The majority of small-toothed WHALEs are called dolphins. They are mammals of the order Cetacea and the families Platanistidae, Delphinidae, and Grampidae and include about 50 species. All have a beaklike snout and sharp, conical teeth. The term porpoise is sometimes applied to many of the same species, but porpoises, strictly speaking, are members of the family Phocaenidae and have a blunt snout and spade- or chisel-shaped teeth. The dolphin fish (mahi-mahi, or dorado), on the other hand, is neither a dolphin nor a porpoise. It is a sport fish related to the mackerels.

Most dolphin species are about 2 m (6 ft) in length, the males averaging 10 to 20 cm (4 to 8 in) longer than females. The largest well-known dolphin is the bottle-nose dolphin, Tursiops truncatus. This species may reach over 3 m (9 ft) in length and 200 kg (440 lb) in weight. The largest dolphins of all are the Orca or Killer Whale, Orcinus Orca. The males can reach 9.8 m (over 29 ft!) and 5,000 kg (11,000 lb)! The smallest species is the buffeo, Sotalia fluviatilis, found in the Amazon River; the buffeo rarely grows over 1.2 m (3.9 ft) in length and 30 kg (66 lb) in weight.

Dolphins are predators and feed on live food, except when trained otherwise in captivity. The primary food is fish, mostly open water types such as herring, mackerel, and sardines. Some species seem to prefer squid; occasionally, shrimp and other crustacea are consumed, and even mollusk shells have been found in their stomach contents. Food consumption is estimated at about 30 kg (66 lb) a day for an individual about 2.5 m (8.2 ft) in length and 100 kg (220 lb) in weight.

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