List of cetaceans

This is a list of cetaceans. The order Cetacea includes whales, dolphins, and porpoises. It has just over eighty 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 a fusiform (streamlined) body shape, paddle-shaped front limbs and vestigial hind limbs. The tail has been flattened into a fluke 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, like 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
Balaenidae is a family of cetaceans that contains two genera. Commonly called the Right Whales as it contains mainly Right Whale species. This name can be confusing, however, since one of the species is the Bowhead Whale, which is different to 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; a slow swimming speed.

Family Balaenopteridae: Rorquals
Rorquals are the largest group of baleen whales, with nine 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.

Rorquals 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 a dorsal fin, a broad, gently curving rostrum 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 what separates them from Right Whales is that they have a dorsal fin, and they have a very distinctive jaw configuration. Pygmy Right Whales also have a head no more than ¼ the size of their body, whereas the Right Whales have heads approximately ⅓ the size of their body.

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 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 a distinct beak (unlike the Porpoises), two or more fused cervical vertebrae and 20 or more pairs of teeth in the upper jaw. None are more than 4 metres 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 a dorsal fin which has been replaced by a tough fibrous ridge just behind the midpoint of the body and is 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 the head to be turned independently of the body. None have any throat grooves.

Family Phocoenidae: Porpoises
The 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 that 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 beak. All carry at least 11 pairs of small teeth in the 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 ⅓ the length of its body; the blowhole is slightly to the left hand side; skin usually wrinkled; and 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 a narrow underslung jaw; the flippers are set far forward, close to the head and the dorsal fin is set far back down the body.

Family Ziphiidae: Beaked Whales
A beaked whale is any of at least 20 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 dolphin 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 that 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: Ganges and Indus River Dolphin
The Platanistidae was originally thought to hold only one species (Ganges and Indus 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, there are two subspecies recognized in the genus Platanista, Platanista gangetica minor (the Indus dolphin) and Platanista gangetica 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