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Whales, Dolphins & Porpoises

Cetacea

Cetaceans (order Cetacea) are fully aquatic mammals that include whales, dolphins, and porpoises. Living cetaceans are commonly divided into two suborders: baleen whales (Mysticeti) and toothed whales (Odontoceti); dolphins and porpoises are odontocetes. Most cetaceans live in the ocean, but some species live in freshwater river systems. Fossil evidence shows early cetaceans appear in the early Eocene (~55 million years ago), with hippos as their closest living relatives (though not their ancestors). Along with sirenians (manatees and dugongs), cetaceans are obligately aquatic—they live essentially their entire lives in water—yet they must surface to breathe air.

Cetaceans (order Cetacea) are fully aquatic mammals that include whales, dolphins, and porpoises. Living cetaceans are commonly divided into two suborders: baleen whales (Mysticeti) and toothed whales (Odontoceti); dolphins and porpoises are odontocetes. Most cetaceans live in the ocean, but some species live in freshwater river systems. Fossil evidence shows early cetaceans appear in the early Eocene (~55 million years ago), with hippos as their closest living relatives (though not their ancestors). Along with sirenians (manatees and dugongs), cetaceans are obligately aquatic—they live essentially their entire lives in water—yet they must surface to breathe air.