Portal:Cetaceans

The Cetaceans Portal

A Sperm Whale fluke

Cetacea (/sɪˈteɪʃə/; from Latin cetus 'whale', from Ancient Greek κῆτος (kêtos) 'huge fish, sea monster') is an infraorder of aquatic mammals belonging to the order Artiodactyla that includes whales, dolphins and porpoises. 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 reside solely in brackish water or fresh water. Having a cosmopolitan distribution, 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, complex social behaviour, and the enormous size of some of the group's members. For example, the blue whale 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 ever known to have existed.

There are approximately 89 living species split into two parvorders: Odontoceti or toothed whales (containing porpoises, dolphins, other predatory whales like the beluga and the sperm whale, and the poorly understood beaked whales) and the filter feeding Mysticeti or baleen whales (which includes species like the blue whale, the humpback whale and the bowhead whale). Despite their highly modified bodies and carnivorous lifestyle, genetic and fossil evidence places cetaceans as nested within even-toed ungulates, most closely related to hippopotamus within the clade Whippomorpha. (Full article...)

Recognized content -

Entries here consist of Good and Featured articles, which meet a core set of high editorial standards.

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  Skull of Janjucetus hunderi at the Melbourne Museum

  
  Janjucetus is an extinct genus of cetacean, and a basal baleen whale (Mysticeti), from the Late Oligocene around 25 million years ago (mya) off south-east Australia, containing one species J. hunderi. Unlike modern mysticetes, it possessed large teeth for gripping and shredding prey, and lacked baleen, and so was likely to have been a predator that captured large single prey animals rather than filter feeding. However, its teeth may have interlocked, much like those of the modern-day filter-feeding crabeater seal (Lobodon carcinophaga), which would have allowed some filter-feeding behaviour. Its hunting behaviour was probably similar to the modern-day leopard seal (Hydrurga leptonyx), probably eating large fish. Like baleen whales, Janjucetus could not echolocate; however, it did have unusually large eyes, and so probably had an acute sense of vision. The only specimen was found on the Jan Juc beach, where the remains of the extinct whales Mammalodon, Prosqualodon and Waipatia have also been discovered. (Full article...)
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  Cast of skull at the Natural History Museum of the University of Pisa

  
  Livyatan is an extinct genus of macroraptorial sperm whale containing one known species: L. melvillei. The genus name was inspired by the biblical sea monster Leviathan, and the species name by Herman Melville, the author of the famous novel Moby-Dick about a white bull sperm whale. Herman Melville often referred to whales as "Leviathans" in his book. It is mainly known from the Pisco Formation of Peru during the Tortonian stage of the Miocene epoch, about 9.9–8.9 million years ago (mya); however, finds of isolated teeth from other locations such as Chile, Argentina, the United States (California), South Africa and Australia imply that either it or a close relative survived into the Pliocene, around 5 mya, and may have had a global presence. It was a member of a group of macroraptorial sperm whales (or "raptorial sperm whales") and was probably an apex predator, preying on whales, seals and so forth. Characteristically of raptorial sperm whales, Livyatan had functional, enamel-coated teeth on the upper and lower jaws, as well as several features suitable for hunting large prey.
  
  Livyatan's total length has been estimated to be about 13.5–17.5 m (44–57 ft), almost similar to that of the modern sperm whale (Physeter macrocephalus), making it one of the largest predators known to have existed. The teeth of Livyatan measured 36.2 cm (1.19 ft), and are the largest biting teeth of any known animal, excluding tusks. It is distinguished from the other raptorial sperm whales by the basin on the skull spanning the length of the snout. The spermaceti organ contained in that basin is thought to have been used in echolocation and communication, or for ramming prey and other sperm whales. The whale may have interacted with the large extinct shark megalodon (Otodus megalodon), competing with it for a similar food source. Its extinction was probably caused by a cooling event at the end of the Miocene period causing a reduction in food populations. The geological formation where the whale has been found has also preserved a large assemblage of marine life, such as sharks and marine mammals. (Full article...)
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  Skeleton at the Museo Capellini di Bologna

  
  Orcinus citoniensis is an extinct species of orca identified in the Late Pliocene of Italy and the Early Pleistocene of England. It was smaller than the modern killer whale (O. orca), 4 m (13 ft) versus 7 to 10 m (23 to 33 ft), and had around 8 more teeth in its jaw. It may have resembled the modern killer whale in appearance, and could represent a transitional species between the modern killer whale and other dolphins. O. citoniensis could have hunted fish and squid in pods, and coexisted with other large predators of the time such as the orcinine Hemisyntrachelus and the extinct shark Otodus megalodon. (Full article...)
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  The blue whale (Balaenoptera musculus) is a marine mammal and a baleen whale. Reaching a maximum confirmed length of 29.9 m (98 ft) and weighing up to 199 t (196 long tons; 219 short tons), it is the largest animal known ever to have existed. The blue whale's long and slender body can be of various shades of greyish-blue on its upper surface and somewhat lighter underneath. Four subspecies are recognized: B. m. musculus in the North Atlantic and North Pacific, B. m. intermedia in the Southern Ocean, B. m. brevicauda (the pygmy blue whale) in the Indian Ocean and South Pacific Ocean, and B. m. indica in the Northern Indian Ocean. There is a population in the waters off Chile that may constitute a fifth subspecies.
  
  In general, blue whale populations migrate between their summer feeding areas near the poles and their winter breeding grounds near the tropics. There is also evidence of year-round residencies, and partial or age/sex-based migration. Blue whales are filter feeders; their diet consists almost exclusively of krill. They are generally solitary or gather in small groups, and have no well-defined social structure other than mother–calf bonds. Blue whales vocalize, with a fundamental frequency ranging from 8 to 25 Hz; their vocalizations may vary by region, season, behavior, and time of day. Orcas are their only natural predators. (Full article...)
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  The harbor porpoise (Phocoena phocoena)

  
  Porpoises (/ˈpɔːrpəsɪz/) are small dolphin-like cetaceans classified under the family Phocoenidae. Although similar in appearance to dolphins, they are more closely related to narwhals and belugas than to the true dolphins. There are eight extant species of porpoise, all among the smallest of the toothed whales. Porpoises are distinguished from dolphins by their flattened, spade-shaped teeth distinct from the conical teeth of dolphins, and lack of a pronounced beak, although some dolphins (e.g. Hector's dolphin) also lack a pronounced beak. Porpoises, and other cetaceans, belong to the clade Cetartiodactyla with even-toed ungulates.
  
  Porpoises range in size from the vaquita, at 1.4 metres (4 feet 7 inches) in length and 54 kilograms (119 pounds) in weight, to the Dall's porpoise, at 2.3 m (7 ft 7 in) and 220 kg (490 lb). Several species exhibit sexual dimorphism in that the females are larger than males. They have streamlined bodies and two limbs that are modified into flippers. Porpoises use echolocation as their primary sensory system. Some species are well adapted for diving to great depths. As all cetaceans, they have a layer of fat, or blubber, under the skin to keep them warm in cold water. (Full article...)
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  Species of the infraorder Cetacea

  
  The evolution of cetaceans is thought to have begun in the Indian subcontinent from even-toed ungulates (Artiodactyla) 50 million years ago (mya) and to have proceeded over a period of at least 15 million years. Cetaceans are fully aquatic mammals belonging to the order Artiodactyla and branched off from other artiodactyls around 50 mya. Cetaceans are thought to have evolved during the Eocene (56-34 mya), the second epoch of the present-extending Cenozoic Era. Molecular and morphological analyses suggest Cetacea share a relatively recent closest common ancestor with hippopotami and that they are sister groups. Being mammals, they surface to breathe air; they have five finger bones (even-toed) in their fins; they nurse their young; and, despite their fully aquatic life style, they retain many skeletal features from their terrestrial ancestors. Research conducted in the late 1970s in Pakistan revealed several stages in the transition of cetaceans from land to sea.
  
  The two modern parvorders of cetaceans – Mysticeti (baleen whales) and Odontoceti (toothed whales) – are thought to have separated from each other around 28–33 mya in a second cetacean radiation, the first occurring with the archaeocetes. The adaptation of animal echolocation in toothed whales distinguishes them from fully aquatic archaeocetes and early baleen whales. The presence of baleen in baleen whales occurred gradually, with earlier varieties having very little baleen, and their size is linked to baleen dependence (and subsequent increase in filter feeding). (Full article...)
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  Archaeopteryx is one of the most famous transitional fossils and gives evidence for the evolution of birds from theropod dinosaurs.

  
  A transitional fossil is any fossilized remains of a life form that exhibits traits common to both an ancestral group and its derived descendant group. This is especially important where the descendant group is sharply differentiated by gross anatomy and mode of living from the ancestral group. These fossils serve as a reminder that taxonomic divisions are human constructs that have been imposed in hindsight on a continuum of variation. Because of the incompleteness of the fossil record, there is usually no way to know exactly how close a transitional fossil is to the point of divergence. Therefore, it cannot be assumed that transitional fossils are direct ancestors of more recent groups, though they are frequently used as models for such ancestors.
  
  In 1859, when Charles Darwin's On the Origin of Species was first published, the fossil record was poorly known. Darwin described the perceived lack of transitional fossils as "the most obvious and gravest objection which can be urged against my theory," but he explained it by relating it to the extreme imperfection of the geological record. He noted the limited collections available at the time but described the available information as showing patterns that followed from his theory of descent with modification through natural selection. Indeed, Archaeopteryx was discovered just two years later, in 1861, and represents a classic transitional form between earlier, non-avian dinosaurs and birds. Many more transitional fossils have been discovered since then, and there is now abundant evidence of how all classes of vertebrates are related, including many transitional fossils. Specific examples of class-level transitions are: tetrapods and fish, birds and dinosaurs, and mammals and "mammal-like reptiles". (Full article...)
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  Artistic reconstruction

  
  Arktocara is an extinct genus of river dolphin from the Oligocene epoch of Alaska, containing one species, A. yakataga. Having been discovered in 25-million-year-old strata near the 60th parallel north, it is perhaps the oldest-known crown toothed whale and the northmost river dolphin discovered. It was a member of the now-extinct family Allodelphinidae, along with the genera Allodelphis, Goedertius, Ninjadelphis, and Zarhinocetus. It measured approximately 2.26 or 2.28 meters (7.4 or 7.5 ft), comparable to its closest living relative, the South Asian river dolphin, which measures 2.4 meters (7.9 ft). However, the animal probably had an elongated beak and neck, so it may have been longer. The animal is known only from a partially preserved skull. Its ecology may have been similar to the modern-day Dall's porpoise, and it may have competed with contemporaneous delphinoids. Its remains were found in the Poul Creek Formation, which has also yielded several mollusk species. (Full article...)
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  The holotype and only specimen

  
  Orcinus meyeri is a fossil species of Orcinus (killer whales) found in the Early Miocene deposits of southern Germany, known from two jaw fragments and 18 isolated teeth. It was originally described as Delphinus acutidens in 1859, but reclassified in 1873. Its validity is disputed, and it may be a synonymous with the ancient sperm whale Physeterula dubusi. It was found in the Alpine town of Stockach in the Molasse basin, which was a coastal area with strong tidal currents. (Full article...)
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  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 family, along with the pygmy sperm whale and dwarf sperm whale of the genus Kogia.
  
  The sperm whale is a pelagic mammal with a worldwide range, and will migrate seasonally for feeding and breeding. Females and young males live together in groups, while mature males (bulls) live solitary lives outside of the mating season. The females cooperate to protect and nurse their young. Females give birth every four to twenty years, and care for the calves for more than a decade. A mature, healthy sperm whale has no natural predators, although calves and weakened adults are sometimes killed by pods of killer whales (orcas). (Full article...)
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  The narwhal (Monodon monoceros) is a species of toothed whale native to the Arctic. It is the only member of the genus Monodon and one of two living representatives of the family Monodontidae. The narwhal has a similar build to the closely related beluga whale, with which it overlaps in range and can interbreed. It is a stocky cetacean with a relatively blunt snout, a large melon, and a shallow ridge in place of a dorsal fin. Males of this species have a large 1.5–3.0 m (4 ft 11 in – 9 ft 10 in) long tusk, which is a left protruded canine thought to serve as a weapon or as a tool for feeding, attracting mates or sensing water salinity. Specially adapted slow-twitch muscles, along with the jointed neck vertebrae and shallow dorsal ridge allow for easy movement through the Arctic environment, where the narwhal spends extended periods at great depths.
  
  The narwhal inhabits the Arctic waters of Canada, Greenland and Russia. Every year, it migrates to ice-free summering grounds, usually in shallow waters, and often returns to the same sites in subsequent years. Its diet mainly consists of polar and Arctic cod, Greenland halibut, cuttlefish, shrimp, and armhook squid. Plunging at depths of up to 2,370 m (7,780 ft), the narwhal is among the deepest-diving cetaceans. It travels in groups of three to eight, with aggregations of up to 1,000 occurring in the summer months. It mates in the offshore pack ice from March to May, and the young are born in July or August of the following year. When communicating, a variety of clicks, whistles and knocks are used. (Full article...)
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  Orca's Song is a 1987 picturebook written by Anne Cameron and illustrated in black and white by Nelle Olsen. Published by Harbour Publishing, the book is an adaptation of a Pacific Northwest Indigenous story. Orca's Song is a pourquoi story about a black orca who falls in love with an osprey; the two mate to create a baby orca with the black and white patterning found on the whales.
  
  While some reviewers appreciated the art and text of the story, it received criticism from Indigenous authors and scholars who disputed Cameron's claim of sole authorship and copyright for the story. Consequently, reprints of the book began to attribute the storyteller Klopinum for the story's inspiration although Cameron retained sole authorship credit and copyright. The story has also been noted as an early example of a lesbian relationship (between Orca and Osprey) in picturebook literature and one of the few such picturebooks published before 2000 to lack a moralising tone. (Full article...)
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  Whaling in the Faroe Islands, or grindadráp (from the Faroese terms grindhvalur, meaning pilot whale, and dráp, meaning killing), is a type of drive hunting that involves herding various species of whales and dolphins, but primarily pilot whales, into shallow bays to be beached, killed, and butchered. Each year, an average of around 700 long-finned pilot whales and several hundred Atlantic white-sided dolphins are caught over the course of the hunt season during the summer.
  
  The practice dates back to the 9th century, and many Faroe Islanders consider eating whales to be an important part of their history. Since 1948, the hunt has been regulated by the Faroese authorities, required its participants to be trained, involved modern boats and communications, and been supervised by police. (Full article...)
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  Sei whale mother and calf

  
  The sei whale (/seɪ/ SAY, Norwegian: [sæɪ]; Balaenoptera borealis) is a baleen whale. It is one of ten rorqual species, and the third-largest member after the blue and fin whales. It can grow to 19.5 m (64 ft) in length and weigh as much as 28 t (28 long tons; 31 short tons). Two subspecies are recognized: B. b. borealis and B. b. schlegelii. The whale's ventral surface has sporadic markings ranging from light grey to white, and its body is usually dark steel grey in colour. It is among the fastest of all cetaceans, and can reach speeds of up to 50 km/h (31 mph) over short distances. 
  
  It inhabits most oceans and adjoining seas, and prefers deep offshore waters. It avoids polar and tropical waters and semi-enclosed bodies of water. The sei whale migrates annually from cool, subpolar waters in summer to temperate, subtropical waters in winter with a lifespan of 70 years. It is a filter feeder, with its diet consisting primarily of copepods, krill, and other zooplankton. It is typically solitary or can be found in groups numbering half a dozen. During the breeding period, a mating pair will remain together. Sei whale vocalizations usually lasts half a second, and occurs at 240–625 hertz. (Full article...)
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  Boudewijn Seapark dolphinarium in Bruges, Belgium

  
  A dolphinarium is an aquarium for dolphins. The dolphins are usually kept in a pool, though occasionally they may be kept in pens in the open sea, either for research or public performances. Some dolphinariums (sometimes called dolphinaria in plural) consist of one pool where dolphins perform for the public, others are part of larger parks, such as marine mammal parks, zoos or theme parks, with other animals and attractions as well.
  
  While cetaceans have been held in captivity since the 1860s, the first commercial dolphinarium was opened only in 1938. Their popularity increased rapidly until the 1960s. Since the 1970s, increasing concern for animal welfare led to stricter regulation, which in several countries ultimately resulted in the closure of some dolphinariums. Despite this trend, dolphinariums are still widespread in Europe, Japan and North America. The most common species of dolphin kept in dolphinariums is the bottlenose dolphin, as it is relatively easy to train and has a long lifespan in captivity. While trade in dolphins is internationally regulated, other aspects of keeping dolphins in captivity, such as the minimum size and characteristics of pools, vary among countries. Though animal welfare is perceived to have improved significantly over the last few decades, many animal rights groups still consider keeping dolphins captive to be a form of animal abuse. (Full article...)

Selected picture

Blue Whale skeleton

Photo credit: Bronwen Lea, 14 May 2004

A Blue whale skeleton, outside the Long Marine Laboratory at the University of California, Santa Cruz.

Blue Whales are the largest animal ever to have existed. Hunting of Blue Whales has led to a severe decline in numbers across the globe.

More did you know...

A Bottlenose Dolphin Breaching the water

• ...dolphins often leap clear of the water when travelling at speed. This is because the density of water is much greater than that of air and they are able to travel faster by leaping out of the water.

• ...both whales and dolphins carry ‘whale lice’ — small crustaceans that inhabit folds in the skin of whales and dolphins, feeding off the loose skin.

• ...whale and dolphin mothers ‘suckle’ their young underwater! Mothers have muscular mammary glands and ‘squirt’ their milk into the calf’s mouth, to ensure that the calf takes in as much of the energy rich milk as possible.

• ...on average, a whale or dolphin will eat four to five percent of its body weight in food per day. That means that a 100 ton blue whale will eat almost five tons of krill per day, or that a 200kg bottlenose dolphin will eat 10kg of fish per day!

• ...newborn cetacean calves ‘suckle’ three to four times each hour and will suckle from their mothers for six months or more.

Things you can do..

Here are some Cetaceans WikiProject tasks you can do. Patrol: Look through the Category:Cetaceans for recent changes Assessment: Unassessed cetacea articles and unknown-importance cetacea articles. Copyedit/Formatting: Bottlenose dolphin, Beached whale, Cetacea Expand: Hector's beaked whale, Ginkgo-toothed beaked whale, Shepherd's beaked whale, Archaeoceti, Cumberland Sound beluga, Blubber, Baiji, Humpback dolphin, Amazon river dolphin Verify: Spinner dolphin, Whale, Dolphin, Cetacea Stubs: Bolivian river dolphin (new species), Cephalorhynchus Images: Pictures of the baiji are wanted.

General images -

The following are images from various cetacean-related articles on Wikipedia.

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  Pacific white-sided dolphins porpoising (from Toothed whale)
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  Orca hunting a Weddell seal (from Toothed whale)
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  World population graph of blue whales
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  The nose of the whale is filled with a waxy substance that was widely used in candles, oil lamps, and lubricants (from Toothed whale)
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  Anatomy of the bottlenose dolphin (from Toothed whale)
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  Gray whale illustration
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  Megalodon hunted Miocene baleen whales (from Baleen whale)
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  Archaeomysticetes, like Janjucetus, had teeth.
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  Fin whale illustration
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  Pygmy right whale illustration
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  Common minke whale illustration
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  A protest against Japan's scientific whaling
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  Japanese scientific whaling on a pair of Antarctic minke whales (from Baleen whale)
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  Fossil of Squalodon (from Toothed whale)
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  The remains of a North Atlantic right whale after it collided with a ship propeller
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  South Atlantic right whale illustration
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  Antarctic minke whale illustration
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  Eden's whale illustration
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  Orange whale lice on a right whale
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  The heart of a blue whale with a person standing next to it
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  Features of a sperm whale skeleton (from Toothed whale)
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  Biosonar by cetaceans (from Toothed whale)
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  A humpback whale skeleton. Notice how the jaw is split into two.
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  Diagram illustrating sound generation, propagation and reception in a toothed whale. Outgoing sounds are red and incoming ones are green (from Toothed whale)
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  An orca by the name of Ulises performing at SeaWorld, 2009 (from Toothed whale)
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  Blue whale illustration
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  Restoration of Janjucetus hunderi (from Baleen whale)
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  Humpback whale illustration
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  Bowhead whale illustration
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  Acrophyseter skull (from Evolution of cetaceans)
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  Species of the infraorder Cetacea (from Evolution of cetaceans)
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  A whale as depicted by Conrad Gessner, 1587, in his Historiae animalium (from Toothed whale)
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  Dolphins (aquatic mammals) and ichthyosaurs (extinct marine reptiles) share a number of unique adaptations for fully aquatic lifestyle and are frequently used as extreme examples of convergent evolution (from Evolution of cetaceans)
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  A phylogenetic tree showing the relationships among cetacean families. (from Evolution of cetaceans)
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  Sei whale illustration
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  Their eyes are relatively small for their size.
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  Bryde's whale (rorqual) (from Baleen whale)
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  Possible relationships between cetaceans and other ungulate groups. (from Evolution of cetaceans)
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  Pakicetus attocki skeleton (from Evolution of cetaceans)
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  Atlantic white-sided dolphin caught in a drive hunt in Hvalba on the Faroe Islands being taken away with a forklift (from Toothed whale)
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  Archaeocetes (like this Basilosaurus) had a heterodont dentition (from Evolution of cetaceans)
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  Humpback whales lunge-feeding in the course of bubble net fishing
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  Spectrogram of dolphin vocalizations. Whistles, whines, and clicks are visible as upside down V's, horizontal striations, and vertical lines, respectively. (from Toothed whale)
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  The skeleton of a bowhead whale with the hind limb and pelvic bone structure circled in red. This bone structure stays internal during the entire life of the species. (from Evolution of cetaceans)
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  North Atlantic right whale illustration
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  Baleen whales vary considerably in size and shape, depending on their feeding behavior. (from Baleen whale)
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  Female right whale with calf
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  Accessory baleen plates taper off into small hairs (from Baleen whale)

Did you know (auto-generated)

• ... that Celia Kaye won the Golden Globe Award for Most Promising Newcomer in 1965 for her starring role in Island of the Blue Dolphins?
• ... that one can swim with humpback whales in the Niue Nukutuluea Multiple-Use Marine Park?
• ... that the South Asian river dolphin is nearly blind and relies on echolocation for navigation?
• ... that one of the first researchers to propose dolphin-assisted therapy for humans later renounced it?

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• List of cetaceans
• List of extinct cetaceans
• List of whale species
• List of dolphin species
• List of porpoise species
• List of whale vocalizations

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