Along with their intellect, gregarious nature, and acrobatic abilities; dolphins are famous for many other things. Here ten of the lesser known facts about these much-loved marine animals are listed.

1. Dolphins are members of the group of mammals called cetaceans (or Cetacea). Cetaceans are then split into two main groups, the toothed whales (or Ondontoceti) and the baleen whales (Mysticeti). Dolphins are toothed whales (Ondontoceti) and they include killer whales, pilot whales, beluga, narwhal and the largest of them all sperm whales. There are also a number of river dolphins.

2. The term 'dolphin' refers to many marine mammals. The term dolphin is not restricted to a single taxonomic class, family or even genera and as a result is an unspecific term. Most of the toothed whales are referred to as dolphins.

3. Oceanic dolphins are also referred to as 'true dolphins' and are the most common and diverse group of cetaceans. Species in the family delphinidae are referred to as 'oceanic' or 'true' dolphins. Delphinidae contains about 32 species and is the largest of all groups in the order cetacea. Species of delphinidae typically inhabit the open ocean and are called pelagic although some inhabit coastal waters or even riverine habitats.

4. Some oceanic dolphins have a rostrum which looks like a beak. In some oceanic dolphins the snout is long and slender due to elongated or the jaw bones. Within the elongated jaw bone sit many conical teeth. Some of the species with prominent rostrums are long and short beaked common dolphins, common and Indo-Pacific bottlenose dolphins, Atlantic humpbacked dolphins, tucuxis, long-snouted spinner dolphins and many others.

5. A dolphin's forelimbs which are known as 'pectoral flippers'. The forelimbs or "arms" of a dolphin are the same anatomically as a terrestrial mammals legs. But the bones which make up the forelimbs in dolphins have been shortened and made more rigid by supporting connective tissue. These pectoral flippers allow the dolphins regulate their speed and turn.

6. Not all dolphin species possess a dorsal fin. The dorsal fin of a dolphin, which is located on the back, acts like a keel when the animal swims. This gives the dolphin directional control and stability within the water column. Northern rightwhale dolphins and the southern rightwhale dolphins however lack dorsal fins.

7. Dolphins' sense of hearing is unique. Prominent external ear openings are absent in dolphins. Instead their ear openings are small slits, positioned just posterior of the eyes; these openings do not connect to the middle ear. Instead, it is thought that sound is conducted to the inner and middle ear by fat-lobes located within the lower jaw and by various bones within the skull.

8. Dolphins have excellent vision both in and out of water. Light changes speed when it passes from air to water and as a result the optical affects are different. This is known as refraction. For marine mammals like dolphins, this means their eyes must correct the refraction so they can see clearly in both conditions. Fortunately the dolphins' lens are specially adapted that enables them to see clearly in and out of the water.

9. The Baiji has since 2006 become the latest dolphin to be declared extinct. The Baiji has suffered dramatic population declines over recent decades due to pollution and heavy industrial use of the Yangtze river, and a team of sciences in 2006 conducted a survey which did not find a single specimens and the species was declared biologically extinct; meaning that there would not be enough individuals in the wild to form a functional population.

10. Dolphins probably do not have a very good sense of smell. All toothed whales lack olfactory lobes and nerves. This means they cannot process olfactory particles in the water. Instead they rely on their excellent eye sight and hearing as well as echolocation to find each other, navigate and find prey.

If you are interested in finding wild dolphins and their larger cousins; whales; there are many wildlife tours and wildlife holidays around which can bring you to the dolphins of the world.