A jaw fragment found in a Swiss cave comes from the earliest known dog, according to scientists who analyzed and radiocarbon-dated the fossil to a period between 14,100-14,600 years ago. Dog origins remain poorly understood, however, and some researchers say that dog fossils much older than the Swiss find have already been excavated.
     The upper-right jaw unearthed in 1873 in Kesslerloch Cave has been recently studied and analyzed by archaeology graduate student Hannes Napierala and archaeozoologist Hans-Peter Uerpmann, study co-authors at the University of Tübingen in Germany. "The Kesslerloch find clearly supports the idea that the dog was an established domestic animal at that time in central Europe," Napierala says. Researchers have also found roughly 14,000-year-old dog fossils among the remains of prehistoric people buried at Germany's Bonn-Oberkassel site.
     Older fossil skulls recently identified by other teams as dogs were probably Ice Age wolves, Napierala and Uerpmann argue. That includes a 31,700-year-old specimen discovered more than a century ago in Belgium's Goyet Cave and reported in 2009 to be the oldest known dog.
     Paleontologist Mietje Germonpré of the Royal Belgian Institute of Natural Sciences in Brussels, who directed the analysis of the Goyet fossil, stands by his conclusions. "The Kesslerloch dog is not the oldest evidence of dog domestication," he says. Numerous wolf fossils lie near alleged dog remains at Kesslerloch Cave and Goyet Cave, raising doubts about whether either site hosted completely domesticated animals, remarks archaeologist Susan Crockford of the University of Victoria in British Columbia. She regards the Swiss jaw as an 'incipient dog' in the early stages of domestication from wolves.
     Scientists disagree about how and when dogs originated, other than that wolves provided the wild stock from which dogs were bred. One investigation of genetic diversity in modern dogs and wolves concluded that domestication occurred in southeastern Asia, whereas another placed canine origins in Eastern Europe or the Middle East. Napierala and Uerpmann suspect that dogs were domesticated from local wolf populations in various parts of Europe, Asia and perhaps northern Africa sometime before 15,000 years ago.
     The Kesslerloch dog jaw and its remaining teeth are considerably smaller than those of wolves recovered from the same site, the scientists say. A space between two of the fossil dog's teeth indicates that domestication must have reached an advanced phase at that time, they argue. During initial stages of domestication, jaws shrink in size faster than teeth, producing dental crowding. Later in the domestication process, teeth get small enough to leave spaces.
     Ancient dogs had shorter, broader snouts, wider mouths and wider brain cases than wolves, responds Germonpré. Brain studies indicate that dogs' retinas became reorganized to focus on the central visual field, perhaps to assist in tracking human faces, at the same time that selective breeding produced shorter noses, he says.

Sources: Science News (22 July 2010), Discovery News (23 July 2010)