Ancient tooth found near Old Crow, Yukon, belongs to earliest woolly mammoth in North America

Scientists have discovered that a tooth found near Old Crow, Yukon, in 2018 belonged to the oldest known woolly mammoth in North America.

The discovery challenges the popular belief that mammoths crossed into North America from Siberia in the last 100,000 years, said Love Dalén, a professor of evolutionary genomics at Stockholm University and one of the scientists behind the research. 

"We have had results in previous research suggesting that mammoths were in North America quite a long time ago, hundreds of thousands of years ago, but those specimens have never been identified," Dalén said. "So finding this really confirms our earlier theory."

The findings are detailed in a paper published last week that reports a million years of genomic evolution in mammoths. Dalén was among a team of scientists that analyzed mitochondrial DNA – genomes in the parts of the cell responsible for generating energy – from samples that spanned more than one million years of time. In doing so, the research team also developed a new method to date specimens, which will help scientists track the movements of ancient mammoths from hundreds of thousands of years ago. 

Yukon paleontologist Grant Zazula, along with a team of researchers, found the tooth in the Old Crow River basin on Vuntut Gwitchin traditional territory in 2018. Each summer, in collaboration with the First Nation, scientists visit the basin in search of ancient fossils. 

"It's still probably one of the most amazing places in the world for ice age paleontology because it seems like every time we go there, there's another spectacular discovery," Zazula said. "For many species, it seems to be the place where we find these very unique specimens."

"We've been on this kind of quest for a number of years looking for North America's first mammoths in the Old Crow region," Zazula said.

In 2018, Zazula and his team were searching in a prominent bed of volcanic ash within the basin. Volcanic ash beds are important, he says, because they provide time markers from the ice age. Any fossils found in that bed are at least 160,000 years old, says Zazula. 

One morning while searching the bed, the team spotted what they had been looking for. 

"We saw just a sliver of this mammoth tooth sticking out of the bluff in a spot that we knew was below the volcanic ash," he said. "When I saw the tooth, I knew that it was morphologically a woolly mammoth."

Zazula sent a sample from the tooth to Dalén's lab, where the team analyzed the tooth's mitochondrial DNA. The analysis confirmed that the tooth belonged to a woolly mammoth and dated it to about 220,000 years old. 

"It really is very old. It's not the last ice age, it's not even the ice age before that, but probably the ice age before that ice age where this mammoth lived," Dalén said.

Discovery leaves scientists with a 'mystery'

The discovery has left scientists with many unanswered questions, says Dalén. 

The mitochondrial DNA analysis also showed that the tooth belongs to a different genetic lineage than most mammoths in North America during the last ice age, he said. 

"There's still a mystery going on here," Dalén said. "What's going on with woolly mammoth evolution in North America that we haven't entirely wrapped our heads around?"

There are three different lineages of woolly mammoths based on their mitochondrial DNA, says Dalén. Two of those lineages have been found in North America, but almost all of the samples from the last ice age belong to a lineage known as clade one. 

However, the tooth that was discovered in Old Crow in 2018 belongs to a lineage known as clade three, Dalén said. 

"So the question is, where is clade one from?" 

In order to determine the origin of woolly mammoths from clade one and their relation to earlier mammoths in clade three, Dalén says scientists need to look for more woolly mammoth remains from the same time period as the tooth from Old Crow.

This summer, Dalén plans to take a team to another location in the Old Crow River basin in search of more fossils to help them unravel this mystery. 

"If we can find some mammoth material at this other site this summer … these could be really important to connect the dots between the earliest mammoths in North America and mammoths in Siberia," Zazula said.