Canids are found on all continents exceptAntarctica, having arrived independently or accompanied byhuman beings over extended periods of time. Canids vary in size from the 2-metre-long (6.6 ft)[citation needed] gray wolf to the 24-centimetre-long (9.4 in)[citation needed]fennec fox. The body forms of canids are similar, typically having long muzzles, upright ears, teeth adapted for cracking bones and slicing flesh, long legs, and bushy tails. They are mostlysocial animals, living together in family units or small groups and behaving co-operatively. Typically, only the dominant pair in a group breeds and a litter of young are reared annually in an undergroundden. Canids communicate byscent signals and vocalizations. One canid, the domestic dog,originated from asymbiotic relationship withUpper Paleolithic humans and is one of the most widely keptdomestic animals.
In the history of the carnivores, the family Canidae is represented by the two extinct subfamilies designated as Hesperocyoninae and Borophaginae, and the extant subfamily Caninae.[5] This subfamily includes all living canids and their most recent fossil relatives.[1] All living canids as a group form a dentalmonophyletic relationship with the extinct borophagines, with both groups having abicuspid (two points) on the lowercarnassialtalonid, which gives this tooth an additional ability inmastication. This, together with the development of a distinctentoconid cusp and the broadening of the talonid of the first lowermolar, and the corresponding enlargement of the talon of the upper first molar and reduction of itsparastyle distinguish these lateCenozoic canids and are the essential differences that identify their clade.[1]: p6
The Canidae are a diverse group of some 37 species ranging in size from the maned wolf with its long limbs to the short-legged bush dog. Modern canids inhabit forests, tundra, savannas, and deserts throughout tropical and temperate parts of the world. The evolutionary relationships between the species have been studied in the past usingmorphological approaches, but more recently, molecular studies have enabled the investigation ofphylogenetics relationships. In some species,genetic divergence has been suppressed by the high level ofgene flow between different populations and where the species have hybridized, largehybrid zones exist.[10]
Carnivorans evolved after theextinction of the non-avian dinosaurs 66 million years ago. Around 50 million years ago, or earlier, in thePaleocene, the Carnivora split into two main divisions:caniform (dog-like) andfeliform (cat-like). By 40 Mya, the first identifiable member of the dog family had arisen. NamedProhesperocyon wilsoni, its fossils have been found in southwest Texas. The chief features which identify it as a canid include the loss of the upper third molar (part of a trend toward a more shearing bite), and the structure of the middle ear which has an enlargedbulla (the hollow bony structure protecting the delicate parts of the ear).Prohesperocyon probably had slightly longer limbs than its predecessors, and also had parallel and closely touching toes which differ markedly from the splayed arrangements of the digits inbears.[11]
Canidae soon divided into three subfamilies, each of which diverged during the Eocene:Hesperocyoninae (about 39.74–15 Mya),Borophaginae (about 34–32 Mya), andCaninae (about 34–30 Mya; the only surviving subfamily). Members of each subfamily showed anincrease in body mass with time and some exhibited specializedhypercarnivorous diets that made them prone to extinction.[12]: Fig. 1
By theOligocene, all three subfamilies (Hesperocyoninae, Borophaginae, and Caninae) had appeared in the fossil record of North America. The earliest and most primitive branch of the Canidae was Hesperocyoninae, which included the coyote-sizedMesocyon of the Oligocene (38–24 Mya). These early canids probably evolved for the fast pursuit of prey in a grassland habitat; they resembled modernviverrids in appearance. Hesperocyonines eventually became extinct in the middle Miocene. One of the early Hesperocyonines, the genusHesperocyon, gave rise toArchaeocyon andLeptocyon. These branches led to the borophagine and canineradiations.[13]
Around 8 Mya, theBeringian land bridge allowed members of the genusEucyon a means to enter Asia from North America and they continued on to colonize Europe.[14]
TheCanis,Urocyon, andVulpes genera developed from canids fromNorth America, where the canine radiation began. The success of these canids was related to the development of lowercarnassials that were capable of bothmastication and shearing.[13] Around 5 million years ago, some of the Old WorldEucyon evolved into the first members ofCanis,[15] In thePliocene, around 4–5 Mya,Canis lepophagus appeared in North America. This was small and sometimes coyote-like. Others were wolf-like.C. latrans (the coyote) is theorized to descend fromC. lepophagus.[16]
The formation of theIsthmus of Panama, about 3 Mya, joinedSouth America to North America, allowing canids toinvade South America, where they diversified. However, the last common ancestor of the South American canids lived in North America some 4 Mya and more than one incursion across the new land bridge is likely given the fact that more than one lineage is present in South America. Two North American lineages found in South America are thegray fox (Urocyon cinereoargentus) and the now-extinctdire wolf (Aenocyon dirus). Besides these, there are species endemic to South America: themaned wolf (Chrysocyon brachyurus), theshort-eared dog (Atelocynus microtis), thebush dog (Speothos venaticus), thecrab-eating fox (Cerdocyon thous), and theSouth American foxes (Lycalopexspp.). The monophyly of this group has been established by molecular means.[14]
During thePleistocene, the North American wolf line appeared, withCanis edwardii, clearly identifiable as a wolf, andCanis rufus appeared, possibly a direct descendant ofC. edwardii. Around 0.8 Mya,Canis ambrusteri emerged in North America. A large wolf, it was found all over North and Central America and was eventually supplanted by the dire wolf, which then spread into South America during the Late Pleistocene.[17]
By 0.3 Mya, a number of subspecies of the gray wolf (C. lupus) had developed and had spread throughout Europe and northern Asia.[18] The gray wolf colonized North America during the lateRancholabrean era across the Bering land bridge, with at least three separate invasions, with each one consisting of one or more different Eurasian gray wolf clades.[19] MtDNA studies have shown that there are at least four extantC. lupus lineages.[20] The dire wolf shared its habitat with the gray wolf, but became extinct in a large-scale extinction event that occurred around 11,500 years ago. It may have been more of a scavenger than a hunter; its molars appear to be adapted for crushing bones and it may have gone extinct as a result of the extinction of the large herbivorous animals on whose carcasses it relied.[17]
In 2015, a study of mitochondrial genome sequences and whole-genome nuclear sequences of African and Eurasian canids indicated that extant wolf-like canids have colonized Africa from Eurasia at least five times throughout the Pliocene and Pleistocene, which is consistent with fossil evidence suggesting that much of African canid fauna diversity resulted from the immigration of Eurasian ancestors, likely coincident with Plio-Pleistocene climatic oscillations between arid and humid conditions. When comparing the African and Eurasian golden jackals, the study concluded that the African specimens represented a distinct monophyletic lineage that should be recognized as a separate species,Canis anthus (African golden wolf). According to a phylogeny derived from nuclear sequences, the Eurasian golden jackal (Canis aureus) diverged from the wolf/coyote lineage 1.9 Mya, but the African golden wolf separated 1.3 Mya. Mitochondrial genome sequences indicated the Ethiopian wolf diverged from the wolf/coyote lineage slightly prior to that.[21]: S1
Wild canids are native to all continents except Australasia and Antarctica, and also occur asferal (human-introduced) in New Guinea and Australia. They inhabit a wide range of different habitats, includingdeserts,mountains,forests, andgrasslands. They vary in size from the fennec fox, which may be as little as 24 cm (9.4 in) in length and weigh 0.6 kg (1.3 lb),[22] to the graywolf, which may be up to 160 cm (63 in) long, and can weigh up to 79 kg (174 lb).[23] Only a few species arearboreal—thegray fox, the closely relatedisland fox[24] and theraccoon dog habitually climb trees.[25][26][27]
All canids have a similar basic form, as exemplified by the gray wolf, although the relative length of muzzle, limbs, ears, and tail vary considerably between species. With the exceptions of the bush dog, the raccoon dog and some domesticdog breeds, canids have relatively long legs and lithe bodies, adapted for chasing prey. The tails are bushy and the length and quality of the pelage vary with the season. The muzzle portion of the skull is much more elongated than that of the cat family. Thezygomatic arches are wide, there is a transverselambdoidal ridge at the rear of thecranium and in some species, asagittal crest running from front to back. The bony orbits around the eye never form a complete ring and the auditory bullae are smooth and rounded.[28] Females have three to seven pairs ofmammae.[29]
All canids aredigitigrade, meaning they walk on their toes. Thetip of the nose is always naked, as are the cushioned pads on the soles of the feet. These latter consist of a single pad behind the tip of each toe and a more-or-less three-lobed central pad under the roots of the digits. Hairs grow between the pads and in the Arctic fox the sole of the foot is densely covered with hair at some times of the year. With the exception of the four-toedAfrican wild dog (Lycaon pictus), five toes are on the forefeet, but the pollex (thumb) is reduced and does not reach the ground. On the hind feet are four toes, but in some domestic dogs, a fifth vestigial toe, known as adewclaw, is sometimes present, but has no anatomical connection to the rest of the foot. In some species, slightly curved nails are non-retractile and more-or-less blunt[28] while other species have sharper, partially-retractile claws.[citation needed]
Thecanine penis contains abaculum and a structure called thebulbus glandis that expands duringcopulation, forming acopulatory tie that lasts for up to an hour.[30] Young canids are born blind, with their eyes opening a few weeks after birth.[31] All living canids (Caninae) have a ligament analogous to thenuchal ligament ofungulates used to maintain the posture of the head and neck with little active muscle exertion; this ligament allows them to conserve energy while running long distances following scent trails with their nose to the ground. However, based on skeletal details of the neck, at least some of the Borophaginae (such asAelurodon) are believed to have lacked this ligament.[32]
Dentition relates to the arrangement of teeth in the mouth, with thedental notation for the upper-jaw teeth using the upper-case letters I to denoteincisors, C forcanines, P forpremolars, and M formolars, and the lower-case letters i, c, p and m to denote themandible teeth. Teeth are numbered using one side of the mouth and from the front of the mouth to the back. Incarnivores, the upper premolar P4 and the lower molar m1 form thecarnassials that are used together in a scissor-like action to shear the muscle and tendon of prey.[33]
Canids use their premolars for cutting and crushing except for the upper fourth premolar P4 (the upper carnassial) that is only used for cutting. They use their molars for grinding except for the lower first molar m1 (the lower carnassial) that has evolved for both cutting and grinding depending on the canid's dietary adaptation. On the lower carnassial, thetrigonid is used for slicing and thetalonid is used for grinding. The ratio between the trigonid and the talonid indicates a carnivore's dietary habits, with a larger trigonid indicating ahypercarnivore and a larger talonid indicating a moreomnivorous diet.[34][35] Because of its low variability, the length of the lower carnassial is used to provide an estimate of a carnivore's body size.[34]
A study of the estimated bite force at the canine teeth of a large sample of living and fossil mammalian predators, when adjusted for their body mass, found that forplacental mammals the bite force at the canines was greatest in the extinct dire wolf (163), followed among the modern canids by the four hypercarnivores that often prey on animals larger than themselves: the African wild dog (142), the gray wolf (136), thedhole (112), and thedingo (108). The bite force at the carnassials showed a similar trend to the canines. A predator's largest prey size is strongly influenced by its biomechanical limits.[36]
Most canids have 42teeth, with adental formula of:3.1.4.23.1.4.3. The bush dog has only one upper molar with two below, the dhole has two above and two below. and thebat-eared fox has three or four upper molars and four lower ones.[28] The molar teeth are strong in most species, allowing the animals to crack open bone to reach themarrow. The deciduous, or baby teeth, formula in canids is3.1.33.1.3, molars being completely absent.[28]
Almost all canids are social animals and live together in groups. In general, they are territorial or have a home range and sleep in the open, using their dens only for breeding and sometimes in bad weather.[37] In most foxes, and in many of the true dogs, amale and female pair work together to hunt and to raise their young. Gray wolves and some of the other larger canids live in larger groups calledpacks. African wild dogs have packs which may consist of 20 to 40 animals and packs of fewer than about seven individuals may be incapable of successful reproduction.[38] Hunting in packs has the advantage that larger prey items can be tackled. Some species form packs or live in small family groups depending on the circumstances, including the type of available food. In most species, some individuals live on their own. Within a canid pack, there is a system of dominance so that the strongest, most experienced animals lead the pack. In most cases, the dominant male and female are the only pack members to breed.[39]
Canids as a group exhibit several reproductive traits that are uncommon among mammals as a whole. They are typicallymonogamous, provide paternal care to their offspring, have reproductive cycles with lengthyproestral anddioestral phases and have a copulatory tie during mating. They also retain adult offspring in the social group, suppressing the ability of these to breed while making use of thealloparental care they can provide to help raise the next generation.[47] Most canid species are spontaneous ovulators,[48] thoughmaned wolves areinduced ovulators.[49]
During the proestral period, increased levels ofestradiol make the female attractive to the male. There is a rise inprogesterone during the estral phase when female is receptive. Following this, the level of estradiol fluctuates and there is a lengthy dioestrous phase during which the female is pregnant.Pseudo-pregnancy often occurs in canids that have ovulated but failed to conceive. A period ofanestrus follows pregnancy or pseudo-pregnancy, there being only one oestral period during each breeding season. Small and medium-sized canids mostly have agestation of 50 to 60 days, while larger species average 60 to 65 days. The time of year in which the breeding season occurs is related to the length of day, as has been shown for several species that have been moved across the equator and experiences a six-month shift of phase. Domestic dogs and certain small canids in captivity may come into oestrus more often, perhaps because thephotoperiod stimulus breaks down under conditions of artificial lighting.[47] Canids have an oestrus period of 1 to 20 days, lasting one week in most species.[50]
The size of a litter varies, with from one to 16 or more pups being born. The young are born small, blind and helpless and require a long period of parental care. They are kept in a den, most often dug into the ground, for warmth and protection.[28] When the young begin eating solid food, both parents, and often other pack members, bring food back for them from the hunt. This is most often vomited up from the adult's stomach. Where such pack involvement in the feeding of the litter occurs, the breeding success rate is higher than is the case where females split from the group and rear their pups in isolation.[51] Young canids may take a year to mature and learn the skills they need to survive.[52] In some species, such as the African wild dog, male offspring usually remain in the natal pack, while females disperse as a group and join another small group of the opposite sex to form a new pack.[53]
One canid, thedomestic dog, entered into a partnership with humans a long time ago. The dog was the first domesticated species.[54][55][56][57] The archaeological record shows the first undisputed dog remains buried beside humans 14,700 years ago,[58] with disputed remains occurring 36,000 years ago.[59] These dates imply that the earliest dogs arose in the time of humanhunter-gatherers and notagriculturists.[60][61]
The fact that wolves are pack animals with cooperative social structures may have been the reason that the relationship developed. Humans benefited from the canid's loyalty, cooperation, teamwork, alertness and tracking abilities, while the wolf may have benefited from the use of weapons to tackle larger prey and the sharing of food. Humans and dogs may have evolved together.[62]
Among canids, only the gray wolf has widely been known to prey on humans.[63][page needed] Nonetheless, at leasttwo records of coyotes killing humans have been published,[64] and at least two other reports of golden jackals killing children.[65] Human beings have trapped and hunted some canid species for their fur and some, especially the gray wolf, the coyote and the red fox, for sport.[66] Canids such as thedhole are nowendangered in the wild because of persecution, habitat loss, a depletion of ungulate prey species and transmission of diseases from domestic dogs.[67]
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^Solé, Floréal; Smith, Thierry; De Bast, Eric; Codrea, Vlad; Gheerbrant, Emmanuel (3 March 2016). "New carnivoraforms from the latest Paleocene of Europe and their bearing on the origin and radiation of Carnivoraformes (Carnivoramorpha, Mammalia)".Journal of Vertebrate Paleontology.36 (2) e1082480.Bibcode:2016JVPal..36E2480S.doi:10.1080/02724634.2016.1082480.ISSN0272-4634.
^Kauhala, K.; Saeki, M. (2004). Raccoon Dog«. Canid Species Accounts. IUCN/SSC Canid Specialist Group. Pridobljeno 15 April 2009.
^Ikeda, Hiroshi (August 1986). "Old dogs, new tricks: Asia's raccoon dog, a venerable member of the canid family is pushing into new frontiers".Natural History.95 (#8): 40, 44.
^Liane Giemsch, Susanne C. Feine, Kurt W. Alt, Qiaomei Fu, Corina Knipper, Johannes Krause, Sarah Lacy, Olaf Nehlich, Constanze Niess, Svante Pääbo, Alfred Pawlik, Michael P. Richards, Verena Schünemann, Martin Street, Olaf Thalmann, Johann Tinnes, Erik Trinkaus & Ralf W. Schmitz. "Interdisciplinary investigations of the late glacial double burial from Bonn-Oberkassel". Hugo Obermaier Society for Quaternary Research and Archaeology of the Stone Age: 57th Annual Meeting in Heidenheim, 7th – 11 April 2015, 36–37
^Germonpre, M. (2009). "Fossil dogs and wolves from Palaeolithic sites in Belgium, the Ukraine and Russia: Osteometry, ancient DNA and stable isotopes".Journal of Archaeological Science.36 (#2):473–490.Bibcode:2009JArSc..36..473G.doi:10.1016/j.jas.2008.09.033.
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