Whales are aquatic mammals of the order Cetacea. The term is now applied to about 80 species of baleen whales and "toothed" whales, which include dolphins, porpoises, and non-baleen whales, as well as extinct whales. Cetaceans range from the largest known animal, the blue whale (Baleanoptera musculus), at a length up to 102 ft (31 m) to the diminutive vaquita (Phoceona sinus) at 5 ft (1.5 m).

Whales evolved from land animals and have lived exclusively in the aquatic environment for at least 50 million years, developing fish-like bodies with no rear limbs, powerful tails, and blow holes for breathing through the top of their heads. They have successfully colonized the seas from polar regions to the tropics, occupying ecological niches from the water's surface to ocean floor.

Baleen whales, such the right whale (Balaena glacialis), the blue whale, and the minke whale (Balaenoptera acutorostrata), differ considerably from the toothed whales in their morphology...