Dolphins: Delphinidae

Dolphins are found in all oceans and many rivers of the world. They are often confused with other aquatic animals. Dolphins arose from the same ancestor as porpoises, but have been a separate family for at least eleven million years. In addition, the common names of some dolphins lead to confusion. For example, the killer whale is actually a dolphin. With genetic testing now available, some re-classification of individual dolphin species is occurring.

Dolphins have long, streamlined, torpedo-shaped bodies adapted to life in the ocean. Generally they are fast, acrobatic, agile swimmers. The bones in what would be the hand and arm of a land animal are compressed into a web of bones to make flippers. Their back legs are so reduced that all that remains are a few internal pelvic bones. They have strong, muscular tails. Dolphins breathe through a single blowhole on top of their head. All dolphins have a melon, a fatty organ on their forehead that they use for echolocation. Echolocation (eck-oh-loh-KAY-shun) involves making sounds that bounce off objects. Sense organs pick up the echo or reflected sound and use information about the echo's timing, direction, and strength to determine the location of objects. They have a single type of cone-shaped tooth, but the number of teeth ranges from four to about 260, and the size varies with the size of the species. Dolphins are able to taste, but not smell.

Within this family there are many physical differences in size and color. The smallest dolphin is the endangered Hector's dolphin. They are about 4.5 feet (1.4 meters) long and weigh about 117 pounds (53 kilograms). The largest is the killer whale, which can measure 30 feet (9 meters) and weigh 12,000 pounds (5,600 kilograms). Dolphins come in many colors, including black, white, gray, tan, brown, orange, and pink. Some have distinctive color patterns, while others are a single color.