Dolphins are cetacean mammals closely
related to whales and porpoises. There are almost forty species of dolphin in
17 genera. They vary in size from 1.2 m (4 ft) and 40 kg (90 lb) (Maui's
dolphin), up to 9.5 m (30 ft) and 10 tonnes (9.8 long tons; 11 short tons) (the
orca or killer whale). They are found worldwide, mostly in the shallower seas
of the continental shelves and are carnivores, eating mostly fish and squid.
The family Delphinidae, the largest in the order Cetacea, evolved relatively
recently, about ten million years ago during the Miocene.