Dolphin Facts

Scientific Name: Odontoceti

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

Dolphins (Odontoceti) are a group of 44 species of toothed whales or cetaceans. There are dolphins in every ocean on Earth, and there are freshwater species of dolphins that inhabit rivers in South Asian and South American. The largest dolphin species (the orca) grows to more than 30 feet long while the smallest, Hector's dolphin, is just 4.5 feet in length. Dolphins are well known for their intellect, their gregarious nature, and their acrobatic abilities. But there are many lesser-known qualities that make a dolphin a dolphin.

Fast Facts: Dolphins

  • Scientific Name: Odontoceti 
  • Common Name: Dolphin (Note: This name refers to the group of 44 species classified as Odontoceti; each has its own scientific and common name.)
  • Basic Animal Group: Mammal
  • Size: 5 feet long to over 30 feet long, depending on the species
  • Weight: Up to 6 tons
  • Lifespan: Up to 60 years depending on the species
  • Diet: Carnivore
  • Habitat: All oceans and some rivers
  • Population: Varies per species
  • Conservation Status: Bottlenose dolphins are considered to be of Least Concern, while about 10 species of dolphins are listed as Severely Threatened. 

Description

Dolphins are small-toothed Cetaceans, 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. Dolphins have curved beaks which means they appear to have permanent smiles.

Dolphins evolved from land mammals whose legs were underneath their bodies. As a result, dolphins tails move up and down as they swim, whereas a fish’s tail moves from side to side.

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.

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.

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.

The dorsal fin of a dolphin (located on the back of the dolphin) acts as 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 Rightwhale Dolphins lack dorsal fins.

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.

Bootlenose dolphin on the blue surface smiling
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Habitat and Distribution

Dolphins live in all of the world’s seas and oceans; many inhabit coastal areas or areas with shallower water. While most dolphins prefer warmer tropical or temperate waters one species, the orca (sometimes called killer whale) lives in both the Arctic Ocean and the Antarctic Southern Ocean. Five dolphin species prefer fresh to salt water; these species inhabit rivers in South America and South Asia.

Diet and Behavior

Dolphins are carnivorous predators. They use their strong teeth to hold their prey, but then either swallow their prey whole tear it into small pieces. They are relatively light eaters; the bottlenose dolphin, for example, eats about 5 percent of its weight each day.

Many species of dolphins migrate to find food. They consume a wide range of animals including fish, squid, crustaceans, shrimp, and octopus. The very large Orca dolphin may also eat marine mammals such as seals or marine birds such as penguins.

Many dolphin species work as a group to herd or coral fish. They may also follow fishing vessels to enjoy the "waste" thrown overboard. Some species will also use their flukes to beat and stun their prey.

Reproduction and Offspring

Most dolphins become sexually mature at between 5 and 8 years old. Dolphins give birth to a single calf once every one to six years and then feed their babies milk through their nipples.

Dolphin pregnancies range in length from 11 to 17 months. Location can make an impact on the gestation period.

When a pregnant female is ready to deliver, she separates herself from the rest of the pod to a location near the water's surface. Dolphin calves are usually born tail first; at birth, calves are about 35–40 inches long and weigh between 23 and 65 pounds. The mother immediately brings her infant to the surface so it can breathe.

Newborn calves look a bit different from their parents; they typically have dark skin with lighter bands which fade over time. Their fins are quite soft but harden very quickly. They can swim almost immediately, but do require the protection of the pod; in fact, young dolphins are typically nursed for the first two to three years of life and may stay with their mothers for up to eight years.

Atlantic spotted dolphins (Stenella frontalis) mother and calf
Georgette Douwma/Getty Images 

Species

Dolphins are members of the order Cetacea, Suborder Odontoceti, Families Delphinidae, Iniidae, and Lipotidae. Within those families, there are 21 genera, 44 species, and several subspecies. The species of dolphins include:

Genus: Delphinus

  • Delphinus capensis (Long-beaked common dolphin)
  • Delphinus delphis (Short-beaked common dolphin)
  • Delphinus tropicalis. (Arabian common dolphin)

Genus: Tursiops

  • Tursiops truncatus (Common bottlenose dolphin)
  • Tursiops aduncus (Indo-Pacific bottlenose dolphin)
  • Tursiops australis (Burrunan dolphin)

Genus: Lissodelphis

  • Lisodelphis borealis (Northern right whale dolphin)
  • Lssodelphis peronii (Southern right whale dolphin)

Genus: Sotalia

  • Sotalia fluviatilis (Tucuxi)
  • Sotalia guianensis (Guiana dolphin)

Genus: Sousa

  • Sousa chinensis (Indo-Pacific humpback dolphin)
    Subspecies:
  • Sousa chinensis chinensis (Chinese white dolphin)
  • Sousa chinensis plumbea (Indo-Pacific humpback dolphin)
  • Sousa teuszii (Atlantic Humpback Dolphin)
  • Sousa plumbea (Indian Humpback dolphin)

Genus: Stenella

  • Stenella frontalis (Atlantic spotted dolphin)
  • Stenella clymene (Clymene dolphin)
  • Stenella attenuata (Pantropical spotted dolphin)
  • Stenella longirostris (Spinner dolphin)
  • Stenella coeruleoalba (Striped dolphin)

Genus: Steno

  • Steno bredanensis (Rough-toothed dolphin)

Genus: Cephalorhynchus

  • Cephalorhynchus eutropia (Chilean dolphin)
  • Cephalorhynchus commersonii (Commerson’s dolphin)
  • Cephalorhynchus heavisidii (Heaviside’s Dolphin)
  • Cephalorhynchus hectori (Hector’s dolphin)

Genus: Grampus

  • Grampus griseus (Risso’s dolphin)

Genus: Lagenodelphis

  • Lagenodelphis hosei (Fraser’s dolphin)

Genus: Lagenorhynchus

  • Lagenorhynchus acutus (Atlantic white-sided dolphin)
  • Lagenorhynchus obscurus (Dusky dolphin)
  • Lagenorhynchus cruciger (Hourglass dolphin)
  • Lagenorhynchus obliquidens (Pacific white-sided dolphin)
  • Lagenorhynchus australis (Peale’s dolphin)
  • Lagenorhynchus albirostris (White-beaked dolphin)

Genus: Peponocephala

  • Peponocephala electra (Melon-headed whale)

Genus: Orcaella

  • Orcaella heinsohni (Australian snubfin dolphin)
  • Orcaella brevirostris (Irrawaddy dolphin)

Genus: Orcinus

  • Orcinus orca (Orca- Killer Whale)

Genus: Feresa

  • Feresa attenuata (Pygmy killer whale)

Genus: Pseudorca

  • Pseudorca crassidens (False Killer whale)

Genus: Globicephala

  • Globicephala melas (Long-finned pilot whale)
  • Globicephala macrorhynchus (Short-finned pilot whale)

Superfamily: Platanistoidea

Genus Inia, Family: Iniidae

  • Inia geoffrensis. (Amazon river dolphin).
  • Inia araguaiaensis (Araguaian river dolphin).

Genus Lipotes, Family: Lipotidae

  • Lipotes vexillifer (Baiji)

Genus Pontoporia, Family: Pontoporiidae

  • Pontoporia blainvillei (La Plata dolphin)

Genus Platanista, family: Platanistidae

  • Platanista gangetica (South Asian river dolphin)
    Subspecies:
  • Platanista gangetica gangetica (Ganges river dolphin)
  • Platanista gangetica minor (Indus river dolphin)

Conservation Status

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.

Dolphins and Humans

Humans have long been fascinated with dolphins, but the relationship between humans and dolphins has been complex. Dolphins are the subject of stories, myths, and legends as well as great works of art. Because of their great intelligence, dolphins have been used for military exercises and therapeutic support. They are also often kept in captivity and trained to perform; in most cases, this practice is now considered to be cruel.

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