This paper gives a brief biological summary of the dolphin. The dolphin is a mammal and member of the Delphinidae family.
Dolphins are mammals, meaning they are warm-blooded like humans. They are called cetaceans and are members of the Delphinidae family. All dolphins are toothed whales. While most people use the terms dolphin and porpoises interchangeably, they actually refer to two different types of animals.  Dolphins possess a distinct beak and sharp conical shaped teeth. They also tend to be larger than porpoises. Porpoises belong to the Phocoenidae family.  They tend to be smaller and more robust, the majority reaching about five to seven feet in length. They do not have distinct peaks, with their foreheads sloping almost uniformly to the tip of their snout and have spade shaped teeth. 
There are thirty two species of oceanic dolphins and five species of river dolphins. Dolphins are very social animals and live together in groups known as pods. Pods have been observed interacting with other pods from time to time. A mother dolphin will stay with her calf for two to three years.  Dolphins form strong bonds that may last a lifetime. They have been observed physically supporting sick or dying members of their pod.  However, they can be quite aggressive. Dominant members of pods have been known to abuse the weaker members. 
Some dolphin species can swim up to 25 miles per hour for long periods of time. Other species have been known to dive as deep as 1,000 feet under the service and jump as high as twenty feet out of the water.  The amount of time a dolphin can hold its breath depends on the species. Some have been known to hold their breath for up to 30 minutes, while others need to breath about every twenty seconds. 
Dolphins have physiological adaptations suited to their marine existence. Dolphin skin is completely smooth allowing them to glide faster through the water and their “eyes produce a special slippery secretion which protects the eyes from foreign objects and water friction.”  Dolphins are voluntary breathers, meaning that they choose when to breathe. Thus, when they sleep, dolphins must shut down only half of their brain, as they need the other half to tell their body when to breathe.  They tend to take short cat-naps floating just under the water’s surface, slowly rising to take a breath. 
Dolphins use a system of sound production and echolocation. They “rely on sound production and reception to navigate, communicate, and hunt in dark” waters.  Dolphins use whistles in order to communicate with other members of their pod. Each dolphin tends to have a signature whistle to identify themselves to the other members. 
The bottlenose dolphin is the most known species as it is typically used in aquatic shows, movies, and TV shows, such as the famous series, Flipper. They use echolocation as a means of communication and as a tool to help them hunt. The eating habits of dolphins depends on the species, but it ranges anywhere from fish, shrimp, squid and crabs to turtles, seals, small dolphins, and infant whales. An adult dolphin can consume up to thirty pounds of fish a day.  The average lifespan of dolphins varies as much as the eating habits. The average lifespan of a river dolphin is around twelve years of age, while oceanic dolphins live up to around forty years.