Cetaceans (Encyclopedia of Science)
Cetaceans (pronounced sih-TAY-shuns) include whales, dolphins, and porpoises. Although ancient people believed they were fish, cetaceans are aquatic mammals that bear live young, produce milk to feed their offspring, and have a bit of hair. The study of cetaceans is called cetology.
Although they have a fishlike shape, cetaceans are descended from land animals and still retain some modified features of their ancestors. They have the remains of a pelvic girdle, and the bones beneath their forelimbs, which are now used as flippers for swimming, show that they once had five fingers. Like land animals they have lungs, but instead of nostrils cetaceans breathe air through blowholes on the top of their head. They have no hind legs, and their tail has developed over time into a horizontal fluke (a flat tail), used to propel the animal through the water. Other physical changes include the addition of a thick layer of blubber to insulate against the cold of the ocean depths.
Cetaceans belong to the order Cetacea and include the baleen whales (ten species that live in the ocean) and the toothed whales, whose many species (including dolphins and porpoises) are found in diverse habitats from deep ocean to freshwater rivers.
Baleen (pronounced buh-LEEN) whales are huge creatures that include the blue whale, the largest...
(The entire section is 820 words.)
Want to Read More?
Subscribe now to read the rest of this article. Plus get complete access to 30,000+ study guides!