Canis

Canis is a genus of the Canidae containing multiple extant species, such as wolves, coyotes and jackals. Species of this genus are distinguished by their moderate to large size, their massive, well-developed skulls and dentition, long legs, and comparatively short ears and tails. The generic name Canis means 'dog' in Latin. The term 'canine' comes from the adjective form, caninus ('of the dog'), from which the term canine tooth is also derived. The canine family has prominent canine teeth, used for killing their prey. The word canis is cognate to the Greek word kūon (Greek: Κύων), which means 'dog', as well as (less transparently) English hound. The tribe Canini (Fischer de Waldheim, 1817) is the sister group to the true foxes (Vulpes), and is represented today by two sub-tribes: Canina, which includes the genus Canis (wolves, jackals, the coyote, and the domestic dog), as well as the dhole and the African wild dog; and Cerdocyonina, which includes the so-called foxes of South America.:p55 The critical features that mark the Canini as a monophyletic group include: the consistent enlargement of the frontal sinus, often accompanied by the correlated loss of the depression in the dorsal surface of the postorbital process; the posterior expansion of the paroccipital process; the enlargement of the mastoid process; and the lack of lateral flare of the orbital border of the zygoma.:p77 While the tribe Canini (above) is monophyletic, the genus Canis is not. The genus Canis (Carl Linnaeus, 1758) was published in the 10th edition of Systema Naturae and included the dog-like carnivores: the domestic dog, wolves, coyotes and jackals. All species within Canis are phylogenetically closely related with 78 chromosomes and can potentially interbreed. In 1926, the International Commission on Zoological Nomenclature (ICZN) in Opinion 91 included Genus Canis on its Official Lists and Indexes of Names in Zoology. In 1955, the ICZN's Direction 22 added Canis familiaris as the type specimen for genus Canis to the official list. The fossil record shows that feliforms and caniforms emerged within the clade Carnivoramorpha 43 million YBP. The caniforms included the fox-like genus Leptocyon whose various species existed from 24 million YBP before branching 11.9 million YBP into Vulpes (foxes) and Canini (canines). The jackal-sized Eucyon existed in North America from 10 million YBP and by the Early Pliocene about 6-5 million YBP the coyote-like Eucyon davisi invaded Eurasia. In North America it gave rise to early Canis which first appeared in the Miocene (6 million YBP) in south-western USA and Mexico. By 5 million YBP the larger Canis lepophagus appeared in the same region.:p58 The canids that had emigrated from North America to Eurasia – Eucyon, Vulpes, and Nyctereutes – were small to medium-sized predators during the Late Miocene and Early Pliocene but they were not the top predators. The position of the canids would change with the arrival of Canis to become a dominant predator across the Holarctic. The wolf-sized C. chihilensis appeared in northern China in the Mid-Pliocene around 4-3 million YBP. This was followed by an explosion of Canis evolution across Eurasia in the Early Pleistocene around 1.8 million YBP in what is commonly referred to as the wolf event. It is associated with the formation of the mammoth steppe and continental glaciation. Canis spread to Europe in the forms of C. arnensis, C. etruscus, and C. falconeri.:p148 One study found that the diversity of the Canis group decreased by the end of the Early Pleistocene to the Middle Pleistocene and was limited in Eurasia to the small wolves of the Canis mosbachensis–Canis variabilis group and the large hypercarnivorous Canis (Xenocyon) lycaonoides. Dentition relates to the arrangement of teeth in the mouth, with the dental notation for the upper-jaw teeth using the upper-case letters I to denote incisors, C for canines, P for premolars, and M for molars, and the lower-case letters i, c, p and m to denote the mandible teeth. Teeth are numbered using one side of the mouth and from the front of the mouth to the back. In carnivores, the upper premolar P4 and the lower molar m1 form the carnassials that are used together in a scissor-like action to shear the muscle and tendon of prey.:74 Canids use their premolars for cutting and crushing except for the upper fourth premolar P4 (the upper carnassial) that is only used for cutting. They use their molars for grinding except for the lower first molar m1 (the lower carnassial) that has evolved for both cutting and grinding depending on the candid's dietary adaptation. On the lower carnassial the trigonid is used for slicing and the talonid is used for grinding. The ratio between the trigonid and the talonid indicates a carnivore's dietary habits, with a larger trigonid indicating a hypercarnivore and a larger talonid indicating a more omnivorous diet. Because of its low variability, the length of the lower carnassial is used to provide an estimate of a carnivore's body size.