Toothed whale porpoise as a fish. Toothed whales, as well as baleen whales, are descendants of land-dwelling mammals of the artiodactyl order (even-toed ungulates). They are closely related to the hippopotamus, sharing a common ancestor that lived around 54 million years ago (mya). The primitive cetaceans, or archaeocetes, first took to the sea approximately 49 mya and became fully aquatic by 5–10 million years later. The adaptation of echolocation and enhanced fat synthesis in blubber occurred when toothed whales split apart from baleen whales, and distinguishes modern toothed whales from fully aquatic archaeocetes. This happened around 34 mya. Unlike toothed whales, baleen
Captive killer whales a limited area, such as Puget Sound or the Strait of Juan de Fuca, are termed "resident" whales, while "transient" whales roam the oceans at will. These "transient" types have to be more aggressive, in order to assert themselves in a wide range of territories and to prey on a variety of different species. This increased aggressiveness does not disappear in captivity. Furthermore, captivity itself has been asserted to aggravate aggressive behavior, resulting in a "cetacean equivalent of anxiety disorder." Captive killer whale attacks on humans seem to fall mostly into the categories of: biting during feeding, ramming in the