There are over 30 species of dolphins, who are members of the Delphinedae family. The largest species of dolphin is the orca, commonly referred to as a killer whale. Adult orcas typically reach lengths of 30 feet. The smallest dolphins, the buffeo, are less than 4 feet long. Most dolphins are characterized by a beak-like snout, sharp cone-shaped teeth, and a powerful body. Ancient dolphin fossils dating back 11 million years have been found by scientists. Artwork containing pictures of dolphins has been traced to 1500 B.C., providing evidence of people's early interest and fascination with dolphins.
The bottle-nosed dolphin is perhaps the best known dolphin species. This is mainly due to their tendency to live near coastlines as well as their ability to adapt well to human contact. Bottle-nose dolphins commonly appear in water shows, aquariums, and even Hollywood productions. They can be found almost anywhere in the world with the exception of the polar seas. This extensive range makes it difficult to estimate their worldwide population.
Dolphins will eat an amount equal to approximately one-third of their body weight per day. They travel in groups, using their sense of hearing and knowledge of the ocean to locate schools of fish and other prey. Dolphins use their sharp teeth and quick reflexes to capture their prey. Muscles located in the back of the mouth allow dolphins to swallow food whole.
Dolphins usually surface once every two minutes and breath through a blowhole located at the top of the head. They swim by propelling their tail up and down while the dorsal fin gives them stability. They can sustain speeds of up to 19 miles per hour with quick bursts of up to 25 miles per hour. Dolphins may leap out of the water, following a path of a parabola. When dolphins land on their side or back, the jump is called a breach. A graceful, headfirst entry is called a bow.
Dolphins emit clicking and whistling sounds. The clicking sound originates from a biological mechanism located near the blowhole. Its purpose is to help dolphins navigate within a group and detect fish and other food sources. The whistling sound comes from a dolphin's larynx. Dolphins whistle for the purpose of communicating, attracting mates, and signaling danger. Dolphins in captivity are capable of mimicking human words. The oldest bottle-nosed dolphin on record lived to an age of 48 years.