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In biological classification, Canidae (/ˈkænɪdiː/; from Latin, canis, "dog") is a taxonomic rank, as well as a taxonomic unit. The family includes three subfamilies: the extant Caninae and the extinct Borophaginae and Hesperocyoninae. The Caninae are known as canines, and include domestic dogs, wolves, coyotes, foxes, jackals and other extant and extinct species.

There are 13 genera and 36 species of canids in the world. Including dogs, wolves, jackals, foxes, etc. The body is medium and well-proportioned, with slender limbs and toes, which is good for fast running. The head and palate are pointed, the face is long, the nose is prominent, the ears are pointed and erect, the sense of smell is sensitive, and the sense of hearing is well developed. Canines and cleft teeth are well developed; upper molars have distinct cusps, and lower molars have a small cusp and heel cusp on the inner side; the diameter of the molar crown is larger than the height of the outer incisor; the tooth type is . The hair is thick and long, and generally has no pattern. The forefoot has 4-5 toes, and the rear foot generally has 4 toes; the claws are thick and blunt, and cannot be stretched or stretched slightly. The tail is hairy and generally more developed. The body structure has evolved to be especially suitable for hunting life.

Good at fast and long-distance running, likes to live in groups, and often chases and preys. Most carnivores feed on herbivores and rodents; some eat carrion, plants or omnivores. Dogs (domestic dogs) are one of the earliest livestock domesticated by humans. They were first domesticated from gray wolves, jackals, jackals, etc. (multiple origins), and now there are more than 200 varieties. Red foxes, arctic foxes, and raccoon dogs are precious fur animals. Canidae is the most widely distributed family of Carnivora, except for a few islands and Antarctica, it covers almost the entire distribution range of terrestrial carnivores.

Scientific classification

Subphylum Vertebrata

History Of Species

The fossil record of canids dates back to the Oligocene and Miocene epochs, making them one of the oldest groups of carnivores in existence.  Canines include foxes, wolves, jackals, and dogs, with 36 species in the family. live all over the world. Among carnivores, dogs are more closely related to bears and weasels than to felines, civet cats, mongooses and hyenas. Canidae were originally endemic to North America, and fossils indicate widespread fossilization during the Late Eocene (about 35 million years ago) and Late Miocene (about 10 million years ago). In the Old World, the earliest fossils are from the Late Miocene of Spain. Then, around 9 million years ago, canids migrated and spread into Eurasia, 4-5 million years ago into Africa, and 2 million years ago into South America.

Carnivoramorpha appeared 43 million years ago. The species in these classifications branched from 34,000,000 to 11,900,000 years ago, and animals of the genera Vulpes and Canis appeared. Jackals existed in North America before 10000000 years ago, and in the early Pliocene about 6000000-5000000 years ago, hyenas invaded Eurasia. Miocene (6,000,000 years ago), in North America, early Canis appeared in the southwestern United States and Mexico. In 500,000 years, the larger Canis lepophagus appeared in the same area.

Wolves originated in the New World about 5,000,000 years ago in the middle of the Pleistocene, and differentiated and developed in the middle of the Pleistocene 1,500,000 years ago. About 65 million years ago, in the late Cretaceous period of the Mesozoic Era, the sudden extinction of dinosaurs gave mammals an excellent opportunity to flourish. In the following 10,000,000 years, as the curtain of the Cenozoic Era gradually opened, various small mammals stepped onto the stage of evolutionary history one after another.

In the Cenozoic Eocene, about 50 million years ago, the common ancestor of modern carnivores began to appear. Marked by the appearance of Miacis, carnivores officially embarked on a long evolutionary road.

The ancestors of the genus Canis can be traced back to the Eocene Epoch 50 million years ago. At that time, there was a small-tailed, long-tailed, and good-running carnivore, the Sertodon, living on the earth. It is the primitive ancestor of all canids. At the end of the Eocene and the beginning of the Cenocene 40,000,000 years ago, the Xenotodon diverged into several branches, one of which developed into a "dog". Later, it evolved into Cynodesmus in the Pliocene, and Tang's bear in the Pliocene. After several million years of development and changes, they further differentiated and developed into modern canids such as wolves, foxes, and raccoon dogs.

The canines originated in the late Eocene, about 40,000,000 years ago, they were the oldest group of carnivores, and they were first differentiated from the kittens. There are three main lines of canine evolution, namely the three subfamilies of the family Canidae: Modern Canisinae, Ancient Canisinae and Dinosaurinae (hyena-like canids). The ancient canine subfamily is an ancient branch of the canine family. It originated and developed in North America 40,000,000 years ago. They look like a cross between a fox and a weasel. About 15,000,000 years ago, this branch gradually became extinct, and the Thomsonii genus evolved into the Dinosaur subfamily and survived. The subfamily Dinosauria appeared 34,000,000 years ago. Like the ancient canines, they are only found in North America. Their size is much larger than that of the ancient canine subfamily, and their appearance is between hyenas and dogs. A large and powerful mouth is their characteristic. 2,500,000 years ago this line also became extinct.

The last branch, the modern canis, evolved into all canids. This branch appeared almost at the same time as the other two, but it did not flourish until 15,000,000 years ago, when the other two began to decline, and then began to grow. This subfamily also existed only in North America until 7,000,000 years ago, in the late Miocene, when it came to Asia via a land bridge. Those that crossed the bridge became the direct ancestors of the present-day canids, which went on to cross the bridge and migrate back and forth between the two continents. This is why red foxes and gray wolves are found in Eurasia and North America.


Wild canids are found on every continent except Antarctica, and inhabit a wide range of different habitats, including deserts, mountains, forests, and grasslands. 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), to the gray wolf, which may be up to 160 cm (5.2 ft) long, and can weigh up to 79 kg (174 lb). Only a few species are arboreal—the gray fox, the closely related island fox and the raccoon dog habitually climb trees.

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 domestic dog 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. 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. The bony orbits around the eye never form a complete ring and the auditory bullae are smooth and rounded. Females have three to seven pairs of mammae.Skeleton of a black-backed jackal (Lupulella mesomelas) on display at the Museum of OsteologyAll canids are digitigrade, meaning they walk on their toes. The tip 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-toed African 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 a dewclaw, 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 while other species have sharper, partially-retractile claws.[citation needed]

The penis in male canids is supported by a baculum and contains a structure called the bulbus glandis, which creates a copulatory tie that lasts for up to an hour during mating. Young canids are born blind, with their eyes opening a few weeks after birth. All living canids (Caninae) have a ligament analogous to the nuchal ligament of ungulates 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 as Aelurodon) are believed to have lacked this ligament.

Canidae is a medium-sized carnivore with a strong body shape, slender limbs, good at running, long face, protruding snout, thick and long tail, and generally thick and fluffy tail hair. The coat is dense, the coat color is single or slightly spotted, and a few genera have discoloration (such as white fox in winter and blue-gray in summer). Jackals and gray foxes have some bright colors in their fur, raccoon dogs have black masks, African wild dogs have black, yellow, and white spots on their bodies, and most species have a lighter belly. In desert species, the ears are pointed, erect, and usually quite large. In addition to detecting sound, large ears are thought to function as heat regulators in species such as the great-eared fox, allowing more heat to be dissipated in hot climates. Arctic fox ears tend to be much smaller, providing less heat loss in areas where heat conservation is important for survival.

Most canids have longer legs, especially the maned wolf of South America. This feature makes canines great for running, as does the fact that they walk on their toes. Canines have extraordinary stamina, but cannot burst out with great speed. In winter, northern species often grow fur on the foot pads to provide traction and protection from the cold on snow. Except for the African hunting dog, all dogs have four well-developed toes, 5 on the front foot and 4 on the hind foot; There is also a claw (a degenerated fifth digit that occurs on the feet of most mammals, reptiles, and birds) lacking a toe claw. Each toe is enclosed by a blunt non-retractable claw (i.e., no sheath to extract), which is blunt and non-retractable. With scent glands and anal glands, body odor glands are usually born at the base of the tail and are used to mark territory.

Most canines have 42 teeth, with non-specialized incisors, and canines are thick, with well-developed clefts, which are used to kill prey. The premolars are narrow and sharp, and the carcass is well developed. Molars form broad surfaces that can crush bone.


Dentition relates to the arrangement of teeth in the mouth, with the dental notation for the upper-jaw teeth using the upper-case letters I to denote incisors, C for canines, P for premolars, and M for molars, and the lower-case letters i, c, p and m to denote the mandible teeth. Teeth are numbered using one side of the mouth and from the front of the mouth to the back. 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.

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, the trigonid is used for slicing and the talonid is used for grinding. The ratio between the trigonid and the talonid indicates a carnivore's dietary habits, with a larger trigonid indicating a hypercarnivore and a larger talonid indicating a more omnivorous diet. Because of its low variability, the length of the lower carnassial is used to provide an estimate of a carnivore's body size.

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). 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.


There are native members of the canine family on every continent except Antarctica and Australia. The dingo in Australia was introduced by humans, albeit thousands of years ago. Canines are absent from New Zealand and most oceanic islands. Every major ecosystem is populated by some canine species. For example, arctic foxes occupy the barren tundra of the Arctic, while fennec foxes inhabit the Sahara desert. In general, however, canines tend to be animals that live in open or grassy areas. The rare serval dog of South America is restricted to forests and wet savannas; the raccoon dog usually lives in tree cavities with entrances close to the ground. Gray foxes prefer wooded areas and will climb trees, while red foxes tend to occupy grasslands and farmland. So, in the North American regions where these foxes exist, they occupy a slightly different ecological niche.


Among the living families in the order Carnivora, the Canidae are the mostancient. The family arose in the late Eocene, when no other living families of car-nivorans had yet emerged (two archaic families, Miacidae and Viverravidae, havea much older history but none survive to the present time). Furthermore,canids still maintain many features that are primitive among all carnivorans, tothe extent that dog skulls are often used to illustrate a generalized mammal in zoological classrooms. Dentally, canids are closest to the ancestral morphotype ofCarnivora. Canids have a relatively unreduced dental formula of 3142/3143(numbers in sequence represent incisors, canines, premolars and molars in theupper (left half before the oblique) and the lower (right half after the oblique)teeth). These are relatively unmodified tribosphenic molars except for the mor-phology of the carnassials (P4, m1), which are typical of all carnivorans. In con-trast, all other carnivoran families generally have a more reduced dental formulaand highly modified cusp patterns.

From this mesocarnivorous (moderately carnivorous) conservative plan,canids generally evolved toward a hypercarnivorous (highly carnivorous) orhypocarnivorous (slightly carnivorous) dental pattern. In the hypercarnivorouspattern (Fig. 1.3B, D) there is a general tendency for the size of the carnassial pairto be enlarged at the expense of the molars behind (see also Enhydrocyon,Aelurodon,Borophagus and Cuon in Fig. 1.4). This modification increases the efficiency of car-nassial shear. A hypocarnivorous pattern (Fig. 1.3A, C) is the opposite, with devel-opment of the grinding part of the dentition (molars) at the expense of carnassialshear (see also Cynarctoides,Phlaocyon and Cynarctus in Fig. 1.4). This configurationwas only possible in the sister-taxa Borophaginae and Caninae, which share abicuspid m1 talonid (Fig. 1.3C). One of the major trends in canid evolution is therepeated development of hyper- and hypocarnivorous forms (see below).


The subfamily Hesperocyoninae is the first major clade (a clade refers to a naturalgroup of organisms that share a common ancestry) with a total of 28 species (Fig.1.4). Its earliest members are species of the small fox-like form, Hesperocyon, thatfirst appeared in the late Eocene (40–37 Ma) (Bryant, 1992) and became abun-dant in the latest Eocene. By the Oligocene (34–30 Ma), early members of foursmall clades of the hesperocyonines had emerged: Paraenhydrocyon,Enhydrocyon,Osbornodon and Ectopocynus. Hesperocyonines experienced their maximum diver-sity of 14 species during the late Oligocene (30–28 Ma), and reached their peakpredatory adaptations (hypercarnivory) in the earliest Miocene with advancedspecies of Enhydrocyon and Paraenhydrocyon. The last species of the subfamily,Osbornodon fricki, became extinct in the middle Miocene (15 Ma), reaching the sizeof a small wolf.

With the exception of the Osbornodon clade, which acquired a bicuspid m1talonid, hesperocyonines are primitively hypercarnivorous in dental adaptationswith tendencies toward reduced last molars and trenchant (single cusped) talonidheels on the lower first molar. Although never reaching the extremes seen in theborophagines (see below), hesperocyonines had modest development of bone-cracking adaptations in their strong premolars. At least three lineages, all speciesof Enhydrocyon and terminal species of Osbornodon and Ectopocynus, have independ-ently evolved their own unique array of bone-cracking teeth. Hesperocyoninesdid not experiment with hypocarnivory.

Hypercarnivorous (b, Aelurodon and d, Euoplocyon) andhypocarnivorous (a, Phlaocyon and c, Cynarctus) dentitions. In hypercarnivorousforms, the upper cheek teeth (B) tend to emphasize the shearing part of thedentition with an elongated and narrow P4, an enlarged parastyle on atransversely elongated M1, and a reduced M2. On the lower teeth (D),hypercarnivory is exemplified by a trenchant talonid due to the increased size andheight of the hypoconid at the expense of the entoconid (reduced to a narrow andlow ridge), accompanied by the enlargement of the protoconid at the expense ofthe metaconid (completely lost in Euoplocyon) and the elongation of the trigonidat the expense of the talonid. In hypocarnivorous forms, on the other hand, theupper teeth (A) emphasize the grinding part of the dentition with a shortened andbroadened P4 (sometimes with a hypocone along the lingual border), a reducedparastyle on a quadrate M1 that has additional cusps (e.g. a conical hypoconealong the internal cingulum) and cuspules, and an enlarged M2. The lower teeth(C) in hypocarnivorous forms possess a basined (bicuspid) talonid on m1 enclosedon either side by the hypoconid and entoconid that are approximately equal insize. Other signs of hypocarnivory on the lower teeth include widened lowermolars, enlarged metaconids, and additional cuspules such as a protostylid.


From the primitive condition of a trenchant talonid heel on the lower first molarseen in the hesperocyonines, borophagines and canines shared a basined (bicus-pid) talonid acquired at the very beginning of their common ancestry (Fig. 1.3C).Along with a more quadrate upper first molar with its hypocone, the basinedtalonid establishes an ancestral state from which all subsequent forms were

Dental evolution of representative canids as shown in upper cheek teeth (P4–M2). Generally the most advanced species in eachgenus is chosen to enhance a sense of dental diversity. Species in the Hesperocyoninae are: Hesperocyon gregarius;Paraenhydrocyonjosephi;Cynodesmus martini;Enhydrocyon crassidens; and Osbornodon fricki. Species in the Borophaginae are: Cynarctoides acridens;Phlaocyon marslandensis;Desmocyon thomsoni;Cynarctus crucidens;Euoplocyon brachygnathus;Aelurodon stirtoni;Paratomarctustemerarius;Carpocyon webbi;Epicyon haydeni; and Borophagus diversidens. Species in the Caninae are: Leptocyon gregorii;Vulpesstenognathus;Urocyon minicephalus;Cerdocyon thous;Eucyon davisi;Canis dirus; and Cuon alpinus. All teeth are scaled to beproportional to their sizes. derived. Such a dental pattern proved to be very versatile and can readily beadapted toward either a hyper- or hypocarnivorous type of dentition, both ofwhich were repeatedly employed by both borophagines and canines 

The history of the borophagines also begins with a small fox-like form,Archaeocyon, in the late Oligocene. Contemporaneous with larger and more preda-tory hesperocyonines, these early borophagines in the late Oligocene and earlyMiocene tended to be more omnivorous (hypocarnivorous) in their dental adap-tations, such as Oxetocyon,Otarocyon and Phlaocyon. One extreme case, Cynarctoidesevolved selenodont-like molars as in modern artiodactyles, a rare occurrence ofherbivory among carnivorans. These early borophagines are generally no largerthan a raccoon, which is probably a good ecological model for someborophagines at a time when procyonids had yet to diversify.

After some transitional forms in the early Miocene, such as Cormocyon andDesmocyon, borophagines achieved their maximum ecological and numerical (i.e.species) diversity in the middle Miocene, with highly omnivorous forms, such asCynarctus, that were almost ursid-like, as well as highly predatory forms, such asAelurodon, that were a larger version of the living African hunting dog Lycaon. Bythen, borophagines had acquired their unique characteristics of a broad muzzle,a bony contact between premaxillary and frontal, multicuspid incisors, and anenlarged parastyle on the upper carnassials (modified from an enlargement of theanterior cingulum).

By the end of the Miocene, borophagines had evolved another lineage ofomnivores, although only modestly in that direction, in the form of Carpocyon.Species of Carpocyon are mostly the size of jackals to small wolves. At the sametime, the emergence of the genus Epicyon from a Carpocyon-like ancestor markedanother major clade of hypercarnivorous borophagines. The terminal species ofEpicyon,E.haydeni, reached the size of a large bear and holds the record as thelargest canid ever to have lived. Closely related to Epicyon is Borophagus, the termi-nal genus of the Borophaginae. Both Epicyon and Borophagus are best known fortheir massive P4 and p4 in contrast to the diminutive premolars in front. This pairof enlarged premolars is designed for cracking bones, mirroring similar adapta-tions by hyaenids in the Old World. Advanced species of Borophagus survived mostof the Pliocene but became extinct near the beginning of the Pleistocene.


As in the hesperocyonines and borophagines, a small fox-sized species of Leptocyonis the earliest recognized member of the subfamily Caninae. Besides sharing abicuspid talonid of m1 and a quadrate M1 with the borophagines, Leptocyon is alsocharacterized by a slender rostrum and elongated lower jaw, and correspondinglynarrow and slim premolars, features that are inherited in all subsequent canines.It first appeared in the early Oligocene and persisted into the late Miocene.Throughout its long existence (no other canid genus had as long a duration),facing intense competition from the larger and diverse hesperocyonines and10 X. Wang and R.H. Tedfordborophagines, Leptocyon generally remains small and inconspicuous, never havingmore than two or three species at a time.

By the latest Miocene, fox-sized niches are widely available in NorthAmerica, left open by extinctions of all small borophagines. The true fox clade,tribe Vulpini, emerges at this time and undergoes a modest diversification to ini-tiate primitive species of both Vulpes and Urocyon (and their extinct relatives). TheNorth American Pliocene record of Vulpes is quite poor. Fragmentary materialsfrom early Blancan indicate the presence of a swift fox-like form in the GreatPlains. Vulpes species were widespread and diverse in Eurasia during the Pliocene(see Qiu and Tedford, 1990), resulting from an immigration event independentfrom that of the Canis clade. Red fox (Vulpes vulpes) and Arctic fox (Vulpes lagopus)appeared in North America only in the late Pleistocene, evidently as a result ofimmigration back to the New World.

Preferring more wooded areas, the grey fox Urocyon has remained in south-ern North America and Middle America. Records of the grey fox clade indicatea more or less continuous presence in North America throughout its existence,with intermediate forms leading to the living species U.cinereoargenteus.Morphologically, the living African bat-eared fox Otocyon is closest to the Urocyonclade, although molecular evidence suggests that the bat-eared fox may lie at thebase of the fox clade or even lower (Geffen et al., 1992; Wayne et al., 1997). If themorphological evidence has been correctly interpreted, then the bat-eared foxmust represent a Pliocene immigration event to the Old World independent ofother foxes. A transitional form, Protocyon, occurs in southern Asia and Africa inthe early Pleistocene.

Advanced members of the Caninae, tribe Canini, first occur in the middleMiocene (9–12 Ma) in the form of a transitional taxon Eucyon. As a jackal-sizedcanid, Eucyon is mostly distinguished from the Vulpini in an expanded paroccipi-tal process and enlarged mastoid process, and in the consistent presence of afrontal sinus. The latter character initiates a series of transformations in the TribeCanini culminating in the elaborate development of the sinuses and a domed skullin Canis lupus. By latest Miocene time, species of Eucyon have appeared in Europe(Rook, 1992) and by the early Pliocene in Asia (Tedford and Qiu, 1996). TheNorth American records all pre-date the European ones, suggesting a westwarddispersal of this form.

Arising from about the same phylogenetic level as Eucyon is the SouthAmerican clade (subtribe Cerdocyonina). Morphological and molecular evidencegenerally agrees that living South American canids, the most diverse group ofcanids on a single continent, belong to a natural group of their own. The SouthAmerican canids are united by morphological characters such as a long palate, alarge angular process of the jaw with a widened scar for attachment of the infe-rior branch of the medial pterygoid muscle, and a relatively long base of the coro-noid process (Tedford et al., 1995). By the close of the Miocene, certainfragmentary materials from southern United States and Mexico indicate that taxaassignable to Cerdocyon (Torres and Ferrusquía-Villafranca, 1981) and Chrysocyonoccur in North America. The presence of these advanced taxa in the NorthEvolutionary History of Canids 11American late Miocene predicts that ancestral stocks of many of the SouthAmerican canids may have been present in southern North America or MiddleAmerica. They appear in the South American fossil record shortly after the for-mation of the Isthmus of Panama in the Pliocene, around 3 Ma (Berta, 1987). Theearliest records are Pseudalopex and its close relative Protocyon, an extinct largehypercarnivore, from the Plio-Pleistocene (around 2.5–1.5 Ma) of Argentina. Bythe latest Pleistocene (50,000–10,000 years ago), most living species or their closerelatives had emerged, along with the extinct North American dire wolf, Canisdirus. By the end of the Pleistocene, all large, hypercarnivorous canids of SouthAmerica (Protocyon,Theriodictis) as well as Canis dirus had become extinct.

The Canis clade within the tribe Canini, the most advanced group in termsof large size and hypercarnivory, arises near the Miocene–Pliocene boundarybetween 5 and 6 Ma in North America. A series of jackal-sized ancestral speciesof Canis thrived in the early Pliocene, such as C.ferox,C.lepophagus and other unde-scribed species. At about the same time, the first records of canids begin to appearin the European late Neogene: Canis cipio in the late Miocene of Spain (Crusafont-Pairó, 1950), Eucyon monticinensis in the latest Miocene of Italy (Rook, 1992), theearliest raccoon-dog Nyctereutes donnezani and the jackal-sized Canis adoxus in theearly Pliocene of France (Martin, 1973; Ginsburg, 1999). The enigmatic C.cipio,only represented by parts of the upper and lower dentition, may pertain to a format the Eucyon level of differentiation rather than truly a species of Canis.

The next phase of Canis evolution is difficult to track. The newly arrived Canisin Eurasia underwent an extensive radiation and range expansion in the latePliocene and Pleistocene, resulting in multiple, closely related species in Europe,Africa and Asia. To compound this problem, the highly cursorial wolf-like Canisspecies apparently belong to a circum-arctic fauna that undergoes expansions andcontractions with the fluctuating climate. Hypercarnivorous adaptations arecommon in the crown-group of species, especially in the Eurasian middle lati-tudes and Africa. For the first time in canid history, phylogenetic studies cannotbe satisfactorily performed on forms from any single continent because of theirHolarctic distribution and faunal intermingling between the New and OldWorlds. Nevertheless some clades were localized in different parts of Holarctica.The vulpines’ major centre of radiation was in the Old World. For the canines,North America remained a centre through the Pliocene producing the coyote asan endemic form. A larger radiation yielding the wolves, dhole, African huntingdog and fossil relatives took place on the Eurasian and African continents. Duringthe Pleistocene elements of the larger canid fauna invaded mid-latitude NorthAmerica – the last invasion of which was the appearance of the grey wolf southof the glacial ice sheets in the latest Pleistocene (about 100,000 years ago).

Phylogenetic Relationships

As mentioned above, there is strong fossil evidence about the antiquity ofthe family Canidae. This basal placement within the suborder Caniformia is12 X. Wang and R.H. Tedfordincreasingly born out by molecular data in recent years, such as DNA–DNAhybridization of single copy DNA, mitochondrial DNA sequence studies, andrecently studies of DNA sequences from nuclear genes (Vrana et al., 1994; Slatteryand Brien, 1995; Flynn and Nedbal, 1998; Murphy et al., 2001; Wang et al.,2004a), although molecular clock calculations tend to place the divergence timesomewhat older, around 50 Ma (Wayne et al., 1989), than is estimated from fossilevidence.

Phylogenetic (genealogical) relationships are traditionally inferred by analy-sis of the morphological characters, but molecular data are increasingly playingimportant, sometimes controversial, roles in the detection of evolutionary rela-tionships. However, in the case of canids that have a substantial history known byfossil records only, morphology is still the only way to allow a comprehensive viewof their entire history.

For the two extinct subfamilies, Hesperocyoninae and Borophaginae, wehave performed an exhaustive analysis of the entire fossil records (Wang, 1994;Wang et al., 1999) and their relationships are roughly shown in Fig. 1.4. For thesubfamily Caninae, we have nearly finished a similar study of monographic revi-sions that deals with the entire fossil history of the canines in North America(Tedford et al., in prep.). As a part of this larger effort to lay down a phylogeneticframework, Tedford et al. (1995) performed a cladistic analysis of living canids onmorphological grounds. The result is a nearly fully resolved relationship based onan 18 taxa by 57 characters matrix at the generic level. This relationship recog-nizes three monophyletic clades in the canines: the fox group (tribe Vulpini), theSouth American canine group, and the wolf group containing hypercarnivorousforms (the latter two form the tribe Canini) (Fig. 1.5, left).

Molecular studies of canid relationships range from investigations in com-parative karyology, allozyme electrophoresis, mitochondrial DNA, to microsatel-lite loci (Wayne and Brien, 1987; Wayne et al., 1987a, b, 1997; Geffen et al., 1992;Bruford and Wayne, 1993; Girman et al., 1993; Gottelli et al., 1994; Vilà et al.,1997, 1999). Trees derived from the mtDNA are based on the widest possiblesample of taxa and are better studied than nuclear DNA (Fig. 1.5, right) (e.g.Wayne et al., 1997). Overall, molecular studies tend to place the foxes near thebasal part, the South American canines in the middle, and the wolves andhunting dogs toward the terminal branches, a pattern that is consistent with themorphological tree. The detailed arrangements, however, differ in a number ofways. The foxes are generally in a paraphyletic arrangement (falling at the stemparts of the tree) in contrast to a monophyletic clade (a natural group that con-tains ancestors and all descendants) in the morphological tree. The grey fox andbat-eared fox are placed at the base despite their highly advanced dental mor-phology compared to other foxes. Similarly, South American canines are nolonger monophyletic under molecular analysis but form at least two paraphyleticbranches. A glaring discrepancy is the Asiatic raccoon dog being allied to thefoxes in the molecular analysis despite its numerous morphological charactersshared with some South American forms. Finally, molecular data suggest inde-pendent origins for the Asiatic and African hunting dogs in contrast to a sister relationship in the morphological tree supported by a large number of charactersrelated to hypercarnivory.

Not surprisingly, there are increased agreements between the molecular andmorphological results when the two data sets are combined in a total evidenceanalysis (Wayne et al., 1997; Zrzavy´ and Ricánková, 2004). Under such condi-tions, the South American canines (except Nyctereutes) become monophyletic, asdoes the clade including the wolf, dhole and African hunting dog. Although mito-chondrial genes are known to evolve relatively quickly and thus are suitable foranalysis on groups that have more recent ancestry, genetic variations in the mito-chondria are only a tiny fraction of the total genome and the gene trees may notreveal the true phylogeny. Nuclear genes, with their vast information content,have the potential of revealing the true relationships, especially for groups oflonger history. Works are underway to search for the most suitable part of thegenome with just the right rate of evolution, neither too slow to offer much insightabout change nor too fast to obscure true relationships. Recently SelenocysteinetRNA (Cf TRSP) and RNase P RNA (Cf RPPH1) genes have been shown to bepromising (Bardeleben et al., 2005), these tend to place the South American formsin a clade and are consistent with morphological results.

As a very successful group of predators, canids are known for their outstandingcursoriality, the ability to run fast and over long distances, and for their social(pack) hunting that requires complex collaborative behaviours. This combinationof long-distance, relay-style running and social hunting to bring down preytogether is a successful strategy in catching larger prey. In this regard, only thehyaenids are comparably equipped, whereas the felids may have reached similarrunning capabilities but more often hunt alone. The increased cursoriality incanids is generally correlated with a similarly increased running ability by theirprey (various groups of ungulates), which are in turn related to the progressivelymore open grassland environments in the late Cenozoic.

Population Status

The fur of some canines is important in the trade market. There was once a mutant fox called the silver fox that formed an important part of the fur farming industry. The red fox is the second most important animal for fur farming after the American weasel. Raccoon dogs still survive in some parts of Russia and Finland. Gray foxes, arctic foxes, coyotes, and gray wolves are also important sources of fur, but several others are occasionally used by the fur trade. In Europe, red foxes are mainly used for a sport called "fox hunting".

The domestic dog (Canis lupus familiaris) is the most economically important dog, especially in Western societies, because of its importance as a pet. This may have been the first wild animal to be domesticated, and dogs have been found to be associated with Neolithic sites dating back more than 10,000 years.

Many canids, especially red foxes, are susceptible to rabies virus. In Europe, the management of fox rabies through culling and distribution of vaccine-laden baits is an expensive program. There is no cure for this deadly disease in humans, but pets and people are vaccinated before the onset of the disease and after human exposure can provide immunity against the disease. Dogs are rarely used as food by humans, but some Native Americans once considered dog meat a delicacy eaten on special occasions. There is also a market and habit of consuming dog meat in East Asia.