Canids are found on all continents except Antarctica, having arrived independently or accompanied by human beings over extended periods of time.

Typically, only the dominant pair in a group breeds and a litter of young are reared annually in an underground den.

[1]: 7 This cladogram shows the phylogenetic position of canids within Caniformia, based on fossil finds:[1] (bears, procyonids, pinnipeds, etc.)

(Mesocyon, Enhydrocyon, Hesperocyon, and other basal canines, e.g. Cynodictis) (Aelurodon, cynarctins, and others) (all modern canids and extinct relatives) 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.

Around 50 million years ago, or earlier, in the Paleocene, the Carnivora split into two main divisions: caniform (dog-like) and feliform (cat-like).

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 in bears.

Members of each subfamily showed an increase in body mass with time and some exhibited specialized hypercarnivorous diets that made them prone to extinction.[10]: Fig.

These early canids probably evolved for the fast pursuit of prey in a grassland habitat; they resembled modern viverrids in appearance.

[11] Around 8 Mya, the Beringian land bridge allowed members of the genus Eucyon a means to enter Asia from North America and they continued on to colonize Europe.

[12] The Canis, Urocyon, and Vulpes genera developed from canids from North America, where the canine radiation began.

Two North American lineages found in South America are the gray fox (Urocyon cinereoargentus) and the now-extinct dire wolf (Aenocyon dirus).

[15] By 0.3 Mya, a number of subspecies of the gray wolf (C. lupus) had developed and had spread throughout Europe and northern Asia.

[19]: S1 Wild canids are found on every continent except Antarctica, and inhabit a wide range of different habitats, including deserts, mountains, forests, and grasslands.

[23][24][25] 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.

The zygomatic arches are wide, there is a transverse lambdoidal ridge at the rear of the cranium and in some species, a sagittal crest running from front to back.

With the exception of the four-toed African wild dog (Lycaon pictus), five toes are on the forefeet, but the pollex (thumb) is reduced and does not reach the ground.

[citation needed] The canine penis contains a baculum and a structure called the bulbus glandis that expands during copulation, forming a copulatory tie that lasts for up to an hour.

In carnivores, the upper premolar P4 and the lower molar m1 form the carnassials that are used together in a scissor-like action to shear the muscle and tendon of prey.

[32] 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 for placental 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), the dhole (112), and the dingo (108).

[26] The molar teeth are strong in most species, allowing the animals to crack open bone to reach the marrow.

Some species form packs or live in small family groups depending on the circumstances, including the type of available food.

[37] Canids communicate with each other by scent signals, by visual clues and gestures, and by vocalizations such as growls, barks, and howls.

They are typically monogamous, provide paternal care to their offspring, have reproductive cycles with lengthy proestral and dioestral 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 the alloparental care they can provide to help raise the next generation.

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 the photoperiod stimulus breaks down under conditions of artificial lighting.

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.

[63] 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.

[64] Canids such as the dhole are now endangered in the wild because of persecution, habitat loss, a depletion of ungulate prey species and transmission of diseases from domestic dogs.