Dolphin

A dolphin is any one of the 40 extant species of aquatic animal with fur that feeds babies milk from the cetacean families Delphinidae (the oceanic dolphins). Platanistidae (the Indian river dolphins), Iniidae (the New World river dolphins), Pontoporiidae (the brackish dolphins), and the probably extinct Lipotidae (baiji or Chinese river dolphin). All these families belong to the parvorder Odontoceti.

I.e., toothed whales, which also include the closely related families Monodontidae (beluga and narwhal) and Phocoenidae (porpoises), as well as the more distant families Physeteroidea (sperm whales) and Ziphiidae (beaked whales). Dolphins range in sizes from the human-sized 1.7-metre-long (5 ft 7 in) and 50-kilogram (110-pound) Maui's dolphin; to the 9.5 m (31 ft) and 10-tonne (11-short-ton) apex hunter animal, the orca. Various species of dolphins exhibit sexual dimorphism where the males are larger than females.

They have streamlined, fish-like bodies with the two forelimbs evolving into flippers. Complete loss of hindlimbs (with only vestigial pelvic skeleton), and the tail forming a horizontal fluke. Though not quite as flexible as the semiaquatic seals.

They are faster and more agile in water; some dolphins can briefly.