What is a dolphin?

Dolphins belong to the group of animals that scientists call cetaceans. This means all the different types of whales, dolphins and porpoises that there are in the world.
This big group is split into two groups, baleen whales and toothed whales. Baleen whales sieve food through special filters called baleen plates. They don`t have any teeth at all. Dolphins are part of the toothed whale group. The two groups have special scientific names:

Mysticetes - baleen whales, eg. Blue Whale, Humpback Whale, Minke Whale.

Odontocetes - toothed whales, eg. Sperm Whale, Orca, Bottlenose Dolphin.

What sort of animal are dolphins?

Dolphins are mammals. They have lungs and breathe air. They give birth to live young which are fed with their mothers` rich milk. The mammal family also includes dogs, cats, elephants, sheep, apes, monkeys, humans and many others.

There are about 79 different kinds of whales, dolphins and porpoises. Some scientists say there are 45 kinds of dolphin. This includes the 26 types of ocean dolphin as well as river dolphins, porpoises, Pilot Whales, Orca, Beluga, Narwhal and others.

The Dolphin and Porpoise families are part of the same big group of animals. They are very similar in many ways so it can be quite confusing. The differences are that most porpoises are quite small, the smallest is the Vaquita, only about 1.5m long. Porpoises don`t have a beak (some dolphins don`t have one either), and only one type of porpoise has a dorsal fin ( a few dolphins don`t have dorsal fins either -we said it was confusing!). But there is one difference that all porpoise share. It is the shape of their teeth. The teeth of a porpoise are flattened and shaped like spades. Dolphin teeth are usually cone shaped.

Tricky! Sometimes size helps as male dolphins are usually larger than females of the same type. Otherwise you need to be very close because all the parts which show which sex an animal is are hidden inside the dolphin`s body. A male dolphin has one slit visible underneath about two thirds of the way along the body towards the tail. A female has a small slit each side of the main one. They hide the mammary glands where her baby will suckle.

Robin Petch and Kris Simpson, Dolphinicity Surveys