Before Europeans began to colonize the Americas about 500 years ago, the land was populated with people who had been here for thousands of years. And their dogs.

The devastation visited on the native human inhabitants of North and South America is well known. Whether their dogs survived in some form, perhaps only as a portion of the DNA of some modern dogs, has been a matter of dispute. The available evidence indicated that only traces were present in current breeds and mixed breed dogs, but questions remained.

An international team of researchers who conducted the most detailed and thorough study yet of ancient and modern dog DNA reported Thursday in the journal Science that new evidence overwhelmingly suggests that the so-called pre-contact dogs have disappeared to an extent similar to the Neanderthals. The study found no more than 4 percent of pre-contact dog DNA in any sample, and those results could be interpreted as zero. By comparison, some modern humans may have a bit more than 2 percent Neanderthal DNA.

In a macabre scientific twist, the study found that the closest living DNA match to the pre-contact dogs is a strange but well-known cancer — a tumor in which the cancerous cells themselves spread from dog to dog during sex. Called canine transmissible venereal tumor, it originated thousands of years ago in one dog, probably from East Asia. The cancer is now present worldwide, still carrying the genome, much mutated but still identifiable, of that original host dog.

Greger Larson at the University of Oxford, an author of the paper, and the leader of an international effort to investigate the evolution and domestication of dogs, said the study emphasizes how inseparable are the fates of humans and their animals.

“The Europeans come through. They knock out the humans. They knock out the dogs,” he said. “It’s a complete disappearance.”

Laurent Frantz, an ancient DNA expert at Queen Mary University of London, who led the research, said that until now, there had not been enough evidence to know “the story of these dogs and what happened to them after the Europeans arrived.” Now, he said, it is clear that the pre-contact dogs were an identifiable group, separate from any other, and that some combination of disease and European persecution of native dogs led to their disappearance.

Fifty researchers collaborated on the study, which included both biological and archaeological evidence. They derived DNA from the remains of 71 ancient dogs from the Americas and Siberia and compared them to genomes of modern dogs. Dogs, which were domesticated at least 15,000 years ago, came over to North America with humans from Siberia, but perhaps not with the first wave of migration.