The order Cetacea 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), used for whales and other huge fish or sea monsters. Cetology is the branch of marine science associated with the study of cetaceans. An ancient ancestor of the whale, Basilosaurus was thought to be a reptile until vestigial parts were recognized.[2]
Fossil evidence suggests that the 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.
