Some 10,000 years ago, in what is now Koster, Illinois, a dog died. Its adopted group of hunter gatherers carefully laid the pup to rest in its own grave among their buried human dead, curled on its side as if it were asleep.
Today, this may not seem surprising — after all, modern dogs are often more “fur baby” than pet. But this ancient Illinois dog, and a duo of other canines buried right nearby, are remarkable: They're the oldest known individually buried canines found anywhere in the world, according to new research on the pre-print server Biorxiv. What's more, they provide the earliest physical evidence for dogs in the Americas.
The remains of these creatures has also proved key to solving an important canine conundrum: What happened to the dogs of ancient North America? Did they intermix with dogs brought by European settlers? And what breeds today can call them ancestors? A second new study, published in the journal Science, uses a battery of DNA analyses of both modern and ancient canines to search for clues.
The results suggest that European pups arriving with settlers in the 1500s completely replaced ancient North American dogs, such as the one buried at Koster 10,000 years ago. The paw prints of these ancient canines, however, are preserved in an unlikely place: Canine transmissible venereal tumors.
Bluntly put, the genetic legacy of ancient North American dogs is “living on in giving other dogs, you know, butt cancer,” says Angela Perri, zooarchaeologist at Durham University and an author of both studies.
Unearthed in the 1970s, the Koster dogs of Illinois, were reportedly 8,500 years old, based on radiocarbon dating of charcoal found near the remains. Since then, the discovery of other, older canine remains pushed the date of domesticated dogs in the Americas back to about 9,200 years ago. But by directly dating the skeletons, Perri and her colleagues have now discovered that the Koster dogs are actually around 10,000 years old—the oldest in the Americas.
The Koster dogs aren't the world's earliest canine burials—that award goes to a 14,000 year old grave in Germany, which houses a well-loved dog and its two humans. The Koster dogs, however, are the earliest yet-discovered canines that have warranted their own separate burials.
The Koster dogs bear no cut marks from butchery, so they were perhaps more friend than food, which is not the case for all early dogs. And their burial marks a certain honoring of the dead canines. At many sites, some dogs were “clearly thrown in the trash,” says Perri, which results in “bits and pieces of dog material all over the place.” Individually buried canines, however, likely represented the top dogs that were adept hunters, she says.
The discovery shows that from very early on in the Americas “dogs had very special place in these indigenous communities,” says Robert Losey of the University of Alberta, who was not part of this work. “They were the only animals that people were living with and they were the only animals people were burying.”
Our modern dogs all descended from gray wolves, but when, where and even how many times they were domesticated remains up for debate. Most researchers believe that by 16,000 years ago dogs were domesticated. And soon after, canines began traveling with their humans around the world, including into the Americas.
Many people like to think their pets—”ancient” breeds like Carolina dogs, Mexican hairless dogs, and chihuahuas, for instance—descend from some of these original pre-European-contact canines. (“Arctic” breeds, like Malamutes and Huskies, arrived in the Americas only about a millennium ago and don't appear to have mixed with dogs further south.)
Modern dog DNA, however, is complicated by thousands of years of cross breeding, Perri explains. “Modern dogs are a soupy mess,” she says, recounting study author Gregor Larson's favorite description of the matter.
So to sort through North American doggy history, researchers turned to analyzing ancient remains. And that's where the Koster dogs come in.
To figure out the origin and fate of the dogs that first set paw in the Americas, Perri and her colleagues analyzed 71 mitochondrial genomes (DNA passed from mother dog to puppy) and seven nuclear genomes of ancient North American and Siberian remains, including one Koster dog. They then compared that to the genetics of more than 5,000 modern dogs, including village dogs and breeds previously suggested to be part of an ancient American lineage.
The results suggest that all of the ancient, or pre-European-contact, dogs in the Americas share a distinct Siberian ancestor, but their genetic signature is unlike that of any other dogs worldwide. It seems these dogged travelers have completely genetically vanished, replaced almost entirely by Eurasian canines brought by European settlers in the 1500s.
“We thought surely there would be some interbreeding,” says Perri. But the genetics say otherwise. Only five of the more than 5,000 modern dogs tested had any evidence of these pre-contact dogs. One single Chihuahua and a mix-breed dog had less than two percent ancient American dog DNA. Three Carolina dogs had traces of ancient DNA, one up to 33 percent, but another they tested had none.
“Everything else we tested was just across the board of Eurasian origin,” she says. “Everything that people think of as kind of these classic American dogs ... are all Eurasian dogs.” It's unclear what these original dogs looked like, Perri adds.
There are a few potential causes for this startling disappearance. For one, European canines, like their humans, may have brought over diseases to which the ancient dogs did not have immunity. European settlers also likely favored their own breeds. “There were some really strong rules about not allowing your nice, 'pure' European breed dogs mate with North American dogs,” says Perri. These canines were seen as “wild” and “vicious,” she says. And often, when Europeans killed the native peoples, they killed their dogs as well.
Losey agrees that the extensiveness of the replacement and lack of interbreeding is striking. “Boy, there's just little genetic evidence for it,” he says.
Based on the researchers' analysis, the story of American dogs can be told in four acts.
The first wave of humans migrating across the Bering land bridge into the Americas were likely dog-less, making the perilous journey between 25,000 and 15,000 years ago. But the canine-loving migrants were right on their heels, likely making it in before the land bridge flooded around 11,000 years ago.
The second scene is up North, where the Thule people passed through with their Arctic dogs just 1,000 years ago. Though this part of the story is still slightly sketchy, those dogs seemed to stick to themselves, Perri says, with no genetic evidence for mating with pups in the lower 48.
Then, starting in the 1492 AD, European settlers came, bringing their Eurasian breeds and devastating the ancient American dog populations. The final act is a second introduction of huskies during the 1900s gold rush. These dogs looked genetically similar to the Thule dogs, says Perri, and seem to all come from that same Siberian dog population.
Though the story is not entirely new, it adds an extra level of genetic detail past studies lacked, says Krishna Veeramah, a geneticist at Stony Brook University who was not involved in the work. “Nothing struck me as 'oh, that's changing our understanding,'” he says. “But I do think on a technical perspective, it is important.” The ancient age of the DNA, and the number of dog genomes in this new study adds to a growing doggy DNA database that will help future researchers ask big questions about canine relations.
“I think their work confirms widely held options,” Losey adds. “It just does so with a far better data set than anybody else has ever had before.”
Though the original North American dogs are likely gone, they left an inauspicious legacy, in the form of Canine transmissible venereal tumors.
Although gruesome, these tumors are not usually lethal. Each time the transmissible tumor cells are passed from dog to dog (usually through mating), it brings a copy of its original DNA. Because of that, it carries a snapshot of the original “founding dog” that developed the disease, explains Elaine Ostrander, chief of the cancer genetics and comparative genomics branch at the National Human Genome Research Institute, who was not involved in the work.
Analysis of modern tumors suggest that the canine Patient Zero lived up
to 8,225 years ago—and was likely a North American dog. “It's the worlds
oldest continuously propagated cell line, which is really, really remarkable,”
Ostrander says, adding that the results of the new study may help researchers
track the origins of other diseases.
“We in other groups have been looking for these signatures of ancient
North American dogs in modern breeds,” says Heidi Parker, staff scientist
at the Dog Genome Project at
the National Human Genome Research Institute. “The thought that there's
actually a preserved signature of one of those early North American dogs
that are extinct today in this tumor, which is just perpetuating it then
forever, is very cool.”
So if you still have you heart stuck on owning an ancient American breed, finding a dog with a venereal tumor may actually be your best bet, Perri jokes. “It's kind of like the original American dogs aren't dead; they live on in venereal cancer,” she says. “It's kind of a sad story, but there it is.”