Dogs and humans have been best friends for thousands of years. Researchers know that dogs regularly lived with humans by about 10,000 years ago, and dogs and people are found buried together as early as 14,000 years ago. And for even longer, perhaps hundreds of thousands of years, humans walked alongside the domestic dog's ancestor, an extinct species of wolf.
Domestic dogs and wolves are part of a large taxonomic family called Canidae, which also includes coyotes, foxes and jackals, according to the Integrated Taxonomic Information System (ITIS). Members of this family are called canids. Domestic dogs are a subspecies called Canis lupus familiaris. [Related: How Did Dogs Get to Be Dogs?]
The Canidae family includes 14 genera and 34 species, according to the University of Michigan Museum of Zoology. With such variety, it is easy to see why there are so many different sizes of dogs. According to the University of Edinburgh, the smallest canid is the Fennec fox. It is only 9.4 inches (24 centimeters) high and weighs only 2.2 lbs. (1 kilogram). The largest canid is the gray wolf, at 6.5 feet (200 cm) high and 3 to 5 feet (1 to 1.5 meters) long. Their tails add an additional 1 to 2 feet. Females typically weigh 60 to 100 lbs., and males weigh 70 to 145 lbs., according to the National Wildlife Federation.
Canids are found all over the world. Coyotes roam North America's forests and mountains. Red foxes live in grasslands, forests, mountains and deserts in the Northern Hemisphere, according to National Geographic. Jackals are found in the savannas, deserts, and arid grasslands of Africa. Wolves live on every continent in the Northern Hemisphere.
Canids are typically social and travel in groups called packs. They are very territorial, though, and mark their territory with scent marking. Even domesticated dogs will mark their yards by leaving their scent on trees, bushes and objects.
Jackals are a little less social and usually travel in pairs, according to the African Wildlife Foundation. Males and females mate for life, which is very rare for mammals.
Wolves, foxes and other dogs don't howl at the moon. They are actually howling at each other as a form of communication. Dogs also yelp, whine, bark and growl to communicate.
Though dogs are omnivores, they eat mostly meat and are born killers. They have non-retractable claws, long legs for speed and teeth that are sharp, pointed and perfect for tearing at meat. Wolves, for example, eat deer, domestic livestock, caribou, beaver, moose and hares. Jackals eat smaller fare such as rodents, young gazelle, lagomorphs and monkeys.
Dogs also have well-developed carnassial molars, according to the University of Illinois at Urbana-Champaign. These teeth are used to crush vegetation such as fruits and grasses.
All of the members of the Canidae family have live births after a gestation period of around 45 to 55 days. Canids typically have many babies at once. Domestic dogs can have as many as 15 young, called pups, at the same time. Other genus types are less prolific. For example, the genus Urocyon has only one to seven young per year, according to the University of Illinois at Urbana-Champaign. The Biological Sciences Department of Smith College reports that there is a correlation between the weight of a canid and reproduction; the larger the female, the larger the litter size.
The taxonomy of dogs, according to ITIS, is:
Species: Atelocynus microtis — short-eared dog, small-eared dog, small eared zorro
Species: Canis adustus — side-striped jackal; Canis aureus — golden jackal; Canis latrans —coyote; Canis lupus — wolf, gray wolf; Canis mesomelas — black-backed jackal; Canis simensis— simian jackal, simien fox, Ethiopian wolf
Subspecies: Canis lupus familiaris — domestic dog
Species: Cerdocyon thous — crab-eating fox
Species: Cerdocyon thous — maned wolf
Species: Cuon alpinus — dhole, Indian dhole, Asiatic wild dog, red dog
Species: Dusicyon australis — Falkland Island wolf, Falkland Islands wolf
Species: Lycalopex culpaeus — culpeo; Lycalopex fulvipes — Darwin's fox; Lycalopex griseus — South American gray fox; Lycalopex gymnocercus — pampas fox; Lycalopex sechurae — Sechuran fox; Lycalopex vetulus — hoary fox
Species: Lycaon pictus — African hunting dog, African wild dog
Species: Nyctereutes procyonoides — raccoon dog
Species: Otocyon megalotis — bat-eared fox, big-eared fox
Species: Speothos venaticus — bush dog
Species: Urocyon cinereoargenteus — gray fox, common gray fox; Urocyon littoralis — island fox, island gray fox, Channel Islands gray fox
Species: Vulpes bengalensis — bengal fox; Vulpes cana — Blanford's fox; Vulpes chama — cape fox; Vulpes corsac — corsac fox; Vulpes ferrilata — Tibetan fox, Tibetan sand fox; Vulpes lagopus — blue fox, ice fox, polar fox, white fox, Arctic fox; Vulpes macrotis — kit fox; Vulpes pallida — pale fox; Vulpes rueppellii — Rüppell's fox; Vulpes velox — swift fox; Vulpes vulpes— red fox; Vulpes zerda — fennec, fennec fox
According to the International Union for Conservation of Nature (IUCN), many of the Canidae family are threatened or near threatened. For example, the short-eared dog and dhole are near threatened. The African wild dog and Ethiopian wolf are endangered, while the red wolf and Darwin's fox are critically endangered. The Falkland Island wolf is the only dog listed as extinct by the IUCN Red List of Threatened Species.
The lifespan of a dog varies, depending on what type it is. Wolves, coyotes, jackals and domestic dogs live around 10 years. Vulpes, or true foxes, live around five years.
Coyotes are scavengers that will eat almost anything. Their diet includes bugs, trash, deer, rodents and snakes. They are also very fast runners and can run up to 40 mph (64 kph), according to National Geographic.
The lead male and female are the only two that typically breed in a wolf pack. Their hierarchy is very strict. A pack is usually lead by a dominate male.