ETYM French dauphin dolphin, dauphin, earlier spelt also doffin.
Any of various small toothed whales with a beaklike snout; larger than porpoises.
Any of various highly intelligent aquatic mammals of the family Delphinidae, which also includes porpoises. There are about 60 species. Most inhabit tropical and temperate oceans, but there are some freshwater forms in rivers in Asia, Africa, and South America. The name “dolphin” is generally applied to species having a beaklike snout and slender body, whereas the name “porpoise” is reserved for the smaller species with a blunt snout and stocky body. Dolphins use sound (echolocation) to navigate, to find prey, and for communication. The common dolphin Delphinus delphis is found in all temperate and tropical seas. It is up to 2.5 m/8 ft long, and is dark above and white below, with bands of gray, white, and yellow on the sides. It has up to 100 teeth in its jaws, which make the 15 cm/6 in “beak” protrude forward from the rounded head. The corners of its mouth are permanently upturned, giving the appearance of a smile, though dolphins cannot actually smile. Dolphins feed on fish and squid.
The river dolphins, of which there are only five species, belong to the family Platanistidae. All river dolphins are threatened by dams and pollution; the whitefin or baiji dolphin Lipotes vexillifer of the Chiang Jiang River, China, is the world’s rarest cetacean and is in danger of extinction. There were an estimated 300 remaining in the early 1990s, but in 1995 experts feared there were less than 100. A rescue scheme is planned for autumn 1995 to capture the remaining dolphins and move them to a lake that was once part of the Chiang Jiang.
As a result of living in muddy water, river dolphins' eyes have become very small. They rely on echolocation to navigate and find food. Some species of dolphin can swim at up to 56 kph/35 mph, helped by special streamlining modifications of the skin.
All dolphins power themselves by beating the tail up and down, and use the flippers to steer and stabilize. The flippers betray dolphins’ land-mammal ancestry with their typical five-toed limb-bone structure. Dolphins have great learning ability and are popular performers in aquariums. The species most frequently seen is the bottle-nosed dolphin Tursiops truncatus, found in all warm seas, mainly gray in color and growing to a maximum 4.2 m/14 ft. The US Navy began training dolphins for military purposes in 1962, and in 1987 six dolphins were sent to detect mines in the Persian Gulf. Marine dolphins are endangered by fishing nets, speedboats, and pollution. In 1990 the North Sea states agreed to introduce legislation to protect them. Also known as dolphin is the totally unrelated true fish Coryphaena hippurus, up to 1.5 m/5 ft long.