For centuries, dogs have helped people travel across the Arctic, hauling supplies, equipment, and other goods through snowy landscapes where other domesticated animals struggled to venture. Now, a new study publishing October 14 in the Cell Press journal iScience finds that sled dogs might have evolved shorter legs that helped them pull loads more efficiently. By examining the ancient remains of ritually buried dogs, the team found that both current sled dogs and dogs that were alive 2,000 ago had 6% shorter leg bones than other similar species—a finding that could help researchers trace the origins of sled dogs and better understand how dog-powered transportation spread across the cold regions of the world over the past 9,000 years.
"Sled dogs have played an indispensable role in communities in the Arctic," says first author Mitya Kletzerman of the University of Haifa in Israel. "Without dogs, people couldn't move as efficiently to hunt, relocate as conditions changed, or travel between communities to exchange knowledge and share new ideas. Understanding how the practice evolved could give us new insights into how people adapted to life in the Arctic."
The earliest archaeological evidence associated with dog sledding dates back to the early Holocene, about 9,000 years ago, on Zhokhov Island in modern-day Russia, where researchers found sled parts alongside dog remains. But because sledding equipment is rarely found in the archaeological record, it has remained difficult to determine when and where the practice first emerged or spread.
Previous research has shown that human-associated work can leave traces in an animal's skeleton. For example, reindeer used for racing, carrying loads, and pulling have limb bone differences compared to their non-working counterparts. Kletzerman's team wondered whether sled dogs also developed certain skeletal traits that helped them adapt to the physical demands of pulling a sled.
To investigate, the team developed a biomechanical model to understand how a dog's body handles the work of pulling a sled. Their model showed that one effective way to pull a loaded sled is for a dog to lower its center of gravity, thereby increasing its ability to generate pulling force.
"When people or animals pull a load, it tends to tip them backward. A lower or more forward position of the center of mass counteracts this effect, allowing greater pulling force," Kletzerman says.
The researchers then tested whether modern sled dogs have skeletal proportions that lower their center of mass. They analyzed bones in 60 canids, including sled dogs, wolves, mongrels, and spitzes. They compared the lengths of five long bones: the humerus, radius, and ulna in their forelegs, and the femur and tibia in the hind legs.
After accounting for overall skeletal size, the researchers found that sled dogs had relatively shorter radius, ulna, and tibia bones than non-sled canids, with these bones measuring about 6% shorter on average.
"It's unclear how this trait developed, but selective pressure may have preserved it, because it gave sled dogs an advantage over other dogs," Kletzerman says.
To understand whether this characteristic already existed in ancient dogs, the team examined 82 ancient dog bones and three skeletons of ritually buried dogs from three archaeological sites associated with ancestral Inuit populations in present-day Chukotka, Russia, dating from about 2,000 to 500 years ago.
About 89% of the bones were classified as consistent with the modern sled-dog pattern of shorter leg bones, as were all three ritually buried dogs. The findings suggest that this skeletal pattern could be an effective way to identify possible sled dogs even when archaeological remains are incomplete or lack direct evidence of sled equipment.
"Dogs have been working alongside humans for thousands of years, but we're only beginning to understand how that partnership shaped them," Kletzerman says.
