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Dolphins are mammals that live in the oceans and seas. They are related to the types of whales that have rows of teeth used for catching fish and marine animals for food. Dolphins are highly intelligent and complex creatures that have a specialised set of organs that enable them to "see" using sound.
Dolphins can emit a high-pitched series of clicks in a narrow beam directly in front of them. As the clicking sounds strike an object, such as a fish, some of the sound is reflected back as an echo to the dolphin, who can hear the sounds and perceive a image of the object or fish. The process is known as echolocation, and is the same principle used in sonar navigation by submarines.
The dolphin has some remarkable structures to produce the sound and to detect the returning echoes. In air chambers close to the blowhole at the top of a dolphin's head, there are a pair of liplike membranes that the dolphin forces air through to produce sound. The membranes resemble the lips of a monkey and are sometimes referred to as "monkey lips." At the front of a dolphin's head, just forward of the sound-producing membranes, there is a rounded dome-like structure known as the "melon" which is made of fatty tissue and oil. The dolphin uses it like a lens, contracting the attached muscles to amplify and focus the sound in a powerful, concentrated beam. The clicks are in a sound-range above the range of human hearing.
The dolphin has specialised structures to receive the sound as well. returning echoes are absorbed by special sound-conducting tissues in the lower jawbones of the dolphin. The sound waves are conducted directly to the dolphin's inner ear. (A dolphin's outer ear has a very small opening that does not seem to have any function.)
The brain of a dolphin is very large, larger proportionally than a human's brain. A big portion of the dolphin's brain is devoted to hearing and the perception of sound. Research indicates that dolphins can actually "see" images from the patterns created by the echoes. They may even have a type of x-ray-like vision that can see the bone structure and other features in fish that are below the skin, since sound waves will travel through softer body tissues and be reflected back in the echoes.
Dolphin sonar or echolocation is very sensitive. They can detect differences in objects as small as a kernel of corn from fifty feet away. A dolphin will often echolocate by emitting clicks while sweeping its head fro side to side. The dolphin will pause between a series of clicks to hear the returning echoes before it emits another series of clicks. Dolphins can even tell which type of fish it sees with its sonar and will avoid the fish it does not like.
There are still unknown elements in the dolphin's sophisticated sonar abilities, and research is ongoing to unravel the mysteries of the talents of this fascinating marine mammal.