Cetaceans

Cetaceans are marine mammals belonging to the infraorder Cetacea (), a secondarily aquatic clade under the order Artiodactyla that include whales, dolphins, porpoises and extinct groups such as Basilosaurus. Most cetaceans live in marine environments, particularly the pelagic zone, but some reside solely in brackish or fresh water. Having a cosmopolitan distribution, they can be found in some rivers and all of Earth's oceans. Many species migrate seasonally over vast ranges for food advantages.

Whales are a widely distributed and diverse group of fully aquatic placental marine mammals. As an informal and colloquial grouping, they correspond to large members of the infraorder Cetacea, i.e. all cetaceans apart from dolphins and porpoises. Dolphins and porpoises may be considered whales from a formal, cladistic perspective. Whales, dolphins and porpoises belong to the order Cetartiodactyla, which consists of even-toed ungulates. Their closest non-cetacean living relatives are the hippopotamuses, from which they and other cetaceans diverged about 54 million years ago. The two parvorders

phenomenon in which a whale becomes stuck on a beach, often causing the whale's death

derivation of cetaceans from an artiodactyl precursor, and the adaptive radiation of cetacean species

behaviour of whales and dolphins when they come to the surface to breathe

intellectual capacity of cetaceans

Praekogia is an extinct genus of cetacean in the family Kogiidae that lived during the Miocene, containing one species: P. cedrosensis. Fossils have been found in Mexico (Baja California).

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accidental capture of porpoises, whales and dolphins