Cetacea is a scientific order of large aquatic mammals that have forelimbs modified into flippers, a horizontally flattened tail, a nostril at the top of the head for breathing, and no hind limbs. Cetaceans include all whales, dolphins, and porpoises.

The word "cetacean" is derived from the Greek word for whale, kētos.

Living cetaceans are further divided into two suborders: the Odontoceti (toothed whales) and the Mysticeti (baleen whales).

Odontoceti is a scientific suborder of whales that have teeth. The word "odontocete" comes from the Greek word for tooth, odontos.

The only other member of this whale family is the narwhal, another arctic species.

Family characteristics

The genus name Delphinapterus, means "dolphin without a fin". The species name leucas, means "white".

Other common names for the beluga include "white whale" and "belukha". They are also nicknamed "sea canaries" because of their vocalizations.

Scientists believe that early whales arose 55 to 60 million years ago from (now extinct) ancient land mammals that ventured back into the sea.

Representatives from the modern family Monodontidae first appear in the fossil record 9 to 10 million years ago in the eastern north Pacific.