Dogs buried without humans in North and Central America still show a loving touch and possibly a ritualized internment. A grave found in what is now Rhode Island, for example, contains a deceased prehistoric dog that was arranged to lie on its left side with its front paw under its head.

The age and condition of the dogs upon death also reveal domestication and the bond with humans, according to Morey.

He described a Middle Archaic burial dating from 6,700 to 7,180 years ago that was found in what is now Tennessee. The male dog discovered in the grave was "unusually old."

Its skeleton indicated the animal suffered from traumatic injuries, arthritis, a persistent infection, and broken bones, some of which had healed, and some that had not.

"The pathological condition of this individual suggests that the owner insured the safety and well-being of the individual throughout its life since it is doubtful that, given all the traumatic and age degenerative manifestations, the dog could have survived in the absence of care," Morey explained.

Christyann Darwent, an assistant professor of anthropology at the University of California at Davis, told Animal Planet News that she agrees with Morey's time window for dog domestication.

"Dogs and humans could have been hanging out together long before 17,000 years ago, but domestication means we were manipulating their breeding, and that probably didn't happen until more recently," she said. "The burials represent some of the best evidence we have for the strong social ties that exist between dogs and humans."

Darwent said domestication has benefited dogs and humans, but she suggested humans should take responsibility for their alteration of canines over the millennia.

"Some dogs, such as my own pet, are so reliant on humans that they could never fend for themselves in the wild," she said. "We must remember that we have manipulated them so much with domestication that they often must depend upon us now for their survival."

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