truncatus) is an aquatic mammal indigenous to Earth. It is a cetacean species.
When Uhura tried to match the sound of the whale probe to the sound of an Earth animal aboard the Klingon Bird-of-Prey HMS Bounty, a bottlenose dolphin was one of the animals shown. (Star Trek IV: The Voyage Home)