139-537: A dolphin is an aquatic mammal in the clade Odontoceti ( toothed whale ). Dolphins belong to the families Delphinidae (the oceanic dolphins), Platanistidae (the Indian river dolphins ), Iniidae (the New World river dolphins), Pontoporiidae (the brackish dolphins), and possibly extinct Lipotidae (baiji or Chinese river dolphin). There are 40 extant species named as dolphins. Dolphins range in size from
278-448: A retina similar to that of nocturnal terrestrial mammals. Additionally, cetaceans have two areas of high ganglion cell concentration ("best-vision areas"), where other aquatic mammals (e.g. seals, manatees, otters) only have one. Among non-placental mammals, which cannot give birth to fully developed young, some adjustments have been made for an aquatic lifestyle. The yapok has a backwards-facing pouch which seals off completely when
417-483: A 197-223 decibel sound level at the production source. The linear directionality of sound production in pygmy killer whales is better than in porpoises but lower than is found in bottlenose dolphins; higher directionality results in sounds that are easier to discern from background noise. Based on similarities to the acoustic parameters of other odontocetes, it is presumed that they use a similar mechanism for producing echolocation clicks. The anatomy for auditory reception
556-403: A biological grouping. Marine mammal adaptation to an aquatic lifestyle vary considerably between species. Both cetaceans and sirenians are fully aquatic and therefore are obligate ocean dwellers. Pinnipeds are semiaquatic; they spend the majority of their time in the water, but need to return to land for important activities such as mating, breeding and molting. In contrast, both otters and
695-540: A common ancestry. The ancestry of Sirenia is distinct from that of Cetacea and Pinnipedia , although they are thought to have evolved an aquatic lifestyle around the same time. The oldest fossil of the modern platypus dates back to about 100,000 years ago, during the Quaternary period. The extinct monotremes Teinolophos and Steropodon were once thought to be closely related to the modern platypus, but more recent studies show that platypodes are more related to
834-433: A deadly run-in with the vessels. However, even natural occurrences, such as droughts and tidal changes, often strand manatees in an unsuitable habitat. Some are killed accidentally by fishing trawls and nets intended for catching sharks. The Amazonian manatee is at risk from pollution, accidental drowning in commercial fishing nets, and the degradation of vegetation by soil erosion resulting from deforestation . Additionally,
973-522: 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 are not a taxon and are not unified by any distinct biological grouping, but rather their dependence on and integral relation to aquatic ecosystems . The level of dependence on aquatic life varies greatly among species. Among freshwater taxa,
1112-433: A few, such as the orca, feed on large mammals such as seals. Male dolphins typically mate with multiple females every year, but females only mate every two to three years. Calves are typically born in the spring and summer months and females bear all the responsibility for raising them. Mothers of some species fast and nurse their young for a relatively long period of time. Dolphins produce a variety of vocalizations, usually in
1251-423: A fully asleep state where both eyes are closed and there is no response to mild external stimuli. In this case, respiration is automatic; a tail kick reflex keeps the blowhole above the water if necessary. Anesthetized dolphins initially show a tail kick reflex. Though a similar state has been observed with wild sperm whales , it is not known if dolphins in the wild reach this state. The Indus river dolphin has
1390-411: A gliding mammal. More recently, Yanoconodon and Liaoconodon have been interpreted as semiaquatic, bearing a long body and paddle-like limbs. A metatherian , the stagodontid Didelphodon , has been suggested to be aquatic, due to molar and skeleton similarities to sea otters . An extinct genus, Satherium , is believed to be ancestral to South American river otters, having migrated to
1529-488: A group of individuals was recorded in the Indian Ocean. Like other oceanic dolphins, pygmy killer whales use echolocation . The centroid of echolocation frequencies is between 70–85 kHz and can range from 32 to 100 kHz. This is similar to the range of other odontocetes such as the bottlenose dolphin but is slightly higher than false killer whales. While echolocating, they produce 8-20 clicks per second with
SECTION 10
#17327723529011668-444: A larger dorsal fin. Finally, pygmy killer whales have a more clearly defined line where the dark dorsal color changes to the lighter lateral color than either of the other two species. Behavioral differences can also be used to differentiate pygmy killer whales from false killer whales. Pygmy killer whales usually move slowly when at the surface whereas false killer whales are highly energetic. Pygmy killer whales rarely bow ride but it
1807-538: A life in the water. Seals are semiaquatic; they spend the majority of their time in the water, but need to return to land for important activities such as mating, breeding and molting. In contrast, many other aquatic mammals, such as hippopotamus, capybara, and water shrews, are much less adapted to aquatic living. Likewise, their diet ranges considerably as well, anywhere from aquatic plants and leaves to small fish and crustaceans. They play major roles in maintaining aquatic ecosystems, beavers especially. Aquatic mammals were
1946-523: A low fat content, and the fat that is present consists of a higher proportion of polyunsaturated fats rather than saturated fats . ...like tender beef, with perhaps more flavour; sometimes like veal ” Cadmium levels are high in moose liver and kidneys , with the result that consumption of these organs from moose more than one year old is prohibited in Finland. Cadmium intake has been found to be elevated amongst all consumers of moose meat, though
2085-465: A male dolphin is, the more likely his body is to be covered with bite scars. Male dolphins can get into disputes over companions and females. Acts of aggression can become so intense that targeted dolphins sometimes go into exile after losing a fight. Male bottlenose dolphins have been known to engage in infanticide . Dolphins have also been known to kill porpoises (porpicide) for reasons which are not fully understood, as porpoises generally do not share
2224-430: A moose may stand erect and walk upright on its hind legs, allowing it to reach plants 14.0 feet (4.26 m) off the ground. Moose are excellent swimmers and are known to wade into water to eat aquatic plants. Moose are thus attracted to marshes and river banks during warmer months as both provide suitable vegetation to eat and water to bathe in. Moose have been known to dive underwater to reach plants on lake bottoms, and
2363-418: A more limited capacity for color vision than most mammals. Most dolphins have slightly flattened eyeballs, enlarged pupils (which shrink as they surface to prevent damage), slightly flattened corneas and a tapetum lucidum (eye tissue behind the retina); these adaptations allow for large amounts of light to pass through the eye and, therefore, a very clear image of the surrounding area. They also have glands on
2502-454: A muddy underwater surface thanks to robust muscles and because all toes are weight-bearing. Some aquatic mammals with flippers (e.g. seals) are amphibious and regularly leave the water, sometimes for extended periods, and maneuver on land by undulating their bodies to move on land, similar to the up-and-down body motion used underwater by fully aquatic mammals (e.g. dolphins and manatees). Beavers, muskrats, otters, and capybara have fur, one of
2641-469: A pile in their ponds, eating the underbark. The dams they build flood areas of surrounding forest, giving the beaver safe access to an important food supply, which is the leaves, buds, and inner bark of growing trees. They prefer aspen and poplar , but will also take birch, maple, willow, alder, black cherry, red oak, beech, ash, hornbeam and occasionally pine and spruce. They will also eat cattails , water lilies and other aquatic vegetation, especially in
2780-557: A published paper describing an encounter with a school of pygmy killer whales was later determined to be either a mixture of pygmy and false killer whales or solely false killer whales. The three species can be differentiated by physical differences between them. One defining difference is, although both species have white around the mouth, on pygmy killer whales the white extends back onto the face. Pygmy killer whales also have rounded-tipped dorsal fins, as opposed to pointed tips. When compared to false killer whales, pygmy killer whales have
2919-976: A pygmy hippo's diet consists of ferns , broad-leaved plants and fruits that have fallen to the forest floor . The wide variety of plants pygmy hippos have been observed eating suggests that they will eat any plants available. This diet is of higher quality than that of the common hippopotamus. The Amazon river dolphin has the most diverse diet among cetaceans, consisting of at least 53 species of fish. They mainly feed on croakers , cichlids , tetras , and piranhas , but they may also target freshwater crabs and river turtles. South Asian river dolphins mainly eat fish (such as carp , catfish , and freshwater sharks ) and invertebrates, mainly prawns . Generally, all aquatic desmans , shrews , and voles make quick dives and catch small fish and invertebrates. The giant otter shrew , for example, makes quick dives that last for seconds and grabs small crabs (usually no bigger than 2.8 inches (7 cm) across). The Lutrine opossum
SECTION 20
#17327723529013058-471: A serious invasive species in the region, due to their massive destruction of forest trees, and efforts are being made for their eradication . In some European countries, such as Belgium, France, and the Netherlands , the muskrat is considered an invasive pest, as its burrowing damages the dikes and levees on which these low-lying countries depend for protection from flooding. In those countries, it
3197-567: A short timespan. The gestation period varies with species; for the small tucuxi dolphin , this period is around 11 to 12 months, while for the orca, the gestation period is around 17 months. Typically dolphins give birth to a single calf, which is, unlike most other mammals, born tail first in most cases. They usually become sexually active at a young age, even before reaching sexual maturity . The age of sexual maturity varies by species and sex. Dolphins are known to display non-reproductive sexual behavior , engaging in masturbation , stimulation of
3336-418: A sleep method that is different from that of other dolphin species. Living in water with strong currents and potentially dangerous floating debris, it must swim continuously to avoid injury. As a result, this species sleeps in very short bursts which last between 4 and 60 seconds. There are various feeding methods among and within species, some apparently exclusive to a single population. Fish and squid are
3475-493: A straight row, eliminating the grinding function suggesting that they were strictly for gripping and not for chewing. This feature of three cusps in a row is similar to the ancestral condition in mammal relatives (as seen in triconodonts ), but is almost certainly a derived character in Castorocauda . These first molars were also recurved in a manner adapted to hold slippery prey once grasped. These teeth are very similar to
3614-459: A study lasting from 1985 to 2007. This population has been observed associating with false killer whales, short-finned pilot whales, and bottlenose dolphins. Pygmy killer whales are not commonly reported to be found in Thailand. On August 3, 2024, three pygmy killer whales were found stranded in the mangroves of Ao Kung, Phuket . Local officials were able to safely rescue them and return them to
3753-408: A thin layer of blubber, which develops at different paces depending on the habitat. Dolphins have a two-chambered stomach that is similar in structure to terrestrial carnivores. They have fundic and pyloric chambers. Dolphins' reproductive organs are located inside the body, with genital slits on the ventral (belly) side. Males have two slits, one concealing the penis and one further behind for
3892-399: A variety of sensory organs: for example, manatees have elongated and highly sensitive whiskers which are used to detect food and other vegetation directly front of them, and toothed whales have evolved echolocation . Aquatic mammals also display a variety of locomotion styles. Cetaceans excel in streamlined body shape and the up-and-down movements of their flukes make them fast swimmers;
4031-628: A wide distribution in tropical and subtropical waters worldwide. They are sighted regularly off Hawaii and Japan. Appearances in bycatch suggest a year-round presence in the Indian Ocean near Sri Lanka and the Lesser Antilles . The species has also been found in the south-west Indian Ocean in the French Southern and Antarctic Lands off Europa Island , Mozambique and South Africa but not yet recorded off East Africa. In
4170-435: 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 the killer whale. It is the smallest cetacean species that has the word "whale" in its common name. Although the species has been known to be extremely aggressive in captivity, this aggressive behavior has not been observed in
4309-447: Is adapted for both air and water; it is so well developed that some can survive even if they are blind. Some species are well adapted for diving to great depths. They have a layer of fat, or blubber , under the skin to keep warm in the cold water. Dolphins are widespread. Most species prefer the warm waters of the tropic zones, but some, such as the right whale dolphin , prefer colder climates. Dolphins feed largely on fish and squid, but
Dolphin - Misplaced Pages Continue
4448-401: Is also known as kinesthesia, is the body's ability to sense its location, movements and actions. Dolphins are sensitive to vibrations and small pressure changes. Blood vessels and nerve endings can be found within the dermis. There is a plexus of parallel running arteries and veins in the dorsal fin, fluke, and flippers. The blubber manipulates the blood vessels to help the dolphin stay warm. When
4587-569: Is called a school or a pod . Male dolphins are called bulls , females are called cows and young dolphins are called calves . In 1933, three hybrid dolphins beached off the Irish coast; they were hybrids between Risso's and bottlenose dolphins. This mating was later repeated in captivity, producing a hybrid calf. In captivity, a bottlenose and a rough-toothed dolphin produced hybrid offspring. A common-bottlenose hybrid lives at SeaWorld California. Other dolphin hybrids live in captivity around
4726-402: Is common in false killer whales. The small size of this species also causes confusion with other dolphins especially where the frontal head shape of the animals encountered remains unseen. Unlike the melon-headed whale, pygmy killer whales do not normally lift the full face above the water as they surface to breathe so it is not easy to confirm the lack of a bottle. Furthermore, in calmer waters
4865-473: Is due to hunting to supply the demand for skins. One problem at Lake Baikal is the introduction of pollutants into the ecosystem. Pesticides such as DDT and hexachlorocyclohexane , as well as industrial waste, mainly from the Baykalsk Pulp and Paper Mill , are thought to have been the cause of several disease epidemics among Baikal seal populations. The chemicals are speculated to concentrate up
5004-405: Is home to elongated spindle neurons that, prior to 2007, were known only in hominids. In humans, these cells are involved in social conduct, emotions, judgment, and theory of mind. Cetacean spindle neurons are found in areas of the brain that are analogous to where they are found in humans, suggesting that they perform a similar function. Brain size was previously considered a major indicator of
5143-697: Is mostly transferred by mothers to daughters, unlike simian primates, where knowledge is generally passed on to both sexes. Using sponges as mouth protection is a learned behavior. Another learned behavior was discovered among river dolphins in Brazil, where some male dolphins use weeds and sticks as part of a sexual display. Forms of care-giving between fellows and even for members of different species(see Moko (dolphin) ) are recorded in various species – such as trying to save weakened fellows or female pilot whales holding up dead calves for long periods. Dolphins engage in acts of aggression towards each other. The older
5282-433: Is much less definitive than when used for primates, because primates can touch the mark or the mirror, while cetaceans cannot, making their alleged self-recognition behavior less certain. Skeptics argue that behaviors that are said to identify self-awareness resemble existing social behaviors, and so researchers could be misinterpreting self-awareness for social responses to another individual. The researchers counter-argue that
5421-544: Is no great difference between the outer and inner environments. Instead of sound passing through the outer ear to the middle ear, dolphins receive sound through the throat, from which it passes through a low-impedance fat-filled cavity to the inner ear. The ear is acoustically isolated from the skull by air-filled sinus pockets, which allow for greater directional hearing underwater. Dolphins generate sounds independently of respiration using recycled air that passes through air sacs and phonic (alternatively monkey) lips. Integral to
5560-618: Is not rigid; interchange is common. They establish strong social bonds, and will stay with injured or ill members, helping them to breathe by bringing them to the surface if needed. This altruism does not appear to be limited to their own species. The dolphin Moko in New Zealand has been observed guiding a female pygmy sperm whale together with her calf out of shallow water where they had stranded several times. They have also been seen protecting swimmers from sharks by swimming circles around
5699-611: Is similar to other odontocetes, with a hollow mandible and a mandibular fat body composed of a low density outer layer and a denser inner core. The inner core comes into direct contact with the tympanoperiotic complex (functionally similar to the auditory bulla in other species - see Cetacea ). Hearing tests performed on two live individuals brought in for rehabilitation exhibited frequency response range and temporal resolution similar to that found in other echolocating dolphins. During those tests, one individual exhibited low frequency hearing loss that might have been related to treatment with
Dolphin - Misplaced Pages Continue
5838-731: Is the bottlenose dolphin , while there are around 60 orcas in captivity . The name is originally from Greek δελφίς ( delphís ), "dolphin", which was related to the Greek δελφύς ( delphus ), "womb". The animal's name can therefore be interpreted as meaning "a 'fish' with a womb". The name was transmitted via the Latin delphinus (the romanization of the later Greek δελφῖνος – delphinos ), which in Medieval Latin became dolfinus and in Old French daulphin , which reintroduced
5977-459: Is the mirror test in which a mirror is introduced to an animal, and the animal is then marked with a temporary dye. If the animal then goes to the mirror in order to view the mark, it has exhibited strong evidence of self-awareness. Some disagree with these findings, arguing that the results of these tests are open to human interpretation and susceptible to the Clever Hans effect. This test
6116-708: Is the most carnivorous opossum, usually consuming small birds, rodents, and invertebrates. Water voles mainly eat grass and plants near the water and at times, they will also consume fruits, bulbs, twigs, buds, and roots. However, a population of water voles living in Wiltshire and Lincolnshire, England have started eating frogs' legs and discarding the bodies. Fur robes were blankets of sewn-together, native-tanned, beaver pelts. The pelts were called castor gras in French and "coat beaver" in English, and were soon recognized by
6255-487: Is trapped, poisoned, and hunted to attempt to keep the population down. Muskrats also eat corn and other farm and garden crops growing near water bodies. Urban and agricultural development, increased damming, and increased use of hydroelectric power in rivers in countries such as Côte d'Ivoire and Ghana are threats to the African manatee 's habitat and life, and thick congestion of boats in waterways may cause them to have
6394-560: Is white while pinkish white skin surrounds the genitals. The average length is just over two meters (6.5 ft.). Upon reaching 2 meters in length, males are considered sexually mature. They have approximately 48 teeth, with 22 teeth on the top jaw and 26 on the lower jaw. They travel approximately 3 km/hour (2 miles/hour) and are predominately found in deeper waters ranging from 500 m to 2000 m (1600–6500 ft.) in depth. Pygmy killer whales are most commonly confused with melon-headed whales and false killer whales . For instance,
6533-610: The Amazonian manatee and river dolphins are completely aquatic and fully dependent on aquatic ecosystems. Semiaquatic freshwater taxa include the Baikal seal , which feeds underwater but rests, molts, and breeds on land; and the capybara and hippopotamus which are able to venture in and out of water in search of food. Mammal adaptation to an aquatic lifestyle vary considerably between species. River dolphins and manatees are both fully aquatic and therefore are completely tethered to
6672-478: The Jurassic mammaliaform Castorocauda . It seems to have been adapted to water much like a beaver, with teeth different in many ways from all other docodonts , presumably due to a difference in diet. Most docodonts had teeth specialized for an omnivorous diet. The teeth of Castorocauda suggest that the animal was a piscivore , feeding on fish and small invertebrates . The first two molars had cusps in
6811-527: The Tethytheria . Tethytheria is thought to have evolved from primitive hoofed mammals (" condylarths ") along the shores of the ancient Tethys Ocean . Tethytheria, combined with Hyracoidea (hyraxes), forms a clade called Paenungulata . Paenungulata and Tethytheria (especially the latter) are among the least controversial mammalian clades, with strong support from morphological and molecular interpretations. That is, elephants, hyraxes , and manatees share
6950-509: The Yangtze river , causes collisions between fast ocean vessels and aquatic mammals, and damming of rivers may land migratory aquatic mammals in unsuitable areas or destroy habitat upstream. The industrialization of rivers led to the extinction of the Chinese river dolphin , with the last confirmed sighting in 2004. One of the first known proto-mammals similar to modern placentals was aquatic,
7089-503: The ancient Roman author and natural philosopher Pliny the Elder . A modern human-dolphin partnership currently operates in Laguna , Santa Catarina, Brazil. Here, dolphins drive fish towards fishermen waiting along the shore and signal the men to cast their nets. The dolphins' reward is the fish that escape the nets. Aquatic mammal Aquatic mammals and semiaquatic mammals are
SECTION 50
#17327723529017228-415: The anus . Females have one genital slit, housing the vagina and the anus, with a mammary slit on either side. The integumentary system is an organ system mostly consisting of skin, hair, nails and endocrine glands. The skin of dolphins is specialized to satisfy specific requirements, including protection, fat storage, heat regulation, and sensory perception. The skin of a dolphin is made up of two parts:
7367-482: The artiodactyl order (even-toed ungulates). They are related to the Indohyus , an extinct chevrotain -like ungulate, from which they split approximately 48 million years ago. The primitive cetaceans, or archaeocetes , first took to the sea approximately 49 million years ago and became fully aquatic by 5–10 million years later. Archaeoceti is a parvorder comprising ancient whales. These ancient whales are
7506-428: The mahi-mahi fish is called the dolphinfish. In common usage, the term whale is used only for the larger cetacean species, while the smaller ones with a beaked or longer nose are considered dolphins. The name dolphin is used casually as a synonym for bottlenose dolphin , the most common and familiar species of dolphin. There are six species of dolphins commonly thought of as whales, collectively known as blackfish :
7645-429: The morphological similarities and adaptations to freshwater habitats arose due to convergent evolution ; thus, a grouping of all river dolphins is paraphyletic . For example, Amazon river dolphins are actually more closely related to oceanic dolphins than to South Asian river dolphins . Sirenians, along with Proboscidea (elephants), group together with the extinct † Desmostylia and likely † Embrithopoda to form
7784-504: The orca , the melon-headed whale , the pygmy killer whale , the false killer whale , and the two species of pilot whales , all of which are classified under the family Delphinidae and qualify as dolphins. Although the terms dolphin and porpoise are sometimes used interchangeably, porpoise usually refers to the Phocoenidae family, which have a shorter beak and spade-shaped teeth and differ in their behavior. A group of dolphins
7923-414: The ph into the word dolphin . The term mereswine ("sea pig") is also used. The term dolphin can be used to refer to most species in the family Delphinidae (oceanic dolphins) and the river dolphin families of Iniidae (South American river dolphins), Pontoporiidae ( La Plata dolphin ), Lipotidae (Yangtze river dolphin) and Platanistidae (Ganges river dolphin and Indus river dolphin). Meanwhile,
8062-714: The polar bear are much less adapted to aquatic living. Likewise, their diet ranges considerably as well; some may eat zooplankton , others may eat small fish, and a few may eat other mammals. While the number of marine mammals is small compared to those found on land, their roles in various ecosystems are large. They, namely sea otters and polar bears, play important roles in maintaining marine ecosystems, especially through regulation of prey populations. Their role in maintaining ecosystems makes them of particular concern considering 25% of marine mammal species are currently threatened. Marine mammals were first hunted by aboriginal peoples for food and other resources. They were also
8201-549: The tucuxi , for example, can reach speeds of 14 miles per hour (23 km/h). The considerably slower sirenians can also propel themselves with their fluke, but they can also walk on the bottom with their forelimbs. The earless seals (Phocidae) swim by moving their hind-flippers and lower body from side to side, while their fore-flippers are mainly used for steering. They are clumsy on land, and move on land by lunging, bouncing and wiggling while their fore-flippers keep them balanced; when confronted with predators, they retreat to
8340-606: The 1.7-metre-long (5 ft 7 in) and 50-kilogram (110-pound) Maui's dolphin to the 9.5 m (31 ft) and 10-tonne (11-short-ton) orca . Various species of dolphins exhibit sexual dimorphism where the males are larger than females. They have streamlined bodies and two limbs that are modified into flippers. Though not quite as flexible as seals , they are faster; some dolphins can briefly travel at speeds of 29 kilometres per hour (18 mph) or leap about 9 metres (30 ft). Dolphins use their conical teeth to capture fast-moving prey . They have well-developed hearing which
8479-485: The 1980s and then to 13 in 1997 when a full-fledged search was conducted. On 13 December 2006, the baiji was declared functionally extinct , after a 45-day search by leading experts in the field failed to find a single specimen. The last verified sighting was in 2004. Moose are hunted as a game species in many of the countries where they are found. While the flesh has protein levels similar to those of other comparable red meats (e.g. beef , deer and elk ), it has
SECTION 60
#17327723529018618-570: The 9.5 m (31 ft 2 in) and 10 t (11 short tons) orca . Overall, they tend to be dwarfed by other Cetartiodactyls . Several species have female-biased sexual dimorphism, with the females being larger than the males. Dolphins have conical teeth, as opposed to porpoises ' spade-shaped teeth. These conical teeth are used to catch swift prey such as fish, squid or large mammals, such as seals. Breathing involves expelling stale air from their blowhole , in an upward blast, which may be visible in cold air, followed by inhaling fresh air into
8757-523: The Atlantic, individuals have been observed as far north as South Carolina on the west and Senegal on the east. In May 2023, a sailor named Bryant Irawan, spotted a pod much further north off the coast of Portugal, which was confirmed by scientists at happywhale.com . They have been observed along the coast of South America and as far north as the Gulf of Mexico where they have been known to breed during
8896-482: The New World during the Pliocene or early Pleistocene . The South American continent houses the otter genus Lontra : the giant otter , the neotropical river otter , the southern river otter , and the marine otter . The smooth-coated otter ( Lutrogale perspicillata ) of Asia may be its closest extant relative; similar behaviour, vocalizations, and skull morphology have been noted. The most popular theory of
9035-558: The North Atlantic right whale, are critically endangered. Other than hunting, marine mammals, dolphins especially, can be killed as bycatch from fisheries, where they become entangled in fixed netting and drown or starve. Increased ocean traffic causes collisions between fast ocean vessels and large marine mammals. Habitat degradation also threatens marine mammals and their ability to find and catch food. Noise pollution , for example, may adversely affect echolocating mammals, and
9174-661: The Roman Catholic Church ruled that the beaver was a fish (beaver flesh was a part of the indigenous peoples' diet, prior to the Europeans' arrival ) for purposes of dietary law. Therefore, the general prohibition on the consumption of meat on Fridays did not apply to beaver meat. This is similar to the Church's classification of other semiaquatic rodents, such as the capybara and muskrat . Pygmy killer whale The pygmy killer whale ( Feresa attenuata )
9313-608: The animal is underwater, while the platypus deposits its young on a burrow on land. Beaver ponds have a profound effect on the surrounding ecosystem. Their first and foremost ecological function is as a reservoir for times of drought, and prevent drying of riverbeds. In the event of a flood, beaver ponds slow down water-flow which reduces erosion on the surrounding soil. Beaver dams hold sediment, which reduces turbidity and thereby improving overall water quality downstream. This supplies other animals with cleaner drinking water and prevents degradation of spawning grounds for fish. However,
9452-399: The animal with an idea on an object's shape and size, though how exactly this works is not yet understood. The small hairs on the rostrum of the boto (river dolphins of South America) are believed to function as a tactile sense , possibly to compensate for the boto's poor eyesight. A dolphin eye is relatively small for its size, yet they do retain a good degree of eyesight. As well as this,
9591-469: The antibiotic amikacin although the researchers believed the more likely cause was slight differences in testing setup. Pygmy killer whales have been observed in groups ranging from 4 to 30 or more individual animals. The only population estimate is of 38,900 individuals in the eastern tropical Pacific Ocean ; however, this estimate had a large coefficient of variation meaning the true population size could be much lower or much higher. The species has
9730-521: The beginning of the 20th century, when legal hunting ended. From 1980 to 1993, 692 rhinos were poached in India. In India's Laokhowa Wildlife Sanctuary , 41 rhinos were killed in 1983, virtually the entire population of the sanctuary. By the mid-1990s, poaching had rendered the species extinct there. In 1950, Chitwan ’s forest and grasslands extended over more than 2,600 km (1,000 sq mi) and were home to about 800 rhinos. When poor farmers from
9869-672: The behaviors shown are evidence of self-awareness, as they are very different from normal responses to another individual. Whereas apes can merely touch the mark on themselves with their fingers, cetaceans show less definitive behavior of self-awareness; they can only twist and turn themselves to observe the mark. In 1995, Marten and Psarakos used television to test dolphin self-awareness. They showed dolphins real-time video of themselves, video of another dolphin and recorded footage. 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
10008-525: The body and to form specialized locomotor structures such as the dorsal fin, propulsive fluke blades and caudal keels. There are many nerve endings that resemble small, onion-like configurations that are present in the superficial portion of the dermis. Mechanoreceptors are found within the interlocks of the epidermis with dermal ridges. There are nerve fibers in the dermis that extend to the epidermis. These nerve endings are known to be highly proprioceptive , which explains sensory perception. Proprioception, which
10147-484: The closest living relatives of cetaceans are the hippopotamuses ; these share a semi-aquatic ancestor that branched off from other artiodactyls some 60 million years ago. Around 40 million years ago, a common ancestor between the two branched off into cetacea and anthracotheres ; anthracotheres became extinct at the end of the Pleistocene two-and-a-half million years ago, eventually leaving only one surviving lineage:
10286-500: The completely aquatic cetaceans . The other branch became the anthracotheres , and all branches of the anthracotheres, except that which evolved into Hippopotamidae , became extinct during the Pliocene without leaving any descendants. River dolphins are thought to have relictual distributions, that is, their ancestors originally occupied marine habitats, but were then displaced from these habitats by modern dolphin lineages. Many of
10425-597: The complex snout may assist the moose in this type of feeding. Moose are the only deer that are capable of feeding underwater. Hippopotamuses leave the water at dusk and travel inland, sometimes up to 10 km (6 mi), to graze on short grasses, their main source of food. They spend four to five hours grazing and can consume 68 kg (150 lb) of grass each night. Like almost any herbivore, they consume other plants if presented with them, but their diet consists almost entirely of grass, with only minimal consumption of aquatic plants. The pygmy hippopotamus emerges from
10564-469: The defining mammalian features, that is long, oily, and waterproof in order to trap air to provide insulation. In contrast, other aquatic mammals, such as dolphins, manatees, seals, and hippopotamuses, have lost their fur in favor of a thick and dense epidermis , and a thickened fat layer ( blubber ) in response to hydrodynamic requirements. Wading and bottom-feeding animals (e.g. moose and manatee) need to be heavier than water in order to keep contact with
10703-401: The dorsal fin, flukes, and flippers. These thermal windows are a good way for dolphins to get rid of excess heat if overheating. Additionally in order to conserve heat, dolphins use countercurrent heat exchange. Blood flows in different directions in order for heat to transfer across membranes. Heat from warm blood leaving the heart will heat up the cold blood that is headed back to the heart from
10842-423: The early spring. Indian rhinoceros are grazers . Their diets consist almost entirely of grasses, but they also eat leaves, branches of shrubs and trees, fruits, and submerged and floating aquatic plants . They feed in the mornings and evenings. They use their prehensile lips to grasp grass stems, bend the stem down, bite off the top, and then eat the grass. They tackle very tall grasses or saplings by walking over
10981-411: The epidermal layer. The thickness of a dolphin's epidermis varies, depending on species and age. Blubber is found within the dermis and subcutis layer. The dermis blends gradually with the adipose layer, which is known as fat, because the fat may extend up to the epidermis border and collagen fiber bundles extend throughout the whole subcutaneous blubber which is fat found under the skin. The thickness of
11120-409: The epidermis and the blubber, which consists of two layers including the dermis and subcutis. The dolphin's skin is known to have a smooth rubber texture and is without hair and glands, except mammary glands. At birth, a newborn dolphin has hairs lined up in a single band on both sides of the rostrum, which is their jaw, and usually has a total length of 16–17 cm . The epidermis is characterized by
11259-510: The extremities, meaning that the heart always has warm blood and it decreases the heat lost to the water in those thermal windows. Dolphins have two pectoral flippers, each containing four digits, a boneless dorsal fin for stability, and a fluke for propulsion. Although dolphins do not possess external hind limbs, some possess discrete rudimentary appendages, which may contain feet and digits. Orcas are fast swimmers in comparison to seals which typically cruise at 9–28 km/h (5.6–17.4 mph);
11398-480: The eyelids and outer corneal layer that act as protection for the cornea. The olfactory lobes and nerve are absent in dolphins, suggesting that they have no sense of smell. Dolphins are not thought to have a good sense of taste, as their taste buds are atrophied or missing altogether. Some have preferences for different kinds of fish, indicating some ability to taste. Dolphins are known to teach, learn, cooperate, scheme, and grieve. The neocortex of many species
11537-511: The eyes of a dolphin are placed on the sides of its head, so their vision consists of two fields, rather than a binocular view like humans have. When dolphins surface, their lens and cornea correct the nearsightedness that results from the water's refraction of light. Their eyes contain both rod and cone cells, meaning they can see in both dim and bright light, but they have far more rod cells than they do cone cells. They lack short wavelength sensitive visual pigments in their cone cells, indicating
11676-499: The felting of wool, rather than enhancing it. By the 1580s, beaver "wool" was the major starting material of the French felt-hatters. Hat makers began to use it in England soon after, particularly after Huguenot refugees brought their skills and tastes with them from France. Sport hunting of the Indian rhinoceros became common in the late 1800s and early 1900s. Indian rhinos were hunted relentlessly and persistently. Reports from
11815-443: The females by their side by means of both physical aggression and intimidation, to increase their chances of reproductive success. Generally, dolphins sleep with only one brain hemisphere in slow-wave sleep at a time, thus maintaining enough consciousness to breathe and to watch for possible predators and other threats. Sleep stages earlier in sleep can occur simultaneously in both hemispheres. In captivity, dolphins seemingly enter
11954-507: The floor or to stay submerged, surface-living animals (e.g. otters) need the opposite, and free-swimming animals living in open waters (e.g. dolphins) need to be neutrally buoyant in order to be able to swim up and down the water column. Typically, thick and dense bone is found in bottom feeders and low bone density is associated with mammals living in deep water. The shape and function of the eyes in aquatic animals are dependent on water depth and light exposure: limited light exposure results in
12093-487: The food chain and weaken the Baikal seal's immune system, making them susceptible to diseases such as canine distemper and the plague, which was the cause of a serious Baikal seal epidemic that resulted in the deaths of thousands of animals in 1997 and 1999. Baikal seal pups have higher levels of DDT and PCB than known in any other population of European or Arctic earless seal. In the 1940s, beavers were brought from Canada to
12232-414: The form of clicks and whistles. Dolphins are sometimes hunted in places such as Japan, in an activity known as dolphin drive hunting . Besides drive hunting, they also face threats from bycatch , habitat loss, and marine pollution . Dolphins have been depicted in various cultures worldwide. Dolphins are sometimes kept in captivity and trained to perform tricks. The most common dolphin species in captivity
12371-533: The genital area of other individuals using the rostrum or flippers, and homosexual contact . Various species of dolphin have been known to engage in sexual behavior including copulation with dolphins of other species, and occasionally exhibit sexual behavior towards other animals , including humans. Sexual encounters may be violent, with male bottlenose dolphins sometimes showing aggressive behavior towards both females and other males. Male dolphins may also work together and attempt to herd females in estrus , keeping
12510-443: The hearing set-up that channeled vibrations from the jaw to the earbone which occurred with Ambulocetus 49 million years ago, a streamlining of the body and the growth of flukes on the tail which occurred around 43 million years ago with Protocetus , the migration of the nasal openings toward the top of the cranium and the modification of the forelimbs into flippers which occurred with Basilosaurus 35 million years ago, and
12649-431: The heart, brain and other organs. Their hemoglobin and myoglobin store oxygen in body tissues, and they have twice as much myoglobin as hemoglobin. [REDACTED] A dolphin 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 dolphins, and other marine mammals, there
12788-585: The indiscriminate release of mercury in mining activities threatens the entire aquatic ecosystem of the Amazon Basin. As China developed economically, pressure on the Chinese river dolphin grew significantly. Industrial and residential waste flowed into the Yangtze. The riverbed was dredged and reinforced with concrete in many locations. Ship traffic multiplied, boats grew in size, and fishermen employed wider and more lethal nets. Noise pollution caused
12927-561: 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 encephalization quotient that can be used as another indication of animal intelligence. Orcas have
13066-401: The island of Tierra Del Fuego in southern Chile and Argentina, for commercial fur production. However, the project failed and the beavers, ten pairs, were released into the wild. Having no natural predators in their new environment, they quickly spread throughout the island, and to other islands in the region, reaching a number of 100,000 individuals within just 50 years. They are now considered
13205-402: The lack of keratin and by a prominent intertwine of epidermal rete pegs and long dermal papillae. The epidermal rete pegs are the epithelial extensions that project into the underlying connective tissue in both skin and mucous membranes. The dermal papillae are finger-like projections that help adhesion between the epidermal and dermal layers, as well as providing a larger surface area to nourish
13344-606: The lips are oil-filled organs called dorsal bursae that have been suggested to be homologous to the sperm whale's spermaceti organ. High-frequency clicks pass through the sound-modifying organs of the extramandibular fat body, intramandibular fat body and the melon . This melon consists of fat, and the skull of any such creature containing a melon will have a large depression. This allows dolphins to use echolocation for orientation. Though most dolphins do not have hair, they do have hair follicles that may perform some sensory function. Beyond locating an object, echolocation also provides
13483-406: The lungs. Dolphins have rather small, unidentifiable spouts. All dolphins have a thick layer of blubber , thickness varying on climate. This blubber can help with buoyancy, protection to some extent as predators would have a hard time getting through a thick layer of fat, and energy for leaner times; the primary usage for blubber is insulation from the harsh climate. Calves, generally, are born with
13622-410: The main food, but the false killer whale and the orca also feed on other marine mammals. Orcas on occasion also hunt whale species larger than themselves. Different breeds of dolphins vary widely in the number of teeth they possess. The orca usually carries 40–56 teeth while the popular bottlenose dolphin has anywhere from 72 to 116 conical teeth and its smaller cousin the common dolphin has 188–268 teeth:
13761-466: The meat was found to contribute only slightly to the daily cadmium intake. However the consumption of moose liver or kidneys significantly increased cadmium intake, with the study revealing that heavy consumers of moose organs have a relatively narrow safety margin below the levels which would probably cause adverse health effects . In the 17th century, based on a question raised by the Bishop of Quebec ,
13900-505: The mid-hills moved to the Chitwan Valley in search of arable land, the area was subsequently opened for settlement, and poaching of wildlife became rampant. The Chitwan population has repeatedly been jeopardized by poaching; in 2002 alone, poachers killed 37 animals to saw off and sell their valuable horns. Otters have been hunted for their pelts since at least the 1700s. There has been a long history of otter pelts being worn around
14039-535: The middle of the 19th century claim that some British military officers in Assam individually shot more than 200 rhinos. By 1908, the population in Kaziranga had decreased to around 12 individuals. In the early 1900s, the species had declined to near extinction. Poaching for rhinoceros horn became the single most important reason for the decline of the Indian rhino after conservation measures were put in place from
14178-435: The mirror test. Some researchers have argued that evidence for self-awareness has not been convincingly demonstrated. Dolphins are highly social animals, often living in pods of up to a dozen individuals, though pod sizes and structures vary greatly between species and locations. In places with a high abundance of food, pods can merge temporarily, forming a superpod ; such groupings may exceed 1,000 dolphins. Membership in pods
14317-507: The modern echidnas than to these ancient forms and that at least Teinolophos was a rather different mammal lacking several speciations seen in platypodes. However, the last common ancestor between platypodes and echidnas probably was aquatic, and echidnas thus secondarily became terrestrial. Monotrematum sudamericanum is currently the oldest aquatic monotreme known. It has been found in Argentina , indicating monotremes were present in
14456-409: The nearly blind animal to collide with propellers. Stocks of the dolphin's prey declined drastically in the late 20th century, with some fish populations declining to one thousandth of their pre-industrial levels. In the 1950s, the population was estimated at 6,000 animals, but declined rapidly over the subsequent five decades. Only a few hundred were left by 1970. Then the number dropped down to 400 by
14595-418: The newly developed felt-hat making industry as particularly useful for felting. Some historians, seeking to explain the term castor gras , have assumed that coat beaver was rich in human oils from having been worn so long (much of the top-hair was worn away through usage, exposing the valuable under-wool), and that this is what made it attractive to the hatters . This seems unlikely, since grease interferes with
14734-410: The number of teeth that an individual carries varies widely between within a single species. Hybrids between common and bottlenose bred in captivity had a number of teeth intermediate between that of their parents. One common feeding method is herding, where a pod squeezes a school of fish into a small volume, known as a bait ball . Individual members then take turns plowing through the ball, feeding on
14873-503: The ongoing effects of global warming degrades arctic environments. Mammals evolved on land, so all aquatic and semiaquatic mammals have brought many terrestrial adaptations into the waters. They do not breathe underwater as fish do, so their respiratory systems had to protect the body from the surrounding water; valvular nostrils and an intranarial larynx exclude water while breathing and swallowing. To navigate and detect prey in murky and turbid waters, aquatic mammals have developed
15012-685: The orca, in comparison, can travel at speeds up to 55.5 km/h (34.5 mph). A study of a Pacific white-sided dolphin in an aquarium found fast burst acceleration, with the individual being able with 5 strokes (2.5 fluke beats) to go from 5.0 m s-1 to 8.7 m s-1 in 0.7 seconds. The fusing of the neck vertebrae, while increasing stability when swimming at high speeds, decreases flexibility, which means most dolphins are unable to turn their heads. River dolphins have non-fused neck vertebrae and can turn their heads up to 90°. Dolphins swim by moving their fluke and rear body vertically, while their flippers are mainly used for steering. Some species porpoise out of
15151-481: The origins of Hippopotamidae suggests that hippos and whales shared a common ancestor that branched off from other artiodactyls around 60 million years ago (mya). This hypothesized ancestral group likely split into two branches around 54 mya. One branch would evolve into cetaceans , possibly beginning about 52 mya, with the protowhale Pakicetus and other early whale ancestors collectively known as Archaeoceti , which eventually underwent aquatic adaptation into
15290-494: The plant, with legs on both sides and using the weight of their bodies to push the end of the plant down to the level of the mouth. Manatees make seasonal movements synchronized with the flood regime of the Amazon Basin. They are found in flooded forests and meadows during the flood season when food is abundant, and move to deep lakes during the dry season. The Amazonian manatee has the smallest degree of rostral deflection (25° to 41°) among sirenians, an adaptation to feed closer to
15429-780: The possibility that all eutriconodonts were aquatic piscivores. However, Zofia Kielan-Jaworowska and other researchers have latter found that the triconodont molars of eutriconodonts were more suited for a carnassial -like shearing action than the piercing and gripping function of piscivorous mammal molars, occluding instead of interlocking, and that Astroconodon' s aquatic occurrences may be of little significance when most terrestrial tetrapod fossils are found in lacustrine environments anyway. However, two other eutriconodonts, Dyskritodon and Ichthyoconodon , occur in marine deposits with virtually no dental erosion, implying that they died in situ and are thus truly aquatic mammals. Nonetheless, Ichthyoconodon may not be aquatic, but instead
15568-421: The predecessors of modern whales, stretching back to their first ancestor that spent their lives near (rarely in) the water. Likewise, the archaeocetes can be anywhere from near fully terrestrial, to semi-aquatic to fully aquatic, but what defines an archaeocete is the presence of visible legs or asymmetrical teeth. Their features became adapted for living in the marine environment . Major anatomical changes include
15707-422: The same diet as dolphins and are therefore not competitors for food supplies. The Cornwall Wildlife Trust records about one such death a year. Possible explanations include misdirected infanticide, misdirected sexual aggression or play behaviour . Dolphin copulation happens belly to belly; though many species engage in lengthy foreplay , the actual act is usually brief, but may be repeated several times within
15846-636: The sea by rescuers, the healthy individuals will often strand again and refuse to leave until the death of the individual in declining health. The pygmy killer whale is classified as least concern by the IUCN . They are covered by the Agreement on the Conservation of Small Cetaceans of the Baltic, North East Atlantic, Irish and North Seas ( ASCOBANS ) and the Agreement on the Conservation of Cetaceans in
15985-465: The sea. This is the first time they have been found in Thailand. Pygmy killer whales have been incidental bycatch in fishing operations. They represent as much as 4% of the cetacean bycatch in drift gill nets used by commercial fisheries in Sri Lanka. Like other cetaceans, they are hosts to parasitic worms such as cestodes and nematodes . The cestode species, Trigonocotyle sexitesticulae,
16124-583: The second largest brain mass of any animal on earth, next to the sperm whale . The brain to body mass ratio in some is second only to humans. 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. The most widely used test for self-awareness in animals
16263-534: The shrinking and eventual disappearance of the hind limbs which took place with the first odontocetes and mysticetes 34 million years ago. The modern dolphin skeleton has two small, rod-shaped pelvic bones thought to be vestigial hind limbs. In October 2006, an unusual bottlenose dolphin was captured in Japan; it had small fins on each side of its genital slit, which scientists believe to be an unusually pronounced development of these vestigial hind limbs. Today,
16402-516: The slower water speed and lack of shade from trees (that have since been cut down to construct the dam), results in the overall temperature increasing. They also house predatory zooplankton which help break down detritus and control algae populations. Beavers are herbivores, and prefer the wood of quaking aspen , cottonwood , willow , alder , birch , maple and cherry trees. They also eat sedges , pondweed , and water lilies . Beavers do not hibernate, but rather they store sticks and logs in
16541-512: The small bow wave pushed in front of the face looks like a bottle from a distance. Prior to the 1950s, the only record of pygmy killer whales was from two skulls identified in 1827 and 1874. In 1952, a specimen was caught and killed in Taiji , Japan which is known for its annual dolphin hunts . Six years later, in 1958, an individual was killed off the coast of Senegal . In 1963, there were two recorded events involving pygmy killer whales. The first
16680-532: The spring season. A resident population of pygmy killer whales lives in the waters around Hawaii. Most sightings have been around the main island, however there are occasional sightings around several of the other islands. The population has a tightly connected social structure with affiliations between individuals that can last up to 15 years. Despite the existence of this resident population, sightings of pygmy killer whales around Hawaii are still quite rare; they accounted for less than 1.5% of all cetaceans sighted in
16819-425: The stunned fish. Corralling is a method where dolphins chase fish into shallow water to catch them more easily. Orcas and bottlenose dolphins have also been known to drive their prey onto a beach to feed on it, a behaviour known as beach or strand feeding. Some species also whack fish with their flukes, stunning them and sometimes knocking them out of the water. Reports of cooperative human-dolphin fishing date back to
16958-409: The subcutaneous blubber or fat depends on the dolphin's health, development, location, reproductive state, and how well it feeds. This fat is thickest on the dolphin's back and belly. Most of the dolphin's body fat is accumulated in a thick layer of blubber. Blubber differs from fat in that, in addition to fat cells, it contains a fibrous network of connective tissue. The blubber functions to streamline
17097-427: The supercontinent of Gondwana when the continents of South America and Australia were joined via Antarctica , or that monotremes existed along the shorelines of Antarctica in the early Cenozoic. Marine mammals are aquatic mammals that rely on the ocean for their existence. They include animals such as sea lions , whales , dugongs , sea otters and polar bears . Like other aquatic mammals, they do not represent
17236-631: The swimmers or charging the sharks to make them go away. Dolphins communicate using a variety of clicks, whistle-like sounds and other vocalizations. Dolphins also use nonverbal communication by means of touch and posturing . Dolphins also display culture, something long believed to be unique to humans (and possibly other primate species). In May 2005, a discovery in Australia found Indo-Pacific bottlenose dolphins ( Tursiops aduncus ) teaching their young to use tools. They cover their snouts with sponges to protect them while foraging. This knowledge
17375-627: The target for commercial industry, leading to a sharp decline in all populations of exploited species, such as beavers. Their pelts, suited for conserving heat, were taken during the fur trade and made into coats and hats . Other aquatic mammals, such as the Indian rhinoceros, were targets for sport hunting and had a sharp population decline in the 1900s. After it was made illegal, many aquatic mammals became subject to poaching . Other than hunting, aquatic mammals can be killed as bycatch from fisheries, where they become entangled in fixed netting and drown or starve. Increased river traffic, most notably in
17514-514: The target for commercial industry, leading to a sharp decline in all populations of exploited species, such as whales and seals . Commercial hunting lead to the extinction of Steller's sea cow and the Caribbean monk seal . After commercial hunting ended, some species, such as the gray whale and northern elephant seal, have rebounded in numbers, however the northern elephant seal has a genetic bottleneck ; conversely, other species, such as
17653-555: The teeth seen in mesonychians , an extinct group of semiaquatic carnivorous ungulates , and resemble, to a lesser degree, the teeth of seals. Another docodontan, the Late Jurassic Haldanodon , has been suggested to be a platypus or desman -like swimmer and burrower, being well adapted to dig and swim and occurring in a wetland environment. The tritylodontid Kayentatherium has been suggested to be semiaquatic. Unlike Castorocauda and Haldanodon , it
17792-427: The temperature drops, the blubber constricts the blood vessels to reduce blood flow in the dolphin. This allows the dolphin to spend less energy heating its own body, ultimately keeping the animal warmer without burning energy as quick. In order to release heat, the heat must pass the blubber layer. There are thermal windows that lack blubber, are not fully insulated and are somewhat thin and highly vascularized, including
17931-401: The two species of hippo. Dolphins have torpedo-shaped bodies with generally non-flexible necks, limbs modified into flippers, a tail fin, and bulbous heads. Dolphin skulls have small eye orbits, long snouts, and eyes placed on the sides of its head; they lack external ear flaps. Dolphins range in size from the 1.7 m (5 ft 7 in) long and 50 kg (110 lb) Maui's dolphin to
18070-457: The water as freshwater phocids have no aquatic predators. Some aquatic mammals have retained four weight-bearing limbs (e.g. hippopotamuses, beavers, otters, muskrats) and can walk on land like fully terrestrial mammals. The long and thin legs of a moose limit exposure to and friction from water in contrast to hippopotamuses who keep most of their body submerged and have short and thick legs. The semiaquatic pygmy hippopotamus can walk quickly on
18209-404: The water at dusk to feed. It relies on game trails to travel through dense forest vegetation. It marks trails by vigorously waving its tail while defecating to further spread its feces. The pygmy hippo spends about six hours a day foraging for food, and they do not eat aquatic vegetation to a significant extent and rarely eat grass because it is uncommon in the thick forests they inhabit. The bulk of
18348-433: The water surface. A moose's diet often depends on its location, but they seem to prefer the new growths from deciduous trees with a high sugar content, such as white birch, trembling aspen and striped maple , among many others. They also eat many aquatic plants such as waterlily and water milfoil . To reach high branches, a moose may bend small saplings down, using its prehensile lip, mouth or body. For larger trees
18487-431: The water, which allows them to travel faster. Their skeletal anatomy allows them to be fast swimmers. All species have a dorsal fin to prevent themselves from involuntarily spinning in the water. Some dolphins are adapted for diving to great depths. In addition to their streamlined bodies, some can selectively slow their heart rate to conserve oxygen. Some can also re-route blood from tissue tolerant of water pressure to
18626-405: The wild. The species had been described by John Gray in 1874, based on two skulls identified in 1827 and 1874. The next recorded sighting was in 1952 which led to its formal naming by Japanese cetologist Munesato Yamada in 1954. The pygmy killer whale is dark gray to black on the cape and has a sharp change to lighter gray on the sides. The flesh around their lips and on the end of their snout
18765-575: The world or have been reported in the wild, such as a bottlenose- Atlantic spotted hybrid. The best known hybrid is the wholphin , a false killer whale-bottlenose dolphin hybrid. The wolphin is a fertile hybrid. Two wolphins currently live at the Sea Life Park in Hawaii; the first was born in 1985 from a male false killer whale and a female bottlenose. Wolphins have also been observed in the wild. Dolphins are descendants of land-dwelling mammals of
18904-631: The world. In China it was standard for the royalty to wear robes made from them. People that were financially high in status also wore them. Otters have also been hunted using dogs, specifically the otterhound . In modern times, TRAFFIC , a joint program of the World Wildlife Fund (WWF) and International Union for Conservation of Nature (IUCN), reported that otters are at serious risk in Southeast Asia and have disappeared from parts of their former range. This decline in populations
19043-429: Was an herbivore, being probably beaver or capybara -like in habits. Another lineage of Mesozoic mammals, the eutriconodonts , have been suggested to be aquatic animals with mixed results. Astroconodon occurred abundantly in freshwater lacustrine deposits and its molars were originally interpreted as being similar to those of piscivorous mammals like cetaceans and pinnipeds; by extension some researchers considered
19182-435: Was first discovered in the corpse of a pygmy killer whale. A pygmy killer whale found stranded on the coast of New Caledonia died from parasitic encephalitis caused by nematodes. They are also victims of opportunistic cookie cutter sharks . Pygmy killer whales are occasionally involved in mass strandings . As seen in other cetaceans, these strandings often involve a sick or injured individual; even when pushed back out to
19321-425: Was in Japan, where 14 individuals were caught and brought into captivity; all 14 animals were dead within 22 days. The second was off the coast of Hawaii where an individual animal was caught and successfully brought into captivity. In 1967, a single pygmy killer whale off of Costa Rica died after becoming entangled in a purse seine net. Finally, in 1969, a pygmy killer whale was killed off the coast of St. Vincent and
#900099