Whales, dolphins and porpoises belong to the order Cetacea. These are aquatic mammals that have streamlined bodies highly evolved for swimming. Their hind limbs have become vestigial as part of this streamlining. All whales, dolphins and porpoises are cetaceans, including the biggest animal ever to have lived - the blue whale.
Scientific name: Cetacea
A comparison of whale and dolphin size in relation to humans - from the 30m long blue whale to the 2.5m long harbour porpoise.
The order Cetacea (pron.: /sɨˈteɪʃⁱə/) includes the marine mammals commonly known as whales, dolphins, and porpoises. Cetus is Latin and is used in biological names to mean "whale"; its original meaning, "large sea animal", was more general. It comes from Ancient Greek κῆτος (kētos), meaning "whale" or "any huge fish or sea monster". In Greek mythology, the monster Perseus defeated was called Ceto, which is depicted by the constellation of Cetus. Cetology is the branch of marine science associated with the study of cetaceans.
Fossil evidence suggests that cetaceans share a common ancestor with land-dwelling mammals that began living in marine environments around 50 million years ago. Today, they are the mammals best adapted to aquatic life. The body of a cetacean is fusiform (spindle-shaped). The forelimbs are modified into flippers. The tiny hindlimbs are vestigial; they do not attach to the backbone and are hidden within the body. The tail has horizontal flukes. Cetaceans are nearly hairless, and are insulated from the cooler water they inhabit by a thick layer of blubber.
Some species are noted for their high intelligence. At the 2012 meeting in Vancouver, Canada, the American Association for the Advancement of Science (the world's biggest science conference), support was reiterated for a cetacean bill of rights, listing cetaceans as "non-human persons".
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