Canis is agenus of theCaninae which includes multipleextant species, such aswolves,dogs,coyotes, andgolden jackals. Species of this genus are distinguished by their moderate to large size, their massive, well-developed skulls and dentition, long legs, and comparatively short ears and tails.[3]
Canis is primitive relative toCuon,Lycaon, andXenocyon in its relatively larger canines and lack of such dental adaptations for hypercarnivory as m1–m2 metaconid and entoconid small or absent; M1–M2 hypocone small; M1–M2 lingual cingulum weak; M2 and m2 small, may be single-rooted; m3 small or absent; and wide palate.
In 2019, a workshop hosted by theIUCN/SSC Canid Specialist Group recommends that because DNA evidence shows theside-striped jackal (Canis adustus) andblack-backed jackal (Canis mesomelas) to form a monophyletic lineage that sits outside of theCanis/Cuon/Lycaon clade, that they should be placed in a distinct genus,Lupulella Hilzheimer, 1906 with the namesLupulella adusta andLupulella mesomelas.[11]
The fossil record shows thatfeliforms andcaniforms emerged within the cladeCarnivoramorpha 43 millionYBP.[12] The caniforms included the fox-like genusLeptocyon, whose various species existed from 24 million YBP before branching 11.9 million YBP intoVulpes (foxes) and Canini (canines). The jackal-sizedEucyon existed in North America from 10 million YBP and by theEarly Pliocene about 6-5 million YBP the coyote-likeEucyon davisi[13] invaded Eurasia. The canids that had emigrated from North America to Eurasia –Eucyon,Vulpes, andNyctereutes – were small to medium-sized predators during the Late Miocene and Early Pliocene but they were not the top predators.
Skulls of dire wolf (Aenocyon dirus), gray wolf (C. lupus), eastern wolf (C. lycaon), red wolf (C. rufus), coyote (C. latrans), African golden wolf (C. lupaster), golden jackal (C. aureus) and black-backed jackal (Lupulella mesomelas)
ForCanis populations in the New World,Eucyon in North America gave rise to early North AmericanCanis which first appeared in theMiocene (6 million YBP) in south-western United States and Mexico. By 5 million YBP the largerCanis lepophagus, ancestor of wolves and coyotes, appeared in the same region.[1]: p58
Around 5 million years ago, some of the Old WorldEucyon evolved into the first members ofCanis,[14] and the position of the canids would change to become a dominant predator across thePalearctic. The wolf-sizedC. chihliensis appeared in northern China in the Mid-Pliocene around 4-3 million YBP. This was followed by an explosion ofCanis evolution across Eurasia in the Early Pleistocene around 1.8 million YBP in what is commonly referred to as thewolf event. It is associated with the formation of themammoth steppe and continental glaciation.Canis spread to Europe in the forms ofC. arnensis,C. etruscus, andC. falconeri.[1]: p148
However, a 2021 genetic study of thedire wolf (Aenocyon dirus), previously considered a member ofCanis, found that it represented the last member of an ancient lineage of canines originally indigenous to the New World that had diverged prior to the appearance ofCanis, and that its lineage had been distinct since the Miocene with no evidence of introgression withCanis. The study hypothesized that theNeogene canids in the New World,Canis armbrusteri andCanis edwardii, were possibly members of the distinct dire wolf lineage that hadconvergently evolved a very similar appearance to members ofCanis. True members ofCanis, namely thegray wolf andcoyote, likely only arrived in the New World during theLate Pleistocene, where their dietary flexibility and/or ability to hybridize with other canids allowed them to survive theQuaternary extinction event, unlike the dire wolf.[14]
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.[1]: 74
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 candid'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.[18][19] Because of its low variability, the length of the lower carnassial is used to provide an estimate of a carnivore's body size.[18]
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 (inNewtons/kilogram of body weight) was greatest in the extinctdire wolf (163), followed among the moderncanids by the four hypercarnivores that often prey on animals larger than themselves: the African hunting dog (142), the gray wolf (136), the dhole (112), and the dingo (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.[20]
There is little variance among male and female canids. Canids tend to live as monogamous pairs. Wolves,coyotes, andjackals live in groups that includebreeding pairs and their offspring. Wolves may live in extended family groups. To take prey larger than themselves gray wolves depend on their jaws as they cannot use their forelimbs to grapple with prey. They work together as a pack consisting of an alpha pair and their offspring from the current and previous years.[21] Social mammal predators prey on herbivores with a body mass similar to that of the combined mass of the predator pack.[22][23] The gray wolf specializes in preying on the vulnerable individuals of large prey,[24] and a pack of timber wolves can bring down a 500 kg (1,100 lb) moose.[25][26]
The genusCanis contains many different species and has a wide range of different mating systems that varies depending on the type of canine and the species.[27] In a study done in 2017, it was found that in some species of canids females use their sexual status to gain food resources. The study looked at wolves and dogs.Wolves are typicallymonogamous and formpair-bonds; whereas dogs are promiscuous when free-range and mate with multiple individuals. The study found that in both species females tried to gain access to food more and were more successful in monopolizing a food resource when in heat. Outside of the breeding season their efforts were not as persistent or successful. This shows that the food-for-sex hypothesis likely plays a role in the food sharing among canids and acts as a direct benefit for the females.[27]
Another study onfree-ranging dogs found that social factors played a significant role in the determination of mating pairs. The study, done in 2014, looked at social regulation of reproduction in the dogs.[28] They found that females inheat searched outdominant males and were more likely to mate with a dominant male who appeared to be a quality leader. The females were more likely to reject submissive males. Furthermore, cases ofmale-male competition were more aggressive in the presence of high ranking females. This suggests that females prefer dominant males and males prefer high ranking females meaning social cues and status play a large role in the determination of mating pairs in dogs.[28]
Canids also show a wide range ofparental care and in 2018 a study showed thatsexual conflict plays a role in the determination ofintersexual parental investment.[29] The studied looked atcoyote mating pairs and found that paternal investment was increased to match or near match the maternal investment. The amount of parental care provided by the fathers also was shown to fluctuated depending on the level of care provided by the mother.
Another study on parental investment showed that in free-ranging dogs, mothers modify their energy and time investment into their pups as they age.[30] Due to the high mortality of free-range dogs at a young age a mother's fitness can be drastically reduced. This study found that as the pups aged the mother shifted from high-energy care to lower-energy care so that they can care for their offspring for a longer duration for a reduced energy requirement. By doing this the mothers increasing the likelihood of their pups surviving infancy and reaching adulthood and thereby increase their own fitness.
A study done in 2017 found that aggression between male and female gray wolves varied and changed with age.[31] Males were more likely to chase away rival packs and lone individuals than females and became increasingly aggressive with age. Alternatively, females were found to be less aggressive and constant in their level of aggression throughout their life. This requires further research but suggests that intersexual aggression levels ingray wolves relates to theirmating system.
Dentition of a wolf showing functions of the teeth.
Tooth breakage is a frequent result of carnivores' feeding behaviour.[32] Carnivores include bothpack hunters and solitary hunters. The solitary hunter depends on a powerful bite at the canine teeth to subdue their prey, and thus exhibits a strongmandibular symphysis. In contrast, a pack hunter, which delivers many shallower bites, has a comparably weaker mandibular symphysis. Thus, researchers can use the strength of the mandibular symphysis in fossil carnivore specimens to determine what kind of hunter it was – a pack hunter or a solitary hunter – and even how it consumed its prey. The mandibles of canids are buttressed behind the carnassial teeth to crack bones with their post-carnassial teeth (molars M2 and M3). A study found that the modern gray wolf and the red wolf (C.rufus) possess greater buttressing than all other extant canids and the extinct dire wolf. This indicates that these are both better adapted for cracking bone than other canids.[33]
A study of nine modern carnivores indicate that one in four adults had suffered tooth breakage and that half of these breakages were of the canine teeth. The highest frequency of breakage occurred in the spotted hyena, which is known to consume all of its prey including the bone. The least breakage occurred in theAfrican wild dog. The gray wolf ranked between these two.[32][34] The eating of bone increases the risk of accidental fracture due to the relatively high, unpredictable stresses that it creates. The most commonly broken teeth are the canines, followed by the premolars, carnassial molars, and incisors. Canines are the teeth most likely to break because of their shape and function, which subjects them to bending stresses that are unpredictable in direction and magnitude.[34] The risk of tooth fracture is also higher when taking and consuming large prey.[34][35]
In comparison to extant gray wolves, the extinctBeringian wolves included many more individuals with moderately to heavily worn teeth and with a significantly greater number of broken teeth. The frequencies of fracture ranged from a minimum of 2% found in theNorthern Rocky Mountain wolf(Canis lupus irremotus) up to a maximum of 11% found in Beringian wolves. The distribution of fractures across the tooth row also differs, with Beringian wolves having much higher frequencies of fracture for incisors, carnassials, and molars. A similar pattern was observed in spotted hyenas, suggesting that increased incisor and carnassial fracture reflects habitual bone consumption because bones are gnawed with the incisors and then cracked with the carnassials and molars.[36]
Thegray wolf (C. lupus), theEthiopian wolf (C. simensis),eastern wolf (C. lycaon), and theAfrican golden wolf (C. lupaster) are four of the manyCanis species referred to as "wolves".[37] Species that are too small to attract the word "wolf" are calledcoyotes in theAmericas andjackals elsewhere.[38] Although these may not be more closely related to each other than they are toC. lupus, they are, as fellowCanis species, more closely related to wolves and domestic dogs than they are tofoxes,maned wolves, or other canids which do not belong to the genusCanis. The word "jackal" is applied to the golden jackal (C. aureus), found across southwestern and south-central Asia, andthe Balkans in Europe.[39]
The first record ofCanis on the African continent isCanis sp. A from South Turkwel, Kenya, dated 3.58–3.2 million years ago.[40] 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 colonised Africa from Eurasia at least 5 times throughout thePliocene andPleistocene, which is consistent with fossil evidence suggesting that much of the African canid fauna diversity resulted from the immigration of Eurasian ancestors, likely coincident withPlio-Pleistocene climatic oscillations between arid and humid conditions.[41]: S1 In 2017, the fossil remains of a newCanis species, namedCanis othmanii, was discovered among remains found at Wadi Sarrat, Tunisia, from deposits that date 700,000 years ago. This canine shows a morphology more closely associated with canids from Eurasia instead of Africa.[42]
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^Van Valkenburgh, Blaire; Sacco, Tyson (2002). "Sexual dimorphism, social behavior, and intrasexual competition in large Pleistocene carnivorans".Journal of Vertebrate Paleontology.22:164–169.doi:10.1671/0272-4634(2002)022[0164:SDSBAI]2.0.CO;2.S2CID86156959.
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