A 13,000-year-old bison fossil has shown the most likely migration route of some of the first native Americans.
DNA from the bison remains has narrowed down when an ice-free corridor opened up along the Rocky Mountains during the late Pleistocene.
That corridor was a vital route for migrations between what is now Alaska and Yukon in the far north and the rest of the North American continent.
Researchers had previously suspected this was the way migrating humans and animals must have travelled, but were unclear about how and when it was used.
But now, a new study published in Proceedings of the National Academy of Sciences, shows the route was fully open by about 13,000 years ago.
While this route was closed when the very first humans moved south of the ice sheets into North America around 15,000 years ago (they probably took a Pacific coastal route), it is thought it later became a well-travelled thoroughfare in both directions.
“The opening of the corridor provided new opportunities for migration and the exchange of ideas between people living north and south of the ice sheets,” said Peter Heintzman, of UC Santa Cruz, who led the DNA analysis.
His coauthor Beth Shapiro, also from UC Santa Cruz, has previously shown that bison populations north and south of the ice sheets were genetically distinct by the time the corridor opened.
So, armed with that knowledge, the researchers have been able track the movement of northern bison southward, and southern bison northward.
“The radiocarbon dates told us how old the fossils were, but the key thing was the genetic analysis, because that told us when bison from the northern and southern populations were able to meet within the corridor,” Heintzman said.