Dolphin delphinidae; Dolphins belong to mammals, cetaceans, toothed cetaceans and dolphins, commonly known as dolphins. There are nearly 62 species of * * *, which are distributed in the oceans of the world. It is 1.2 ~ 4.2 meters long and weighs 23 ~ 225 kilograms. Dolphins generally have sharp mouths, and there are about 100 sharp teeth in the upper and lower jaws. They mainly feed on small fish, squid, shrimp and crab. Dolphins like to live a "collective" life, and the number ranges from a few to hundreds. Dolphin is a marine mammal with superb skills and intelligence. After training, I can play table tennis, jump in the ring of fire and so on. Dolphin's brain is the most developed animal species except human beings. Human brain accounts for 2. 1% of his body weight, and dolphin brain accounts for 1.7% of his body weight. The dolphin's brain consists of two completely separate parts. When one part is at work, the other part gets enough rest, so it can stay awake for life. Dolphins judge the distance, direction, position, shape and even the nature of objects by echolocation. Some people do experiments, blindfold dolphins and wade in muddy water. They can catch up with the food thrown at them quickly and accurately. Dolphins not only have amazing hearing, but also superb swimming and unusual diving skills. Some tests show that the diving record of dolphins is 300 meters deep, while people can only dive 20 meters without diving suits. As for its swimming speed, it is unmatched by human beings. The speed of dolphins can reach 40 kilometers per hour, which is equivalent to the medium speed of torpedo speedboats.