Dolphins are part of large group of animals called whales. Generally, they are among the smaller whales. Dolphins are from 1.5 metres (4.9 ft) to 4 metres (13 ft) long, but the largest dolphin, the killer whale (or orca), can be up to 8 metres (26 ft) long.

There are more than 35 species of dolphin. They are divided into two groups: oceanic dolphins and river dolphins. Oceanic dolphins live in all of the world's oceans. The most widespread species are the common dolphin and the bottlenose dolphin. Three of the four species of river dolphins live in fresh water rivers of South America and Asia, while La Plata dolphin lives in saltwater estuaries and the ocean coastline waters.

The name 'dolphin' comes from the Ancient Greek δελφίς (delphis) meaning "with a womb", because it was first thought to be a fish with a womb. It is now known to be a mammal. Dolphins breathe air. A dolphin's nose is on top of its head so the dolphin can easily breathe on the surface of the water. The skin of a dolphin has no scales. It is grey, soft and smooth. However, it is very firm, due to how much muscle they have.

Dolphins are always social. They can help each other fight off predators. Dolphins have fought off sharks in this way. They can kill large sharks by ramming them over and over again with their snouts and heads. They look after the young, when the mothers need to leave their calves to hunt for food. Since the food may be in deeper waters while the young need to breathe more often than the adults.

Sources: https://simple.wikipedia.org/wiki/Dolphin

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