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 they are successful, and withholding it when they are not. Secondary reinforcement—things not essential to life, such as play time, tactile rewards and fun games—can also be used as rewards. The practice of keeping killer whales in captivity is controversial, and organizations such as World Animal Protection and the Whale and Dolphin Conservation campaign against the captivity of killer whales. Orcas in captivity may develop physical pathologies, such as the dorsal fin collapse seen in 80–90% of captive males. The captive environment bears little resemblance to their wild habitat, and the social groups that the killer whales are put into