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Canidae is the family of carnivorous and omnivorous mammals commonly known as canines. It includes dogs, wolves, foxes, coyotes, and jackals. These animals are all digitigrades, meaning they walk on their toes.

Note that the subdivision of Canidae into "foxes" and "true dogs" may not be in accordance with the actual relations, and that the taxonomic classification of several canines is disputed. Recent DNA analysis has shown, however, that Canini and Vulpini are valid clades, which exclude two genera: Nyctereutes and Otocyon. These are basal canids and are not closely related to either vulpines or canines. (Some evidence also suggests the same for Urocyon.)

Speothos and Chrysocyon are primitive members of Canini, but might be placed in their own clade. Cuon may in fact be part of Canis and there is evidence that Alopex and Fennecus are not valid clades, but are both part of Vulpes.

The Domestic Dog is listed by some authorities as Canis familiaris and others (including the Smithsonian Institution and the American Society of Mammalogists) as a subspecies of the Gray Wolf (i.e., Canis lupus familiaris); the Red Wolf may or may not be a full species; and the Dingo, which is variously classified as Canis dingo, Canis lupus dingo, Canis familiaris dingo and Canis lupus familiaris dingo. At least one subspecies of wolf has recently been listed as a separate species - the Eastern Canadian Wolf, Canis lycaon. This is, however, a controversial classification.

When copulating, a male canine initially mounts the female from behind, as with most tetrapods, a position known informally as doggy style. The female will hold her tail to the side, if receptive, a gesture used by horses and other animals too, known as flagging. The male will often move around as he tries to get a good purchase upon her, and whilst attempting penetration of his penis to the female's vulva. At this point, the penis is not erect, it is slender and held rigid by a small bone inside, known as the os penis, which canines (but not humans) have.

When the male achieves penetration, he will often hold tighter and thrust faster, and it is at this point when he is mating that his penis grows. Canine reproduction is different from human sexual intercourse, because human males become erect first, and then enter the female; canine males enter first, then swell and become erect.

The male dog has a bulbus glandis at the base of the penis, a spherical erectile tissue which traps the penis inside the female's vagina during copulation as it becomes engorged with blood. more

Once the penis is locked into the vagina by the bulbus glandis, the male will usually lift a leg and swing it over the female's back while turning around. The two stand with their hind ends touching and the penis locked inside the vagina while ejaculation occurs, decreasing leakage of semen from the vagina. After some time, typically 5 - 20 minutes (but sometimes longer), the bulbus glandis disengorges, allowing the mates to separate. Virgin dogs can become quite distressed at finding themselves unable to separate during their first copulation, and may try to pull away or run.

Note that similar canine mounting behavior (sometimes with pelvic thrusting) is also used by dominant canines of both genders. Dominance mounting, with or without thrusting, should not be confused with copulatory mounting, in which the thrusting is short term until a "tie" is achieved.

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