porpoise, small whale of the family Phocaenidae, allied to the dolphin. Porpoises, like other whales, are mammals; they are warm-blooded, breathe air, and give birth to live young, which they suckle with milk. They are distinguished from dolphins by their smaller size and their rounded, beakless heads. Porpoises are 4 to 6 ft (120-180 cm) long and are black above and white below. The finned porpoises, species of the genus Phocaena, have a dorsal fin. They are distributed throughout the world and include the common porpoise, Phocaena phocaena, found throughout the Northern Hemisphere. The finless porpoise, Neomeris phocaenoides, is found in the Indian and W Pacific oceans. Traveling in schools, porpoises prey on fish, often pursuing them long distances up rivers. The fat of the porpoise yields a lubricating oil, and the flesh is sometimes eaten. In North America the dolphins (family Delphinidae) are sometimes called porpoises and the bottle-nosed dolphin is sometimes called the common porpoise. True porpoises are classified in the phylum Chordata, subphylum Vertebrata, class Mammalia, order Cetacea, family Phocaenidae.

Any toothed whale in the family Phocoenidae (or, by some authorities, part of the dolphin family Delphinidae). The four species (genus Phocoena) of the common, or harbour, porpoise are primarily fish eaters that travel in pairs or large groups. They are gray or black above and white below. The shy P. phocoena, found throughout the Northern Hemisphere, rarely leaps. The other species of Phocoena are found along Californian and South American coasts. The active, gregarious Dall porpoise (Phocoenoides dalli) of the North Pacific and the True porpoise (P. truei) of Japan often swim with ships, usually in groups of 2 to 20. Both eat cephalopods and fishes and are black with a large white patch on each side. The black finless porpoise (Neomeris phocoenoides), a small, slow animal, inhabits the Pacific and Indian oceans. At most 7 ft (2 m) long, porpoises are shorter and chubbier than dolphins and have a blunt snout. Like the dolphins, they are known for their high intelligence.

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