List of cetaceans

This is a list of cetaceans. The order Cetacea includes whales, dolphins, and porpoises. It has 88 living species, divided into the suborders Odontoceti (the toothed whales, including dolphins and porpoises) and Mysticeti (the baleen whales). In addition, numerous species of extinct cetaceans exist, but they are not listed here. This list contains only the known, extant cetacean species including several recent discoveries (the baiji is also included, though it is believed to have gone extinct in 2006).

Cetaceans are aquatic mammals characterised by having fusiform (streamlined) body shapes, paddle-shaped front limbs and vestigial hind limbs. Their tails have been flattened into flukes to aid propulsion.

Suborder Mysticeti: baleen whales
The baleen whales, also called whalebone whales or great whales, form the Mysticeti, one of two suborders of the Cetacea (whales, dolphins and porpoises). Baleen whales are characterized by having baleen plates for filtering food from water, rather than having teeth, as with the Odontocetes. This distinguishes them from the other suborder of cetaceans, the toothed whales or Odontoceti. Living Mysticeti species have teeth only during the embryonal phase. Fossil Mysticeti had teeth before baleen evolved.

Family Balaenidae: right whales
The Balaenidae family of cetaceans contains two genera. Commonly called the right whales, it contains mainly right whale species. This name can be confusing, however, since one of the species is the bowhead whale, which is different from the right whale. All the Balaenidae whales have the following features: a smooth belly and chin, with no ventral grooves; a distinctive head shape with strongly arched, narrow rostrum (anatomy) and bowed lower jaw; lower lips that enfold the sides and front of the rostrum; long, narrow, elastic baleen plates (up to 9 times longer longer than wide) with fine baleen fringes; the fusion of all the cervical vertebrae and other skeletal characteristics; and a slow swimming speed.

Family Balaenopteridae: rorquals
Rorquals are the largest group of baleen whales, with 9 species in two genera. They include the largest animal that has ever lived, the blue whale, which can reach 150 tonnes, two others that easily pass 50 tonnes, and even the smallest of the group, the northern minke whale, reaches 9 tonnes. They take their name from a Norwegian word meaning "furrow whale": all members of the family have a series of longitudinal folds of skin running from below the mouth back to the navel (except the sei whale, which has shorter grooves). These are understood to allow the mouth to expand immensely when feeding. All rorquals have ventral grooves, and are the only cetaceans to have them. Additionally, they all have dorsal fins, broad, gently curving rostra and short baleen plates.

Family Eschrichtiidae: gray whale
The gray whale has been placed in a family of its own as it is sufficiently different from the right whales and the rorquals. The gray whale is the only benthic feeding baleen whale, filtering small organisms from the mud of shallow seas. They also have a gestation period of over a year, which is unusual for baleen whales.

Family Neobalaenidae: pygmy right whale
The pygmy right whale shares several characteristics with the right whales, although having dorsal fins separates them from right whales, and they have a very distinctive jaw configuration. Pygmy right whales' heads are no more than one-fourth the size of their bodies, whereas the right whales' heads are about one-third the size of their bodies.

Suborder Odontoceti: toothed whales
The toothed whales (systematic name Odontoceti) form a suborder of the cetaceans. As the name suggests, the suborder is characterized by having teeth (rather than baleen). Toothed whales are active hunters, feeding on fish, squid, and in some cases other marine mammals.

Family Delphinidae: oceanic dolphins
Oceanic dolphins are the members of the Delphinidae family of cetaceans. These aquatic mammals are related to whales and porpoises. As the name implies, these dolphins tend to be found in the open seas, unlike the river dolphins, although a few species such as the Irrawaddy dolphin are coastal or riverine. Six of the larger species in the Delphinidae, the killer whale (orca) and its relatives, are commonly called whales, rather than dolphins. They are also sometimes collectively known as "blackfish".

The Delphinidae are characterised by having distinct beaks (unlike the Phocoenidae), two or more fused cervical vertebrae and 20 or more pairs of teeth in their upper jaws. None is more than 4 m long.

Family Monodontidae: narwhal and beluga
The cetacean family Monodontidae comprises two unusual whale species, the narwhal, in which the male has a long tusk, and the white beluga.

The Monodontidae lack dorsal fins, which have been replaced by tough, fibrous ridges just behind the midpoints of their bodies and are probably an adaptation to swimming under ice, as both do in their Arctic habitat. The flippers are small, rounded and tend to curl up at the ends in adulthood. All, or almost all, the cervical vertebrae are unfused, allowing their heads to be turned independently of their bodies. None has any throat grooves.

Family Phocoenidae: porpoises
Porpoises are small cetaceans of the family Phocoenidae. They are distinct from dolphins, although the word "porpoise" has been used to refer to any small dolphin, especially by sailors and fishermen. The most obvious visible difference between the two groups is porpoises have spatulate (flattened) teeth distinct from the conical teeth of dolphins. In addition, porpoises are relatively r-selected compared with dolphins: that is, they rear more young more quickly than dolphins. All six species have small flippers, notched tail flukes, and no beaks. All carry at least 11 pairs of small teeth in their upper and lower jaws.

Porpoises, divided into six species, live in all oceans, mostly near the shore. Probably best known is the harbour porpoise, which can be found across the Northern Hemisphere.

Family Physeteridae: sperm whale
The sperm whale characteristically has a large, squarish head one-third the length of its body; the blowhole is slightly to the left hand side; the skin is usually wrinkled; and it has no teeth on the upper jaw.

Family Kogiidae: dwarf and pygmy sperm whales
The dwarf and pygmy sperm whales resemble sperm whales, but are far smaller. They are dark grey, dorsally, while ventrally they are lighter. They have blunt, squarish heads with narrow, underslung jaws; the flippers are set far forward, close to the head and their dorsal fins are set far back down the body.

Family Ziphiidae: beaked whales
A beaked whale is any of at least 21 species of small whale in the family Ziphiidae. They are one of the least-known families of large mammals: several species have only been described in the last two decades, and it is entirely possible that more remain as yet undiscovered. Six genera have been identified.

They possess a unique feeding mechanism known as suction feeding. Instead of catching their prey with teeth, it is sucked into their oral cavity. Their tongue can move very freely, and when suddenly retracted at the same time as the gular floor is distended, the pressure immediately drops within their mouth and the prey is sucked in with the water. The family members are characterized by having a lower jaw that extends at least to the tip of the upper jaw, a shallow or non-existent notch between the tail flukes, a dorsal fin set well back on the body, three of four fused cervical vertebrae, extensive skull asymmetry and two conspicuous throat grooves forming a 'V' pattern.

Superfamily Platanistoidea: river dolphins
River dolphins are five species of dolphins which reside in freshwater rivers and estuaries. They are classed in the Platanistoidea superfamily of cetaceans. Four species live in fresh water rivers. The fifth species, the La Plata dolphin, lives in saltwater estuaries and the ocean. However, it is scientifically classed in the river dolphin family rather than the oceanic dolphin family. All species have adaptations to facilitate fish catching: a long, forceps-like beak with numerous small teeth in both jaws, broad flippers to allow tight turns, small eyes, and unfused neck vertebrae to allow the head to move in relation to the body.

Family Iniidae: river dolphins
The Iniidae family of river dolphins contains only one genus and one species.
 * Amazon river dolphin – I. geoffrensis
 * I. geoffrensis geoffrensis – Amazon basin population (excluding Madeira river drainage area, above the Teotonio Rapids in Bolivia)
 * I. geoffrensis humboldtiana – Orinoco basin population
 * Bolivian river dolphin – I. boliviensis – Amazon basin population in the Madeira drainage area

Family Lipotidae: baiji
The Lipotidae family is another monotypic taxon, containing only the baiji. Fossil records suggest the dolphin first appeared 25 million years ago and migrated from the Pacific Ocean to the Yangtze River 20 million years ago. The species was declared functionally extinct in 2006 after an expedition to record population numbers.

Family Platanistidae: South Asian river dolphin
The Platanistidae were originally thought to hold only one species (the South Asian river dolphin), but based on differences in skull structure, vertebrae and lipid composition, scientists declared the two populations as separate species in the early 1970s. In 1998, the results of these studies were questioned and the classification reverted to the pre-1970 consensus. Thus, at present, two subspecies are recognized in the genus Platanista, P. gangetica minor (the Indus dolphin) and P. g. gangetica (the Ganges river dolphin).

Family Pontoporiidae: La Plata river dolphin
The La Plata river dolphin is the only species of the Pontoporiidae family and of the Pontoporia genus.

Notes and references

 * General references