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An ancient dog fossil helps trace the path of humans to the Americas

An ancient bone of a dog, discovered in a cave in southeast Alaska, hints at when and how humans entered the Americas at the end of the Ice Age.

The bone, just the fragment of a femur, comes from a dog that lived about 10,150 years ago, based on radiocarbon dating. That makes this dog one of the oldest fossils, or possibly the oldest, found in the Americas, researchers reported on Feb. 24.

Bone DNA analysis, about the same age as three other dogs dating from about the same time period previously found buried in the Midwest (SN: 4/16/18), suggests that the dog belonged to a dog lineage. which were divided from Siberian dogs about 16,700 years ago. The timing of that division suggests that the dog’s ancestors, probably following along with humans, had left Asia by that time.

"Dog movement and domestication is obviously very, very associated with humans. So the interesting thing is that if you're following dog movement, it can also tell you something about humans," says Charlotte Lindqvist, an evolutionary biologist at University of Buffalo in New York.

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The new finding also adds to an ongoing debate about the route humans have taken after reaching North America via a land bridge in Alaska. A long-standing idea is that these early settlers traveled inland through an ice-free corridor (SN: 8/8/18). But about 16,700 years ago, that corridor would have been covered in ice. Thus, the existence of this ancient dog supports an alternative idea: that these colonizers embraced the Pacific coast as they moved south, possibly traveling by boat.

The piece of bone, smaller than a penny, was originally thought to be of a bear. But when Lindqvist and colleagues analyzed the DNA in the bone, it turned out to be canine. Comparing DNA with that of wolves, ancient dogs, and modern dog breeds allowed the team to calculate the last time the dog shared an ancestor with Siberian dogs.

This discovery is a big problem, says Angela Perri, an archaeologist at Durham University in England, whose recent genetic research suggests that domesticated dogs accompanied the first humans to the Americas about 15,000 years ago. This new work suggests that “at least about 16,700 years ago, humans and dogs seemed to move to the Americas,” he says. "And that would be almost 2,000 years earlier than we thought."

Kelsey Witt, a geneticist at Brown University in Providence, R.I., awaits additional discoveries from the first American dogs. By finding more ancient fossils and studying more DNA, Witt says, "I think we'll have a better picture of how people migrated and when dogs passed."

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