Cetacean

cetacean, (order Cetacea), any member of an entirely aquatic group of mammals commonly known as whales, dolphins, and porpoises. The ancient Greeks recognized that cetaceans breathe air, give birth to live young, produce milk, and have hair—all features of mammals. Because of their body form, however, cetaceans were commonly grouped with the fishes. Cetaceans are entirely carnivorous, although members of the order Sirenia (manatees, dugongs, and Steller’s sea cow) were once referred to as the “herbivorous Cetacea.” In the past cetaceans were important resources (see whaling), but by the end of the 20th century their economic importance was almost solely due to whale watching, a tourist activity and major source of income for certain coastal regions of many countries.