Could the bison provide clues to the mystery of ancient American settlement?

Bones of giant steppe bison and traces of their ice-age hunters have led researchers to conclude that early humans likely colonized North America south from Alaska along the Pacific coast – not through the Rocky Mountains as previously thought. But when and how this happened remains a mystery.

Not Through The Rocky Mountains Corridor?

The first ancient people in America are thought to have reached their destination from Siberia using an ice-free corridor up along the Rocky Mountains during the late Pleistocene era. It remains uncertain when the crossing was created and how the people spread across the rest of America.

The traditional assumption is that people swept into the continent in a single wave 13,500 years ago, but there has been contradicting evidence that human societies have settled far east 14,500 years earlier and far south over 15,000 years earlier.

More recent proof shows, too, that the Rocky Mountain corridor was open until about 21,000 years ago, at the height of the last ice age when east and west ice sheets coalesced and completely separated populations.

Now, using radiocarbon dating and DNA analysis, researchers from University of California Santa Cruz followed ancient hunters and tracked bison movements. Studying 78 bison fossils, they found two distinct populations to the north and south, as well as traced when the animals migrated and interbred.

They discovered southern bison started moving in first with the opening of the southern part of the corridor, followed by the northern bison. The two started to mingle in the open pass approximately 13,000 years ago.

What this means: the mountains likely cleared of ice over a thousand years post-human colonization in the south – a suggestion that early humans first inhabited the Americas along the Pacific coast.

"When the corridor opened, people were already living south of there,” said study author and ecology and evolutionary biology professor Beth Shapiro. “And because those people were bison hunters, we can assume they would have followed the bison as they moved north into the corridor.”

First author and postdoc researcher Peter Heintzman said that given these results, one would be pressed to think otherwise.

“Fourteen to 15,000 years ago, there’s still a hell of a lot of ice around everywhere,” he told the Guardian. “And if that wasn’t opened up you’d have to go around the ice, and going the coastal route is the simplest explanation.”

The Rocky Mountains corridor, however, remains important for its role in later migrations and idea exchange between people north and south, Heintzman added.

 The Late Great Steppe Bison

Heintzman pointed to tidal erosion for little archeological evidence along the Pacific coast to vouch for its use among ancient people in migrating south. In the north, on the other hand, site dating is improving, but there are only a handful found in the land bridge along the Bering Strait.

Here enters fossils of bison, which are deemed the most numerous mammals of their kind in western North America. These animals, unlike most other large mammals like sloths and dire wolves, also survived mass extinction events.

The over-6-foot tall steppe bison of this period were much more massive than their living counterparts, according to author Duane Froese from the University of Alberta in Canada. Modern bison descended from these giants, Heintzman said, although they reside south of the range of their ancestors.

Many of the fossil samples came from the Royal Alberta Museum and other institutions’ collections. They were revealed through mining operations and later made available for scientific research.

The findings were published on June 6 in the journal Proceedings of the National Academy of Sciences.