Koster Dog illinois

Americans love their pet dogs — all 78 million of them, in fact. Caring for pet pups is a tradition in the Americas that stretches back millennia, though scientists only recently discovered exactly how long ago dog domestication really took place. Last week, at the annual meeting of the Society for American Archaeology, researchers revealed the ages of a trio of pups buried in ancient graves in southern Illinois. These dogs, deeply cared for by their owners, are older than anyone previously guessed.

At the conference, study leader and Max Planck Institute for Evolutionary Anthropology zoologist Angela Perri, Ph.D. presented the results of radiocarbon dating on dog fossils previously uncovered at the Stilwell and Koster archaeological sites in southern Illinois. These dogs were clearly buried intentionally, and the lack of damage to their bones indicates that they died of natural causes rather than as a result of human butchery (which scientists have found evidence of in Texas). Past attempts at dating them, which were based on measurements of the age of wood burned nearby the site, suggested they were around 8,500 years old, reported Science News on Tuesday. The new analysis, however, shows that they’re actually closer to 10,000 years old, making them the earliest directly dated evidence of domesticated dogs in the Americas and the oldest evidence of intentional burials of individual dogs in global archaeological history.

A 3D rendering of the Koster Dog fossil.

The new date “presents a conundrum both temporally and spatially,” the researchers write in the abstract for their study. That’s because dogs, which are thought to have been domesticated anytime (and any number of times) between 15,000 and 40,000 years ago, are thought to have been brought over from Eurasia by the first groups of human migrants to the Americas. If that’s true, then it’s extremely puzzling that there’s evidence of ancient domesticated dogs in the American midwest but not in the north and west near the Bering Strait, which the migrants would have had to cross.

The dogs from the Stilwell and Koster sites, the former discovered in 1960 and the latter discovered in 1970, are thought to be part of a lineage that led to the “All-American dog.” In April 2017, a different team of researchers writing in Cell Reports presented a genetic signature in present-day dog breeds that was clearly passed down by the “New World Dog,” a subspecies of pup that’s thought to have been brought over by humans that migrated from Eurasia. Previous studies had suggested that the “New World Dog” had been outcompeted by Old World dog species, but the genes of present-day pups shows that their ancient ancestors persisted. The Stilwell and Koster dogs, thoughtfully buried by their masters on their sides, indicate why they might have survived so long.

Recent discoveries in the field of canine archeology have revealed not only how far back our relationship with dogs goes but also how deep it went. In a February study on 14,000-year-old dog remains discovered in Germany, researchers showed that the dog’s owner almost certainly nursed it through periods of ill health — just like Americans who spend some $63 billion annually on pets do today.

At 10,000 years old, these dog fossils are the oldest we’ve found in the Americas — for now. Future research may uncover even older burial sites in the vast space between the Bering Strait and the Midwest, pushing back the anniversary of humankind’s greatest friendship even further into history.