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The arrival of European settlers, in the Americas, beginning in the 15th century, all but wiped out the dogs that had lived alongside people on the continent for thousands of years, according to new Oxford University-led research published today in Science. However, one close relative of these native dogs lives on in an unexpected place - as a transmissible cancer whose genome is that of the original dog in which it appeared, but which has since spread throughout the world. The study conducted by researchers from the Oxford School of Archaeology, in collaboration with researchers from the University of Cambridge, Queen Mary University of London, and Durham University used genetic information from 71 archaeological dog remains from the Americas. The findings reveal that pre-contact American dogs, which arrived alongside people over 10,000 years ago, and spread throughout North, Central and South America, had genetic signatures unlike dogs found anywhere else in the world. Comparison of ancient and modern American dog genomes revealed that these unique, pre-contact American dogs rapidly disappeared following the arrival of European settlers and left little to no trace in modern American dogs. This disappearance was most likely due to a combination of factors, including new diseases, cultural preferences for European breeds, and extermination of native dogs. A dog burial site from the Koster site in Illinois, dated c. 10,000 years ago - the earliest known dogs in the Americas.