Dolphins are marine mammals closely related to whales. There are almost forty species of dolphin and they are found worldwide. Dolphins are thought to be among the most intelligent creatures. They often travel in packs and make great performing animals. A dolphin's brain is very complex in structure, and is fairly large compared to its body size. There have been many stories through the history of time, of how intelligent dolphins have touched the lives of people and other animals, rescuing drowning swimmers and dogs.