Canines -- defined!
All dogs -- wild and domestic, extinct and living -- belong to the canid family (family Canidæ). Canids have been around a long time and are the earliest known carnivores (order Carnivora.) In fact, dogs first appeared in the fossil record about 40 million years ago, well before other carnivore families like cats or bears.
Dogs and most other carnivores have a pair of blade-like teeth called the carnassials (car NAS ee uhls) in their upper and lower jaws. These teeth work like scissors to slice through muscle and skin.
Modern canines number several dozen species
The canid family tree includes 35 living species. Though there are a few lone lineages, there are three main groups:
South American zorros (foxes)
Wolf-like canines, including the coyote, jackals, wolves, and dogs
Fox-like canines, including the red fox and its relatives
The domestic dog's closest kin is the gray wolf (Canis lupus). Study the phylogeny to see a short line connecting these two species.
From wolf to dog
Fossil and genetic evidence confirms that all dogs are the descendants of wolves. In fact, skeletons of the earliest dogs and their wild wolf cousins can be tough to tell apart. Some of the key differences that scientists look for are:
Dog skulls often have a more prominent "stop" (the break in the downward slope from the forehead to the tip of the nose).
Dogs' teeth are squatter than those of similar-sized wolves.
Many dogs have already become extinct
Dogs have been around for millions of years. The fossil record shows three main groups of dogs.
The first group evolved in North America about 40 million years ago. Fossil evidence tells us that these first dogs looked like a cross between a weasel and fox. The name Hesperocyon (hess pur oh SYE on) means "western dog." The hesperocyonines became extinct about 15 million years ago.
The second group, the borophagines (bohr oh FAY... [continues]
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