Toothed whale

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Toothed whales
Temporal range: Eocene–recent
Tursiops truncatus 01.jpg
Bottlenose dolphin
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Artiodactyla
Clade: Cetancodontamorpha
Suborder: Whippomorpha
Infraorder: Cetacea
Parvorder: Odontoceti
Flower, 1869

See text.

Around 73; see List of cetaceans or below

The toothed whales (systematic name Odontoceti) form a parvorder of the artiodactyl infraorder Cetacea, including sperm whales, beaked whales, dolphins, and porpoises. As the name suggests, the parvorder is characterized by the presence of teeth rather than the baleen of other whales. There are 73 species of toothed whale. They are thought to have split from baleen whales, parvorder Mysticeti, around 34 million years ago. Whales and dolphins, the paraphyletic groups of cetacea, as well as porpoises, belong to the clade Cetartiodactyla with even-toed ungulates; their closest living relatives are the hippopotamuses which diverged about 40 million years ago.

Toothed whales range in size from the 4.5 feet (1.4 m) and 120 pounds (54 kg) vaquita to the 6-to-8-metre (20 to 26 ft) and 3-to-4-metric-ton (3.3-to-4.4-short-ton) killer whale. Several species of odontocete exhibit sexual dimorphism, in that the females are larger than males. They have streamlined bodies and two limbs that are modified into flippers. Some can travel at up to 20 knots. Odontocetes have conical teeth designed for catching fish or squid. They have well-developed hearing, that is well adapted for both air and water, so much so that some can survive even if they are blind. Some species are well adapted for diving to great depths. Almost all have a layer of fat, or blubber, under the skin to keep warm in the cold water, with the exception of river dolphins.

Toothed whales consist of some of the most widespread mammals, but some, as with the vaquita, are restricted to certain areas. Odontocetes feed largely on fish and squid, but a few, like the killer whale, feed on mammals, such as pinnipeds. Males typically mate with multiple females every year, but females only mate every two to three years, making them polygynous. Calves are typically born in the spring and summer months and females bear the responsibility for raising them, but more sociable species rely on the family group to care for calves. Many species, mainly dolphins, are highly sociable, with some pods reaching over a thousand individuals.

Once hunted for their products, cetaceans are now protected by international law. Some species are attributed with high levels of intelligence. At the 2012 meeting of the American Association for the Advancement of Science, support was reiterated for a cetacean bill of rights, listing cetaceans as non-human persons. Besides whaling and drive hunting, they also face threats from bycatch and marine pollution. The Baiji, for example, is considered functionally extinct by the IUCN, with the last sighting in 2004, due to heavy pollution to the Yangtze river. Whales occasionally feature in literature and film, as in the great white whale of Herman Melville's Moby Dick. Small odontocetes, mainly dolphins, are kept in captivity and trained to perform tricks, but breeding success has been poor. Whale watching has become a form of tourism around the world.




Anatomy of the bottlenose dolphin
Features of a sperm whale skeleton

Toothed whales have torpedo shaped bodies with non-flexible necks, limbs modified into flippers, non-existent external ear flaps, a large tail fin, and bulbous (with the exception of sperm whales). Their skulls have small eye orbits, long beaks (with the exception sperm whales) and eyes placed on the sides of its head. Toothed whales range in size from the 4.5 feet (1.4 m) and 120 pounds (54 kg) vaquita to the 6-to-8-metre (20 to 26 ft) and 3-to-4-metric-ton (3.3-to-4.4-short-ton) killer whale. Overall, they tend to be dwarfed their relatives, the baleen whales (Mysticeti). Several species have female-biased sexual dimorphism, with the females being larger than the males. One exception is with the sperm whale, which has males larger than the females.[1][2]

Odontocetes, such as the sperm whale, possess teeth with cementum cells overlying dentine cells. Unlike human teeth, which are composed mostly of enamel on the portion of the tooth outside of the gum, whale teeth have cementum outside the gum. Only in larger whales, where the cementum is worn away on the tip of the tooth, does enamel show.[1] Except for the sperm whale, most toothed whales are smaller than the baleen whales. The teeth differ considerably among the species. They may be numerous, with some dolphins bearing over 100 teeth in their jaws. At the other extreme are the narwhals with its single long tusk and the almost toothless beaked whales with tusk-like teeth only in males.[3]Not all species are believed to use their teeth for feeding. For instance, the sperm whale likely uses its teeth for aggression and showmanship.[1]

Breathing involves expelling stale air from their one blowhole, forming an upward, steamy spout, followed by inhaling fresh air into the lungs. Spout shapes differ among species, which facilitates identification. The spout only forms when warm air from the lungs meets cold air, so it does not form in warmer climates, as with river dolphins.[1][4][5]

Almost all cetaceans have a thick layer of blubber, with the exception of river dolphins. In species that live near the poles, the blubber can be as thick as 11 inches. This blubber can help with buoyancy, protection to some extent as predators would have a hard time getting through a thick layer of fat, energy for fasting during leaner times, and insulation from the harsh climates. Calves are born with only a thin layer of blubber, but some species compensate for this with thick lanugos.[1][6]

Toothed whales have a two chambered stomach that is similar in structure to terrestrial carnivores. They have fundic and pyloric chambers.[7]


Cetaceans have two flippers on the front, and a tail fin. These flippers contain four digits. Although toothed whales do not possess fully developed hind limbs, some, such as the sperm whale, possess discrete rudimentary appendages, which may contain feet and digits. Toothed whales are fast swimmers in comparison to seals, which typically cruise at 5–15 kn, or 9–28 kilometres per hour (5.6–17.4 mph); the sperm whale, in comparison, can travel at speeds up to 35 kilometres per hour (22 mph). The fusing of the neck vertebrae, while increasing stability when swimming at high speeds, decreases flexibility, rendering them incapable of turning their head; river dolphin, however, have unfused neck-vertebrae and can turn their head. When swimming, toothed whales rely on their tail fin propel them through the water. Flipper movement is continuous. They swim by moving their tail fin and lower body up and down, propelling themselves through vertical movement, while their flippers are mainly used for steering. Some species log out of the water, which may allow then to travel faster. Their skeletal anatomy allows them to be fast swimmers. Most species have a dorsal fin.[1][6]

Most toothed whales are adapted for diving to great depths, porpoises are one exception. In addition to their streamlined bodies, they can slow their heart rate to conserve oxygen; blood is rerouted from tissue tolerant of water pressure to the heart and brain among other organs; haemoglobin and myoglobin store oxygen in body tissue; and they have twice the concentration of myoglobin than haemoglobin. Before going on long dives, many toothed whales exhibit a behaviour known as sounding; they stay close to the surface for a series of short, shallow dives while building their oxygen reserves, and then make a sounding dive.[8][9]


Biosonar by cetaceans

Toothed whale eyes are relatively small for its size, yet they do retain a good degree of eyesight. As well as this, the eyes are placed on the sides of its head, so their vision consists of two fields, rather than a binocular view like humans have. When belugas surface, their lens and cornea correct the nearsightedness that results from the refraction of light; they contain both rod and cone cells, meaning they can see in both dim and bright light. They do, however, lack short wavelength sensitive visual pigments in their cone cells indicating a more limited capacity for colour vision than most mammals.[10] Most toothed whales have slightly flattened eyeballs, enlarged pupils (which shrink as they surface to prevent damage), slightly flattened corneas and a tapetum lucidum; these adaptations allow for large amounts of light to pass through the eye and, therefore, a very clear image of the surrounding area. In water, a whale can see around 10.7 metres (35 ft) ahead of itself, but, of course, they have a smaller range above water. They also have glands on the eyelids and outer corneal layer that act as protection for the cornea.[1][11]:505–519

The olfactory lobes are absent in toothed whales, and, unlike baleen whales, they lack the vomeronasal organ, suggesting that they have no sense of smell.[11]:481–505

Toothed whales are not thought to have a good sense of taste, as their taste buds are atrophied or missing altogether. However, some dolphins have preferences between different kinds of fish, indicating some sort of attachment to taste.[11]:447–455


Spectrogram of dolphin vocalizations. Whistles, whines, and clicks are visible as upside down V's, horizontal striations, and vertical lines, respectively.

Toothed whales are capable of making a broad range of sounds using nasal airsacs located just below the blowhole. Roughly three categories of sounds can be identified: frequency modulated whistles, burst-pulsed sounds, and clicks. Dolphins communicate with whistle-like sounds produced by vibrating connective tissue, similar to the way human vocal cords function,[12] and through burst-pulsed sounds, though the nature and extent of that ability is not known. The clicks are directional and are used for echolocation, often occurring in a short series called a click train. The click rate increases when approaching an object of interest. Toothed whale biosonar clicks are amongst the loudest sounds made by marine animals.[13]

The cetacean ear has specific adaptations to the marine environment. In humans, the middle ear works as an impedance equalizer between the outside air's low impedance and the cochlear fluid's high impedance. In whales, and other marine mammals, there is no great difference between the outer and inner environments. Instead of sound passing through the outer ear to the middle ear, whales receive sound through the throat, from which it passes through a low-impedance fat-filled cavity to the inner ear.[14] The ear is acoustically isolated from the skull by air-filled sinus pockets, which allow for greater directional hearing underwater.[15] Odontocetes send out high frequency clicks from an organ known as a melon. This melon consists of fat, and the skull of any such creature containing a melon will have a large depression. The melon size varies between species, the bigger the more dependent they are of it. A beaked whale for example has a small bulge sitting on top of its skull, whereas a sperm whale's head is filled up mainly with the melon.[1][11]:1–19[16][17]

Bottlenose dolphins have been found to have signature whistles, a whistle that is unique to a specific individual. These whistles are used in order for dolphins to communicate with one another by identifying an individual. It can be seen as the dolphin equivalent of a name for humans.[18] Because dolphins are generally associated in groups, communication is necessary. Signal masking is when other similar sounds (conspecific sounds) interfere with the original acoustic sound.[19] In larger groups, individual whistle sounds are less prominent. Dolphins tend to travel in pods, upon which there are groups of dolphins that range from two to a thousand.[20]

Life history and behaviour[edit]


Main article: Cetacean intelligence

Cetaceans are known to teach, learn, cooperate, scheme, and grieve.[21] The neocortex of many species of dolphin is home to elongated spindle neurons that, prior to 2007, were known only in hominids.[22] In humans, these cells are involved in social conduct, emotions, judgement, and theory of mind. Dolphin spindle neurons are found in areas of the brain that are homologous to where they are found in humans, suggesting that they perform a similar function.[1]

Brain size was previously considered a major indicator of the intelligence of an animal. 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 more complex cognitive tasks. Allometric analysis indicates that mammalian brain size scales at approximately the ⅔ or ¾ exponent of the body mass. Comparison of a particular animal's brain size with the expected brain size based on such allometric analysis provides an encephalisation quotient that can be used as another indication of animal intelligence. Sperm whales have the largest brain mass of any animal on earth, averaging 8,000 cubic centimetres (490 in3) and 7.8 kilograms (17 lb) in mature males, in comparison to the average human brain which averages 1,450 cubic centimetres (88 in3) in mature males.[23] The brain to body mass ratio in some odontocetes, such as belugas and narwhals, is second only to humans.[24] In some, however, it is less than half that of humans: 0.9% versus 2.1%. This comparison seems more favourable if the large amount of blubber that some whales require for insulation is omitted.

Dolphins are known to engage in complex play behaviour, which includes such things as producing stable underwater toroidal air-core vortex rings or "bubble rings". There are two main methods of bubble ring production: rapid puffing of a burst 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 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. Dolphins are known to use this method during hunting.[25]

Self-awareness is seen, by some, to be a sign of highly developed, abstract thinking. Self-awareness, though not well-defined scientifically, is believed to be the precursor to more advanced processes like meta-cognitive reasoning (thinking about thinking) that are typical of humans. Research in this field has suggested that cetaceans, among others, possess self-awareness.[26] The most widely used test for self-awareness in animals is the mirror test in which a temporary dye is placed on an animal's body, and the animal is then presented with a mirror; they then see if the animal shows signs of self-recognition.[27]

In 1995, Marten and Psarakos used television to test dolphin self-awareness.[28] 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 repeated since then, dolphins have since passed the mirror test.[27]

Life cycle[edit]

Toothed whales are fully aquatic creatures, which means that birth and courtship behaviours are very different from terrestrial and semi-aquatic creatures. Since they are unable to go onto land to calve, they deliver the baby with the fetus positioned for tail-first delivery. This prevents the baby from drowning either upon or during delivery. To feed the new-born, toothed whales, being aquatic, must squirt the milk into the mouth of the calf. Being mammals, they, of course, have mammary glands used for nursing calves; they are weaned off at about 11 months of age. This milk contains high amounts of fat which is meant to hasten the development of blubber; it contains so much fat that it has the consistency of toothpaste.[29] Females deliver a single calf with gestation lasting about a year, dependency until one to two years, and maturity around seven to ten years, all varying between the species. This mode of reproduction produces few offspring, but increases the survival probability of each one. Females, referred to as "cows", carry the responsibility of childcare as males, referred to as "bulls", play no part in raising calves.

Foraging and predation[edit]

Polar bear with the remains of a beluga

All whales are carnivorous and predatory. Odontocetes, as a whole, mostly feed on fish and cephalopods, and then followed by crustaceans and bivalves. All species are generalist and opportunistic feeders. Some may forage with other kinds of animals, such as other species of whales or certain species of pinnipeds.[6][30]

Odontocetes, with the exception of the sperm whale, are preyed on by the killer whale or orca (another species of toothed whale). To subdue and kill whales, orcas continuously ram them with their heads; this can sometimes kill bowhead whales, or severely injure them. Other times they corral their prey before striking. They are typically hunted by groups of 10 or fewer orcas, but they are seldom attacked by an individual. Calves are more commonly taken by orcas, but adults can be targeted as well.[31]

These cetaceans are also targeted by terrestrial predators. The polar bear is well adapted for hunting Arctic whales and calves. Bears are known to use sit-and-wait tactics as well as active stalking and pursuit of prey on ice or water. Whales lessen the chance of predation by gathering in groups. This however means less room around the breathing hole as the ice slowly closes the gap. When out at sea, whales dive out of the reach of surface-hunting orcas. Polar bear attacks on belugas and narwhals are usually successful in winter, but rarely inflict any damage in summer.[32]

For most of the smaller species of dolphins, only a few of the larger sharks, such as the bull shark, dusky shark, tiger shark and great white shark, are a potential risk, especially for calves.[33]

Interaction with humans[edit]


Sperm whaling[edit]

Main article: Sperm whaling
The nose of the whale is filled with a waxy substance that was widely used in candles, oil lamps, and lubricants.

The head of the sperm whale is filled with a waxy liquid called spermaceti. This liquid can be refined into spermaceti wax and sperm oil. These were much sought after by 18th, 19th and 20th century whalers. These substances found a variety of commercial applications, such as candles, soap, cosmetics, machine oil, other specialized lubricants, lamp oil, pencils, crayons, leather waterproofing, rust-proofing materials and many pharmaceutical compounds.[34] [35][36][37] Ambergris, a solid, waxy, flammable substance produced in the digestive system of sperm whales, was also sought as a fixative in perfumery.

Sperm whaling in the 18th century began with small sloops carrying only a pair of whaleboats (sometimes only one). As the scope and size of the fleet increased so did the rig of the vessels change, as brigs, schooners, and finally ships and barks were introduced. In the 19th century stubby, square-rigged ships (and later barks) dominated the fleet, being sent to the Pacific (the first being the British whaleship Emilia, in 1788),[38] the Indian Ocean (1780s), and as far away as the Japan grounds (1820) and the coast of Arabia (1820s), as well as Australia (1790s) and New Zealand (1790s).[39][40]

A sperm whale is killed and stripped of its blubber and spermaceti.

Hunting for sperm whales during this period was a notoriously dangerous affair for the crews of the 19th century whaleboats. Although a properly harpooned sperm whale generally exhibited a fairly consistent pattern of attempting to flee underwater to the point of exhaustion (at which point it would surface and offer no further resistance), it was not uncommon for bull whales to become enraged and turn to attack pursuing whaleboats on the surface, particularly if it had already been wounded by repeated harpooning attempts. A commonly reported tactic was for the whale to invert itself and violently thrash the surface of the water with its fluke, flipping and crushing nearby boats.

It is estimated that the historic worldwide sperm whale population numbered 1,100,000 before commercial sperm whaling began in the early 18th century.[41] By 1880 it had declined an estimated 29 per cent.[41] From that date until 1946 the population appears to have recovered somewhat as whaling pressure lessened, but after the Second World War, with the industry's focus again on sperm whales, the population declined even further to only 33 per cent.[41] It has been estimated that in the 19th century between 184,000 and 236,000 sperm whales were killed by the various whaling nations,[42] while in the modern era, at least 770,000 were taken, the majority between 1946 and 1980.[43] Remaining sperm whale populations are large enough so that the species' conservation status is vulnerable, rather than endangered.[41] However, the recovery from the whaling years is a slow process, particularly in the South Pacific, where the toll on males of a breeding age was severe.[44]

Drive hunting[edit]

Main article: Dolphin drive hunting
Atlantic White-sided Dolphin caught in a drive hunt in Hvalba on the Faroe Islands being taken away with a forklift

Dolphins and porpoises are hunted in an activity known as dolphin drive hunting. This is accomplished by driving a pod together with boats and 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, Peru, and Japan, the most well-known practitioner of this method. By numbers, dolphins are mostly hunted for their meat, though some end up in dolphinariums.[45] Despite the controversial nature of the hunt resulting in international criticism, and the possible health risk that the often polluted meat causes,[46] thousands of dolphins are caught in drive hunts each year.[47]

In Japan, the hunting is done by a select group of fishermen.[48] When a pod of dolphins has been spotted, they're driven into a bay by the fishermen while banging on metal rods in the water to scare and confuse the dolphins. When the dolphins are in the bay, it is quickly closed off with nets so the dolphins cannot escape. The dolphins are usually not caught and killed immediately, but instead left to calm down over night. The following day, the dolphins are caught one by one and killed. The killing of the animals used to be done by slitting their throats, but the Japanese government banned this method and now dolphins may officially only be killed by driving a metal pin into the neck of the dolphin, which causes them to die within seconds according to a memo from Senzo Uchida, the executive secretary of the Japan Cetacean Conference on Zoological Gardens and Aquariums.[49] A veterinary team's analysis of a 2011 video footage of Japanese hunters killing striped dolphins using this method suggested that, in one case, death took over four minutes.[50]

Since much of the criticism is the result of photos and videos taken during the hunt and slaughter, it is now common for the final capture and slaughter to take place on site inside a tent or under a plastic cover, out of sight from the public. The most circulated footage is probably that of the drive and subsequent capture and slaughter process taken in Futo, Japan in October 1999, shot by the Japanese animal welfare organization Elsa Nature Conservancy.[51] Part of this footage was, amongst others, shown on CNN. In recent years, the video has also become widespread on the internet and was featured in the animal welfare documentary Earthlings, though the method of killing dolphins as shown in this video is now officially banned. In 2009, a critical documentary on the hunts in Japan titled The Cove was released and shown amongst others at the Sundance Film Festival.[52]

Other threats[edit]

Toothed whales can also be threatened by humans more indirectly. They are unintentionally caught in fishing nets by commercial fisheries as bycatch and accidentally swallow fishing hooks. Gillnetting and Seine netting is a significant cause of mortality in cetaceans and other marine mammals.[53] Porpoises are commonly entangled in fishing nets. Whales are also affected by marine pollution. High levels of organic chemicals accumulate in these animals since they are high in the food chain. They have large reserves of blubber, more so for toothed whales as they are higher up the food chain than baleen whales. Lactating mothers can pass the toxins on to their young. These pollutants can cause gastrointestinal cancers and greater vulnerability to infectious diseases.[54] They can also be poisoned by swallowing litter, such as plastic bags.[55] Pollution of the Yangtze river has led to the extinction of the Baiji.[56] Environmentalists speculate that advanced naval sonar endangers some whales. Some scientists suggest that sonar may trigger whale beachings, and they point to signs that such whales have experienced decompression sickness.[57][58][59][60]


Currently, no international convention gives universal coverage to all small whales, although the International Whaling Commission has attempted to extend its jurisdiction over them. ASCOBANS was negotiated to protect all small whales in the North and Baltic Seas and in the northeast Atlantic. ACCOBAMS protects all whales in the Mediterranean and Black Seas. The global UNEP Convention on Migratory Species currently covers seven toothed whale species or populations on its Appendix I, and 37 species or populations on Appendix II. All oceanic cetaceans are listed in CITES appendices, meaning international trade in them and products derived from them is very limited.[61][62]

There are numerous organisation dedicated to protecting certain species who do not fall under any international treaty, such as CIRVA (Committee for the Recovery of the Vaquita), and the Wuhan Institute of Hydrobiology (for the Yangtze finless porpoise).

In captivity[edit]


Shamu the killer whale, 2009

Various species of toothed whales, mainly dolphins, are kept in captivity as well as several other species of porpoise such as Harbour Porpoises and Finless Porpoises. These small cetaceans are more often than not kept in theme parks, such as SeaWorld, commonly known as a dolphinarium. Bottlenose Dolphins are the most common species of dolphin kept in dolphinariums as they are relatively easy to train, have a long lifespan in captivity and have a friendly appearance. Hundreds if not thousands of Bottlenose Dolphins live in captivity across the world, though exact numbers are hard to determine. Orcas are well known for their performances in shows, but the number of Orcas kept in captivity is very small, especially when compared to the number of bottlenose dolphins, with only 44 captive orcas being held in aquaria as of 2012.[63] Other species kept in captivity are Spotted Dolphins, False Killer Whales and Common Dolphins, Commerson's Dolphins, as well as Rough-toothed Dolphins, but all in much lower numbers than the Bottlenose Dolphin. There are also fewer than ten Pilot Whales, Amazon River Dolphins, Risso's Dolphins, Spinner Dolphins, or Tucuxi in captivity. Two unusual and very rare hybrid dolphins, known as Wolphins, are kept at the Sea Life Park in Hawaii, which is a cross between a Bottlenose Dolphin and a False Killer Whale. Also, two Common/Bottlenose hybrids reside in captivity: one at Discovery Cove and the other at SeaWorld San Diego.[64]


Organisations such as World Animal Protection and the Whale and Dolphin Conservation Society campaign against the captivity of dolphins and killer whales; SeaWorld, which holds most of the world's captive killer whales, is cited for its role.

Aggression among captive killer whales is common. In August 1989, a dominant female killer whale, Kandu V, attempted to rake a newcomer whale, Corky II, with her mouth during a live show, and smashed her head into a wall. Kandu V broke her jaw which severed an artery and then bled to death.[65] In November 2006, a dominant female killer whale, Kasatka, repeatedly dragged experienced trainer, Ken Peters, to the bottom of the stadium pool during a show after hearing her calf crying for her in the back pools.[66] In February 2010, an experienced female trainer at SeaWorld Orlando, Dawn Brancheau, was killed by killer whale Tilikum shortly after a show in Shamu Stadium.[67] Tilikum had been associated with the deaths of two people previously.[65][68] In May 2012 Occupational Safety and Health Administration administrative law judge Ken Welsch cited SeaWorld for two violations in the death of Dawn Brancheau and fined the company a total of $12,000.[69] Trainers were banned from making close contact with the orcas.[70] In April 2014 the US Court of Appeals for the District of Columbia denied an appeal by SeaWorld.[71]

In 2013, SeaWorld's treatment of killer whales in captivity was the basis of the movie Blackfish, which documents the history of Tilikum, a killer whale captured by SeaLand of the Pacific, later transported to SeaWorld Orlando who has been involved in the deaths of three people.[72] In the aftermath of the release of the film, Martina McBride, 38 Special, REO Speedwagon, Cheap Trick, Heart, Barenaked Ladies, Trisha Yearwood, and Willie Nelson canceled scheduled concerts at SeaWorld parks.[73][74] SeaWorld disputes the accuracy of the film and in December 2013 released an ad countering the allegations and emphasizing its contributions to the study of cetaceans and their conservation.[75]


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