As dogs cross the finish line in the grueling 1,150-mile (1,850-kilometer) Iditarod this week, they’ll probably be feted with extra treats. But we owe sled dogs a really great tummy scratch, too, for their role in human history. Ancient dog bones uncovered in the Arctic are showing that humans have had a close and complex relationship with dogs for thousands of years, from eating them to burying them lovingly with ornaments—and, of course, using them to haul things around. (Discover 5 surprising facts about the Iditarod.)

"Dogs have been critical to human habitation in the Far North," says Robert Losey of the University of Alberta, who specializes in the archaeology of human-animal relationships. Losey has excavated canine burials in Siberia that go back some 8,000 years. These dogs were not only interred in cemeteries, but also buried with jewelry and sometimes even alongside people. (Read about new clues on how and when wolves became dogs.)

Watch: Ancient dog burials in Siberia suggest that humans loved and cared for dogs even in prehistoric times. Courtesy University of Alberta.

Fast-forward several thousand years, and dogs in the North meet a different fate. At the 2,000-year-old site of Ust'-Polui in the Siberian Arctic, Losey notes that man's best friend was often dinner. The remains of more than 100 dogs have been recovered from Ust'-Polui—roughly four times as many as archaeologists usually see in Arctic sites—and of those remains, more than half belong to young dogs that were butchered and eaten.

View Images This 2,000-year-old knife handle from the Siberian Arctic site of Ust'-Polui may feature the world's oldest depiction of a sled dog wearing a harness. Photograph by Robert Losey

Putting Dogs to Work

Ust'-Polui also happens to be the site of the earliest known depiction of a sled dog, so Losey is particularly intrigued by what the dogs that weren't being eaten there were up to.

Dogs that pulled or carried people and cargo have been, until very recently, crucial to life in the Arctic, yet archaeologists know surprisingly little about sled dog history. "Think about how dogs could have affected human migration and the speed at which it could be done. It's very different when you have sled dogs than when you're just moving on foot or by boat," says Losey. "There are implications for a wide range of human history here." (What makes a great sled dog?)

While archaeologists have also recovered the remains of sleds at Ust'-Polui, there's no smoking gun in the form of dog remains still fitted with a sledding harness. So instead Losey and his colleagues are studying the dogs' bones for signs of stress, such as changes in bone shape or strength, that may show if any of the Ust'-Polui dogs carried or pulled heavy loads.

Is There a "Sled-Dog Signature?"

To identify exactly what a sled dog's bones would look like, Losey is analyzing the remains of sled dogs from historic Inuit communities, early 20th century sled dogs (including dogs from Robert E. Peary’s 1896-1897 expedition to Greenland), modern pet dogs, and modern wolves.

So far, the archaeologist is seeing that the limbs of modern sled dogs reflect signs of hauling: their bones are fairly short and very robust. "These are incredibly strong animals," says Losely. "In a sense, they look like a cross between a human weight-lifter and a long-distance runner.”

View Images Kristin Knight Pace and Piper at home in Healy, Alaska. Pace is a rookie in the 2016 Iditarod and Yukon Quest finisher. She operates Hey Moose Kennel with her husband Andy. Photograph by Katie Orlinsky

Losey is now comparing his analysis of modern sled dog bone structure to the dogs found at Ust'-Polui, most of which resemble modern Siberian Huskies in size and skull shape, and is confident that some of his ancient samples will show the "sled-dog-signature."

"Truthfully, I feel that the tradition of dogsledding is probably very, very old—much older than Ust'Polui, but it's just not obvious in the archaeological record," says Losey. "Very early use of dogs in pulling sleds was probably opportunistic, here and there, with smaller sleds and less weight being pulled. We may only see the classic "sled-dog" skeletal signature when dogsledding approaches modern practices, when it gets really intensive."

While Losey continues to look for evidence on dogsledding in ancient times, he keeps his work at the office. "I have a black lab who doesn't pull sleds," he concedes, "though she can pull on the leash pretty hard."