The smallest cetaceans are Hector's dolphin, Commerson's dolphin, Franciscana dolphin, and Tucuxi dolphin. These dolphins average 4-6 ft. The largest dolphin is the killer whale. Dolphins are small whales, and dolphins are very ancient creatures. Rare dolphin species live in rivers in the Amazon and China, but most dolphins live in the temperate oceans .
Cetaceans comprise all whales, porpoises, and dolphins.
He noted that dolphins bore their young alive, dolphins suckled their young, dolphins breathed air, and dolphins communicated by underwater dolphin sounds. People and dolphins have had a special bond for centuries. During the 20th Century the navies of Russia and the United States carried out extensive maneuvers with dolphins, who acted as underwater couriers for the navy. Generally, dolphin missions were affixing bombs to enemy ships. In October 2000 Russia retired most of their dolphins.