102-445: Chevrotains , or mouse-deer , are diminutive, even-toed ungulates that make up the family Tragulidae , and are the only living members of the infraorder Tragulina . The 10 extant species are placed in three genera, but several species also are known only from fossils . The extant species are found in forests in South and Southeast Asia; a single species, the water chevrotain ,
204-443: A burst of speed, usually on a near vertical incline, releasing gametes at the apex, followed by a rapid return to the lake or sea floor or fish aggregation. Sneaking males do not take part in courtship. In salmon and trout, for example, jack males are common. These are small silvery males that migrate upstream along with the standard, large, hook-nosed males and that spawn by sneaking into redds to release sperm simultaneously with
306-507: A chin gland for marking each other as mates or antagonists, and, in the case of the water chevrotain, anal and preputial glands for marking territory . Their territories are relatively small, on the order of 13–24 hectares (32–59 acres), but neighbors generally ignore each other, rather than compete aggressively. Some of the species show a remarkable affinity with water, often remaining submerged for prolonged periods to evade predators or other unwelcome intrusions. This has also lent support to
408-462: A female they bite into her skin, releasing an enzyme that digests the skin of their mouths and her body and fusing the pair down to the blood-vessel level. The male then slowly atrophies , losing first his digestive organs, then his brain, heart, and eyes, ending as nothing more than a pair of gonads , which release sperm in response to hormones in the female's bloodstream indicating egg release. This extreme sexual dimorphism ensures that, when
510-493: A female was reported as sex, while anal intercourse with orgasm between males was only [categorized as] 'revolving around' dominance , competition or greetings." In the 21st century, liberal social or sexual views are often projected upon animal subjects of research. Popular discussions of bonobos are a frequently cited example. Current research frequently expresses views such as that of the Natural History Museum at
612-723: A few bumps. In contrast, camels and ruminants have bumps that are crescent-shaped cusps ( selenodont ). Animal sexual behavior Animal sexual behaviour takes many different forms, including within the same species . Common mating or reproductively motivated systems include monogamy , polygyny , polyandry , polygamy and promiscuity . Other sexual behaviour may be reproductively motivated (e.g. sex apparently due to duress or coercion and situational sexual behaviour ) or non-reproductively motivated (e.g. homosexual sexual behaviour , bisexual sexual behaviour, cross-species sex , sexual arousal from objects or places , sex with dead animals , etc.). When animal sexual behaviour
714-409: A few days and replace the dominant male. This is found amongst coral reef fishes such as groupers , parrotfishes and wrasses . As an example, most wrasses are protogynous hermaphrodites within a haremic mating system. It is less common for a male to switch to a female ( protandry ). A common example of a protandrous species are clownfish —if the larger, dominant female dies, in many cases,
816-469: A few rare species, the incidence of genetic monogamy is 100%, with all offspring genetically related to the socially monogamous pair. But genetic monogamy is strikingly low in other species. Barash and Lipton note: The highest known frequency of extra-pair copulations are found among the fairy-wrens , lovely tropical creatures technically known as Malurus splendens and Malurus cyaneus . More than 65% of all fairy-wren chicks are fathered by males outside
918-403: A fight may also have the chance to mate with a larger number of females and will therefore pass on his genes to their offspring. Historically, it was believed that only humans and a small number of other species performed sexual acts other than for reproduction, and that animals' sexuality was instinctive and a simple " stimulus-response " behaviour. However, in addition to homosexual behaviours,
1020-410: A lifelong bond. In contrast, montane voles have a polygamous mating system. When montane voles mate, they form no strong attachments, and separate after copulation. Studies on the brains of these two species have found that it is two neurohormones and their respective receptors that are responsible for these differences in mating strategies. Male prairie voles release vasopressin after copulation with
1122-682: A lifetime, such as in pigeons , or it may occasionally change from one mating season to another, such as in emperor penguins . In contrast with tournament species , these pair-bonding species have lower levels of male aggression, competition and little sexual dimorphism . Zoologists and biologists now have evidence that monogamous pairs of animals are not always sexually exclusive. Many animals that form pairs to mate and raise offspring regularly engage in sexual activities with extra-pair partners . This includes previous examples, such as swans . Sometimes, these extra-pair sexual activities lead to offspring. Genetic tests frequently show that some of
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#17328548198071224-415: A major role in parent child relationships, it is also found to play a role in adult sexual relationships. Its secretion affects the nature of the relationship or if there will even be a relationship at all. Studies have shown that oxytocin is higher in monkeys in lifelong monogamous relationships compared to monkeys which are single. Furthermore, the oxytocin levels of the couples correlate positively; when
1326-785: A mate to prefer that mate not to have any unusual, peculiar or deviant features. Similarly, animals preferentially choose mates with low fluctuating asymmetry . However, animal sexual ornaments can evolve through runaway selection, which is driven by (usually female) selection for non-standard traits. The field of study of sexuality in non-human species was a long-standing taboo . In the past, researchers sometimes failed to observe, miscategorised or misdescribed sexual behaviour which did not meet their preconceptions —their bias tended to support what would now be described as conservative sexual mores. An example of overlooking behaviour relates to descriptions of giraffe mating: When nine out of ten pairings occur between males, "[e]very male that sniffed
1428-497: A mated pair. This behaviour is an evolutionarily stable strategy for reproduction, because it is favoured by natural selection just like the "standard" strategy of large males. Hermaphroditism occurs when a given individual in a species possesses both male and female reproductive organs, or can alternate between possessing first one, and then the other. Hermaphroditism is common in invertebrates but rare in vertebrates. It can be contrasted with gonochorism , where each individual in
1530-422: A notable exception being bonobos . Polygyny occurs when one male gets exclusive mating rights with multiple females. In some species, notably those with harem -like structures, only one of a few males in a group of females will mate. Technically, polygyny in sociobiology and zoology is defined as a system in which a male has a relationship with more than one female, but the females are predominantly bonded to
1632-644: A pair of animals socially monogamous does not necessarily make them sexually or genetically monogamous. Social monogamy, sexual monogamy, and genetic monogamy can occur in different combinations. Social monogamy is relatively rare in the animal kingdom. The actual incidence of social monogamy varies greatly across different branches of the evolutionary tree. Over 90% of avian species are socially monogamous. This stands in contrast to mammals. Only 3% of mammalian species are socially monogamous, although up to 15% of primate species are. Social monogamy has also been observed in reptiles , fish, and insects . Sexual monogamy
1734-422: A partner, and an attachment to their partner then develops. Female prairie voles release oxytocin after copulation with a partner, and similarly develop an attachment to their partner. Neither male nor female montane voles release high quantities of oxytocin or vasopressin when they mate. Even when injected with these neurohormones, their mating system does not change. In contrast, if prairie voles are injected with
1836-491: A period scientifically described as oestrus but commonly described as being "in season" or "in heat". Sexual behaviour may occur outside oestrus, and such acts as do occur are not necessarily harmful. Some mammals (e.g. domestic cats, rabbits and camelids) are termed "induced ovulators" . For these species, the female ovulates due to an external stimulus during, or just prior to, mating, rather than ovulating cyclically or spontaneously. Stimuli causing induced ovulation include
1938-500: A range of species masturbate and may use objects as tools to help them do so. Sexual behaviour may be tied more strongly to the establishment and maintenance of complex social bonds across a population which support its success in non-reproductive ways. Both reproductive and non-reproductive behaviours can be related to expressions of dominance over another animal or survival within a stressful situation (such as sex due to duress or coercion). In sociobiology and behavioural ecology ,
2040-428: A rank in the hierarchy. Various neurohormones stimulate sexual wanting in animals. In general, studies have suggested that dopamine is involved in sexual incentive motivation, oxytocin and melanocortins in sexual attraction, and noradrenaline in sexual arousal. Vasopressin is also involved in the sexual behaviour of some animals. The mating system of prairie voles is monogamous ; after mating, they form
2142-559: A similar aquatic lifestyle. Hippopotamuses appeared in the late Miocene and occupied Africa and Asia—they never got to the Americas. The camels ( Tylopoda ) were, during large parts of the Cenozoic , limited to North America; early forms like Cainotheriidae occupied Europe. Among the North American camels were groups like the stocky, short-legged Merycoidodontidae . They first appeared in
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#17328548198072244-477: A simple stomach that digests food. Thus, they were grouped together as non-ruminants (Porcine). All other even-toed ungulates have molars with a selenodont construction (crescent-shaped cusps) and have the ability to ruminate , which requires regurgitating food and re-chewing it. Differences in stomach construction indicated that rumination evolved independently between tylopods and ruminants ; therefore, tylopods were excluded from Ruminantia . The taxonomy that
2346-463: A single male. Should the active male be driven out, killed, or otherwise removed from the group, in a number of species the new male will ensure that breeding resources are not wasted on another male's young. The new male may achieve this in many different ways, including: Von Haartman specifically described the mating behaviour of the European pied flycatcher as successive polygyny. Within this system,
2448-469: A slim build, lanky legs, and a long tail. Their hind legs were much longer than their front legs. The early to middle Eocene saw the emergence of the ancestors of most of today's mammals. Two formerly widespread, but now extinct, families of even-toed ungulates were Entelodontidae and Anthracotheriidae . Entelodonts existed from the middle Eocene to the early Miocene in Eurasia and North America. They had
2550-425: A species is either male or female, and remains that way throughout their lives. Most fish are gonochorists, but hermaphroditism is known to occur in 14 families of teleost fishes. Usually hermaphrodites are sequential , meaning they can switch sex , usually from female to male ( protogyny ). This can happen if a dominant male is removed from a group of females. The largest female in the harem can switch sex over
2652-468: A stocky body with short legs and a massive head, which was characterized by two humps on the lower jaw bone. Anthracotheres had a large, porcine ( pig -like) build, with short legs and an elongated muzzle . This group appeared in the middle Eocene up until the Pliocene , and spread throughout Eurasia, Africa, and North America. Anthracotheres are thought to be the ancestors of hippos, and, likewise, probably led
2754-439: A thermoregulatory innoviation that allows other artiodactyls to exploit hot arid habitats. Though most species feed exclusively on plant material, the water chevrotain occasionally takes insects and crabs or scavenges meat and fish. Like other ruminants, they lack upper incisors . They give birth to only a single young. In other respects, however, they have primitive features, closer to nonruminants such as pigs. All species in
2856-424: A very flexible body, contributing to their speed by increasing their stride length. Many even-toed ungulates have a relatively large head. The skull is elongated and rather narrow; the frontal bone is enlarged near the back and displaces the parietal bone , which forms only part of the side of the cranium (especially in ruminants). Four families of even-toed ungulates have cranial appendages. These Pecora (with
2958-552: Is also rare among animals. Many socially monogamous species engage in extra-pair copulations , making them sexually non-monogamous. For example, while over 90% of birds are socially monogamous, "on average, 30% or more of the baby birds in any nest [are] sired by someone other than the resident male." Patricia Adair Gowaty has estimated that, out of 180 different species of socially monogamous songbirds, only 10% are sexually monogamous. The incidence of genetic monogamy, determined by DNA fingerprinting, varies widely across species. For
3060-413: Is an umbrella term used to refer generally to non-monogamous matings. As such, polygamous relationships can be polygynous, polyandrous or polygynandrous. In a small number of species, individuals can display either polygamous or monogamous behaviour depending on environmental conditions. An example is the social wasp Apoica flavissima . In some species, polygyny and polyandry is displayed by both sexes in
3162-409: Is found at the top. Only two clownfish, a male and a female, in a group reproduce through external fertilisation. Clownfish are sequential hermaphrodites, meaning that they develop into males first, and when they mature, they become females. If the female clownfish is removed from the group, such as by death, one of the largest and most dominant males will become a female. The remaining males will move up
Chevrotain - Misplaced Pages Continue
3264-404: Is found in the rainforests of Central and West Africa . In November 2019, conservation scientists announced that they had photographed silver-backed chevrotains ( Tragulus versicolor ) in a Vietnamese forest for the first time since the last confirmed sightings in 1990. They are solitary , or live in loose groupings or pairs, and feed almost exclusively on plant material. Chevrotains are
3366-471: Is more adapted to a squeezing mastication , which is characteristic of omnivores . Camels and ruminants have fewer teeth; there is often a yawning diastema , a designated gap in the teeth where the molars are aligned for crushing plant matter. The incisors are often reduced in ruminants, and are completely absent in the upper jaw . The canines are enlarged and tusk-like in the Suina, and are used for digging in
3468-458: Is proving to be false as, "most hormones don't influence behaviour directly. Rather, they affect thinking and emotions in variable ways (Azar, 40)." There is much more involved in sexual behaviour in the mammalian animal than oxytocin and vasopressin can explain. It is often assumed that animals do not have sex for pleasure, or alternatively that humans , pigs , bonobos (and perhaps dolphins and one or two more species of primates) are
3570-491: Is reproductively motivated, it is often termed mating or copulation ; for most non-human mammals , mating and copulation occur at oestrus (the most fertile period in the mammalian female's reproductive cycle), which increases the chances of successful impregnation . Some animal sexual behaviour involves competition , sometimes fighting, between multiple males. Females often select males for mating only if they appear strong and able to protect themselves. The male that wins
3672-418: Is the most common form of polygamy among vertebrates (including humans), it has been studied far more extensively than polyandry or polygynandry. Polyandry occurs when one female gets exclusive mating rights with multiple males. In some species, such as redlip blennies , both polygyny and polyandry are observed. The males in some deep sea anglerfishes are much smaller than the females. When they find
3774-704: Is therefore focused on anthracotheres (family Anthracotheriidae); one dating from the Eocene to Miocene was declared to be "hippo-like" upon discovery in the 19th century. A study from 2005 showed that the anthracotheres and hippopotamuses had very similar skulls , but differed in the adaptations of their teeth. It was nevertheless believed that cetaceans and anthracothereres descended from a common ancestor, and that hippopotamuses developed from anthracotheres. A study published in 2015 confirmed this, but also revealed that hippopotamuses were derived from older anthracotherians. The newly introduced genus Epirigenys from Eastern Africa
3876-525: Is thus the sister group of hippos. Linnaeus postulated a close relationship between camels and ruminants as early as the mid-1700s. Henri de Blainville recognized the similar anatomy of the limbs of pigs and hippos, and British zoologist Richard Owen coined the term "even-toed ungulates" and the scientific name "Artiodactyla" in 1848. Internal morphology (mainly the stomach and the molars) were used for classification. Suines (including pigs ) and hippopotamuses have molars with well-developed roots and
3978-510: The Malay Annals , King Parameswara , seeking a place to found a new city, came to a place where he saw a mouse deer ( kancil in Malay ) kicking his hunting dog into the river . He thought this boded well, remarking, 'this place is excellent, even the mouse deer is formidable; it is best that we establish a kingdom here'. He then founded there the city of Malacca . In memory of this founding legend,
4080-555: The Indian spotted chevrotain is jarini pandi , which literally means "a deer and a pig". In Kannada , it is called barka (ಬರ್ಕ), in Malayalam , it is called കൂരമാൻ kūramān , and the Konkani name for it is barinka . The Tamil term is சருகு மான் sarukumāṉ "leaf-pile deer". The Sinhala name meeminna roughly translates to "mouse-like deer". This was used in the scientific name of
4182-674: The Old World , exist today only in the Americas . South America was settled by even-toed ungulates only in the Pliocene, after the land bridge at the Isthmus of Panama formed some three million years ago. With only the peccaries, lamoids (or llamas ), and various species of capreoline deer , South America has comparatively fewer artiodactyl families than other continents, except Australia, which has no native species. The classification of artiodactyls
Chevrotain - Misplaced Pages Continue
4284-688: The Sri Lankan spotted chevrotain , M. meminna . The family was widespread and successful from the Oligocene (34 million years ago) through the Miocene (about 5 million years ago), but has remained almost unchanged over that time and remains as an example of an archaic ruminant type. They have four-chambered stomachs to ferment tough plant foods, but the third chamber is poorly developed. Unlike other artiodactyls, they lack an carotid rete , and so cannot heat exchange cool blood entering their brains,
4386-634: The coat of arms of Malacca depicts two mouse deer. The mouse deer or Sang Kancil is also a clever character from several Malay folktales. Even-toed ungulate Cetartiodactyla Montgelard et al. 1997 Artiodactyls are placental mammals belonging to the order Artiodactyla ( / ˌ ɑːr t i oʊ ˈ d æ k t ɪ l ə / AR -tee-oh- DAK -tih-lə , from Ancient Greek ἄρτιος , ártios 'even' and δάκτυλος , dáktylos 'finger, toe'). Typically, they are ungulates which bear weight equally on two (an even number) of their five toes (the third and fourth, often in
4488-507: The hind legs have a reduction in the number of toes to three. The central axis of the leg is between the third and fourth toe. The first toe is missing in modern artiodactyls, and can only be found in now-extinct genera. The second and fifth toes are adapted differently between species: When camels have only two toes present, the claws are transformed into nails (while both are made of keratin , claws are curved and pointed while nails are flat and dull). These claws consist of three parts:
4590-412: The ruminants as the sister group of cetaceans. Subsequent studies established the close relationship between hippopotamuses and cetaceans; these studies were based on casein genes , SINEs , fibrinogen sequences, cytochrome and rRNA sequences, IRBP (and vWF ) gene sequences, adrenergic receptors , and apolipoproteins . In 2001, the fossil limbs of a Pakicetus (amphibioid cetacean
4692-665: The Middle French word chevrot (kid or fawn), derived from chèvre (goat). The single African species is consistently known as "chevrotain". The names "chevrotain" and "mouse-deer" have been used interchangeably among the Asian species, though recent authorities typically have preferred chevrotain for the species in the genus Moschiola and mouse-deer for the species in the genus Tragulus . Consequently, all species with pale-spotted or -striped upper parts are known as "chevrotain" and without are known as "mouse-deer". The Telugu name for
4794-472: The University of Oslo , which in 2006 held an exhibition on animal sexuality: Many researchers have described homosexuality as something altogether different from sex. They must realise that animals can have sex with who they will, when they will and without consideration to a researcher's ethical principles. Other animal activities may be misinterpreted due to the frequency and context in which animals perform
4896-461: The act. This assumption is confirmed by the behaviour of males, who in the case of many species are prepared to work to get access to female animals, especially if the female animal is in oestrus, and males who for breeding purposes are used to having sperm collected become very eager, when the equipment they associate with the collection is taken out. . . . There is nothing in female mammals ' anatomy or physiology that contradicts that stimulation of
4998-405: The amount of promiscuity is particularly striking because bonobos use sex to alleviate social conflict as well as to reproduce. This mutual promiscuity is the approach most commonly used by spawning animals, and is perhaps the "original fish mating system." Common examples are forage fish , such as herrings , which form huge mating shoals in shallow water. The water becomes milky with sperm and
5100-463: The behaviour. For example, domestic ruminants display behaviours such as mounting and head-butting. This often occurs when the animals are establishing dominance relationships and are not necessarily sexually motivated. Careful analysis must be made to interpret what animal motivations are being expressed by those behaviours. Copulation is the union of the male and female sex organs , the sexual activity specifically organized to transmit male sperm into
5202-407: The body of the female. Alternative male strategies which allow small males to engage in cuckoldry can develop in species such as fish where spawning is dominated by large and aggressive males. Cuckoldry is a variant of polyandry , and can occur with sneak spawners . A sneak spawner is a male that rushes in to join the spawning rush of a spawning pair. A spawning rush occurs when a fish makes
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#17328548198075304-448: The bottom is draped with millions of fertilised eggs. Female and male sexual behaviour differ in many species. Often, males are more active in initiating mating, and bear the more conspicuous sexual ornamentation like antlers and colourful plumage. This is a result of anisogamy , where sperm are smaller and much less costly (energetically) to produce than eggs . This difference in physiological cost means that males are more limited by
5406-511: The breeding season is typically concentrated to a few short days in the spring. Some species, such as the Rana clamitans (green frog), spend from June to August defending their territory. In order to protect these territories, they use five vocalizations. Like many coral reef dwellers, the clownfish spawn around the time of the full moon in the wild. In a group of clownfish, there is a strict dominance hierarchy. The largest and most aggressive female
5508-458: The early Eocene (about 53 million years ago). Since these findings almost simultaneously appeared in Europe , Asia , and North America , it is very difficult to accurately determine the origin of artiodactyls. The fossils are classified as belonging to the family Diacodexeidae ; their best-known and best-preserved member is Diacodexis . These were small animals, some as small as a hare , with
5610-609: The early Cenozoic ( Paleocene and Eocene ), which had hooves instead of claws on their feet. Their molars were adapted to a carnivorous diet, resembling the teeth in modern toothed whales , and, unlike other mammals, had a uniform construction. The suspected relations can be shown as follows: Artiodactyla [REDACTED] Mesonychia † [REDACTED] Cetacea [REDACTED] Molecular findings and morphological indications suggest that artiodactyls, as traditionally defined, are paraphyletic with respect to cetaceans. Cetaceans are deeply nested within
5712-400: The evolution-related purpose of mating can be said to be reproduction, it is not actually the creating of offspring which originally causes them to mate. It is probable that they mate because they are motivated for the actual copulation, and because this is connected with a positive experience. It is therefore reasonable to assume that there is some form of pleasure or satisfaction connected with
5814-419: The exception of the musk deer ), have one of four types of cranial appendages: true horns, antlers , ossicones , or pronghorns . True horns have a bone core that is covered in a permanent sheath of keratin, and are found only in the bovids . Antlers are bony structures that are shed and replaced each year; they are found in deer (members of the family Cervidae ). They grow from a permanent outgrowth of
5916-538: The family Tragulidae. In 2004, T. nigricans and T. versicolor were split from T. napu , and T. kanchil and T. williamsoni were split from T. javanicus . In 2005, M. indica and M. kathygre were split from M. meminna . With these changes, the 10 extant species are: The Hypertragulidae were closely related to the Tragulidae. The six extinct chevrotain genera include: The extinct chevrotains might also include According to
6018-413: The family lack antlers and horns, but both sexes have elongated canine teeth . These are especially prominent in males, where they project out on either side of the lower jaw, and are used in fights. Their legs are short and thin, which leave them lacking in agility, but also helps to maintain a smaller profile to aid in running through the dense foliage of their environments. Other pig-like features include
6120-504: The female function. In the grey slug , the sharing of cost leads to a spectacular display, where the mates suspend themselves high above the ground from a slime thread, ensuring none of them can refrain from taking on the cost of egg-bearer. Many animal species have specific mating (or breeding) periods e.g. ( seasonal breeding ) so that offspring are born or hatch at an optimal time. In marine species with limited mobility and external fertilisation like corals , sea urchins and clams ,
6222-592: The female is ready to spawn, she has a mate immediately available. A single anglerfish female can "mate" with many males in this manner. Polygynandry occurs when multiple males mate indiscriminately with multiple females. The numbers of males and females need not be equal, and in vertebrate species studied so far, there are usually fewer males. Two examples of systems in primates are promiscuous mating chimpanzees and bonobos . These species live in social groups consisting of several males and several females. Each female copulates with many males, and vice versa. In bonobos,
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#17328548198076324-633: The form of a hoof ). The other three toes are either present, absent, vestigial , or pointing posteriorly. By contrast, most perissodactyls bear weight on an odd number of the five toes. Another difference between the two orders is that many artiodactyls (except for Suina ) digest plant cellulose in one or more stomach chambers rather than in their intestine (as perissodactyls do). Molecular biology, along with new fossil discoveries, has found that cetaceans ( whales , dolphins , and porpoises ) fall within this taxonomic branch, being most closely related to hippopotamuses . Some modern taxonomists thus apply
6426-553: The form of monogamous marriage. Sexual monogamy is defined as an exclusive sexual relationship between a female and a male based on observations of sexual interactions. Finally, the term genetic monogamy is used when DNA analyses can confirm that a female-male pair reproduce exclusively with each other. A combination of terms indicates examples where levels of relationships coincide, e.g., sociosexual and sociogenetic monogamy describe corresponding social and sexual, and social and genetic monogamous relationships, respectively. Whatever makes
6528-1015: The former; the two groups together form a monophyletic taxon, for which the name Cetartiodactyla is sometimes used. Modern nomenclature divides Artiodactyla (or Cetartiodactyla) in four subordinate taxa: camelids (Tylopoda), pigs and peccaries (Suina), ruminants (Ruminantia), and hippos plus cetaceans (Whippomorpha). The presumed lineages within Artiodactyla can be represented in the following cladogram : Tylopoda (camels) [REDACTED] Suina (pigs) [REDACTED] Tragulidae (mouse deer) [REDACTED] Pecora (horn bearers) [REDACTED] Hippopotamidae (hippopotamuses) [REDACTED] Cetacea (whales) [REDACTED] The four summarized Artiodactyla taxa are divided into ten extant families: Although deer, musk deer, and pronghorns have traditionally been summarized as cervids (Cervioidea), molecular studies provide different—and inconsistent—results, so
6630-668: The frontal bone called the pedicle and can be branched, as in the white-tailed deer ( Odocoileus virginianus ), or palmate , as in the moose ( Alces alces ). Ossicones are permanent bone structures that fuse to the frontal or parietal bones during an animal's life and are found only in the Giraffidae . Pronghorns , while similar to horns in that they have keratinous sheaths covering permanent bone cores, are deciduous. All these cranial appendages can serve for posturing, battling for mating privilege, and for defense. In almost all cases, they are sexually dimorphic, and are often found only on
6732-401: The ground and for defense. In ruminants, the males' upper canines are enlarged and used as a weapon in certain species (mouse deer, musk deer, water deer ); species with frontal weapons are usually missing the upper canines. The lower canines of ruminants resemble the incisors, so that these animals have eight uniform teeth in the frontal part of the lower jaw . The molars of porcine have only
6834-577: The idea that whales evolved from water-loving creatures that looked like small deer. Tragulidae's placement within Artiodactyla can be represented in the following cladogram : Tylopoda (camels) [REDACTED] Suina (pigs) [REDACTED] Tragulidae (mouse deer) [REDACTED] Pecora (horn bearers) [REDACTED] Hippopotamidae (hippopotamuses) [REDACTED] Cetacea (whales) [REDACTED] Traditionally, only four extant species were recognized in
6936-473: The inner genitals are seen e.g. also during orgasm for women. It is therefore reasonable to assume that sexual intercourse may be linked with a positive experience for female animals. Koinophilia is the love of the "normal" or phenotypically common (from the Greek κοινός , koinós , meaning "usual" or "common"). The term was introduced to scientific literature in 1990, and refers to the tendency of animals seeking
7038-533: The late Eocene and developed a great diversity of species in North America. Only in the late Miocene or early Pliocene did they migrate from North America into Eurasia. The North American varieties became extinct around 10,000 years ago. Suina (including pigs ) have been around since the Eocene. In the late Eocene or the Oligocene , two families stayed in Eurasia and Africa; the peccaries , which became extinct in
7140-407: The limbs are predominantly localized, which ensures that artiodactyls often have very slender legs. A clavicle is never present, and the scapula is very agile and swings back and forth for added mobility when running. The special construction of the legs causes the legs to be unable to rotate, which allows for greater stability when running at high speeds. In addition, many smaller artiodactyls have
7242-634: The males are consistently larger and heavier than the females. In deer, only the males boast antlers, and the horns of bovines are usually small or not present in females. Male Indian antelopes have a much darker coat than females. Almost all even-toed ungulates have fur, with the exception being the nearly hairless hippopotamus. Fur varies in length and coloration depending on the habitat. Species in cooler regions can shed their coat. Camouflaged coats come in colors of yellow, gray, brown, or black tones. Even-toed ungulates bear their name because they have an even number of toes (two or four)—in some peccaries,
7344-428: The males leave their home territory once their primary female lays her first egg. Males then create a second territory, presumably in order to attract a secondary female to breed. Even when they succeed at acquiring a second mate, the males typically return to the first female to exclusively provide for her and her offspring. Polygynous mating structures are estimated to occur in up to 90% of mammal species. As polygyny
7446-459: The males. One exception is the species Rangifer tarandus , known as reindeer in Europe or caribou in North America, where both sexes can grow antlers yearly, though the females' antlers are typically smaller and not always present. There are two trends in terms of teeth within Artiodactyla. The Suina and hippopotamuses have a relatively large number of teeth (with some pigs having 44); their dentition
7548-422: The mother rat is given injections of an oxytocin receptor antagonist , they no longer experience these maternal motivations. Prolactin influences social bonding in rats. Oxytocin plays a similar role in non-human primates as it does in humans. Grooming, sex, and cuddling frequencies correlate positively with levels of oxytocin. As the level of oxytocin increases so does sexual motivation. While oxytocin plays
7650-421: The mouse deer, often reaches a body length of only 45 centimeters (18 in) and a weight of 1.5 kilograms (3.3 lb). The largest member, the hippopotamus, can grow up to 5 meters (16 ft) in length and weigh 4.5 metric tons (5 short tons), and the giraffe can grow to be 5.5 meters (18 ft) tall and 4.7 meters (15 ft) in body length. All even-toed ungulates display some form of sexual dimorphism :
7752-948: The name Cetartiodactyla ( / s ɪ ˌ t ɑːr t i oʊ ˈ d æ k t ɪ l ə / ) to this group, while others opt to include cetaceans within the existing name of Artiodactyla. Some researchers use " even-toed ungulates " to exclude cetaceans and only include terrestrial artiodactyls, making the term paraphyletic in nature. The roughly 270 land-based even-toed ungulate species include pigs , peccaries , hippopotamuses , antelopes , deer , giraffes , camels , llamas , alpacas , sheep , goats and cattle . Many are herbivores, but suids are omnivorous, whereas cetaceans are entirely carnivorous. Artiodactyls are also known by many extinct groups such as anoplotheres , cainotheriids , merycoidodonts , entelodonts , anthracotheres , basilosaurids , and palaeomerycids . Many artiodactyls are of great dietary, economic, and cultural importance to humans. The oldest fossils of even-toed ungulates date back to
7854-414: The neurohormones, they may form a lifelong attachment, even if they have not mated. The differing response to the neurohormones between the two species is due to a difference in the number of oxytocin and vasopressin receptors. Prairie voles have a greater number of oxytocin and vasopressin receptors compared to montane voles, and are therefore more sensitive to those two neurohormones. It's believed that it's
7956-439: The number of mates they can secure, while females are limited by the quality of genes of her mates, a phenomenon known as Bateman's principle . Many females also have extra reproductive burdens in that parental care often falls mainly, or exclusively, on them. Thus, females are more limited in their potential reproductive success . In species where males take on more of the reproductive costs, such as sea horses and jacanas ,
8058-518: The offspring raised by a monogamous pair come from the female mating with an extra-pair male partner. These discoveries have led biologists to adopt new ways of talking about monogamy. According to Ulrich Reichard (2003): Social monogamy refers to a male and female's social living arrangement (e.g., shared use of a territory, behaviour indicative of a social pair, and/or proximity between a male and female) without inferring any sexual interactions or reproductive patterns. In humans, social monogamy takes
8160-424: The only species that do. This is sometimes stated as "animals mate only for reproduction". This view is considered a misconception by some scholars. Jonathan Balcombe argues that the prevalence of non-reproductive sexual behaviour in certain species suggests that sexual stimulation is pleasurable. He also points to the presence of the clitoris in some female mammals, and evidence for female orgasm in primates. On
8262-445: The other hand, it is impossible to know the subjective feelings of animals, and the notion that non-human animals experience emotions similar to humans is a contentious subject. A 2006 Danish Animal Ethics Council report, which examined current knowledge of animal sexuality in the context of legal queries concerning sexual acts by humans, has the following comments, primarily related to domestically common animals: Even though
8364-470: The other to be female, thus carrying the majority of the cost of reproduction. Post mating, banana slugs will some times gnaw off their partners penis as an act of sperm competition called apophallation. This is costly as they must heal, and spend more energy courting conspecifics that can act as male and female. A hypothesis suggests these slugs may be able to compensate the loss of the male function by directing energy that would have been put towards it to
8466-419: The oxytocin secretion of one increases, the other one also increases. Higher levels of oxytocin are related to monkeys expressing more behaviours such as cuddling, grooming and sex, while lower levels of oxytocin reduce motivation for these activities. Research on oxytocin's role in the animal brain suggests that it plays less of a role in behaviours of love and affection than previously believed. "When oxytocin
8568-442: The plate (top and sides), the sole (bottom), and the bale (rear). In general, the claws of the forelegs are wider and blunter than those of the hind legs, and they are farther apart. Aside from camels, all even-toed ungulates put just the tip of the foremost phalanx on the ground. In even-toed ungulates, the bones of the stylopodium (upper arm or thigh bone) and zygopodiums (tibia and fibula) are usually elongated. The muscles of
8670-570: The population. Polygamy in both sexes has been observed in red flour beetle ( Tribolium castaneum ). Polygamy is also seen in many Lepidoptera species including Mythimna unipuncta (true armyworm moth). A tournament species is one in which "mating tends to be highly polygamous and involves high levels of male-male aggression and competition." Tournament behaviour often correlates with high levels of sexual dimorphism , examples of species including chimpanzees and baboons . Most polygamous species present high levels of tournament behaviour, with
8772-459: The presence of four toes on each foot, the absence of facial scent glands , premolars with sharp crowns, and the form of their sexual behaviour and copulation . They are solitary or live in pairs. The young are weaned at three months of age, and reach sexual maturity between 5 and 10 months, depending on species. Parental care is relatively limited. Although they lack the types of scent glands found in most other ruminants, they do possess
8874-445: The quantity of receptors, rather than the quantity of the hormones, that determines the mating system and bond-formation of either species. Mother rats experience a postpartum estrus which makes them highly motivated to mate. However, they also have a strong motivation to protect their newly born pups. As a consequence, the mother rat solicits males to the nest but simultaneously becomes aggressive towards them to protect her young. If
8976-413: The question of phylogenetic systematics of infraorder Pecora (the horned ruminants) for the time being, cannot be answered. Artiodactyls are generally quadrupeds . Two major body types are known: suinids and hippopotamuses are characterized by a stocky body, short legs, and a large head; camels and ruminants, though, have a more slender build and lanky legs. Size varies considerably; the smallest member,
9078-411: The role is reversed, and the females are larger, more aggressive and more brightly coloured than the males. In hermaphroditic animals, the costs of parental care can be evenly distributed between the sexes, e.g. earthworms . In some species of planarians , sexual behaviour takes the form of penis fencing . In this form of copulation, the individual that first penetrates the other with the penis, forces
9180-472: The sequence with that of other living beings—the more similar they are, the more closely they are related. Comparison of even-toed ungulate and cetaceans genetic material has shown that the closest living relatives of whales and hippopotamuses is the paraphyletic group Artiodactyla. Dan Graur and Desmond Higgins were among the first to come to this conclusion, and included a paper published in 1994. However, they did not recognize hippopotamuses and classified
9282-445: The sexual behaviour of coitus, sperm and pheromones. Domestic cats have penile spines . Upon withdrawal of a cat's penis , the spines rake the walls of the female's vagina , which may cause ovulation. For many amphibians, an annual breeding cycle applies, typically regulated by ambient temperature, precipitation, availability of surface water and food supply. This breeding season is accentuated in temperate regions, in boreal climate
9384-494: The sexual organs and mating is able to be a positive experience. For instance, the clitoris acts in the same way as with women, and scientific studies have shown that the success of reproduction is improved by stimulation of clitoris on (among other species) cows and mares in connection with insemination, because it improves the transportation of the sperm due to contractions of the inner genitalia. This probably also applies to female animals of other animal species, and contractions in
9486-659: The size of a wolf) and Ichthyolestes (an early whale the size of a fox) were found in Pakistan. They were both archaeocetes ("ancient whales") from about 48 million years ago (in the Eocene). These findings showed that archaeocetes were more terrestrial than previously thought, and that the special construction of the talus (ankle bone) with a double-rolled joint surface, previously thought to be unique to even-toed ungulates, were also in early cetaceans. The mesonychians , another type of ungulate, did not show this special construction of
9588-637: The smallest hoofed mammals in the world. The Asian species weigh between 1–4 kg (2–9 lb), while the African chevrotain is considerably larger, at 7–16 kg (15–35 lb). With an average length of 45 cm (18 in) and an average height of 30 cm (12 in), the Java mouse-deer is the smallest surviving ungulate (hoofed) mammal, as well as the smallest artiodactyl (even-toed ungulate). Despite their common name of "mouse deer", they are not closely related to true deer. The word "chevrotain" comes from
9690-461: The supposed breeding group. Such low levels of genetic monogamy have surprised biologists and zoologists, forcing them to rethink the role of social monogamy in evolution. They can no longer assume social monogamy determines how genes are distributed in a species. The lower the rates of genetic monogamy among socially monogamous pairs, the less of a role social monogamy plays in determining how genes are distributed among offspring. The term polygamy
9792-516: The talus, and thus was concluded to not have the same ancestors as cetaceans. The oldest cetaceans date back to the early Eocene (53 million years ago), whereas the oldest known hippopotamus dates back only to the Miocene (15 million years ago). The hippopotamids are descended from the anthracotheres, a family of semiaquatic and terrestrial artiodactyls that appeared in the late Eocene, and are thought to have resembled small- or narrow-headed hippos. Research
9894-479: The term "mating system" is used to describe the ways in which animal societies are structured in relation to sexual behaviour. The mating system specifies which males mate with which females, and under what circumstances. There are four basic systems: Monogamy occurs when one male and one female mate exclusively with each other. A monogamous mating system is one in which individuals form long-lasting pairs and cooperate in raising offspring. These pairs may last for
9996-789: The timing of the common spawning is the only externally visible form of sexual behaviour. In areas with continuously high primary production , some species have a series of breeding seasons throughout the year. This is the case with most primates (who are primarily tropical and subtropical animals). Some animals ( opportunistic breeders ) breed dependent upon other conditions in their environment aside from time of year. Mating seasons are often associated with changes to herd or group structure, and behavioural changes, including territorialism amongst individuals. These may be annual (e.g. wolves ), biannual (e.g. dogs ) or more frequently (e.g. horses). During these periods, females of most mammalian species are more mentally and physically receptive to sexual advances,
10098-479: The traditional order Artiodactyla and infraorder Cetacea are sometimes subsumed into the more inclusive Cetartiodactyla taxon. An alternative approach is to include both land-dwelling even-toed ungulates and ocean-dwelling cetaceans in a revised Artiodactyla taxon. In the 1990s, biological systematics used not only morphology and fossils to classify organisms, but also molecular biology . Molecular biology involves sequencing an organism's DNA and RNA and comparing
10200-402: Was first discovered in 1909, it was thought mostly to influence a mother's labour contractions and milk let-down. Then, in the 1990s, research with prairie voles found that giving them a dose of oxytocin resulted in the formation of a bond with their future mate (Azar, 40)." Oxytocin has since been treated by the media as the sole player in the "love and mating game" in mammals. This view, however,
10302-426: Was hotly debated because ocean-dwelling cetaceans evolved from land-dwelling even-toed ungulates. Some semiaquatic even-toed ungulates ( hippopotamuses ) are more closely related to ocean-dwelling cetaceans than to other even-toed ungulates. Phylogenetic classification only recognizes monophyletic taxa; that is, groups that descend from a common ancestor and include all of its descendants. To address this problem,
10404-621: Was widely accepted by the end of the 20th century was: Suidae [REDACTED] Hippopotamidae [REDACTED] Tylopoda [REDACTED] Tragulidae [REDACTED] Pecora [REDACTED] Modern cetaceans are highly adapted sea creatures which, morphologically, have little in common with land mammals; they are similar to other marine mammals , such as seals and sea cows , due to convergent evolution . However, they evolved from originally terrestrial mammals. The most likely ancestors were long thought to be mesonychians—large, carnivorous animals from
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