==Taxonomy==Mammals have returned to the water in at least nine separate evolutionary lineages (Cetacea, Sirenia, Desmostylia, Pinnipedia, "Ursus maritimus" (polar bear), "Kolponomos" (marine bear), "Thalassocnus" (aquatic sloth), "Enhydra lutris" (sea otter) and "Lontra feline" (marine otter)).