Dolphins, like whales, arecetaceans - mammals that evolved and adapted to a full aquaticlifestyle. Their closest land-based relative is the hippopotamus.There are 40 species of dolphin spread throughout the oceans, andeven freshwater rivers in some cases. While many dolphins prefer awarmer climate, some (like the southern right whale dolphin)inhabit colder waters.
Dolphins are known for their intelligence, their playfulnature, and their wide range of vocalizations which includes avariety of clicks, whistles and other noises. Many species ofdolphin are currently endangered, and all face threats from climatechange and pollution. Dolphins can also become tangled in netsmeant to catch fish.