Canidae

Canidae (from Latin, canis, "dog") is a biological family of caniform carnivorans. A member of this family is called a canid, and canids are often called dogs. The family has three subfamilies: the Caninae, and the extinct Borophaginae and Hesperocyoninae. The Caninae are the canines. They include domestic dogs, wolves, coyotes, raccoon dogs, foxes, jackals, and other species.

Canids live on every continent except Antarctica. They reached these places on their own or by travelling with humans over a long time. Canids come in many sizes. A gray wolf can be about 2 metres (6.6 feet) long, while the fennec fox is only about 24 centimetres (9.4 inches) long.

Most canids have similar body shapes. They usually have long muzzles, upright ears, long legs, and bushy tails. Their teeth are good for cracking bones and cutting meat. Many canids are social animals. They live together in family groups or small packs and work as a team. Usually, only the breeding pair in a group has young. Each year, a litter is raised in an underground den.

Canids communicate using scent signals and sounds. The domestic dog originated from a symbiotic relationship with people during the Upper Paleolithic period. Today, it is one of the most widely kept domestic animals.

Taxonomy

See also: List of canids

In the history of carnivores, the family Canidae has two extinct subfamilies, Hesperocyoninae and Borophaginae, and one living subfamily, Caninae. Caninae includes all living canids and their most recent fossil relatives. All living canids form a monophyletic group with the extinct borophagines. Both groups have a bicuspid (two points) on the carnassial lower talonid, which helps this tooth with mastication (chewing). Together with a distinct entoconid cusp, a wider talonid on the first lower molar, a larger talon on the upper first molar, and a smaller parastyle, these features set these late Cenozoic canids apart and mark their group.

The cat-like Feliformia and dog-like Caniformia appeared within the Carnivoramorpha about 45–42 Mya (million years ago). Canids first appeared in North America during the Late Eocene (37.8-33.9 Mya). They did not reach Eurasia until the Late Miocene, or South America until the Late Pliocene. A cladogram shows where canids fit within Caniformia.

Evolution

See also: Caninae § Phylogenetic relationships

The Canidae are a varied group of about 37 species. They range from the maned wolf with its long legs to the short-legged bush dog. Canids live in forests, tundra, grasslands, and deserts in warm and cool parts of the world. Scientists first learned how species are related by comparing their body shapes, using morphological methods. More recently, they have studied genetic material to learn about phylogenetics relationships. In some species, genetic divergence has been limited by gene flow between different groups. Where species have mixed, large hybrid zones exist.

Carnivorans evolved after the extinction of the non-avian dinosaurs 66 million years ago. Around 50 million years ago, or earlier, during the Paleocene, the Carnivora split into two main groups: caniform (dog-like) and feliform (cat-like). By 40 million years ago, the first clearly identifiable member of the dog family had appeared. It was named Prohesperocyon wilsoni, and its fossils have been found in southwest Texas. Canidae soon split into three subfamilies: Hesperocyoninae, Borophaginae, and Caninae, the only one still living. By the Oligocene, all three had appeared in North America. Early canids such as Mesocyon probably hunted quickly in grasslands. Later, the Beringian land bridge let Eucyon reach Asia. Around 3 million years ago, the Isthmus of Panama joined North and South America. This allowed canids to invade South America, where they spread out. Some South American canids, such as the maned wolf, the bush dog, and the crab-eating fox, are found only there. During the Pleistocene, the gray wolf (C. lupus) spread through Europe and northern Asia. Later, it reached North America across the Bering land bridge. The dire wolf lived alongside it until it died out about 11,500 years ago.

Characteristics

Wild canids live on every continent except Australasia and Antarctica. Feral canids, which are animals that humans brought to new places, also live in New Guinea and Australia. Canids live in deserts, mountains, forests, and grasslands.

They come in many sizes. The fennec fox is about 24 cm long. The gray wolf can be up to 160 cm long and weigh up to 79 kg. Only a few kinds, the gray fox, the island fox, and the raccoon dog, often climb trees. Most canids have a similar basic body, though the length of their muzzle, legs, ears, and tail varies. Most have long legs and slim bodies for chasing prey, bushy tails, and a long, narrow muzzle. Their skulls have wide zygomatic arches, a lambdoidal ridge at the back of the cranium, and in some species a sagittal crest. Females have three to seven pairs of mammae.

Canids are digitigrade, which means they walk on their toes. The tip of the nose and the foot pads are bare. In the Arctic fox, the soles of the feet can be covered with hair at certain times of the year. Most canids have five toes on the front feet and four on the back, though the African wild dog has four toes on the front. Some domestic dogs also have a dewclaw.

Canids have many other special features. Young canids are born blind. Living canids have a nuchal ligament, like the one found in ungulates. This helps hold up the head and neck with little effort, so they can run long distances while following scents. Some extinct canids, such as Aelurodon, may not have had this ligament.

Canid teeth are described using dentition and the dental notation. This labels incisors, canines, premolars, and molars in the upper and lower jaw. In carnivores, the carnassials work like scissors to cut meat. The shape of the lower carnassial, including the trigonid and talonid, shows whether an animal is a hypercarnivore or has a more omnivorous diet. A study of placental mammals found that the extinct dire wolf had the strongest bite among canids. The African wild dog, gray wolf, dhole, and dingo came after it. Most canids have 42 teeth. Their strong molars can crack bone to reach the marrow. The bat-eared fox has a different number of molars.

Life history

See also: Wolf § Behaviour, Dog behavior, Red fox § Behaviour, and African wild dog § Behaviour

See also: Dog communication and Wolf communication

See also: Canine reproduction

Almost all canids are social animals that live together in groups. They usually have a home area. They often sleep in the open and use their dens mainly for raising young and sometimes for shelter in bad weather. In most foxes and many true dogs, a male and female pair work together to hunt and raise their young. Gray wolves and some other large canids live in bigger groups called packs. Canids talk to each other using scent signals, visual clues, gestures, and sounds such as growls, barks, and howls. Groups usually have a home territory and chase away other conspecifics. They use urine scent marks to mark their food caches or warn intruders. Glands on the tail, anal glands, preputial glands, and supracaudal glands also help with social behavior.

Canids are usually monogamous. They care for their young together and often keep adult offspring in the group. Those offspring usually do not have young of their own. Instead, they help raise the next litter through alloparental care. Most species are spontaneous ovulators, though maned wolves are induced ovulators. Breeding has proestral and dioestral phases. Rising estradiol makes the female attractive to the male, and progesterone rises when she is ready to accept him. After a pregnancy, there is often a rest period called anestrus. A pseudo-pregnancy can happen when a canid has ovulated but has not become pregnant. Small and medium canids usually carry their young for 50 to 60 days. Larger ones average 60 to 65 days. The length of day, called a photoperiod, affects when the breeding season occurs. Litters range from one to 16 or more pups. The pups are born small, blind, and helpless. They stay in a den for warmth and protection, and both parents, often with other pack members, bring them food. Young canids may take a year to grow up.

Canids and humans

Further information: Dog

The domestic dog was the first animal that humans tamed. The oldest known dog remains buried next to humans are about 14,700 years old. Some disputed remains may be about 36,000 years old. These dates suggest that the first dogs appeared when humans were hunter-gatherers, not agriculturists. Wolves live in close family groups called packs, and this may have helped the friendship grow. Humans gained loyalty, teamwork, alertness and tracking skills from canids. Wolves may have benefited from human tools and from sharing food.

Attacks by canids on humans are rare, but some deaths have been recorded. Only the gray wolf is known to hunt humans, and at least two records of coyotes killing humans have been published. Pet dogs cause more deaths than wild canids. Dog attacks cause some deaths each year in the United States. Humans trap and hunt some canids for their fur, and some are hunted for sport. The dhole is now endangered in the wild. Other canids, such as the coyote, have done well alongside humans. The coyote has spread across North America. This is partly because humans removed large meat-eating animals, and partly because coyotes can adapt to urban ecosystems. Red foxes have also adapted well to cities. They have formed new populations in places where people brought them, such as Australia.