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.