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?]

Size

The Canidae family includes 14 genera and 34 species, according to the University of Michigan's Animal Diversity Web. 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.

Habitat

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.

Habits

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.

It is a myth that domesticated dogs only see black and white. They are actually red-green colorblind, according to a small 2017 Italian study on 16 dogs. "If you are planning to train your dog to fetch a ball that fell on the green grass of your garden, think of using a blue, and not red, ball," said study lead researcher Marcello Siniscalchi, a professor in the department of veterinary medicine at the University of Bari, in Italy. This is most likely due to the fact that dogs have evolved from creatures that hunted during dusk and dawn, which doesn't require color vision. [Doggone: Your Best Friend Is Red-Green Colorblind]

Domestic dogs are also very expressive in their facial expressions, particularly when they are getting attention from humans, according to a 2017 study published in the journal Scientific Reports.

"The findings appear to support evidence [that] dogs are sensitive to humans' attention and that [their] expressions are potentially active attempts to communicate, not simple emotional displays," lead study author Juliane Kaminski, a senior lecturer in psychology and leader of the Dog Cognition Centre at the University of Portsmouth in England, said in a statement. "Domestic dogs have a unique history — they have lived alongside humans for 30,000 years, and during that time, selection pressures seem to have acted on dogs' ability to communicate with us."

Diet

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, rabbits and monkeys.

Dogs also have well-developed carnassial molars, upper and lower teeth that are paired and have flat edges that allow self-sharpening when they pass by each other. According to the University of Illinois at Urbana-Champaign, these teeth are used to crush vegetation such as fruits and grasses.

Offspring

All members of the Canidae family have live births after a gestation period of 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, gray foxes (genus Urocyon) have 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 fennec fox is the smallest member of the Canidae family. (Image credit: nattanan726 Shutterstock)

Classification/Taxonomy

The taxonomy of dogs, according to ITIS, is:

Kingdom: Animalia Subkingdom: Bilateria Infrakingdom: Deuterostomia Phylum: Chordata Subphylum: Vertebrata Infraphylum: Gnathostomata Superclass: Tetrapoda Class: Mammalia Subclass: Theria Infraclass: Eutheria Order: Carnivora Suborder: Caniformia Family: Canidae Genera & species:

Atelocynus microtis — short-eared dog, small-eared dog, small-eared zorroCanis adustus — side-striped jackalCanis aureus — golden jackalCanis latrans — coyoteCanis lupus — wolf, gray wolf (Subspecies: Canis lupus familiaris — domestic dog)Canis mesomelas — black-backed jackalCanis simensis — simian jackal, simian fox, Ethiopian wolfCerdocyon thous — crab-eating foxChrysocyon brachyurus — maned wolf Cuon alpinus — dhole, Indian dhole, Asiatic wild dog, red dogDusicyon australis — Falkland Island wolf, Falkland Islands wolfLycalopex culpaeus — culpeoLycalopex fulvipes — Darwin's foxLycalopex griseus — South American gray foxLycalopex gymnocercus — pampas foxLycalopex sechurae — Sechuran foxLycalopex vetulus — hoary foxLycaon pictus — African hunting dog, African wild dogNyctereutes procyonoides — raccoon dogOtocyon megalotis — bat-eared fox, big-eared foxSpeothos venaticus — bush dogUrocyon cinereoargenteus — gray fox, common gray foxUrocyon littoralis — island fox, island gray fox, Channel Islands gray foxVulpes bengalensis — bengal foxVulpes cana — Blanford's foxVulpes chama — cape foxVulpes corsac — corsac foxVulpes ferrilata — Tibetan fox, Tibetan sand foxVulpes lagopus — blue fox, ice fox, polar fox, white fox, Arctic foxVulpes macrotis — kit foxVulpes pallida — pale foxVulpes rueppellii — Rüppell's foxVulpes velox — swift foxVulpes vulpes — red foxVulpes zerda — fennec, fennec fox

Conservation status

The International Union for Conservation of Nature (IUCN) has many dogs on its Red List of Threatened Species.

Near threatened (mostly due to small geographical range and habitat loss) are the short-eared dog (Atelocynus microtis), maned wolf (Chrysocyon brachyurus), Sechuran fox (Lycalopex sechurae), island fox (Urocyon littoralis) and bush dog (Speothos venaticus).

Darwin's fox (Lycalopex fulvipes) — with a population of 659 to 2,499 mature individuals; the African wild dog (Lycaon pictus) — only 1,400 mature individuals; the dhole(Cuon alpinus) — 949 to 2,215 mature individuals; and the Ethiopian wolf (Canis simensis) — only 197 mature individuals — are endangered.

The red wolf (Canis rufus) is critically endangered. The species was extinct in the wild by 1980, and only exists now in a reintroduced population in eastern North Carolina. The total population is less than 150 individuals — and no more than 50 are mature.

The Falklands wolf (Dusicyon australis) has been extinct since 1876.

Other facts

The life span of a dog varies, depending on what type it is. Wolves, coyotes, jackals and domestic dogs live 10 years or more. 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 km/h), 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 dominant male.

Dogs can get the flu. [Coughing Canines? 6 Things to Know About Dog Flu]

Additional resources

Encyclopedia of Life: CanidaeUniversity of Illinois at Urbana–Champaign: Family CanidaeAfrican Wildlife Federation: African Wild Dogs