Ancient Bone Fragment Holds Clues on How Dogs Got to North America

A bone fragment discovered in southeast Alaska reveals the earliest confirmed domesticated dog in the Americas.

This bone fragment, found in Southeast Alaska, belongs to a dog that lived about 10,150 years ago, a study concludes. Scientists say the remains, a piece of a femur, provide insight into the question of when dogs and humans first entered the Americas, and what route they took to get there. (Douglas Levere / University at Buffalo)

(CN) — Humans share an intricately connected timeline with canines, the first animal to be domesticated. Now scientists believe they have discovered the oldest dog to have traveled with humans along the Alaskan coast.

In a new study published Tuesday in the journal Proceedings of the Royal Society B, researchers at the University of Buffalo and the University of South Dakota discuss how a serendipitous finding offered another piece to the puzzle in the complex history of humans’ relationships with canines.

The finding in question occurred when a team of scientists, led by lead author Charlotte Lindqvist, an associate professor of biological sciences in the UB College of Arts and Sciences, were studying a collection of fossils excavated in southeast Alaska. These fossils were obtained by a team of researchers, including Timothy Heaton, professor of earth sciences at the University of South Dakota.

While performing DNA sequencing on the bones, the scientists noticed a suspicious femur fragment that at first appeared to be from a bear. It was later discovered to have belonged to an ancient dog, which analysis confirmed would have lived there approximately 10,150 years ago.

“This all started out with our interest in how Ice Age climatic changes impacted animals’ survival and movements in this region,” Lindqvist says. “Southeast Alaska might have served as an ice-free stopping point of sorts, and now — with our dog — we think that early human migration through the region might be much more important than some previously suspected.”

The team deduced the ancient dog’s ancestry from clues in the mitochondrial genome within the DNA, which revealed that its breed had evolved from Siberian dogs around 16,700 years ago. This was around the same time experts suspect ancient humans were traveling to North America, taking a route along the Alaskan coast which coincidentally would have passed through southeast Alaska.

A map showing the study area. (Bob Wilder / University at Buffalo)

“We now have genetic evidence from an ancient dog found along the Alaskan coast. Because dogs are a proxy for human occupation, our data help provide not only a timing but also a location for the entry of dogs and people into the Americas. Our study supports the theory that this migration occurred just as coastal glaciers retreated during the last Ice Age,” said Lindqvist.

“There have been multiple waves of dogs migrating into the Americas, but one question has been when did the first dogs arrive? And did they follow an interior ice-free corridor between the massive ice sheets that covered the North American continent, or was their first migration along the coast,” Lindqvist continued.

After confirming the bone belonged to a dog, the team compared the mitochondrial genome to other known canines. They found their dog shared an ancestor with dogs who lived in the Americas before European colonizers settled here with their own dogs.

The authors add they look at mitochondrial DNA to view a fragment of an organism’s genetic makeup inherited from its mother, and it is the next best thing to having a complete nuclear genome which requires more DNA material.

“The fossil record of ancient dogs in the Americas is incomplete, so any new remains that are found provide important clues,” said co-author Flavio Augusto da Silva Coelho, a UB doctoral student in biological sciences. “Before our study, the earliest ancient American dog bones that had their DNA sequenced were found in the U.S. Midwest.”

Furthermore, the team also performed a test called carbon isotope analysis on the bone fragment and were able to see the dog’s diet. According to their findings, it consisted of mostly fish and scraps from seals and whales, likely fed to them by their human companions who had similar diets.

Lindqvist notes the research marks another spot on the map of dogs coming to the Americas, which was a lengthy process with multiple arrivals including Arctic dogs from East Asia and Siberian huskies during the Gold Rush, which to this day carry the most ancient American dog genes.

Fossil records show that once the Europeans arrived with their domesticated dogs, existing dogs in the Americas started dying in large numbers. Scientists hypothesize that colonists may have killed them to avoid mixing bloodlines with their dogs bred specially for hunting and herding, or perhaps resorted to hunting them for food when resources were scarce. Though the most likely explanation is diseases introduced by the colonizers’ arrival.

Nevertheless, this study adds another fascinating chapter to human and domesticated dog migration into the Americas, successfully placing another instance on the timeline.

“Our early dog from southeast Alaska supports the hypothesis that the first dog and human migration occurred through the Northwest Pacific coastal route instead of the central continental corridor, which is thought to have become viable only about 13,000 years ago,” Coelho concluded.

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