Dog Family - biology.

Dog Family - biology. I INTRODUCTION Dog Family, group of intelligent, carnivorous mammals that includes domestic dogs and their relatives, coyotes, wolves, foxes, jackals, dholes, raccoon dogs, and bush dogs. The dog family is known scientifically as Canidae, and its members are commonly called canids. The earliest known doglike animals can be traced to the Eocene Epoch, dating from 55 to 38 million years ago. Today, canids live on every continent except Antarctica. Their presence on many islands--including the island continent of Australia--is the result of introduction by humans. Wild Australian dingoes, for example, were probably brought to the continent as domestic dogs by aboriginal people thousands of years ago. Canids thrive in a variety of habitats. Bush dogs, for example live in the humid tropical forests of South and Central America, while arctic foxes inhabit the ice floes and arctic tundra of the far north. Fennecs survive in the arid deserts of North Africa and the Middle East. A few dog species, such as gray wolves and red foxes, have extraordinarily broad distributions that span several continents with a variety of environmental conditions. Some dogs have evolved adaptations for hunting and evading predators in unique habitats--gray foxes are able to climb low trees; many dogs are excellent swimmers; and the bush dog is even an accomplished diver. Currently, there is considerable interest but little consensus about how members of the dog family are related to each other. Domestic dogs, wolves, most foxes, coyotes, and jackals are clearly closely related. The relationships of raccoon dogs, African hunting dogs, bat-eared foxes, bush dogs, and dholes are less clear. Scientists agree, however, that the nearest relatives of the dog family are the bears, raccoons, weasels, and probably seals and sea lions. II PHYSICAL CHARACTERISTICS A number of physical traits distinguish the canids. Intermediate in size among mammals, canids range from the tiny fennec, which weighs less than 2 kg (4 lb) to the imposingly large gray wolf, which can reach 80 kg (176 lb). Most canids have compact, fur-covered bodies and long, bushy tails. Many have a patch of dark fur on the top of the tail near its base, marking the position of a scent gland. Canids have a long, pointed snout and mouth. Their ears are usually erect, often pointed, and can be quite large in some species; bat-eared foxes, for example, were named for their conspicuously large, wide ears that better resemble those of a bat than a fox. Canids have a large number of powerfully built teeth used for killing and holding prey, in fighting, and in threat displays. While most canids have 42 teeth, some species such as bush dogs have only 38 teeth while bat-eared foxes have 50. Like humans, canids have different types of teeth that are distinguished by shape, position in the mouth, and function. The chisel-like incisors, used for cutting food and in grooming, are located in the front of the mouth. The incisors are followed by a pair of daggershaped canine teeth used in fighting and hunting. Premolars and molars, located near the back of the mouth, are used for grasping, slicing, and crushing meat and bone. The molars at the very back of the mouth are adapted for feeding on items such as insects, fruit, and leafy vegetation, as well as meat. Some canids include a high proportion of fruits, seeds, and other vegetable matter in their diets. All of the canids are excellent hunters, with keen senses of smelling and hearing, although their eyesight is not exceptional. They usually prey on mice and other rodents, rabbits, antelope, caribou, and deer--depending on their species and habitat. Canids are well adapted for long-distance pursuits of prey. They can run exceptionally fast and have remarkable endurance for covering long distances. For example, greyhounds have been clocked at 70 km/h (44 mph) and African hunting dogs can maintain speeds of 50 to 60 km/h (31 to 37 mph) for several kilometers. A number of physical adaptations enable canids to maintain high speeds over great distances. They have long leg, wrist, and ankle bones and they are digitigrade--that is, they stand on their toes rather than on flat feet. These characteristics give canids a long stride that is further lengthened when the animal arches its backbone as it runs. Canids have small feet, and in most cases their feet have only four toes in contact with the ground. A small fifth toe, called the dewclaw, is usually present high up on both forefeet. All toes have strong, blunt claws. The small size and weight of their feet and limbs require less energy to move, enabling canids to run more efficiently than heavier-limbed animals. III REPRODUCTION Canid reproduction is distinguished by large litters of up to 15 pups, although 6 to 7 is more common, usually born once a year. Canid gestation periods range from 51 to 80 days. The young are blind and helpless at birth and require an extended period of parental care. Pups consume only their mother's milk until two to six weeks in age, when they learn to eat solid food as adult animals bring them dead prey or regurgitate partially digested food. After about a year, most canid pups reach sexual maturity, although the larger species, such as the gray wolf, can take up to three years to mature. Mating occurs when female canids are in heat, a time when hormonal changes make females both attractive and attracted to males. In most canid species, sexually mature females are in heat once a year. Domestic dogs are often in heat twice a year. Mating in canids includes a distinctive feature called the copulatory tie. Following mating, the male and female reproductive organs remain linked together for up to an hour. This adaptation may have evolved to prevent other males from mating with the female during this time. IV TYPES OF CANIDS The most familiar members of the dog family belong to the genus Canis. These include domestic dogs, wolves, coyotes, and jackals. Wolves are the largest wild members of the dog family. Two species are alive today: gray wolves (also called timber wolves) and red wolves. Gray wolves once ranged throughout most of the northern hemisphere, but they are now found in just a few wild areas of northern North America and Asia, particularly in Siberia. These animals are well known for their pack structure and complex social behavior. Red wolves were once widespread in the southeastern United States, but they are now nearly extinct in the wild. Maintained in captivity, they have been reintroduced in North Carolina but are still threatened by habitat destruction and by interbreeding with coyotes. Domestic dogs are derived from and are still very closely related to gray wolves. In fact, many scientists consider them to be members of the same species. Domestic dogs have been selectively bred by people into a great many shapes and sizes. They range from tiny chihuahuas and other toy breeds weighing less that 1 kg (2 lb) to huge mastiffs weighing more than 80 kg (176 lb). Coyotes are similar to wolves in shape and in many of their habits, but they are substantially smaller, weighing up to about 15 kg (33 lb). Like wolves, coyotes live in family groups consisting of a pair of adult parents and their offspring. They usually hunt alone, but they may team up with one or two other coyotes to chase prey. Jackals include four species found in the eastern hemisphere from Africa to central Asia. They are slender animals, even smaller than coyotes, with large, upright ears and bushy tails. They may live near villages and towns, where they sometimes earn a reputation as scavengers and livestock predators. With about 21 distinct species, foxes comprise the largest group of canids. Foxes are small, ranging in size from 1.5 to 9 kg (3 to 20 lb). They have sharply pointed muzzles, long and bushy tails, and large ears. Many foxes hunt by stalking prey and then leaping on it with a distinctive, stiff-legged pounce. Once thought to be solitary animals, foxes are now known to live in groups of up to six individuals. The remaining canids are each highly distinctive. Raccoon dogs and bush dogs are the least doglike canids in appearance. Raccoon dogs, found in eastern Asia, have stubby legs, a stout body, short ears, shaggy fur, and a black face mask that resembles a raccoon's. Bush dogs, found only in South and Central America, look more like small bears than dogs: they have short legs, a compact body, and small ears. Bush dogs probably hunt in groups, but they are rare animals and little is known of their biology in the wild. V SOCIAL BEHAVIOR Canids are often social animals, living and hunting in groups with complex communication systems and organizational structures. Canids communicate with vocalizations--usually barks, whimpers, growls, and howls. Canids also use body positions, head movements, and scents from scent glands to mark hunting territories, display authority, or advertise their receptivity to mating. Social behavior among canids is based on the family group, which centers on a breeding pair. In wolves, for example, the breeding male, called the alpha, maintains dominance over other pack members using dominant body postures, facial displays, vocalizations such as growls and barks, scent marking, and when necessary, fighting. The second in charge, known as the beta, is the breeding female. The size and composition of the family group varies from species to species. It is also influenced by the available food supply and by the habitat where the animals live. African hunting dogs are perhaps the most strongly social of all canids. They have been known to gather in packs of hundreds of individuals, but the usual number ranges from 10 to 30. The dominant female is typically the only female in the pack to breed, but all pack members help to raise the young by regurgitating food for the pups. Sick or injured adults are also assisted in the same way. Quarrels in the pack are unusual, and serious fights are rare. Unlike almost all other mammals, young females of this species--instead of young males-leave the pack to breed with members of other packs. Canid packs, especially African hunting dogs and dholes, often hunt cooperatively, enabling them to pursue and kill much larger animals. They are able to do this using a technique called relay hunting, in which one member of the pack chases prey, then another takes over, followed by another, continuing until the prey animal is exhausted. The canids then attack and kill the prey. Red foxes live in much smaller groups and usually hunt alone. A monogamous male and female pair typically defends a territory in which they hunt and raise their young. Sometimes several female foxes, usually a mother and her daughters, are found with a single male. The younger adults are helpers, assisting the breeding pair in territorial defense and providing food for the young. VI HUMANS AND THE DOG FAMILY One member of Canidae, the domestic dog, shares a special relationship with human beings. Records of dogs helping humans date from about 4500 years ago, but the association is thousands of years older. The first domesticated dogs were wolf pups. Scientists think that the highly social behavior of wolves allowed them to accept a relationship with humans and to become part of a human family. The first domesticated dogs used their excellent scent and hearing to help humans hunt for food. They also probably served as sentinels, warning of predators or other intruders. Ancient breeds of dogs include salukis and basenjis, which exist today almost exactly as they appear in carvings and paintings from ancient Egypt. Since then, dogs have been selectively bred to bring out special traits that are useful to people. Dogs today are used for hunting, herding, guarding, and simply providing companionship. The American Kennel Club now recognizes more than 100 breeds. Until recent decades, many wild canids were hunted by humans for bounties and were considered scourges to livestock and other wildlife. Habitat destruction has also hurt some canid populations. The elimination of coyotes and foxes from some areas has resulted in huge increases in rodent populations that eat vegetation intended for desirable livestock and wildlife. Scientific classification: Dogs and their relatives make up the family Canidae in the order Carnivora. The gray wolf is classified as Canis lupus; the coyote as Canis latrans; the red fox as Vulpes vulpes; the fennec as Vulpes zerda; the kit fox as Vulpes velox; the arctic fox as Alopex lagopus; the raccoon dog as Nyctereutes procyonoides; the African hunting dog as Lycaon pictus; and the dhole is classified as Cuon alpinus. The domestic dog, formerly classified as Canis familiaris, is now classified as Canis lupus familiaris. Contributed By: Philip Myers Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.