Cetacea

Article By:

Thewissen, J. G. M. Department of Anatomy and Neurobiology, Northeast Ohio Medical University, Rootstown, Ohio.

Last reviewed:February 2020

DOI:https://doi.org/10.1036/1097-8542.122700

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• Cetacea, published December 2015:Download PDF Get Adobe Acrobat Reader
• Cetacea, published June 2014:Download PDF Get Adobe Acrobat Reader

An aquatic mammalian order comprising approximately 90 living species of whales, dolphins, and porpoises and their fossil relatives. Like all other mammals, members of the order Cetacea (cetaceans) nurse their young with milk produced by the mother, are endothermic (warm-blooded), breathe air, have a lower jaw that consists of a single bony element (the dentary), and have three small bones (malleus, incus, and stapes) to transmit sound within the ear. Unlike most mammals, living cetaceans are aquatic animals that cannot live on land. They have streamlined bodies (Fig. 1), with the nasal opening (blowhole) on top of the head. Their forelimbs are modified into flippers, they lack external hind limbs, and their tail forms a flat horizontal fluke. Modern cetaceans lack hair, except for whiskers in the young of most species. Many of these features are common in aquatic vertebrates, and they have evolved convergently as adaptations for life in water. See also: Adaptation (biology); Mammalia

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