According to Aiwen Education Network, dolphins are small to medium-sized whales, weighing 30- 14000 kg and about 1.2-9.5 meters long. Males are usually bigger than females. Most dolphins have unique head characteristics. Because of the existence of bean-like fat, the forehead before the beak bulges, which is also called "forehead bulge" This structure helps to collect echolocation and foraging sounds.

Dolphin is an aquatic mammal of Dolphinidae, a small or medium-sized toothed whale. They live widely in the oceans of the world, and are also distributed in the salty and 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.