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 water, and holding under water. Killer whales biting trainers during feeding or shows is generally the mildest form of attack seen, but can escalate to an animal dragging the trainer underwater and holding them there until they lose consciousness or drown. Trainers who have had killer whales ram into them in the water tend to suffer from a range of injuries including internal bleeding, broken bones, ruptured organs, and heart attack. Tilikum, a large bull male killer whale who died in early 2017, had been involved in the death of three individuals since his capture near Iceland in November 1983.