Dolphins are a group of aquatic mammals of Kingfisher family, which are small or medium-sized toothed whales. They are widely distributed in the world's oceans, and also in brackish fresh water near inland sea and river estuaries. Some species are found in inland rivers. Usually like to live in groups and prey on fish, squid and so on.

Dolphinidae evolved from Miocene about/kloc-0.0 million years ago, with nearly 40 species belonging to/kloc-0.7 genus, which is the largest family among cetaceans. Black whales, such as pilot whales and killer whales, also belong to this family and are essentially large dolphins. The modern close relatives of Dolphinidae are Dolphinidae and Monoodontidae, and these three families together constitute Phallidae.

Dolphins have a spindle-shaped trunk, smooth and hairless skin, vigorous and flexible body, and are good at jumping and diving. It is the fastest mammal in the water. With a developed sonar system, it mainly relies on the echolocation function when moving, and has excellent hearing in water and air. The nose is on the top of the head, used for ventilation of water. The body size ranges from 1 m 30 kg (Jurassic dolphin) to 9.5 m 14 ton (killer whale), and the morphological characteristics are also different.

Their brains are complicated and their memories are good. They can learn many actions under human training. They are one of the most intelligent animal families. They are gentle, friendly and lively, and are widely loved by people all over the world.