Dolphins and porpoises are marine mammals belonging to the order cetaceans, which also includes whales.
The World Conservation Union's Cetacean Specialist Group recognises about 43 dolphin and porpoise species, which are generally referred to as small cetaceans.
Some confusion exists about the terms dolphin and porpoise.
Generally, the family of Delphinidae are called dolphins, and the family of Phocoenidae are called porpoises.
Descriptions of the two species usually refer to dolphins as being larger than porpoises and having a more pronounced 'beak'.
Dolphins are playful and social, following ships and sometimes swimming with humans, while porpoises are usually solitary and keep a lower profile. Behaviour Dolphins and porpoises are found in oceans, estuaries and rivers. Different species have different habits: while some travel over long distances, others remain in the same area their entire life.