| Summary: | Marine mammals arc often considered as a group by the general public, biologists, natural resource managers and legislators. Nonetheless, they comprise members of three very different orders of animals with different evolutionary histories. The Carnivora includes 36 extant and recently extinct species of seals, sealions and walruses (Rice 1998) as well as the polar bear and two species of marine otters. Systematists disagree about the exact number of species of the order Cetacea (whales, dolphins and porpoises). Rice (1998) lists 83 species in two sub-orders: the Mysticeti (baleen whales) and Odontoceti (toothed whales). There are four extant species of Sirenia (manatees and dugongs). The gigantic Steller's sea cow (Hydrodamalis gigas) was hunted to extinction by sealers in the eighteenth cetury.
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