10 Facts About Dolphins

Mozambique, Ponta do Ouro, Three bottlenose dolphins in clear water
cormacmccreesh / Getty Images

Dolphins are well known for their intellect, their gregarious nature, and their acrobatic abilities. But there are much lesser known qualities that make a dolphin a dolphin. Here we'll explore ten characteristics of dolphins and learn more about these much-loved marine mammals.

1. Dolphins Belong to a Group of Mammals Referred to as Cetaceans

Cetaceans are a group of marine mammals that evolved from land mammals. They have developed numerous adaptations that make them well suited for life in water including a streamlined body, flippers, blowholes and a layer of blubber for insulation. Cetaceans are divided into two main groups, the baleen whales (which include the large filter feeding whales such as the blue whale, sei whale, northern right whale and others) and the toothed whales (the group to which dolphins belong). Other toothed whales include killer whales, pilot whales, beluga, narwhal, sperm whales, and several groups of river dolphins.

2. The Term 'Dolphin' Refers to a Diverse Assortment of Marine Mammals

The term dolphin is not restricted to a single taxonomic class and therefore it is an unspecific term. The groups of toothed whales whose members are often referred to as dolphins include the oceanic dolphins (Delphinidae), river dolphins (Iniidae), and the Indian river dolphins (Platanistidae). Of these groups, the oceanic dolphins are by far the most diverse.

3. Oceanic Dolphins Are Also Referred to as 'True Dolphins' and Are the Most Diverse Group of Cetaceans

The species of dolphins that belong to the Family Delphinidae are referred to as 'oceanic' or 'true' dolphins. The Delphinidae group includes about 32 species and is the largest of all subgroups of the cetaceans. Species of oceanic dolphins (Delphinidae) inhabit the open ocean, though this is not a strict rule for the group (in some cases, oceanic dolphins inhabit coastal waters or riverine habitats).

4. Some Oceanic Dolphins Have a Prominent Beak Also Known as a 'Rostrum'

The snout of some oceanic dolphins is long and slender due to their elongated, prominent jaw bones. Within the dolphins' elongated jaw bone sits numerous conical teeth (some species have as many as 130 teeth in each jaw). Species that have prominent beaks include, for example, Common Dolphin, Bottlenose Dolphin, Atlantic Humpbacked Dolphin, Tucuxi, Long-Snouted Spinner Dolphin, and numerous others.

5. A Dolphin's Forelimbs Are Known as 'Pectoral Flippers'

The forelimbs of a dolphin are anatomically equivalent to the forelimbs of other mammals (for example, they are analogous to arms in humans). But the bones within the forelimbs of dolphins have been shortened and made more rigid by supporting connective tissue. Pectoral flippers enable dolphins to steer and modulate their speed.

6. Some Dolphin Species Lack a Dorsal Fin

The dorsal fin of a dolphin (located on the back of the dolphin) acts like a keel when the animal swims, giving the animal directional control and stability within the water. But not all dolphins have a dorsal fin. For example, the Northern Rightwhale Dolphins and the Southern Right whale Dolphins lack dorsal fins.

7. Dolphins Have a Unique Sense of Hearing

Dolphins do not have prominent external ear openings. Their ear openings are small slits (located behind their eyes) which do not connect to the middle ear. Instead, scientists suggest 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 in and Out of the Water

When light passes from air to water, it changes speed. The creates an optical effect referred to as refraction. For dolphins, this means their eyes must correct for these differences if they are to see clearly in both conditions. Fortunately, dolphins have specially adapted lens and cornea that enable them to see clearly in and out of the water.

9. The Baiji Is a Critically Endangered River Dolphin That Inhabits the Murky Waters of the Yangtze River in China

The Baiji has suffered dramatic population declines over recent decades due to pollution and heavy industrial use of the Yangtze River. In 2006, a scientific expedition set out to locate any remaining Baiji but failed to find a single individual in the Yangtze. The species was declared functionally extinct.

10. Dolphins Probably Do Not Have a Very Strong Olfactory Sense

Dolphins, like all toothed whales, lack olfactory lobes and nerves. Because dolphins do not possess these anatomical features, they most likely have a poorly developed sense of smell.