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Cetacea (; , ) is an infraorder of
aquatic mammal Aquatic and semiaquatic mammals are a diverse group of mammals that dwell partly or entirely in bodies of water. They include the various marine mammals who dwell in oceans, as well as various freshwater species, such as the European otter. They ...
s that includes whales, dolphins, and
porpoises Porpoises are a group of fully aquatic marine mammals, all of which are classified under the family Phocoenidae, parvorder Odontoceti (toothed whales). Although similar in appearance to dolphins, they are more closely related to narwhals an ...
. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively carnivorous diet. They propel themselves through the water with powerful up-and-down movement of their tail which ends in a paddle-like fluke, using their flipper-shaped forelimbs to maneuver. While the majority of cetaceans live in marine environments, a small number exclusively reside in
brackish water Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estuari ...
or fresh water. Having a
cosmopolitan distribution In biogeography, cosmopolitan distribution is the term for the range of a taxon that extends across all or most of the world in appropriate habitats. Such a taxon, usually a species, is said to exhibit cosmopolitanism or cosmopolitism. The ext ...
, they can be found in some rivers and all of Earth's oceans, and many species inhabit vast ranges where they migrate with the changing of the seasons. Cetaceans are famous for their high intelligence and complex social behaviour as well as for the enormous size of some of the group's members, such as the
blue whale The blue whale (''Balaenoptera musculus'') is a marine mammal and a baleen whale. Reaching a maximum confirmed length of and weighing up to , it is the largest animal known to have ever existed. The blue whale's long and slender body can b ...
which reaches a maximum confirmed length of 29.9 meters (98 feet) and a weight of 173 tonnes (190 short tons), making it the largest animal known to have ever existed.Wood, Gerald ''The Guinness Book of Animal Facts and Feats'' (1983) There are approximately 89 living species split into two parvorders:
Odontoceti The toothed whales (also called odontocetes, systematic name Odontoceti) are a parvorder of cetaceans that includes dolphins, porpoises, and all other whales possessing teeth, such as the beaked whales and sperm whales. Seventy-three species of ...
or toothed whales (containing
porpoise Porpoises are a group of fully aquatic marine mammals, all of which are classified under the family Phocoenidae, parvorder Odontoceti (toothed whales). Although similar in appearance to dolphins, they are more closely related to narwhals a ...
s, dolphins, other predatory whales like the
beluga The beluga whale (/bɪˈluːɡə/) (Delphinapterus leucas) is an Arctic and sub-Arctic cetacean. It is one of two members of the family Monodontidae, along with the narwhal, and the only member of the genus Delphinapterus. It is also known as the wh ...
and the
sperm whale The sperm whale or cachalot (''Physeter macrocephalus'') is the largest of the toothed whales and the largest toothed predator. It is the only living member of the genus '' Physeter'' and one of three extant species in the sperm whale fami ...
, and the poorly understood
beaked whale Beaked whales ( systematic name Ziphiidae) are a family of cetaceans noted as being one of the least known groups of mammals because of their deep-sea habitat and apparent low abundance. Only three or four of the 24 species are reasonably well- ...
s) and the filter feeding Mysticeti or
baleen Baleen is a filter-feeding system inside the mouths of baleen whales. To use baleen, the whale first opens its mouth underwater to take in water. The whale then pushes the water out, and animals such as krill are filtered by the baleen and r ...
whales (which includes species like the
blue whale The blue whale (''Balaenoptera musculus'') is a marine mammal and a baleen whale. Reaching a maximum confirmed length of and weighing up to , it is the largest animal known to have ever existed. The blue whale's long and slender body can b ...
, the
humpback whale The humpback whale (''Megaptera novaeangliae'') is a species of baleen whale. It is a rorqual (a member of the family Balaenopteridae) and is the only species in the genus ''Megaptera''. Adults range in length from and weigh up to . The hu ...
and the
bowhead whale The bowhead whale (''Balaena mysticetus'') is a species of baleen whale belonging to the family Balaenidae and the only living representative of the genus '' Balaena''. They are the only baleen whale endemic to the Arctic and subarctic waters, a ...
). Despite their highly modified bodies and carnivorous lifestyle, genetic and fossil evidence places cetaceans as nested within
even-toed ungulate The even-toed ungulates (Artiodactyla , ) are ungulates—hoofed animals—which bear weight equally on two (an even number) of their five toes: the third and fourth. The other three toes are either present, absent, vestigial, or pointing poste ...
s, most closely related to
hippopotamus The hippopotamus ( ; : hippopotamuses or hippopotami; ''Hippopotamus amphibius''), also called the hippo, common hippopotamus, or river hippopotamus, is a large semiaquatic mammal native to sub-Saharan Africa. It is one of only two extant ...
within the clade
Whippomorpha Whippomorpha or Cetancodonta is a group of animals that contains all living cetaceans ( whales, dolphins, etc.) and hippopotamuses, as well as their extinct relatives, i.e. Entelodonts and Andrewsarchus. All Whippomorphs are descendants of the ...
. Cetaceans have been extensively hunted for their meat,
blubber Blubber is a thick layer of vascularized adipose tissue under the skin of all cetaceans, pinnipeds, penguins, and sirenians. Description Lipid-rich, collagen fiber-laced blubber comprises the hypodermis and covers the whole body, except for ...
and oil by commercial operations. Although the
International Whaling Commission The International Whaling Commission (IWC) is a specialised regional fishery management organisation, established under the terms of the 1946 International Convention for the Regulation of Whaling (ICRW) to "provide for the proper conservation ...
has agreed on putting a halt to commercial whaling, whale hunting is still going on, either under IWC quotas to assist the subsistence of Arctic native people or in the name of scientific research, although a large spectrum of non-lethal methods are now available to study marine mammals in the wild. Cetaceans also face severe environmental hazards from underwater
noise pollution Noise pollution, also known as environmental noise or sound pollution, is the propagation of noise with ranging impacts on the activity of human or animal life, most of them are harmful to a degree. The source of outdoor noise worldwide is mai ...
, entanglement in abandonned ropes and nets, collisions with ships, plastic and heavy metals build-up, to accelerating climate change, but how much they are affected varies widely from species to species, from minimally in the case of the
southern bottlenose whale The southern bottlenose whale (''Hyperoodon planifrons'') is a species of whale, in the Ziphiid family, one of two members of the genus ''Hyperoodon''. Seldom observed, the southern bottlenose whale is resident in Antarctic waters. The species w ...
to the
baiji The baiji (; IPA: ; ''Lipotes vexillifer'', ''Lipotes'' meaning "left behind" and ''vexillifer'' "flag bearer") is a possibly extinct species of freshwater dolphin native to the Yangtze river system in China. It is thought to be the first dolph ...
(or Chinese river dolphin) which is considered to be functionally extinct due to human activity.


Baleen whales and toothed whales

The two parvorders,
baleen whale Baleen whales (systematic name Mysticeti), also known as whalebone whales, are a parvorder of carnivorous marine mammals of the infraorder Cetacea ( whales, dolphins and porpoises) which use keratinaceous baleen plates (or "whalebone") in the ...
s (Mysticeti) and
toothed whale The toothed whales (also called odontocetes, systematic name Odontoceti) are a parvorder of cetaceans that includes dolphins, porpoises, and all other whales possessing teeth, such as the beaked whales and sperm whales. Seventy-three species of ...
s (Odontoceti), are thought to have diverged around thirty-four million years ago. Baleen whales have bristles made of keratin instead of
teeth A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tea ...
. The bristles filter
krill Krill are small crustaceans of the order Euphausiacea, and are found in all the world's oceans. The name "krill" comes from the Norwegian word ', meaning "small fry of fish", which is also often attributed to species of fish. Krill are cons ...
and other small invertebrates from seawater.
Grey whale The gray whale (''Eschrichtius robustus''), also known as the grey whale,Britannica Micro.: v. IV, p. 693. gray back whale, Pacific gray whale, Korean gray whale, or California gray whale, is a baleen whale that migrates between feeding and bree ...
s feed on bottom-dwelling mollusks.
Rorqual Rorquals () are the largest group of baleen whales, which comprise the family Balaenopteridae, containing ten extant species in three genera. They include the largest animal that has ever lived, the blue whale, which can reach , and the fin wha ...
family (balaenopterids) use throat pleats to expand their mouths to take in food and sieve out the water. Balaenids (
right whales Right whales are three species of large baleen whales of the genus ''Eubalaena'': the North Atlantic right whale (''E. glacialis''), the North Pacific right whale (''E. japonica'') and the Southern right whale (''E. australis''). They are clas ...
and
bowhead whales The bowhead whale (''Balaena mysticetus'') is a species of baleen whale belonging to the family Balaenidae and the only living representative of the genus ''Balaena''. They are the only baleen whale endemic to the Arctic and subarctic waters, an ...
) have massive heads that can make up 40% of their body mass. Most mysticetes prefer the food-rich colder waters of the Northern and Southern Hemispheres, migrating to the Equator to give birth. During this process, they are capable of fasting for several months, relying on their fat reserves. The parvorder of Odontocetes – the toothed whales – include sperm whales, beaked whales, orcas, dolphins and porpoises. Generally the teeth are designed for catching fish, squid or other
marine invertebrates Marine invertebrates are the invertebrates that live in marine habitats. Invertebrate is a blanket term that includes all animals apart from the vertebrate members of the chordate phylum. Invertebrates lack a vertebral column, and some have ev ...
, not for chewing them, so prey is swallowed whole. Teeth are shaped like cones (dolphins and sperm whales), spades (
porpoise Porpoises are a group of fully aquatic marine mammals, all of which are classified under the family Phocoenidae, parvorder Odontoceti (toothed whales). Although similar in appearance to dolphins, they are more closely related to narwhals a ...
s), pegs (
beluga The beluga whale (/bɪˈluːɡə/) (Delphinapterus leucas) is an Arctic and sub-Arctic cetacean. It is one of two members of the family Monodontidae, along with the narwhal, and the only member of the genus Delphinapterus. It is also known as the wh ...
s), tusks (
narwhals The narwhal, also known as a narwhale (''Monodon monoceros''), is a medium-sized toothed whale that possesses a large "tusk" from a protruding canine tooth. It lives year-round in the Arctic waters around Greenland, Canada and Russia. It is ...
) or variable (beaked whale males). Female beaked whales' teeth are hidden in the gums and are not visible, and most male beaked whales have only two short tusks. Narwhals have vestigial teeth other than their tusk, which is present on males and 15% of females and has millions of nerves to sense water temperature, pressure and salinity. A few toothed whales, such as some orcas, feed on mammals, such as pinnipeds and other whales. Toothed whales have well-developed senses – their eyesight and hearing are adapted for both air and water, and they have advanced sonar capabilities using their
melon A melon is any of various plants of the family Cucurbitaceae with sweet, edible, and fleshy fruit. The word "melon" can refer to either the plant or specifically to the fruit. Botanically, a melon is a kind of berry, specifically a " pepo". The ...
. Their hearing is so well-adapted for both air and water that some blind specimens can survive. Some species, such as sperm whales, are well adapted for diving to great depths. Several species of toothed whales show sexual dimorphism, in which the males differ from the females, usually for purposes of sexual display or aggression.


Anatomy

Cetacean bodies are generally similar to those of fish, which can be attributed to their lifestyle and the habitat conditions. Their body is well-adapted to their habitat, although they share essential characteristics with other higher mammals (
Eutheria Eutheria (; from Greek , 'good, right' and , 'beast'; ) is the clade consisting of all therian mammals that are more closely related to placentals than to marsupials. Eutherians are distinguished from noneutherians by various phenotypic tra ...
). They have a streamlined shape, and their forelimbs are flippers. Almost all have a
dorsal fin A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through co ...
on their backs, but this can take on many forms, depending on the species. A few species, such as the
beluga whale The beluga whale () (''Delphinapterus leucas'') is an Arctic and sub-Arctic cetacean. It is one of two members of the family Monodontidae, along with the narwhal, and the only member of the genus ''Delphinapterus''. It is also known as the wh ...
, lack them. Both the flipper and the fin are for stabilization and steering in the water. The male genitals and the mammary glands of females are sunken into the body. The body is wrapped in a thick layer of fat, known as
blubber Blubber is a thick layer of vascularized adipose tissue under the skin of all cetaceans, pinnipeds, penguins, and sirenians. Description Lipid-rich, collagen fiber-laced blubber comprises the hypodermis and covers the whole body, except for ...
. This provides thermal insulation and gives cetaceans their smooth, streamlined body shape. In larger species, it can reach a thickness up to half a meter (1.6 ft). Sexual dimorphism evolved in many toothed whales. Sperm whales, narwhals, many members of the
beaked whale Beaked whales ( systematic name Ziphiidae) are a family of cetaceans noted as being one of the least known groups of mammals because of their deep-sea habitat and apparent low abundance. Only three or four of the 24 species are reasonably well- ...
family, several species of the
porpoise Porpoises are a group of fully aquatic marine mammals, all of which are classified under the family Phocoenidae, parvorder Odontoceti (toothed whales). Although similar in appearance to dolphins, they are more closely related to narwhals a ...
family, orcas,
pilot whale Pilot whales are cetaceans belonging to the genus ''Globicephala''. The two extant species are the long-finned pilot whale (''G. melas'') and the short-finned pilot whale (''G. macrorhynchus''). The two are not readily distinguishable at sea, ...
s, eastern
spinner dolphin The spinner dolphin (''Stenella longirostris'') is a small dolphin found in off-shore tropical waters around the world. It is famous for its acrobatic displays in which it rotates around its longitudinal axis as it leaps through the air. It is a ...
s and northern right whale dolphins show this characteristic. Males in these species developed external features absent in females that are advantageous in combat or display. For example, male sperm whales are up to 63% percent larger than females, and many beaked whales possess tusks used in competition among males. Hind legs are not present in cetaceans, nor are any other external body attachments such as a pinna and hair.


Head

Whales have an elongated head, especially
baleen whales Baleen whales ( systematic name Mysticeti), also known as whalebone whales, are a parvorder of carnivorous marine mammals of the infraorder Cetacea ( whales, dolphins and porpoises) which use keratinaceous baleen plates (or "whalebone") in t ...
, due to the wide overhanging jaw. Bowhead whale plates can be long. Their nostril(s) make up the blowhole, with one in toothed whales and two in baleen whales. The nostrils are located on top of the head above the eyes so that the rest of the body can remain submerged while surfacing for air. The back of the skull is significantly shortened and deformed. By shifting the nostrils to the top of the head, the nasal passages extend perpendicularly through the skull. The teeth or baleen in the upper jaw sit exclusively on the maxilla. The braincase is concentrated through the nasal passage to the front and is correspondingly higher, with individual cranial bones that overlap. In toothed whales, connective tissue exists in the
melon A melon is any of various plants of the family Cucurbitaceae with sweet, edible, and fleshy fruit. The word "melon" can refer to either the plant or specifically to the fruit. Botanically, a melon is a kind of berry, specifically a " pepo". The ...
as a head buckle. This is filled with air sacs and fat that aid in buoyancy and
biosonar Echolocation, also called bio sonar, is a biological sonar used by several animal species. Echolocating animals emit calls out to the environment and listen to the echoes of those calls that return from various objects near them. They use these ...
. The sperm whale has a particularly pronounced melon; this is called the
spermaceti organ The spermaceti organ is an organ present in the heads of toothed whales of the family Physeteroidea, in particular the sperm whale. This organ contains a waxy liquid called spermaceti and is involved in the generation of sound. Description I ...
and contains the eponymous spermaceti, hence the name "sperm whale". Even the long tusk of the narwhal is a vice-formed tooth. In many toothed whales, the depression in their skull is due to the formation of a large melon and multiple, asymmetric air bags. River dolphins, unlike most other cetaceans, can turn their head 90°. Most other cetaceans have fused neck vertebrae and are unable to turn their head at all. The
baleen Baleen is a filter-feeding system inside the mouths of baleen whales. To use baleen, the whale first opens its mouth underwater to take in water. The whale then pushes the water out, and animals such as krill are filtered by the baleen and r ...
of baleen whales consists of long, fibrous strands of keratin. Located in place of the teeth, it has the appearance of a huge fringe and is used to sieve the water for plankton and krill.


Brain

The neocortex of many cetaceans is home to elongated
spindle neurons Von Economo neurons (VENs), also called spindle neurons, are a specific class of mammalian cortical neurons characterized by a large spindle-shaped soma (or body) gradually tapering into a single apical axon (the ramification that ''transmits ...
that, prior to 2019, were known only in
hominids The Hominidae (), whose members are known as the great apes or hominids (), are a taxonomic family of primates that includes eight extant species in four genera: '' Pongo'' (the Bornean, Sumatran and Tapanuli orangutan); ''Gorilla'' (the eas ...
. In humans, these cells are thought to be involved in social conduct, emotions, judgment and theory of mind. Cetacean spindle neurons are found in areas of the brain homologous to where they are found in humans, suggesting they perform a similar function.
Brain size The size of the brain is a frequent topic of study within the fields of anatomy, biological anthropology, animal science and evolution. Brain size is sometimes measured by weight and sometimes by volume (via MRI scans or by skull volume). Neu ...
was previously considered a major indicator of intelligence. Since most of the brain is used for maintaining bodily functions, greater ratios of brain to body mass may increase the amount of brain mass available for cognitive tasks.
Allometric Allometry is the study of the relationship of body size to shape, anatomy, physiology and finally behaviour, first outlined by Otto Snell in 1892, by D'Arcy Thompson in 1917 in ''On Growth and Form'' and by Julian Huxley in 1932. Overview Allom ...
analysis of the relationship between mammalian brain mass (weight) and body mass for different species of mammals shows that larger species generally have larger brains. However, this increase is not fully proportional. Typically the brain mass only increases in proportion to somewhere between the two-thirds power (or the square of the cube root) and the three-quarters power (or the cube of the fourth root) of the body mass. ''m''''brain'' ∝ (''m''''body'')''k'' where ''k'' is between two-thirds and three-quarters. Thus if Species B is twice the size of Species A, its brain size will typically be somewhere between 60% and 70% higher. Comparison of a particular animal's brain size with the expected brain size based on such an analysis provides an
encephalization quotient Encephalization quotient (EQ), encephalization level (EL), or just encephalization is a relative brain size measure that is defined as the ratio between observed to predicted brain mass for an animal of a given size, based on nonlinear regress ...
that can be used as an indication of animal intelligence. Sperm whales have the largest brain mass of any animal on Earth, averaging and in mature males. The
brain to body mass ratio A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a ve ...
in some odontocetes, such as belugas and narwhals, is second only to humans. In some whales, however, it is less than half that of humans: 0.9% versus 2.1%.


Skeleton

The cetacean skeleton is largely made up of
cortical bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, an ...
, which stabilizes the animal in the water. For this reason, the usual terrestrial compact bones, which are finely woven
cancellous bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, an ...
, are replaced with lighter and more elastic material. In many places, bone elements are replaced by cartilage and even fat, thereby improving their hydrostatic qualities. The ear and the muzzle contain a bone shape that is exclusive to cetaceans with a high density, resembling porcelain. This conducts sound better than other bones, thus aiding
biosonar Echolocation, also called bio sonar, is a biological sonar used by several animal species. Echolocating animals emit calls out to the environment and listen to the echoes of those calls that return from various objects near them. They use these ...
. The number of
vertebrae The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic i ...
that make up the spine varies by species, ranging from forty to ninety-three. The
cervical spine In tetrapods, cervical vertebrae (singular: vertebra) are the vertebrae of the neck, immediately below the skull. Truncal vertebrae (divided into thoracic and lumbar vertebrae in mammals) lie caudal (toward the tail) of cervical vertebrae. In sau ...
, found in all mammals, consists of seven vertebrae which, however, are reduced or fused. This fusion provides stability during swimming at the expense of mobility. The fins are carried by the thoracic vertebrae, ranging from nine to seventeen individual vertebrae. The sternum is cartilaginous. The last two to three pairs of ribs are not connected and hang freely in the body wall. The stable lumbar and tail include the other vertebrae. Below the
caudal vertebrae The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic i ...
is the chevron bone. The front limbs are paddle-shaped with shortened arms and elongated finger bones, to support movement. They are connected by cartilage. The second and third fingers display a proliferation of the finger members, a so-called hyperphalangy. The shoulder joint is the only functional joint in all cetaceans except for the
Amazon river dolphin The Amazon river dolphin (''Inia geoffrensis''), also known as the boto, bufeo or pink river dolphin, is a species of toothed whale classified in the family Iniidae. Three subspecies are currently recognized: ''I. g. geoffrensis'' (Amazon rive ...
. The
collarbone The clavicle, or collarbone, is a slender, S-shaped long bone approximately 6 inches (15 cm) long that serves as a strut between the shoulder blade and the sternum (breastbone). There are two clavicles, one on the left and one on the righ ...
is completely absent.


Fluke

Cetaceans have a
cartilaginous Cartilage is a resilient and smooth type of connective tissue. In tetrapods, it covers and protects the ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, the neck and ...
fluke at the end of their tails that is used for propulsion. The
fluke Fluke may refer to: Biology * Fluke (fish), a species of marine flatfish * Fluke (tail), the lobes of the tail of a cetacean, such as dolphins or whales, ichthyosaurs, mosasaurs, plesiosaurs, and metriorhynchids. * Fluke (flatworm), parasiti ...
is set horizontally on the body, unlike fish, which have vertical tails.


Physiology


Circulation

Cetaceans have powerful hearts. Blood oxygen is distributed effectively throughout the body. They are warm-blooded, i.e., they hold a nearly constant body temperature.


Respiration

Cetaceans have lungs, meaning they breathe air. An individual can last without a breath from a few minutes to over two hours depending on the species. Cetacea are deliberate breathers who must be awake to inhale and exhale. When stale air, warmed from the lungs, is exhaled, it condenses as it meets colder external air. As with a terrestrial mammal breathing out on a cold day, a small cloud of 'steam' appears. This is called the 'spout' and varies across species in shape, angle and height. Species can be identified at a distance using this characteristic. The structure of the
respiratory The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies gre ...
and circulatory systems is of particular importance for the life of
marine mammals Marine mammals are aquatic mammals that rely on the ocean and other marine ecosystems for their existence. They include animals such as seals, whales, manatees, sea otters and polar bears. They are an informal group, unified only by their re ...
. The oxygen balance is effective. Each breath can replace up to 90% of the total lung volume. For land mammals, in comparison, this value is usually about 15%. During inhalation, about twice as much oxygen is absorbed by the lung tissue as in a land mammal. As with all mammals, the oxygen is stored in the blood and the lungs, but in cetaceans, it is also stored in various tissues, mainly in the muscles. The muscle pigment, myoglobin, provides an effective bond. This additional oxygen storage is vital for deep diving, since beyond a depth around , the lung tissue is almost completely compressed by the water pressure.


Abdominal organs

The stomach consists of three chambers. The first region is formed by a loose gland and a muscular forestomach (missing in beaked whales); this is followed by the main stomach and the
pylorus The pylorus ( or ), or pyloric part, connects the stomach to the duodenum. The pylorus is considered as having two parts, the ''pyloric antrum'' (opening to the body of the stomach) and the ''pyloric canal'' (opening to the duodenum). The ''pylori ...
. Both are equipped with glands to help digestion. A bowel adjoins the stomachs, whose individual sections can only be distinguished
histologically Histology, also known as microscopic anatomy or microanatomy, is the branch of biology which studies the microscopic anatomy of biological tissues. Histology is the microscopic counterpart to gross anatomy, which looks at larger structures vis ...
. The liver is large and separate from the gall bladder. The kidneys are long and flattened. The salt concentration in cetacean blood is lower than that in seawater, requiring kidneys to excrete salt. This allows the animals to drink seawater.


Senses

Cetacean eyes are set on the sides rather than the front of the head. This means only species with pointed 'beaks' (such as dolphins) have good
binocular vision In biology, binocular vision is a type of vision in which an animal has two eyes capable of facing the same direction to perceive a single three-dimensional image of its surroundings. Binocular vision does not typically refer to vision where an a ...
forward and downward. Tear glands secrete greasy tears, which protect the eyes from the salt in the water. The lens is almost spherical, which is most efficient at focusing the minimal light that reaches deep water. Odontocetes have little to no ability to taste or smell, while mysticetes are believed to have some ability to smell because of their reduced, but functional olfactory system. Cetaceans are known to possess excellent hearing. At least one species, the tucuxi or Guiana dolphin, is able to use
electroreception Electroreception and electrogenesis are the closely-related biological abilities to perceive electrical stimuli and to generate electric fields. Both are used to locate prey; stronger electric discharges are used in a few groups of fishes to stu ...
to sense prey.


Ears

The external ear has lost the pinna (visible ear), but still retains a narrow
external auditory meatus The ear canal (external acoustic meatus, external auditory meatus, EAM) is a pathway running from the outer ear to the middle ear. The adult human ear canal extends from the pinna to the eardrum and is about in length and in diameter. Struct ...
. To register sounds, instead, the posterior part of the
mandible In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...
has a thin lateral wall (the pan bone) fronting a concavity that houses a fat pad. The pad passes anteriorly into the greatly enlarged
mandibular foramen The mandibular foramen is an opening on the internal surface of the ramus of the mandible. It allows for divisions of the mandibular nerve and blood vessels to pass through. Structure The mandibular foramen is an opening on the internal surfac ...
to reach in under the teeth and posteriorly to reach the thin lateral wall of the ectotympanic. The ectotympanic offers a reduced attachment area for the tympanic membrane. The connection between this auditory complex and the rest of the skull is reduced—to a single, small cartilage in
oceanic dolphin Oceanic dolphins or Delphinidae are a widely distributed family of dolphins that live in the sea. Close to forty extant species are recognised. They include several big species whose common names contain "whale" rather than "dolphin", such as th ...
s. In odontocetes, the complex is surrounded by spongy tissue filled with air spaces, while in mysticetes, it is integrated into the skull as with land mammals. In odontocetes, the tympanic membrane (or ligament) has the shape of a folded-in umbrella that stretches from the ectotympanic ring and narrows off to the
malleus The malleus, or hammer, is a hammer-shaped small bone or ossicle of the middle ear. It connects with the incus, and is attached to the inner surface of the eardrum. The word is Latin for 'hammer' or 'mallet'. It transmits the sound vibrations fr ...
(quite unlike the flat, circular membrane found in land mammals.) In mysticetes, it also forms a large protrusion (known as the "glove finger"), which stretches into the external
meatus In anatomy, a meatus (, ),'' OED'' 2nd edition, 1989, as . plural "meatus" or "meatuses",
and the stapes are larger than in odontocetes. In some small sperm whales, the malleus is fused with the ectotympanic. The ear
ossicles The ossicles (also called auditory ossicles) are three bones in either middle ear that are among the smallest bones in the human body. They serve to transmit sounds from the air to the fluid-filled labyrinth ( cochlea). The absence of the audit ...
are pachyosteosclerotic (dense and compact) and differently shaped from land mammals (other aquatic mammals, such as
sirenia The Sirenia (), commonly referred to as sea-cows or sirenians, are an order of fully aquatic, herbivorous mammals that inhabit swamps, rivers, estuaries, marine wetlands, and coastal marine waters. The Sirenia currently comprise two distinct f ...
ns and earless seals, have also lost their pinnae). T semicircular canals are much smaller relative to body size than in other mammals. The
auditory bulla The tympanic part of the temporal bone is a curved plate of bone lying below the squamous part of the temporal bone, in front of the mastoid process, and surrounding the external part of the ear canal. It originates as a separate bone (tympanic ...
is separated from the skull and composed of two compact and dense bones (the periotic and tympanic) referred to as the tympanoperiotic complex. This complex is located in a cavity in the middle ear, which, in the Mysticeti, is divided by a bony projection and compressed between the exoccipital and squamosal, but in the odontoceti, is large and completely surrounds the bulla (hence called "peribullar"), which is, therefore, not connected to the skull except in physeterids. In the Odontoceti, the cavity is filled with a dense foam in which the bulla hangs suspended in five or more sets of ligaments. The pterygoid and peribullar
sinuses Paranasal sinuses are a group of four paired air-filled spaces that surround the nasal cavity. The maxillary sinuses are located under the eyes; the frontal sinuses are above the eyes; the ethmoidal sinuses are between the eyes and the spheno ...
that form the cavity tend to be more developed in shallow water and riverine species than in pelagic Mysticeti. In Odontoceti, the composite auditory structure is thought to serve as an acoustic isolator, analogous to the lamellar construction found in the temporal bone in
bat Bats are mammals of the order Chiroptera.''cheir'', "hand" and πτερόν''pteron'', "wing". With their forelimbs adapted as wings, they are the only mammals capable of true and sustained flight. Bats are more agile in flight than most bi ...
s. Cetaceans use sound to
communicate Communication (from la, communicare, meaning "to share" or "to be in relation with") is usually defined as the transmission of information. The term may also refer to the message communicated through such transmissions or the field of inqu ...
, using groans, moans, whistles, clicks or the 'singing' of the humpback whale.


Echolocation

Odontoceti The toothed whales (also called odontocetes, systematic name Odontoceti) are a parvorder of cetaceans that includes dolphins, porpoises, and all other whales possessing teeth, such as the beaked whales and sperm whales. Seventy-three species of ...
are generally capable of echolocation. They can discern the size, shape, surface characteristics, distance and movement of an object. They can search for, chase and catch fast-swimming prey in total darkness. Most Odontoceti can distinguish between prey and nonprey (such as humans or boats); captive Odontoceti can be trained to distinguish between, for example, balls of different sizes or shapes. Echolocation clicks also contain characteristic details unique to each animal, which may suggest that toothed whales can discern between their own click and that of others. Mysticeti have exceptionally thin, wide basilar membranes in their
cochlea The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, in humans making 2.75 turns around its axis, the modiolus. A core component of the cochlea is the Organ of Corti, the sensory org ...
e without stiffening agents, making their ears adapted for processing low to
infrasonic Infrasound, sometimes referred to as low status sound, describes sound waves with a frequency below the lower limit of human audibility (generally 20 Hz). Hearing becomes gradually less sensitive as frequency decreases, so for humans to perce ...
frequencies.


Chromosomes

The initial
karyotype A karyotype is the general appearance of the complete set of metaphase chromosomes in the cells of a species or in an individual organism, mainly including their sizes, numbers, and shapes. Karyotyping is the process by which a karyotype is disce ...
includes a set of chromosomes from 2n = 44. They have four pairs of telocentric chromosomes (whose
centromeres The centromere links a pair of sister chromatids together during cell division. This constricted region of chromosome connects the sister chromatids, creating a short arm (p) and a long arm (q) on the chromatids. During mitosis, spindle fibers a ...
sit at one of the
telomeres A telomere (; ) is a region of repetitive nucleotide sequences associated with specialized proteins at the ends of linear chromosomes. Although there are different architectures, telomeres, in a broad sense, are a widespread genetic feature mos ...
), two to four pairs of subtelocentric and one or two large pairs of submetacentric chromosomes. The remaining chromosomes are metacentric—the centromere is approximately in the middle—and are rather small. All cetaceans have chromosomes 2n = 44, except the
sperm whale The sperm whale or cachalot (''Physeter macrocephalus'') is the largest of the toothed whales and the largest toothed predator. It is the only living member of the genus '' Physeter'' and one of three extant species in the sperm whale fami ...
s and
pygmy sperm whale The pygmy sperm whale (''Kogia breviceps'') is one of two extant species in the family Kogiidae in the sperm whale superfamily. They are not often sighted at sea, and most of what is known about them comes from the examination of stranded speci ...
s, which have 2n = 42.


Ecology


Range and habitat

Cetaceans are found in many aquatic habitats. While many marine species, such as the
blue whale The blue whale (''Balaenoptera musculus'') is a marine mammal and a baleen whale. Reaching a maximum confirmed length of and weighing up to , it is the largest animal known to have ever existed. The blue whale's long and slender body can b ...
, the
humpback whale The humpback whale (''Megaptera novaeangliae'') is a species of baleen whale. It is a rorqual (a member of the family Balaenopteridae) and is the only species in the genus ''Megaptera''. Adults range in length from and weigh up to . The hu ...
and the orca, have a distribution area that includes nearly the entire ocean, some species occur only locally or in broken populations. These include the
vaquita The vaquita ( ; ''Phocoena sinus'') is a species of porpoise endemic to the northern end of the Gulf of California in Baja California, Mexico. Averaging (females) or (males) in length, it is the smallest of all living cetaceans. The species i ...
, which inhabits a small part of the Gulf of California and
Hector's dolphin Hector's dolphin (''Cephalorhynchus hectori'') is one of four dolphin species belonging to the genus '' Cephalorhynchus''. Hector's dolphin is the only cetacean endemic to New Zealand, and comprises two subspecies: ''C. h. hectori'', the more n ...
, which lives in some coastal waters in New Zealand. River dolphin species live exclusively in fresh water. Many species inhabit specific latitudes, often in tropical or subtropical waters, such as
Bryde's whale Bryde's whale ( Brooder's), or the Bryde's whale complex, putatively comprises three species of rorqual and maybe four. The "complex" means the number and classification remains unclear because of a lack of definitive information and research. ...
or Risso's dolphin. Others are found only in a specific body of water. The
southern right whale dolphin The southern right whale dolphin (''Lissodelphis peronii'') is a small and slender species of cetacean, found in cool waters of the Southern Hemisphere. It is one of two species of right whale dolphin (genus ''Lissodelphis''). This genus is char ...
and the
hourglass dolphin The hourglass dolphin (''Lagenorhynchus cruciger'') is a small dolphin in the family Delphinidae that inhabits offshore Antarctic and sub-Antarctic waters. It is commonly seen from ships crossing the Drake Passage, but has a circumpolar distr ...
live only in the Southern Ocean. The narwhal and the
beluga The beluga whale (/bɪˈluːɡə/) (Delphinapterus leucas) is an Arctic and sub-Arctic cetacean. It is one of two members of the family Monodontidae, along with the narwhal, and the only member of the genus Delphinapterus. It is also known as the wh ...
live only in the Arctic Ocean.
Sowerby's beaked whale Sowerby's beaked whale (''Mesoplodon bidens''), also known as the North Atlantic or North Sea beaked whale, is a species of toothed whale. It was the first mesoplodont whale to be described. James Sowerby, an English naturalist and artist, firs ...
and the
Clymene dolphin The Clymene dolphin (''Stenella clymene''), in older texts known as the short-snouted spinner dolphin, is a dolphin endemic to the Atlantic Ocean. It is the only confirmed case of hybrid speciation in marine mammals, descending from the spinner ...
exist only in the Atlantic and the
Pacific white-sided dolphin The Pacific white-sided dolphin (''Lagenorhynchus obliquidens''), also known as the hookfin porpoise, is an active dolphin found in the cool or temperate waters of the North Pacific Ocean. Taxonomy The Pacific white-sided dolphin was named by Sm ...
and the northern straight dolphin live only in the North Pacific. Cosmopolitan species may be found in the Pacific, Atlantic and Indian Oceans. However, northern and southern populations become genetically separated over time. In some species, this separation leads eventually to a divergence of the species, such as produced the southern right whale,
North Pacific right whale The North Pacific right whale (''Eubalaena japonica'') is a very large, thickset baleen whale species that is extremely rare and endangered. The Northeast Pacific population, which summers in the southeastern Bering Sea and Gulf of Alaska, may ...
and North Atlantic right whale. Migratory species' reproductive sites often lie in the tropics and their feeding grounds in polar regions. Thirty-two species are found in European waters, including twenty-five toothed and seven baleen species.


Whale migration

Many species of whales migrate on a latitudinal basis to move between seasonal habitats. For example, the gray whale migrates round trip. The journey begins at winter birthing grounds in warm lagoons along Baja California, and traverses of coastline to summer feeding grounds in the Bering, Chuckchi and Beaufort seas off the coast of Alaska.


Behaviour


Sleep

Conscious breathing cetaceans sleep but cannot afford to be unconscious for long, because they may drown. While knowledge of sleep in wild cetaceans is limited, toothed cetaceans in captivity have been recorded to exhibit unihemispheric slow-wave sleep (USWS), which means they sleep with one side of their brain at a time, so that they may swim, breathe consciously and avoid both predators and social contact during their period of rest. A 2008 study found that sperm whales sleep in vertical postures just under the surface in passive shallow 'drift-dives', generally during the day, during which whales do not respond to passing vessels unless they are in contact, leading to the suggestion that whales possibly sleep during such dives.


Diving

While diving, the animals reduce their oxygen consumption by lowering the heart activity and blood circulation; individual organs receive no oxygen during this time. Some
rorqual Rorquals () are the largest group of baleen whales, which comprise the family Balaenopteridae, containing ten extant species in three genera. They include the largest animal that has ever lived, the blue whale, which can reach , and the fin wha ...
s can dive for up to 40 minutes,
sperm whales The sperm whale or cachalot (''Physeter macrocephalus'') is the largest of the toothed whales and the largest toothed predator. It is the only living member of the genus ''Physeter'' and one of three extant species in the sperm whale fam ...
between 60 and 90 minutes and
bottlenose whale ''Hyperoodon'' (or ''Hyperoödon'') is a genus of beaked whale, containing just two species: the Northern and Southern bottlenose whales. While not in the genus ''Hyperoodon'', Longman's beaked whale The tropical bottlenose whale (''Indopac ...
s for two hours. Diving depths average about . Species such as sperm whales can dive to , although more commonly .


Social relations

Most cetaceans are social animals, although a few species live in pairs or are solitary. A group, known as a pod, usually consists of ten to fifty animals, but on occasion, such as mass availability of food or during mating season, groups may encompass more than one thousand individuals. Inter-species socialization can occur. Pods have a fixed hierarchy, with the priority positions determined by biting, pushing or ramming. The behavior in the group is aggressive only in situations of stress such as lack of food, but usually it is peaceful. Contact swimming, mutual fondling and nudging are common. The playful behavior of the animals, which is manifested in air jumps, somersaults, surfing, or fin hitting, occurs more often than not in smaller cetaceans, such as dolphins and porpoises.


Whale song

Males in some baleen species communicate via whale song, sequences of high pitched sounds. These "songs" can be heard for hundreds of kilometers. Each population generally shares a distinct song, which evolves over time. Sometimes, an individual can be identified by its distinctive vocals, such as the
52-hertz whale The 52-hertz whale, colloquially referred to as 52 Blue, is an individual whale of unidentified species that calls at the unusual frequency of 52 hertz. This pitch is at a higher frequency than that of the other whale species with migratio ...
that sings at a higher frequency than other whales. Some individuals are capable of generating over 600 distinct sounds. In baleen species such as humpbacks, blues and fins, male-specific song is believed to be used to attract and display fitness to females.


Hunting

Pod groups also hunt, often with other species. Many species of dolphins accompany large tunas on hunting expeditions, following large schools of fish. The orca hunts in pods and targets belugas and even larger whales. Humpback whales, among others, form in collaboration bubble carpets to herd krill or plankton into bait balls before lunging at them.


Intelligence

Cetacea are known to teach, learn, cooperate, scheme and grieve. Smaller cetaceans, such as dolphins and porpoises, engage in complex play behavior, including such things as producing stable underwater toroidal air-core vortex rings or "
bubble ring A bubble ring, or toroidal bubble, is an underwater vortex ring where an air bubble occupies the core of the vortex, forming a ring shape. The ring of air as well as the nearby water spins poloidally as it travels through the water, much like a ...
s". The two main methods of bubble ring production are rapid puffing of air into the water and allowing it to rise to the surface, forming a ring, or swimming repeatedly in a circle and then stopping to inject air into the
helical Helical may refer to: * Helix A helix () is a shape like a corkscrew or spiral staircase. It is a type of smooth space curve with tangent lines at a constant angle to a fixed axis. Helices are important in biology, as the DNA molecule is for ...
vortex currents thus formed. They also appear to enjoy biting the vortex rings, so that they burst into many separate bubbles and then rise quickly to the surface. Whales produce bubble nets to aid in herding prey. Larger whales are also thought to engage in play. The southern right whale elevates its tail fluke above the water, remaining in the same position for a considerable time. This is known as "sailing". It appears to be a form of play and is most commonly seen off the coast of Argentina and South Africa. Humpback whales also display this behaviour.
Self-awareness In philosophy of self, self-awareness is the experience of one's own personality or individuality. It is not to be confused with consciousness in the sense of qualia. While consciousness is being aware of one's environment and body and lifest ...
appears to be a sign of abstract thinking. Self-awareness, although not well-defined, is believed to be a precursor to more advanced processes such as metacognitive reasoning (thinking about thinking) that humans exploit. Dolphins appear to possess self-awareness. The most widely used test for self-awareness in animals is the
mirror test The mirror test—sometimes called the mark test, mirror self-recognition (MSR) test, red spot technique, or rouge test—is a behavioral technique developed in 1970 by American psychologist Gordon Gallup Jr. as an attempt to determine whether a ...
, in which a temporary dye is placed on an animal's body and the animal is then presented with a mirror. Researchers then explore whether the animal shows signs of self-recognition. Critics claim that the results of these tests are susceptible to the
Clever Hans Clever Hans ( German: ''der Kluge Hans''; c. 1895 - c. 1916) was a horse that was claimed to have performed arithmetic and other intellectual tasks. After a formal investigation in 1907, psychologist Oskar Pfungst demonstrated that the horse was ...
effect. This test is much less definitive than when used for primates. Primates can touch the mark or the mirror, while dolphins cannot, making their alleged self-recognition behavior less certain. Skeptics argue that behaviors said to identify self-awareness resemble existing social behaviors, so researchers could be misinterpreting self-awareness for social responses. Advocates counter that the behaviors are different from normal responses to another individual. Dolphins show less definitive behavior of self-awareness, because they have no pointing ability. In 1995, Marten and Psarakos used video to test dolphin self-awareness. They showed dolphins real-time footage of themselves, recorded footage and another dolphin. They concluded that their evidence suggested self-awareness rather than social behavior. While this particular study has not been replicated, dolphins later "passed" the mirror test.


Life history


Reproduction and brooding

Most cetaceans sexually mature at seven to 10 years. An exception to this is the La Plata dolphin, which is sexually mature at two years, but lives only to about 20. The sperm whale reaches sexual maturity within about 20 years and has a lifespan between 50 and 100 years. For most species, reproduction is seasonal.
Ovulation Ovulation is the release of eggs from the ovaries. In women, this event occurs when the ovarian follicles rupture and release the secondary oocyte ovarian cells. After ovulation, during the luteal phase, the egg will be available to be fertilize ...
coincides with male fertility. This cycle is usually coupled with seasonal movements that can be observed in many species. Most toothed whales have no fixed bonds. In many species, females choose several partners during a season. Baleen whales are largely monogamous within each reproductive period. Gestation ranges from 9 to 16 months. Duration is not necessarily a function of size. Porpoises and blue whales gestate for about 11 months. As with all mammals other than marsupials and monotremes, the embryo is fed by the placenta, an organ that draws nutrients from the mother's bloodstream. Mammals without placentas either lay minuscule eggs (monotremes) or bear minuscule offspring (marsupials). Cetaceans usually bear one calf. In the case of twins, one usually dies, because the mother cannot produce sufficient milk for both. The fetus is positioned for a tail-first delivery, so that the risk of drowning during delivery is minimal. After birth, the mother carries the infant to the surface for its first breath. At birth, they are about one-third of their adult length and tend to be independently active, comparable to terrestrial mammals.


Suckling

Like other placental mammals, cetaceans give birth to well-developed calves and nurse them with milk from their mammary glands. When suckling, the mother actively splashes milk into the mouth of the calf, using the muscles of her mammary glands, as the calf has no lips. This milk usually has a high-fat content, ranging from 16 to 46%, causing the calf to increase rapidly in size and weight. In many small cetaceans, suckling lasts for about four months. In large species, it lasts for over a year and involves a strong bond between mother and offspring. The mother is solely responsible for brooding. In some species, so-called "aunts" occasionally suckle the young. This reproductive strategy provides a few offspring that have a high survival rate.


Lifespan

Among cetaceans, whales are distinguished by an unusual longevity compared to other higher mammals. Some species, such as the
bowhead whale The bowhead whale (''Balaena mysticetus'') is a species of baleen whale belonging to the family Balaenidae and the only living representative of the genus '' Balaena''. They are the only baleen whale endemic to the Arctic and subarctic waters, a ...
(''Balaena mysticetus''), can reach over 200 years. Based on the annual rings of the bony otic capsule, the age of the oldest known specimen is a male determined to be 211 years at the time of death.


Death

Upon death, whale carcasses fall to the deep ocean and provide a substantial habitat for marine life. Evidence of whale falls in present-day and fossil records shows that deep-sea whale falls support a rich assemblage of creatures, with a global diversity of 407 species, comparable to other neritic biodiversity hotspots, such as
cold seep A cold seep (sometimes called a cold vent) is an area of the ocean floor where hydrogen sulfide, methane and other hydrocarbon-rich fluid seepage occurs, often in the form of a brine pool. ''Cold'' does not mean that the temperature of the see ...
s and
hydrothermal vent A hydrothermal vent is a fissure on the seabed from which geothermally heated water discharges. They are commonly found near volcanically active places, areas where tectonic plates are moving apart at mid-ocean ridges, ocean basins, and hotspot ...
s. Deterioration of whale carcasses happens through three stages. Initially, organisms such as sharks and hagfish scavenge the soft tissues at a rapid rate over a period of months and as long as two years. This is followed by the colonization of bones and surrounding sediments (which contain organic matter) by enrichment opportunists, such as
crustaceans Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group c ...
and polychaetes, throughout a period of years. Finally, sulfophilic bacteria reduce the bones releasing hydrogen sulfide enabling the growth of
chemoautotrophic A Chemotroph is an organism that obtains energy by the oxidation of electron donors in their environments. These molecules can be organic ( chemoorganotrophs) or inorganic (chemolithotrophs). The chemotroph designation is in contrast to phototro ...
organisms, which in turn, support organisms such as mussels, clams, limpets and sea snails. This stage may last for decades and supports a rich assemblage of species, averaging 185 per site.


Disease

Brucellosis Brucellosis is a highly contagious zoonosis caused by ingestion of unpasteurized milk or undercooked meat from infected animals, or close contact with their secretions. It is also known as undulant fever, Malta fever, and Mediterranean fever. Th ...
affects almost all mammals. It is distributed worldwide, while fishing and pollution have caused porpoise population density pockets, which risks further infection and disease spreading. ''
Brucella ceti ''Brucella ceti'' is a gram negative bacterial pathogen of the Brucellaceae family that causes brucellosis in cetaceans. ''Brucella ceti'' has been found in both classes of cetaceans, mysticetes and odontocetes. Brucellosis in some dolphins an ...
'', most prevalent in dolphins, has been shown to cause
chronic disease A chronic condition is a health condition or disease that is persistent or otherwise long-lasting in its effects or a disease that comes with time. The term ''chronic'' is often applied when the course of the disease lasts for more than three mo ...
, increasing the chance of failed birth and
miscarriage Miscarriage, also known in medical terms as a spontaneous abortion and pregnancy loss, is the death of an embryo or fetus before it is able to survive independently. Miscarriage before 6 weeks of gestation is defined by ESHRE as biochemical lo ...
s,
male infertility Male infertility refers to a sexually mature male's inability to impregnate a fertile female. In humans it accounts for 40–50% of infertility. It affects approximately 7% of all men. Male infertility is commonly due to deficiencies in the semen, ...
, neurobrucellosis, cardiopathies, bone and skin lesions, strandings and death. Until 2008, no case had ever been reported in porpoises, but isolated populations have an increased risk and consequentially a high mortality rate.


Evolution


Phylogenetics

Molecular biology and
immunology Immunology is a branch of medicineImmunology for Medical Students, Roderick Nairn, Matthew Helbert, Mosby, 2007 and biology that covers the medical study of immune systems in humans, animals, plants and sapient species. In such we can see ther ...
show that cetaceans are phylogenetically closely related with the
even-toed ungulate The even-toed ungulates (Artiodactyla , ) are ungulates—hoofed animals—which bear weight equally on two (an even number) of their five toes: the third and fourth. The other three toes are either present, absent, vestigial, or pointing poste ...
s (Artiodactyla). Whales' direct lineage began in the early Eocene, around 55.8 million years ago, with early artiodactyls. Fossil discoveries at the beginning of the 21st century confirmed this. Most molecular biological evidence suggests that
hippos A hippo or hippopotamus is either of two species of large African mammal which live mainly in and near water: * Hippopotamus * Pygmy hippopotamus Hippo or Hippos may also refer to: Toponymy * The ancient city of Hippo Regius (modern Annaba, Alg ...
are the closest living relatives. Common anatomical features include similarities in the
morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines *Morphology (archaeology), study of the shapes or forms of artifacts *Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies, ...
of the posterior molars, and the bony ring on the temporal bone (bulla) and the involucre, a skull feature that was previously associated only with cetaceans. The fossil record, however, does not support this relationship, because the hippo lineage dates back only about 15 million years. The most striking common feature is the talus, a bone in the upper ankle. Early cetaceans,
archaeocetes Archaeoceti ("ancient whales"), or Zeuglodontes in older literature, is a paraphyletic group of primitive cetaceans that lived from the Early Eocene to the late Oligocene (). Representing the earliest cetacean radiation, they include the initial ...
, show double castors, which occur only in even-toed ungulates. Corresponding findings are from
Tethys Sea The Tethys Ocean ( el, Τηθύς ''Tēthús''), also called the Tethys Sea or the Neo-Tethys, was a prehistoric ocean that covered most of the Earth during much of the Mesozoic Era and early Cenozoic Era, located between the ancient continents ...
deposits in northern India and Pakistan. The Tethys Sea was a shallow sea between the Asian continent and northward-bound Indian plate. Mysticetes evolved baleen around 25 million years ago and lost their teeth.


Development


Ancestors

The direct ancestors of today's cetaceans are probably found within the
Dorudontidae Dorudontinae are a group of extinct cetaceans that are related to ''Basilosaurus''.. Retrieved July 2013. Classification * Subfamily Dorudontinae ** Genus ''Ancalecetus'' *** ''Ancalecetus simonsi'' ** Genus ''Chrysocetus'' *** ''Chrysocetus f ...
whose most famous member, ''
Dorudon ''Dorudon'' ("spear-tooth") is a genus of extinct basilosaurid ancient whales that lived alongside '' Basilosaurus'' 40.4 to 33.9 million years ago in the Eocene. It was a small whale, with ''D. atrox'' measuring long and weighing . ''Dorudon'' ...
'', lived at the same time as ''
Basilosaurus ''Basilosaurus'' (meaning "king lizard") is a genus of large, predatory, prehistoric archaeocete whale from the late Eocene, approximately 41.3 to 33.9 million years ago (mya). First described in 1834, it was the first archaeocete and prehistor ...
''. Both groups had already developed the typical anatomical features of today's whales, such as hearing. Life in the water for a formerly terrestrial creature required significant adjustments such as the fixed bulla, which replaces the mammalian eardrum, as well as sound-conducting elements for submerged directional hearing. Their wrists were stiffened and probably contributed to the typical build of flippers. The hind legs existed, however, but were significantly reduced in size and with a vestigial pelvis connection.


Transition from land to sea

The fossil record traces the gradual transition from terrestrial to aquatic life. The regression of the hind limbs allowed greater flexibility of the spine. This made it possible for whales to move around with the vertical tail hitting the water. The front legs transformed into flippers, costing them their mobility on land. One of the oldest members of ancient cetaceans (
Archaeoceti Archaeoceti ("ancient whales"), or Zeuglodontes in older literature, is a paraphyletic group of primitive cetaceans that lived from the Early Eocene to the late Oligocene (). Representing the earliest cetacean radiation, they include the initial ...
) is '' Pakicetus'' from the Middle Eocene. This is an animal the size of a wolf, whose skeleton is known only partially. It had functioning legs and lived near the shore. This suggests the animal could still move on land. The long snout had
carnivorous A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other so ...
dentition. The transition from land to sea dates to about 49 million years ago, with the ''
Ambulocetus ''Ambulocetus'' (Latin ''ambulare'' "to walk" + ''cetus'' "whale") is a genus of early amphibious cetacean from the Kuldana Formation in Pakistan, roughly 48 or 47 million years ago during the Early Eocene ( Lutetian). It contains one species ...
'' ("running whale"), discovered in Pakistan. It was up to long. The limbs of this archaeocete were leg-like, but it was already fully aquatic, indicating that a switch to a lifestyle independent from land happened extraordinarily quickly. The snout was elongated with overhead nostrils and eyes. The tail was strong and supported movement through water. ''Ambulocetus'' probably lived in mangroves in
brackish water Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estuari ...
and fed in the riparian zone as a predator of fish and other vertebrates. Dating from about 45 million years ago are species such as ''
Indocetus ''Indocetus'' is a protocetid early whale known from the late early Eocene (Lutetian, ) Harudi Formation (, paleocoordinates ) in Kutch, India. The holotype of is a partial skull in two pieces with the frontal shield and the right occiput a ...
'', ''
Kutchicetus ''Kutchicetus'' is an extinct genus of early whale of the family Remingtonocetidae that lived during Early-Middle Eocene (Lutetian and Ypresian) in what is now the coastal border of Pakistan and India (, paleocoordinates ). It is closely rela ...
'', ''
Rodhocetus ''Rodhocetus'' (from ''Rodho'', the geological anticline at the type locality, and ''cetus'', Latin for whale) is an extinct genus of protocetid early whale known from the Lutetian of Pakistan. The best-known protocetid, ''Rodhocetus'' is known ...
'' and ''
Andrewsiphius ''Andrewsiphius'' is an extinct remingtonocetid early whale known from the Eocene (Lutetian, ) of Gujarat and Kutch, India and Balochistan, Pakistan. Discovery and naming The first specimen was collected by who described it as mandibular fr ...
'', all of which were adapted to life in water. The hind limbs of these species were regressed and their body shapes resemble modern whales.
Protocetidae Protocetidae, the protocetids, form a diverse and heterogeneous group of extinct cetaceans known from Asia, Europe, Africa, South America, and North America. Description There were many genera, and some of these are very well known (e.g., '' ...
family member ''Rodhocetus'' is considered the first to be fully aquatic. The body was streamlined and delicate with extended hand and foot bones. The merged pelvic lumbar spine was present, making it possible to support the floating movement of the tail. It was likely a good swimmer, but could probably move only clumsily on land, much like a modern
seal Seal may refer to any of the following: Common uses * Pinniped, a diverse group of semi-aquatic marine mammals, many of which are commonly called seals, particularly: ** Earless seal, or "true seal" ** Fur seal * Seal (emblem), a device to impr ...
.


Marine animals

Since the late Eocene, about 40 million years ago, cetaceans populated the subtropical oceans and no longer emerged on land. An example is the 18-m-long ''
Basilosaurus ''Basilosaurus'' (meaning "king lizard") is a genus of large, predatory, prehistoric archaeocete whale from the late Eocene, approximately 41.3 to 33.9 million years ago (mya). First described in 1834, it was the first archaeocete and prehistor ...
'', sometimes referred to as ''Zeuglodon''. The transition from land to water was completed in about 10 million years. The Wadi Al-Hitan ("Whale Valley") in Egypt contains numerous skeletons of ''Basilosaurus'', as well as other marine vertebrates.


Taxonomy

Molecular findings and morphological indications suggest that
artiodactyl The even-toed ungulates (Artiodactyla , ) are ungulates—hoofed animals—which bear weight equally on two (an even number) of their five toes: the third and fourth. The other three toes are either present, absent, vestigial, or pointing poster ...
s as traditionally defined are paraphyletic with respect to cetaceans. Cetaceans are deeply nested within the former; the two groups together form a monophyletic taxon, for which the name
Cetartiodactyla The even-toed ungulates (Artiodactyla , ) are ungulates—hoofed animals—which bear weight equally on two (an even number) of their five toes: the third and fourth. The other three toes are either present, absent, vestigial, or pointing poster ...
is sometimes used. Modern nomenclature divides Artiodactyla (or Cetartiodactyla) in four subordinate taxa: camelids (Tylopoda), pigs and peccaries (Suina), ruminants (Ruminantia), and hippos plus whales (Whippomorpha). Cetacea's presumed location within
Artiodactyla The even-toed ungulates (Artiodactyla , ) are ungulates—hoofed animals—which bear weight equally on two (an even number) of their five toes: the third and fourth. The other three toes are either present, absent, vestigial, or pointing poster ...
can be represented in the following
cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...
: (see e.g. Fig S10) Within Cetacea, the two parvorders are
baleen whales Baleen whales ( systematic name Mysticeti), also known as whalebone whales, are a parvorder of carnivorous marine mammals of the infraorder Cetacea ( whales, dolphins and porpoises) which use keratinaceous baleen plates (or "whalebone") in t ...
( Mysticeti) which owe their name to their baleen, and toothed whales (
Odontoceti The toothed whales (also called odontocetes, systematic name Odontoceti) are a parvorder of cetaceans that includes dolphins, porpoises, and all other whales possessing teeth, such as the beaked whales and sperm whales. Seventy-three species of ...
), which have teeth shaped like cones, spades, pegs, or tusks, and can perceive their environment through
biosonar Echolocation, also called bio sonar, is a biological sonar used by several animal species. Echolocating animals emit calls out to the environment and listen to the echoes of those calls that return from various objects near them. They use these ...
. The terms ''whale'' and ''dolphin'' are informal: * Mysticeti: :* Whales, with four families:
Balaenidae Balaenidae () is a family of whales of the parvorder Mysticeti that contains two living genera: the right whales (genus ''Eubalaena''), and in a separate genus, the closely related bowhead whale (genus '' Balaena''). Evolutionary history Bale ...
(right and bowhead whales),
Cetotheriidae Cetotheriidae is a family of baleen whales (parvorder Mysticeti). The family is known to have existed from the Late Oligocene to the Early Pleistocene before going extinct. Although some phylogenetic studies conducted by recovered the living py ...
(pygmy right whales),
Balaenopteridae Rorquals () are the largest group of baleen whales, which comprise the family Balaenopteridae, containing ten extant species in three genera. They include the largest animal that has ever lived, the blue whale, which can reach , and the fin wha ...
(rorquals),
Eschrichtiidae Eschrichtiidae or the gray whales is a family of baleen whale (Parvorder Mysticeti) with a single extant species, the gray whale (''Eschrichtius robustus''), as well as three described fossil genera: '' Archaeschrichtius'' and '' Eschrichtioides' ...
(grey whales) *
Odontoceti The toothed whales (also called odontocetes, systematic name Odontoceti) are a parvorder of cetaceans that includes dolphins, porpoises, and all other whales possessing teeth, such as the beaked whales and sperm whales. Seventy-three species of ...
: :* Whales: with four families: Monodontidae (belugas and narwhals), Physeteridae (sperm whales), Kogiidae (dwarf and pygmy sperm whales), and
Ziphiidae Beaked whales (systematic name Ziphiidae) are a family of cetaceans noted as being one of the least known groups of mammals because of their deep-sea habitat and apparent low abundance. Only three or four of the 24 species are reasonably well-kn ...
(beaked whales) :* Dolphins, with five families: Delphinidae (oceanic dolphins),
Platanistidae Platanistidae is a family of river dolphins containing the extant Ganges river dolphin and Indus river dolphin The Indus river dolphin (''Platanista minor''), also known as the ''bhulan'' in Urdu and Sindhi, is a species of toothed whale in th ...
( South Asian river dolphins),
Lipotidae Lipotidae is a family of river dolphins containing the possibly extinct baiji of China and the fossil genus ''Parapontoporia'' from the Late Miocene and Pliocene of the Pacific coast of North America. The genus '' Prolipotes'', which is based ...
(old world river dolphins)
Iniidae Iniidae is a family of river dolphins containing one living genus, ''Inia'', and four extinct genera. The extant genus inhabits the river basins of South America, but the family formerly had a wider presence across the Atlantic Ocean. Iniida ...
(new world river dolphins), and Pontoporiidae ( La Plata dolphins) :*
Porpoise Porpoises are a group of fully aquatic marine mammals, all of which are classified under the family Phocoenidae, parvorder Odontoceti (toothed whales). Although similar in appearance to dolphins, they are more closely related to narwhals a ...
s, with one family:
Phocoenidae Porpoises are a group of fully aquatic marine mammals, all of which are classified under the family Phocoenidae, parvorder Odontoceti (toothed whales). Although similar in appearance to dolphins, they are more closely related to narwhals an ...
The term 'great whales' covers those currently regulated by the
International Whaling Commission The International Whaling Commission (IWC) is a specialised regional fishery management organisation, established under the terms of the 1946 International Convention for the Regulation of Whaling (ICRW) to "provide for the proper conservation ...
: the Odontoceti families Physeteridae (sperm whales), Ziphiidae (beaked whales), and Kogiidae (pygmy and dwarf sperm whales); and all the Mysticeti families Balaenidae (right and bowhead whales), Cetotheriidae (pygmy right whales), Eschrichtiidae (grey whales), and some of the Balaenopteridae (minke, Bryde's, sei, blue and fin; not Eden's and Omura's whales).


Status


Threats

The primary threats to cetaceans come from people, both directly from whaling or drive hunting and indirect threats from fishing and pollution.


Whaling

Whaling is the practice of hunting whales, mainly baleen and sperm whales. This activity has gone on since the Stone Age. In the Middle Ages, reasons for whaling included their meat,
oil An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) & lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturated ...
usable as fuel and the jawbone, which was used in house construction. At the end of the Middle Ages, early whaling fleets aimed at
baleen whales Baleen whales ( systematic name Mysticeti), also known as whalebone whales, are a parvorder of carnivorous marine mammals of the infraorder Cetacea ( whales, dolphins and porpoises) which use keratinaceous baleen plates (or "whalebone") in t ...
, such as bowheads. In the 16th and 17th centuries, the Dutch fleet had about 300 whaling ships with 18,000 crewmen. In the 18th and 19th centuries, baleen whales especially were hunted for their
baleen Baleen is a filter-feeding system inside the mouths of baleen whales. To use baleen, the whale first opens its mouth underwater to take in water. The whale then pushes the water out, and animals such as krill are filtered by the baleen and r ...
, which was used as a replacement for wood, or in products requiring strength and flexibility such as
corset A corset is a support garment commonly worn to hold and train the torso into a desired shape, traditionally a smaller waist or larger bottom, for aesthetic or medical purposes (either for the duration of wearing it or with a more lasting effe ...
s and
crinoline A crinoline is a stiff or structured petticoat designed to hold out a woman's skirt, popular at various times since the mid-19th century. Originally, crinoline described a stiff fabric made of horsehair ("crin") and cotton or linen which w ...
skirts. In addition, the spermaceti found in the
sperm whale The sperm whale or cachalot (''Physeter macrocephalus'') is the largest of the toothed whales and the largest toothed predator. It is the only living member of the genus '' Physeter'' and one of three extant species in the sperm whale fami ...
was used as a machine lubricant and the
ambergris Ambergris ( or , la, ambra grisea, fro, ambre gris), ''ambergrease'', or grey amber is a solid, waxy, flammable substance of a dull grey or blackish colour produced in the digestive system of sperm whales. Freshly produced ambergris has a mari ...
as a material for pharmaceutical and perfume industries. In the second half of the 19th century, the explosive
harpoon A harpoon is a long spear-like instrument and tool used in fishing, whaling, sealing, and other marine hunting to catch and injure large fish or marine mammals such as seals and whales. It accomplishes this task by impaling the target ani ...
was invented, leading to a massive increase in the catch size. Large ships were used as "mother" ships for the whale handlers. In the first half of the 20th century, whales were of great importance as a supplier of raw materials. Whales were intensively hunted during this time; in the 1930s, 30,000 whales were killed. This increased to over 40,000 animals per year up to the 1960s, when stocks of large baleen whales collapsed. Most hunted whales are now threatened, with some great whale populations exploited to the brink of extinction. Atlantic and Korean gray whale populations were completely eradicated and the North Atlantic right whale population fell to some 300–600. The
blue whale The blue whale (''Balaenoptera musculus'') is a marine mammal and a baleen whale. Reaching a maximum confirmed length of and weighing up to , it is the largest animal known to have ever existed. The blue whale's long and slender body can b ...
population is estimated to be around 14,000. The first efforts to protect whales came in 1931. Some particularly endangered species, such as the
humpback whale The humpback whale (''Megaptera novaeangliae'') is a species of baleen whale. It is a rorqual (a member of the family Balaenopteridae) and is the only species in the genus ''Megaptera''. Adults range in length from and weigh up to . The hu ...
(which then numbered about 100 animals), were placed under international protection and the first protected areas were established. In 1946, the
International Whaling Commission The International Whaling Commission (IWC) is a specialised regional fishery management organisation, established under the terms of the 1946 International Convention for the Regulation of Whaling (ICRW) to "provide for the proper conservation ...
(IWC) was established, to monitor and secure whale stocks. Whaling of 14 large species for commercial purposes was prohibited worldwide by this organization from 1985 to 2005, though some countries do not honor the prohibition. The stocks of species such as humpback and blue whales have recovered, though they are still threatened. The United States Congress passed the Marine Mammal Protection Act of 1972 sustain the marine mammal population. It prohibits the taking of marine mammals except for several hundred per year taken in Alaska. Japanese whaling ships are allowed to hunt whales of different species for ostensibly scientific purposes.
Aboriginal whaling Indigenous whaling is the hunting of whales by indigenous peoples recognised by either IWC (International Whaling Commission) or the hunting is considered as part of indigenous activity by the country. It is permitted under international reg ...
is still permitted. About 1,200 pilot whales were taken in the
Faroe Islands The Faroe Islands ( ), or simply the Faroes ( fo, Føroyar ; da, Færøerne ), are a North Atlantic archipelago, island group and an autonomous territory of the Danish Realm, Kingdom of Denmark. They are located north-northwest of Scotlan ...
in 2017, and about 900 narwhals and 800 belugas per year are taken in Alaska, Canada, Greenland, and Siberia. About 150 minke are taken in Greenland per year, 120 gray whales in Siberia and 50 bowheads in Alaska, as aboriginal whaling, besides the 600 minke taken commercially by Norway, 300 minke and 100 sei taken by Japan and up to 100 fin whales taken by Iceland. Iceland and Norway do not recognize the ban and operate commercial whaling. Norway and Japan are committed to ending the ban. Dolphins and other smaller cetaceans are sometimes hunted in an activity known as dolphin drive hunting. This is accomplished by driving a pod together with boats, usually into a bay or onto a beach. Their escape is prevented by closing off the route to the ocean with other boats or nets. Dolphins are hunted this way in several places around the world, including the Solomon Islands, the
Faroe Islands The Faroe Islands ( ), or simply the Faroes ( fo, Føroyar ; da, Færøerne ), are a North Atlantic archipelago, island group and an autonomous territory of the Danish Realm, Kingdom of Denmark. They are located north-northwest of Scotlan ...
, Peru and Japan (the most well-known practitioner). Dolphins are mostly hunted for their meat, though some end up in dolphinaria. Despite the controversy thousands of dolphins are caught in drive hunts each year.


Fishing

Dolphin pods often reside near large tuna shoals. This is known to fishermen, who look for dolphins to catch tuna. Dolphins are much easier to spot from a distance than tuna, since they regularly breathe. The fishermen pull their nets hundreds of meters wide in a circle around the dolphin groups, in the expectation that they will net a tuna shoal. When the nets are pulled together, the dolphins become entangled under water and drown. Line fisheries in larger rivers are threats to
river dolphins River dolphins are a polyphyletic group of fully aquatic mammals that reside exclusively in freshwater or brackish water. They are an informal grouping of dolphins, which itself is a paraphyletic group within the infraorder Cetacea. Extant riv ...
. A greater threat than by-catch for small cetaceans is targeted hunting. In Southeast Asia, they are sold as fish-replacement to locals, since the region's edible fish promise higher revenues from exports. In the Mediterranean, small cetaceans are targeted to ease pressure on edible fish.


Strandings

A stranding is when a cetacean leaves the water to lie on a beach. In some cases, groups of whales strand together. The best known are mass strandings of
pilot whale Pilot whales are cetaceans belonging to the genus ''Globicephala''. The two extant species are the long-finned pilot whale (''G. melas'') and the short-finned pilot whale (''G. macrorhynchus''). The two are not readily distinguishable at sea, ...
s and sperm whales. Stranded cetaceans usually die, because their as much as body weight compresses their lungs or breaks their ribs. Smaller whales can die of heatstroke because of their thermal insulation. The causes are not clear. Possible reasons for mass beachings are: * toxic contaminants * debilitating parasites (in the respiratory tract, brain or middle ear) * infections (bacterial or viral) * flight from predators (including humans) * social bonds within a group, so that the pod follows a stranded animal * disturbance of their magnetic senses by natural anomalies in the Earth's magnetic field * injuries *
noise pollution Noise pollution, also known as environmental noise or sound pollution, is the propagation of noise with ranging impacts on the activity of human or animal life, most of them are harmful to a degree. The source of outdoor noise worldwide is mai ...
by shipping traffic, seismic surveys and military sonar experiments Since 2000, whale strandings frequently occurred following military sonar testing. In December 2001, the US Navy admitted partial responsibility for the beaching and the deaths of several marine mammals in March 2000. The coauthor of the interim report stated that animals killed by active sonar of some Navy ships were injured. Generally, underwater noise, which is still on the increase, is increasingly tied to strandings; because it impairs communication and sense of direction. Climate change influences the major wind systems and ocean currents, which also lead to cetacean strandings. Researchers studying strandings on the Tasmanian coast from 1920 to 2002 found that greater strandings occurred at certain time intervals. Years with increased strandings were associated with severe storms, which initiated cold water flows close to the coast. In nutrient-rich, cold water, cetaceans expect large prey animals, so they follow the cold water currents into shallower waters, where the risk is higher for strandings. Whales and dolphins who live in pods may accompany sick or debilitated pod members into shallow water, stranding them at low tide.


Environmental hazards

Heavy metals, residues of many plant and insect venoms and plastic waste
flotsam In maritime law, flotsam'','' jetsam'','' lagan'','' and derelict are specific kinds of shipwreck. The words have specific nautical meanings, with legal consequences in the law of admiralty and marine salvage. A shipwreck is defined as the rema ...
are not biodegradable. Sometimes, cetaceans consume these hazardous materials, mistaking them for food items. As a result, the animals are more susceptible to disease and have fewer offspring. Damage to the
ozone layer The ozone layer or ozone shield is a region of Earth's stratosphere that absorbs most of the Sun's ultraviolet radiation. It contains a high concentration of ozone (O3) in relation to other parts of the atmosphere, although still small in relat ...
reduces plankton reproduction because of its resulting radiation. This shrinks the food supply for many marine animals, but the filter-feeding baleen whales are most impacted. Even the Nekton is, in addition to intensive exploitation, damaged by the radiation. Food supplies are also reduced long-term by
ocean acidification Ocean acidification is the reduction in the pH value of the Earth’s ocean. Between 1751 and 2021, the average pH value of the ocean surface has decreased from approximately 8.25 to 8.14. The root cause of ocean acidification is carbon dioxide ...
due to increased absorption of increased atmospheric carbon dioxide. The CO2 reacts with water to form carbonic acid, which reduces the construction of the calcium carbonate skeletons of food supplies for zooplankton that baleen whales depend on. The military and resource extraction industries operate strong sonar and blasting operations. Marine seismic surveys use loud, low-frequency sound that show what is lying underneath the Earth's surface. Vessel traffic also increases noise in the oceans. Such noise can disrupt cetacean behavior such as their use of
biosonar Echolocation, also called bio sonar, is a biological sonar used by several animal species. Echolocating animals emit calls out to the environment and listen to the echoes of those calls that return from various objects near them. They use these ...
for orientation and communication. Severe instances can panic them, driving them to the surface. This leads to bubbles in blood gases and can cause decompression sickness. Naval exercises with sonar regularly results in fallen cetaceans that wash up with fatal decompression. Sounds can be disruptive at distances of more than . Damage varies across frequency and species.


Relationship to humans


Research history

In Aristotle's time, the fourth century BCE, whales were regarded as fish due to their superficial similarity. Aristotle, however, observed many physiological and anatomical similarities with the terrestrial vertebrates, such as blood (circulation), lungs, uterus and fin anatomy. His detailed descriptions were assimilated by the Romans, but mixed with a more accurate knowledge of the dolphins, as mentioned by Pliny the Elder in his '' Natural history''. In the art of this and subsequent periods, dolphins are portrayed with a high-arched head (typical of porpoises) and a long snout. The
harbour porpoise The harbour porpoise (''Phocoena phocoena'') is one of eight extant species of porpoise. It is one of the smallest species of cetacean. As its name implies, it stays close to coastal areas or river estuaries, and as such, is the most familiar ...
was one of the most accessible species for early
cetologists Cetology (from Greek , ''kētos'', " whale"; and , ''-logia'') or whalelore (also known as whaleology) is the branch of marine mammal science that studies the approximately eighty species of whales, dolphins, and porpoises in the scientific order ...
; because it could be seen close to land, inhabiting shallow coastal areas of Europe. Much of the findings that apply to all cetaceans were first discovered in porpoises. One of the first anatomical descriptions of the airways of a harbor porpoise dates from 1671 by John Ray. It nevertheless referred to the porpoise as a fish. In the
10th edition of Systema Naturae The 10th edition of ''Systema Naturae'' is a book written by Swedish naturalist Carl Linnaeus and published in two volumes in 1758 and 1759, which marks the starting point of zoological nomenclature. In it, Linnaeus introduced binomial nomencl ...
(1758), Swedish biologist and taxonomist Carl Linnaeus asserted that cetaceans were mammals and not fish. His groundbreaking binomial system formed the basis of modern whale classification.


Culture

Cetaceans have played a role in human culture through history.


Prehistoric

Stone Age
petroglyphs A petroglyph is an image created by removing part of a rock surface by incising, picking, carving, or abrading, as a form of rock art. Outside North America, scholars often use terms such as "carving", "engraving", or other descriptions ...
, such as those in Roddoy and Reppa (Norway), and the
Bangudae Petroglyphs Korea's National Treasure No. 285, the Bangudae Petroglyphs, are located mainly on flat vertical rock faces around 8m wide and around 5m high on steep cliffs on the riverside of the Daegokcheon stream, a branch of the Taehwa River, which runs eas ...
in South Korea, depict them. Whale bones were used for many purposes. In the Neolithic settlement of Skara Brae on
Orkney Orkney (; sco, Orkney; on, Orkneyjar; nrn, Orknøjar), also known as the Orkney Islands, is an archipelago in the Northern Isles of Scotland, situated off the north coast of the island of Great Britain. Orkney is 10 miles (16 km) nort ...
sauce pans were made from whale vertebrae.


Antiquity

The whale was first mentioned in
ancient Greece Ancient Greece ( el, Ἑλλάς, Hellás) was a northeastern Mediterranean civilization, existing from the Greek Dark Ages of the 12th–9th centuries BC to the end of classical antiquity ( AD 600), that comprised a loose collection of cult ...
by Homer. There, it is called Ketos, a term that initially included all large marine animals. From this was derived the Roman word for whale,
Cetus Cetus () is a constellation, sometimes called 'the whale' in English. The Cetus was a sea monster in Greek mythology which both Perseus and Heracles needed to slay. Cetus is in the region of the sky that contains other water-related constell ...
. Other names were phálaina ( Aristotle, Latin form of ballaena) for the female and, with an ironic characteristic style, musculus (Mouse) for the male. North Sea whales were called Physeter, which was meant for the sperm whale ''Physter macrocephalus''. Whales are described in particular by Aristotle,
Pliny Pliny may refer to: People * Pliny the Elder (23–79 CE), ancient Roman nobleman, scientist, historian, and author of ''Naturalis Historia'' (''Pliny's Natural History'') * Pliny the Younger (died 113), ancient Roman statesman, orator, w ...
and
Ambrose Ambrose of Milan ( la, Aurelius Ambrosius; ), venerated as Saint Ambrose, ; lmo, Sant Ambroeus . was a theologian and statesman who served as Bishop of Milan from 374 to 397. He expressed himself prominently as a public figure, fiercely promot ...
. All mention both live birth and suckling. Pliny describes the problems associated with the lungs with spray tubes and Ambrose claimed that large whales would take their young into their mouth to protect them. In the Bible especially, the leviathan plays a role as a
sea monster Sea monsters are beings from folklore believed to dwell in the sea and often imagined to be of immense size. Marine monsters can take many forms, including sea dragons, sea serpents, or tentacled beasts. They can be slimy and scaly and are o ...
. The essence, which features a giant crocodile or a dragon and a whale, was created according to the Bible by God and should again be destroyed by him. In the
Book of Job The Book of Job (; hbo, אִיּוֹב, ʾIyyōḇ), or simply Job, is a book found in the Ketuvim ("Writings") section of the Hebrew Bible (Tanakh), and is the first of the Poetic Books in the Old Testament of the Christian Bible. Scholars are ...
, the leviathan is described in more detail. In Jonah there is a more recognizable description of a whale alongside the prophet
Jonah Jonah or Jonas, ''Yōnā'', "dove"; gr, Ἰωνᾶς ''Iōnâs''; ar, يونس ' or '; Latin: ''Ionas'' son of Amittai, is a prophet in the Hebrew Bible and the Quran, from Gath-hepher of the northern kingdom of Israel in about the 8th cen ...
, who, on his flight from the city of Nineveh is swallowed by a whale. Dolphins are mentioned far more often than whales. Aristotle discusses the sacred animals of the Greeks in his '' Historia Animalium'' and gives details of their role as aquatic animals. The Greeks admired the dolphin as a "king of the aquatic animals" and referred to them erroneously as fish. Its intelligence was apparent both in its ability to escape from fishnets and in its collaboration with fishermen. River dolphins are known from the Ganges and – erroneously – the
Nile The Nile, , Bohairic , lg, Kiira , Nobiin: Áman Dawū is a major north-flowing river in northeastern Africa. It flows into the Mediterranean Sea. The Nile is the longest river in Africa and has historically been considered the longest ri ...
. In the latter case it was equated with sharks and catfish. Supposedly they attacked even
crocodile Crocodiles (family Crocodylidae) or true crocodiles are large semiaquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. The term crocodile is sometimes used even more loosely to include all extant mem ...
s. Dolphins appear in Greek mythology. Because of their intelligence, they rescued multiple people from drowning. They were said to love music – probably not least because of their own song – they saved, in the legends, famous musicians such as
Arion Arion (; grc-gre, Ἀρίων; fl. c. 700 BC) was a kitharode in ancient Greece, a Dionysiac poet credited with inventing the dithyramb. The islanders of Lesbos claimed him as their native son, but Arion found a patron in Periander, tyrant of ...
of
Lesbos Lesbos or Lesvos ( el, Λέσβος, Lésvos ) is a Greek island located in the northeastern Aegean Sea. It has an area of with approximately of coastline, making it the third largest island in Greece. It is separated from Asia Minor by the na ...
from
Methymna Mithymna () ( el, Μήθυμνα, also sometimes spelled ''Methymna'') is a town and former municipality on the island of Lesbos, North Aegean, Greece. Since the 2019 local government reform it is part of the municipality of West Lesbos, of whic ...
or Kairanos from Miletus. Because of their mental faculties, dolphins were considered to be associated with the god Dionysus. Dolphins belong to the domain of Poseidon and led him to his wife
Amphitrite In ancient Greek mythology, Amphitrite (; grc-gre, Ἀμφιτρίτη, Amphitrítē) was the goddess of the sea, the queen of the sea, and the wife of Poseidon. She was a daughter of Nereus and Doris (or Oceanus and Tethys).Roman, L., & ...
. Dolphins are associated with other gods, such as
Apollo Apollo, grc, Ἀπόλλωνος, Apóllōnos, label=genitive , ; , grc-dor, Ἀπέλλων, Apéllōn, ; grc, Ἀπείλων, Apeílōn, label=Arcadocypriot Greek, ; grc-aeo, Ἄπλουν, Áploun, la, Apollō, la, Apollinis, label= ...
, Dionysus and
Aphrodite Aphrodite ( ; grc-gre, Ἀφροδίτη, Aphrodítē; , , ) is an ancient Greek goddess associated with love, lust, beauty, pleasure, passion, and procreation. She was syncretized with the Roman goddess . Aphrodite's major symbols include ...
. The Greeks paid tribute to both whales and dolphins with their own constellation. The constellation of the Whale (Ketos, lat. Cetus) is located south of the Dolphin (Delphi, lat. Delphinus) north of the zodiac. Ancient art often included dolphin representations, including the Cretan Minoans. Later they appeared on reliefs, gems, lamps, coins, mosaics and gravestones. A particularly popular representation is that of Arion or the Taras (mythology) riding on a dolphin. In early
Christian art Christian art is sacred art which uses subjects, themes, and imagery from Christianity. Most Christian groups use or have used art to some extent, including early Christian art and architecture and Christian media. Images of Jesus and narrativ ...
, the dolphin is a popular motif, at times used as a symbol of
Christ Jesus, likely from he, יֵשׁוּעַ, translit=Yēšūaʿ, label=Hebrew/Aramaic ( AD 30 or 33), also referred to as Jesus Christ or Jesus of Nazareth (among other Names and titles of Jesus in the New Testament, names and titles), was ...
.


Middle Ages to the 19th century

St. Brendan Brendan of Clonfert (c. AD 484 - c.577), is one of the early Irish monastic saints and one of the Twelve Apostles of Ireland. He is also referred to as Brendan the Navigator, Brendan the Voyager, Brendan the Anchorite, Brendan the Bold. The ...
described in his travel story ''Navigatio Sancti Brendani'' an encounter with a whale, between the years 565–573. He described how he and his companions entered a treeless island, which turned out to be a giant whale, which he called Jasconicus. He met this whale seven years later and rested on his back. Most descriptions of large whales from this time until the whaling era, beginning in the 17th century, were of beached whales, which resembled no other animal. This was particularly true for the sperm whale, the most frequently stranded in larger groups. Raymond Gilmore documented seventeen sperm whales in the estuary of the Elbe from 1723 to 1959 and thirty-one animals on the coast of Great Britain in 1784. In 1827, a blue whale beached itself off the coast of Ostend. Whales were used as attractions in museums and traveling exhibitions. Whalers from the 17th to 19th centuries depicted whales in drawings and recounted tales of their occupation. Although they knew that whales were harmless giants, they described battles with harpooned animals. These included descriptions of sea monsters, including huge whales, sharks, sea snakes, giant squid and octopuses. Among the first whalers who described their experiences on whaling trips was Captain William Scoresby from Great Britain, who published the book ''Northern Whale Fishery'', describing the hunt for northern baleen whales. This was followed by
Thomas Beale Thomas Beale (c. 1775–1841) was a Scottish naturalist, opium speculator and general merchant operating in the Far East during the 19th century. Biography Thomas was the younger brother of Daniel Beale and the cousin of Thomas Chaye Beale. ...
, a British surgeon, in his book ''Some observations on the natural history of the sperm whale'' in 1835; and Frederick Debell Bennett's ''The tale of a whale hunt'' in 1840. Whales were described in narrative literature and paintings, most famously in the novels '' Moby Dick'' by
Herman Melville Herman Melville ( born Melvill; August 1, 1819 – September 28, 1891) was an American novelist, short story writer, and poet of the American Renaissance period. Among his best-known works are ''Moby-Dick'' (1851); ''Typee'' (1846), a r ...
and ''
20,000 Leagues Under the Sea ''Twenty Thousand Leagues Under the Seas'' (french: Vingt mille lieues sous les mers) is a classic science fiction adventure novel by French writer Jules Verne. The novel was originally serialized from March 1869 through June 1870 in Pierre-Jul ...
'' by Jules Verne. Baleen was used to make vessel components such as the bottom of a bucket in the Scottish National Museum. The Norsemen crafted ornamented plates from baleen, sometimes interpreted as
ironing Ironing is the use of a machine, usually a heated tool (an iron), to remove wrinkles and unwanted creases from fabric. The heating is commonly done to a temperature of 180–220 °Celsius (356-428 Fahrenheit), depending on the fabric. Ironing wor ...
boards. In the Canadian Arctic (east coast) in Punuk and Thule culture (1000–1600 C.E.), baleen was used to construct houses in place of wood as roof support for winter houses, with half of the building buried under the ground. The actual roof was probably made of animal skins that were covered with soil and moss.


Modern culture

In the 20th century perceptions of cetaceans changed. They transformed from monsters into creatures of wonder, as science revealed them to be intelligent and peaceful animals. Hunting was replaced by whale and dolphin tourism. This change is reflected in films and novels. For example, the protagonist of the series Flipper was a bottle-nose dolphin. The TV series SeaQuest DSV (1993–1996), the movies
Free Willy ''Free Willy'' is a 1993 American family drama film, directed by Simon Wincer, produced by Lauren Shuler Donner and Jennie Lew Tugend, written by Keith A. Walker and Corey Blechman from a story by Walker and distributed by Warner Bros. Picture ...
, Star Trek IV: The Voyage Home and the book series
The Hitchhiker's Guide to the Galaxy ''The Hitchhiker's Guide to the Galaxy'' (sometimes referred to as ''HG2G'', ''HHGTTG'', ''H2G2'', or ''tHGttG'') is a comedy science fiction franchise created by Douglas Adams. Originally a 1978 radio comedy broadcast on BBC Radio 4, it ...
by Douglas Adams are examples. The study of whale song also produced a popular album, '' Songs of the Humpback Whale''.


Captivity

Whales and dolphins have been kept in captivity for use in education, research and entertainment since the 19th century.


Belugas

Beluga whale The beluga whale () (''Delphinapterus leucas'') is an Arctic and sub-Arctic cetacean. It is one of two members of the family Monodontidae, along with the narwhal, and the only member of the genus ''Delphinapterus''. It is also known as the wh ...
s were the first whales to be kept in captivity. Other species were too rare, too shy or too big. The first was shown at Barnum's Museum in New York City in 1861. For most of the 20th century, Canada was the predominant source. They were taken from the
St. Lawrence River The St. Lawrence River (french: Fleuve Saint-Laurent, ) is a large river in the middle latitudes of North America. Its headwaters begin flowing from Lake Ontario in a (roughly) northeasterly direction, into the Gulf of St. Lawrence, connecting t ...
estuary until the late 1960s, after which they were predominantly taken from the Churchill River estuary until capture was banned in 1992. Russia then became the largest provider. Belugas are caught in the Amur Darya delta and their eastern coast and are transported domestically to aquaria or dolphinaria in Moscow,
St. Petersburg Saint Petersburg ( rus, links=no, Санкт-Петербург, a=Ru-Sankt Peterburg Leningrad Petrograd Piter.ogg, r=Sankt-Peterburg, p=ˈsankt pʲɪtʲɪrˈburk), formerly known as Petrograd (1914–1924) and later Leningrad (1924–1991), i ...
and
Sochi Sochi ( rus, Со́чи, p=ˈsotɕɪ, a=Ru-Сочи.ogg) is the largest resort city in Russia. The city is situated on the Sochi River, along the Black Sea in Southern Russia, with a population of 466,078 residents, up to 600,000 residents in ...
, or exported to countries such as Canada. They have not been domesticated. As of 2006, 30 belugas lived in Canada and 28 in the United States. 42 deaths in captivity had been reported. A single specimen can reportedly fetch up to US$100,000 (GB£64,160). The beluga's popularity is due to its unique color and its facial expressions. The latter is possible because while most cetacean "smiles" are fixed, the extra movement afforded by the beluga's unfused cervical vertebrae allows a greater range of apparent expression.


Orcas

The orca's intelligence, trainability, striking appearance, playfulness in captivity and sheer size have made it a popular exhibit at aquaria and aquatic theme parks. From 1976 to 1997, fifty-five whales were taken from the wild in Iceland, nineteen from Japan and three from Argentina. These figures exclude animals that died during capture. Live captures fell dramatically in the 1990s and by 1999, about 40% of the forty-eight animals on display in the world were captive-born. Organizations such as World Animal Protection and the Whale and Dolphin Conservation campaign against the practice of keeping them in captivity. In captivity, they often develop pathologies, such as the
dorsal fin A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through co ...
collapse seen in 60–90% of captive males. Captives have reduced life expectancy, on average only living into their 20s, although some live longer, including several over 30 years old and two, Corky II and Lolita, in their mid-40s. In the wild, females who survive infancy live 46 years on average and up to 70–80 years. Wild males who survive infancy live 31 years on average and can reach 50–60 years. Captivity usually bears little resemblance to wild habitat and captive whales' social groups are foreign to those found in the wild. Critics claim captive life is stressful due to these factors and the requirement to perform circus tricks that are not part of wild orca behavior. Wild orca may travel up to in a day and critics say the animals are too big and intelligent to be suitable for captivity. Captives occasionally act aggressively towards themselves, their tankmates, or humans, which critics say is a result of stress. Orcas are well known for their performances in shows, but the number of orcas kept in captivity is small, especially when compared to the number of bottlenose dolphins, with only forty-four
captive orcas A number of orcas, also called killer whales, are held in captivity by humans for breeding or performance purposes. The practice of capturing and displaying orcas in exhibitions began in the 1960s, and they soon became popular attractions at publ ...
being held in aquaria as of 2012. Each country has its own tank requirements; in the US, the minimum enclosure size is set by the
Code of Federal Regulations In the law of the United States, the ''Code of Federal Regulations'' (''CFR'') is the codification of the general and permanent regulations promulgated by the executive departments and agencies of the federal government of the United States. ...
, 9 CFR E § 3.104, under the ''Specifications for the Humane Handling, Care, Treatment and Transportation of Marine Mammals''. Aggression among captive orcas is common. They attack each other and their trainers as well. In 2013, SeaWorld's treatment of orcas in captivity was the basis of the movie ''
Blackfish Blackfish is a common name for the following species of fish, dolphins, and whales: Fish * Alaska blackfish, (''Dallia pectoralis''), an Esocidae from Alaska, Siberia and the Bering Sea islands * Black fish (''Carassioides acuminatus'') a cyprin ...
'', which documents the history of
Tilikum Tillicum or Tilikum is a word in Chinook Jargon that means people, family, tribe, and relatives, and may refer to: Places * Tilikum Crossing, a bridge in Portland, Oregon * Tillicum, Lakewood, a neighborhood in Lakewood, Washington ** Tillicum st ...
, an orca at SeaWorld Orlando, who had been involved in the deaths of three people. The film led to proposals by some lawmakers to ban captivity of cetaceans, and led SeaWorld to announce in 2016 that it would phase out its orca program after various unsuccessful attempts to restore its revenues, reputation, and stock price.


Others

Dolphins and porpoises are kept in captivity.
Bottlenose dolphin Bottlenose dolphins are aquatic mammals in the genus ''Tursiops.'' They are common, cosmopolitan members of the family Delphinidae, the family of oceanic dolphins. Molecular studies show the genus definitively contains two species: the comm ...
s are the most common, as they are relatively easy to train, have a long lifespan in captivity and have a friendly appearance. Bottlenose dolphins live in captivity across the world, though exact numbers are hard to determine. Other species kept in captivity are spotted dolphins,
false killer whale The false killer whale (''Pseudorca crassidens'') is a species of oceanic dolphin that is the only extant representative of the genus '' Pseudorca''. It is found in oceans worldwide but mainly in tropical regions. It was first described in 18 ...
s and
common dolphin The common dolphin (''Delphinus delphis'') is the most abundant cetacean in the world, with a global population of about six million. Despite this fact and its vernacular name, the common dolphin is not thought of as the archetypal dolphin, wi ...
s,
Commerson's dolphin Commerson's dolphin (''Cephalorhynchus commersonii''), also referred to by the common names jacobita, skunk dolphin, piebald dolphin, panda dolphin, or tonina overa (in South America), is a small oceanic dolphin of the genus ''Cephalorhynchus'' ...
s, as well as
rough-toothed dolphin The rough-toothed dolphin (''Steno bredanensis'') is a species of dolphin that can be found in deep warm and tropical waters around the world. The species was first described by Georges Cuvier in 1823. The genus name ''Steno'', of which this spe ...
s, but all in much lower numbers. There are also fewer than ten
pilot whale Pilot whales are cetaceans belonging to the genus ''Globicephala''. The two extant species are the long-finned pilot whale (''G. melas'') and the short-finned pilot whale (''G. macrorhynchus''). The two are not readily distinguishable at sea, ...
s,
Amazon river dolphin The Amazon river dolphin (''Inia geoffrensis''), also known as the boto, bufeo or pink river dolphin, is a species of toothed whale classified in the family Iniidae. Three subspecies are currently recognized: ''I. g. geoffrensis'' (Amazon rive ...
s, Risso's dolphins,
spinner dolphin The spinner dolphin (''Stenella longirostris'') is a small dolphin found in off-shore tropical waters around the world. It is famous for its acrobatic displays in which it rotates around its longitudinal axis as it leaps through the air. It is a ...
s, or tucuxi in captivity. Two unusual and rare
hybrid Hybrid may refer to: Science * Hybrid (biology), an offspring resulting from cross-breeding ** Hybrid grape, grape varieties produced by cross-breeding two ''Vitis'' species ** Hybridity, the property of a hybrid plant which is a union of two dif ...
dolphins, known as wolphins, are kept at
Sea Life Park Sea Life Park Hawaii is a marine mammal park, bird sanctuary and aquarium in Waimānalo near Makapuʻu Point, north of Hanauma Bay on the island of Oahu in Hawaii, United States. The park first opened in 1964, and includes exhibits that let visit ...
in Hawaii, which is a cross between a bottlenose dolphin and a
false killer whale The false killer whale (''Pseudorca crassidens'') is a species of oceanic dolphin that is the only extant representative of the genus '' Pseudorca''. It is found in oceans worldwide but mainly in tropical regions. It was first described in 18 ...
. Also, two common/bottlenose hybrids reside in captivity at
Discovery Cove Discovery Cove is a theme park owned and operated by SeaWorld Parks & Entertainment, and located in Orlando, Florida. It is the sister park of SeaWorld Orlando and Aquatica Orlando. Visitors to the park can interact with a range of marine animal ...
and SeaWorld San Diego. In repeated attempts in the 1960s and 1970s, narwhals kept in captivity died within months. A breeding pair of
pygmy right whale The pygmy right whale (''Caperea marginata'') is a species of baleen whale. It may be a member of the cetotheres, a family of baleen whales which until 2012 were thought to be extinct; ''C. marginata'' has otherwise been considered the monotyp ...
s were retained in a netted area. They were eventually released in South Africa. In 1971, SeaWorld captured a California gray whale calf in Mexico at Scammon's Lagoon. The calf, later named Gigi, was separated from her mother using a form of lasso attached to her flukes. Gigi was displayed at SeaWorld San Diego for a year. She was then released with a radio beacon affixed to her back; however, contact was lost after three weeks. Gigi was the first captive baleen whale. JJ, another gray whale calf, was kept at SeaWorld San Diego. JJ was an orphaned calf that beached itself in April 1997 and was transported two miles to SeaWorld. The calf was a popular attraction and behaved normally, despite separation from his mother. A year later, the then whale though smaller than average, was too big to keep in captivity, and was released on April 1, 1998. A captive
Amazon river dolphin The Amazon river dolphin (''Inia geoffrensis''), also known as the boto, bufeo or pink river dolphin, is a species of toothed whale classified in the family Iniidae. Three subspecies are currently recognized: ''I. g. geoffrensis'' (Amazon rive ...
housed at Acuario de Valencia is the only trained river dolphin in captivity. Here is a list of all the cetaceans that have been taken into captivity for either conservation, research or human entertainment and education purposes currently or in the past, temporarily or permanently. * Orca *
Vaquita The vaquita ( ; ''Phocoena sinus'') is a species of porpoise endemic to the northern end of the Gulf of California in Baja California, Mexico. Averaging (females) or (males) in length, it is the smallest of all living cetaceans. The species i ...
*
False killer whale The false killer whale (''Pseudorca crassidens'') is a species of oceanic dolphin that is the only extant representative of the genus '' Pseudorca''. It is found in oceans worldwide but mainly in tropical regions. It was first described in 18 ...
*
Pygmy killer whale The pygmy killer whale (''Feresa attenuata'') is a poorly known and rarely seen oceanic dolphin. It is the only species in the genus ''Feresa''. It derives its common name from sharing some physical characteristics with the orca also known as t ...
*
Long-finned pilot whale The long-finned pilot whale (''Globicephala melas'') is a large species of oceanic dolphin. It shares the genus '' Globicephala'' with the short-finned pilot whale (''Globicephala macrorhynchus''). Long-finned pilot whales are known as such be ...
* Short-finned pilot whale *
Bottlenose dolphin Bottlenose dolphins are aquatic mammals in the genus ''Tursiops.'' They are common, cosmopolitan members of the family Delphinidae, the family of oceanic dolphins. Molecular studies show the genus definitively contains two species: the comm ...
*
Beluga whale The beluga whale () (''Delphinapterus leucas'') is an Arctic and sub-Arctic cetacean. It is one of two members of the family Monodontidae, along with the narwhal, and the only member of the genus ''Delphinapterus''. It is also known as the wh ...
*
Pacific white-sided dolphin The Pacific white-sided dolphin (''Lagenorhynchus obliquidens''), also known as the hookfin porpoise, is an active dolphin found in the cool or temperate waters of the North Pacific Ocean. Taxonomy The Pacific white-sided dolphin was named by Sm ...
* Risso's dolphin *
Atlantic white-sided dolphin The Atlantic white-sided dolphin (''Lagenorhynchus acutus'') is a distinctively coloured dolphin found in the cool to temperate waters of the North Atlantic Ocean. Description The dolphin is slightly larger than most other oceanic dolphins. It ...
* Narwhal *
Spotted dolphin Spotted dolphin refers to either one of two closely related dolphin species, being: * Atlantic spotted dolphin, ''Stenella frontalis'' * pantropical spotted dolphin, ''Stenella attenuata'' While the pantropical spotted dolphin can be found aroun ...
*
Spinner dolphin The spinner dolphin (''Stenella longirostris'') is a small dolphin found in off-shore tropical waters around the world. It is famous for its acrobatic displays in which it rotates around its longitudinal axis as it leaps through the air. It is a ...
*
Common dolphin The common dolphin (''Delphinus delphis'') is the most abundant cetacean in the world, with a global population of about six million. Despite this fact and its vernacular name, the common dolphin is not thought of as the archetypal dolphin, wi ...
*
Harbour porpoise The harbour porpoise (''Phocoena phocoena'') is one of eight extant species of porpoise. It is one of the smallest species of cetacean. As its name implies, it stays close to coastal areas or river estuaries, and as such, is the most familiar ...
*
Finless porpoise ''Neophocaena'' is a genus of porpoise native to the Indian and Pacific oceans, as well as the freshwater habitats of the Yangtze River basin in China China, officially the People's Republic of China (PRC), is a country in East Asia. I ...
*
Commerson's dolphin Commerson's dolphin (''Cephalorhynchus commersonii''), also referred to by the common names jacobita, skunk dolphin, piebald dolphin, panda dolphin, or tonina overa (in South America), is a small oceanic dolphin of the genus ''Cephalorhynchus'' ...
*
Rough-toothed dolphin The rough-toothed dolphin (''Steno bredanensis'') is a species of dolphin that can be found in deep warm and tropical waters around the world. The species was first described by Georges Cuvier in 1823. The genus name ''Steno'', of which this spe ...
*
Boto Boto is a Portuguese name given to several types of dolphins and river dolphins native to the Amazon and the Orinoco River tributaries. A few botos exist exclusively in fresh water, and these are often considered primitive dolphins. Classificatio ...
* Tucuxi *
Wholphin A wholphin (portmanteau of whale + dolphin) is an extremely rare cetacean hybrid born from a mating of a female common bottlenose dolphin (''Tursiops truncatus'') with a male false killer whale (''Pseudorca crassidens''). The name implies a hy ...
* Gray whale *
Pygmy sperm whale The pygmy sperm whale (''Kogia breviceps'') is one of two extant species in the family Kogiidae in the sperm whale superfamily. They are not often sighted at sea, and most of what is known about them comes from the examination of stranded speci ...
* Irrawaddy dolphin *
Indo-Pacific humpback dolphin The Indo-Pacific humpback dolphin (''Sousa chinensis'') is a species of humpback dolphin inhabiting coastal waters of the eastern Indian and western Pacific Oceans. This species is often referred to as the Chinese white dolphin in mainland Chi ...
*
Baiji The baiji (; IPA: ; ''Lipotes vexillifer'', ''Lipotes'' meaning "left behind" and ''vexillifer'' "flag bearer") is a possibly extinct species of freshwater dolphin native to the Yangtze river system in China. It is thought to be the first dolph ...
*
Melon-headed whale The melon-headed whale (''Peponocephala electra''), also known less commonly as the electra dolphin, little killer whale, or many-toothed blackfish, is a toothed whale of the oceanic dolphin family (Delphinidae). The common name is derived from t ...
* South Asian river dolphin *
Minke whale The minke whale (), or lesser rorqual, is a species complex of baleen whale. The two species of minke whale are the common (or northern) minke whale and the Antarctic (or southern) minke whale. The minke whale was first described by the Danish n ...


References


External links

* * *
Scottish Cetacean Research & Rescue
– see page o
Taxonomy
* *
EIA Cetacean campaign
Reports and latest info.
EIA in USA
reports etc. {{Portal bar, Cetaceans, Marine life, Mammals, Animals, Biology, Oceans Extant Ypresian first appearances Mammal infraorders Taxa named by Mathurin Jacques Brisson