Canids are medium-sized carnivores, but are more designed to be omnivorous than felids. Because of this, canids have many adaptations that felids do not have. Canids have more teeth in their jaw than felids. This is necessary for an animal that eats plant matter and insects as well as animal flesh. Many canid species' entire diet consists of insects. Canids have 38 - 42 teeth, with the canine teeth being large but not as sharp as felids. They have large, yet not sharp, carnassials, the hallmark of the order carnivora. These specialized teeth help to shear meat, however, canids tend to bolt down their food rather than shear it. Canids, unlike felids, can move their jaws in many directions. The skull is elongated and narrow. They also have a prominent saggital crest (the bony plate that protrudes from the base of the skull). This is used to anchor the powerful temporalis jaw muscles, and is bigger in larger canid species like wolves and coyotes than in foxes, where it is nonexistent.
Canids' body structure is characterized by a long lithe body set on long, thin legs. They are digitigrade, meaning they walk on the toes of their feet. In general, they have five toes on the front foot and four on the back, the exception is the African wild dog (Lycaon pictus), which was only four toes on the front feet. Unlike felids, canids were built for speed and endurance. Many species often run their prey to death. They can keep a steady gallop for a very long distance without tiring. Canids have unretractable claws, which help it to grip the ground while it is running.
Like many carnivores, canids have a bony structure in their penis called a baculum. This engorges and locks the mating pair in a copulatory "tie" for several minutes up to an hour, depending on the species.
The fur of canids depends on the climate in which they live. Since they live in very diverse climates, the fur is very diverse as well. Those living in arctic and holarctic regions have thick long fur, while those that live in more tropical regions tend to have less dense and very short fur. Generally, canids tend to be less vibrantly colored than felids, and they do not have the flashy spots, rosettes, stripes and tabby markings of their felid cousins. The exception is the African wild dog, who has vibrant yellow, black and white markings all over its body. Typically, canids are usually a greyish or reddish color, with lighter fur on the underbody, face and legs, with darker markings above the eyes, around the ears and on the back and tail. Their tail generally has thicker and longer fur than the rest of their body. The ears are erect and usually triangular shaped, and lined with thick lighter-colored fur.
Dogs have very highly developed senses. Their sense of smell is the most highly developed sense, as they rely on scent to hunt their prey as well as communication. Hearing is next highest developed, especially in canids that hunt mostly rodents. They can hear the soft rustle of a mouse walking through grass as well as the high-pitched squeak of them communicating to one another, noises that are inaudible to humans. They also use hearing and sound to communicate with each other, and this is important for canids that live in heavily wooded areas. Of all the senses, eyesight is the least developed, since they do not rely on eyesight as much as felids. However, eyesight is important for picking up visual cues of distress from their prey as well as recognizing communication patterns from their own kind. Canid whiskers are also less-developed than felids, since they do not do a lot of hunting in areas that are cramped or dark.
The larger canids are usually highly social, while smaller canids, such as foxes, tend to be more solitary in their habits. Pack life tends to be more suited for the larger canids, as they hunt larger prey. Pack canids have a strict social hierarchy. Packs consist of a male and a female, which are the only ones that breed, and their young for several generations. Oftentimes, relatives of the parents make up the pack. The parents, known as the alpha pair, have absolute dominance over all members of the pack. The rest of the members of the pack are left to determine their own rank through ritualized fighting. The rank in the pack determines how the individual will be treated as well as the order at feeding time. The female often represses her female offspring from coming into heat.
Wild canids only breed once a year, generally during a set breeding season that corresponds to availability of food. Territoriality and aggression rise during the breeding period, as the males compete for limited numbers of breeding females. Gestation period ranges from 50 - 80 days, depending on the species. Litters are variable, and can contain a single pup up to large litters of 15 or more. Cubs are born with their eyes and ears closed, and are entirely dependent upon their parents for food and care. They are cared for by their parents for a very long time, and are typically weaned by 4-8 weeks. Usually, both male and female parents rear the young, with the male helping to provide the female with protection and food.
Regardless of social structure, all canids are territorial. They keep large home ranges, in which they wander in search of food. Boundaries are marked off by urine sprayed on raised objects, fecal deposits at latrines, and secretions from specialized glands located in the anus and face.
Communication is vocal, visual and olfactory. Canids are the most vocal carnivores, making wide ranges of howls, barks, whines, growls, woofs, and chuffing. They communicate using scent by marking using urine and feces as well as possessing several scent glands, located on their face, anus and base of the tail. The chemicals given off by these scent glands signals a canid's sex, physical condition and sexual status. Canids in heat give off chemicals that attract members of the opposite sex. Canids also use a wide variety of body postures to indicate mood.
All the world's mammals that exist today evolved from small insectivorous rat-like animals that began to evolve during the Cretaceous period. At the end of the age of dinosaurs, some 65 million years ago, these animals now had the opportunity to evolve and become more specialized. The order Carnivora began to emerge approximately 60 million years ago, during the Paleocene period. The primitive carnivores that made up this group were called miacids. This common ancestor gave rise to all dogs, bears, seals, cats, hyenas, weasels, and civets. About 48 million years ago, the suborders of Feliforma and Caniforma arose from the miacids.
Canids originated in the late Eocene more than 40 million years ago. They are the most ancient group of carnivores, and the first to evolve from the miacids. The family Canidae had three major co-existing radiations, represented by the subfamilies of Caninae (modern dogs), Hesperocyoninae (ancient canids), and Borophaginae (hyena-like canines).
The subfamily Hesperocyoninae was an archaic group of canids that originated and remained in North America. They existed about 40 million years ago, and looked like a cross between a fox and a weasel. They are the most ancient group, and were the dominant carnivores of their time. They became extinct about 15 million years ago. From the Nothocyon line of the Hesperocyonids came Tomarctus, which gave rise to the Borophaginae.
The second group, the Borophaginae, existed about 34 million years ago. Like Hesperocyoinae, they existed solely in North America. They were much larger than the Hesperocyonids, loooking like a cross between hyenas and dogs. This group contained the largest canid ever to exist, Epicyon haydeni, which was about the size of a bear. Canids in this subfamily had very large, powerful jaws. They filled a wide range of niches from raccoon-like omnivores to the top predators. They became extinct about 2.5 million years ago.
The last group, Caninae, is the subfamily that gave rise to all the canids alive today. They existed at about the same time as the other two subfamilies, but did not flourish until about 15 million years ago, when the other two subfamilies began to wane. This group evolved solely in North America until the late Miocene (about 7 million years ago), when they crossed the land bridge into Asia. One of the earliest canids of this group, Eucyon, which existed between 11 - 4 mya, is considered to be the direct ancestor to all modern canids.
The canids that crossed the land bridge became the direct ancestors for the canids that existed there. These animals continued to cross over the land bridge, back and forth between the two continents. This is why there are grey wolves in both Eurasia and North America.
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