Canis

Canis is a genus in the subfamily Caninae that includes living species like wolves, domestic dogs, coyotes, and golden jackals. Members of this genus are typically medium to large in size, with robust skulls and strong teeth, long legs, and relatively short ears and tails.

The genus was first described by Carl Linnaeus in 1758 in the tenth edition of *Systema Naturae*, where it grouped dog-like carnivores including domestic dogs, wolves, coyotes, and jackals. All Canis species are closely related genetically, share 78 chromosomes, and can potentially interbreed. In 1926, the International Commission on Zoological Nomenclature (ICZN) placed Canis on its Official Lists and Indexes of Names in Zoology, and in 1955, the ICZN designated *Canis familiaris* as the type species for the genus.

Compared to the genera *Cuon*, *Lycaon*, and *Xenocyon*, Canis is considered more primitive. It retains relatively larger canines and lacks certain dental adaptations for hypercarnivory, such as reduced or absent metaconid and entoconid on the lower molars, a small hypocone on the upper molars, a weak lingual cingulum, small or single-rooted second molars, a small or absent third lower molar, and a wide palate.

A DNA-based cladogram from Lindblad-Toh et al. (2005), updated with later findings, shows the relationships among Canis species. In 2019, a workshop hosted by the IUCN/SSC Canid Specialist Group recommended that the side-striped jackal (*Canis adustus*) and black-backed jackal (*Canis mesomelas*) be placed in a separate genus, *Lupulella*, because DNA evidence indicates they form a lineage outside the main *Canis*/*Cuon*/*Lycaon* clade.

The fossil record indicates that feliforms and caniforms split within Carnivoramorpha about 43 million years ago. The caniforms included the fox-like *Leptocyon*, which existed from 24 million years ago and branched into *Vulpes* (foxes) and Canini (canines) around 11.9 million years ago. The jackal-sized *Eucyon* lived in North America from 10 million years ago, and by the Early Pliocene (about 6–5 million years ago), the coyote-like *Eucyon davisi* spread to Eurasia. These early canids—*Eucyon*, *Vulpes*, and *Nyctereutes*—were small to medium predators in the Late Miocene and Early Pliocene, but not top predators.

In the New World, *Eucyon* gave rise to early North American Canis, which first appeared in the Miocene (6 million years ago) in the southwestern United States and Mexico. By 5 million years ago, the larger *Canis lepophagus*, an ancestor of wolves and coyotes, appeared in the same region. Around 5 million years ago, some Old World *Eucyon* evolved into the first members of Canis, which then became dominant predators across the Palearctic. The wolf-sized *Canis chihliensis* appeared in northern China in the Mid-Pliocene (4–3 million years ago). This was followed by a burst of Canis evolution across Eurasia in the Early Pleistocene (about 1.8 million years ago), known as the wolf event, linked to the formation of the mammoth steppe and continental glaciation. Canis spread to Europe as *C. arnensis*, *C. etruscus*, and *C. falconeri*.

A 2021 genetic study of the dire wolf (*Aenocyon dirus*), once considered a Canis species, found it was the last member of an ancient New World canine lineage that diverged before Canis appeared, with no evidence of interbreeding with Canis. The study suggested that the Neogene New World canids *Canis armbrusteri* and *Canis edwardii* might belong to this distinct dire wolf lineage, having convergently evolved a similar appearance to Canis. True Canis members—the gray wolf and coyote—likely reached the New World only in the Late Pleistocene, where their flexible diets and ability to hybridize helped them survive the Quaternary extinction event, unlike the dire wolf.

*Xenocyon* (strange wolf) is an extinct subgenus of Canis. By the end of the Early Pleistocene to the Middle Pleistocene, Canis diversity in Eurasia was reduced to the small wolves of the *Canis mosbachensis*–*Canis variabilis* group and the large hypercarnivorous *Canis (Xenocyon) lycaonoides*. The hypercarnivore *Xenocyon* gave rise to the modern dhole and African wild dog.

Dentition in canids is described using standard notation: upper teeth are labeled I (incisors), C (canines), P (premolars), and M (molars); lower teeth use lowercase i, c, p, and m. Teeth are numbered from the front of the mouth on one side. In carnivores, the upper premolar P4 and lower molar m1 form the carnassials, which work like scissors to shear muscle and tendon. Canids use premolars for cutting and crushing, except for P4, which is used only for cutting. Molars are used for grinding, except for the lower first molar m1, which has evolved for both cutting and grinding depending on diet. On the lower carnassial, the trigonid slices and the talonid grinds; the ratio of trigonid to talonid indicates dietary habits—a larger trigonid suggests hypercarnivory, a larger talonid suggests omnivory. Because its length varies little, the lower carnassial is used to estimate body size in carnivores.