Dogs generally have brown eyes and wolves almost always have amber or light colored eyes.[49] The skin of domestic dogs tends to be thicker than that of wolves, with some Inuit tribes favoring the former for use as clothing due to its greater resistance to wear and tear in harsh weather.[50] The paws of a dog are half the size of those of a wolf, and their tails tend to curl upwards, another trait not found in wolves.[51] The dog has developed into hundreds of varied breeds, and shows more behavioral and morphological variation than any other land mammal.[52]
Human emigrants from Siberia that came across the Bering land bridge into North America likely had dogs in their company. Although one writer[139] even suggests that the use of sled dogs may have been critical to the success of the waves that entered North America roughly 12,000 years ago,[139] the earliest archaeological evidence of dog-like canids in North America dates from about 9,400 years ago.[132]:104[140] Dogs were an important part of life for the Athabascan population in North America, and were their only domesticated animal. Dogs as pack animals may have contributed migration of the Apache and Navajo tribes 1,400 years ago. This use of dogs in these cultures often persisted after the introduction of the horse to North America.[141]
In Christianity, dogs represent faithfulness.[208] Within the Roman Catholic denomination specifically, the iconography of Saint Dominic includes a dog, after the hallow's mother dreamt of a dog springing from her womb and becoming pregnant shortly thereafter.[214] As such, the Dominican Order (Ecclesiastical Latin: Dominicanus) means "dogs of the Lord" or "hounds of the Lord" (Ecclesiastical Latin: domini canis).[214] In Christian folklore, a church grim often takes the form of a black dog to guard Christian churches and their churchyards from sacrilege.[215]
There are many different shapes for dog tails: straight, straight up, sickle, curled, or cork-screw. As with many canids, one of the primary functions of a dog's tail is to communicate their emotional state, which can be important in getting along with others. In some hunting dogs, however, the tail is traditionally docked to avoid injuries.[38] In some breeds, such as the Braque du Bourbonnais, puppies can be born with a short tail or no tail at all.[39]
As humans became more sophisticated, so did their dogs. Eventually, there emerged specific breeds of dogs, custom-bred to suit the breeders’ local needs and circumstances. The Greyhound, for instance, was the foundation type for the immense Irish Wolfhound and the dainty Italian Greyhound. All three have a distinct family resemblance, but you’d never mistake one for another.

Dogs have lived and worked with humans in many roles. In addition to dogs' role as companion animals, dogs have been bred for herding livestock (collies, sheepdogs),[154][17] hunting (hounds, pointers),[43] and rodent control (terriers).[17] Other types of working dogs include search and rescue dogs,[155] detection dogs trained to detect illicit drugs[156] or chemical weapons;[157] guard dogs; dogs who assist fishermen with the use of nets; and dogs that pull loads.[17] In 1957, the dog Laika became the first animal to be launched into Earth orbit, aboard the Soviets' Sputnik 2; she died during the flight.[158][159]
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