International scientists said on Thursday that unusual stone dart tips found in an Oregon cave may have been made by a little known people who were perhaps the oldest inhabitants of North America.
The findings, published in the journal Science, add new information to a long-running debate over who were the first people to inhabit North America and become the founding culture of the Native Americans.
An analysis of stone tools and human faeces excavated from the Paisley Caves shows that people lived there about 13 200 years ago, around the same time or even before the Clovis people are known to have arrived on the continent.
Standard theory holds that the first inhabitants of the Americas, known as the Clovis people, arrived from Asia by crossing a land bridge into Alaska at the end of the last Ice Age.
But the discovery of weaponry that was made in drastically different ways - the so-called Western Stem tradition - has cast doubt on the theory that a single group colonised the land, and adds to a growing body of evidence that the Clovis were not alone.
"These two approaches to making projectile points were really quite different," said co-author Loren Davis from Oregon State University.
"And the fact that Western Stemmed point-makers fully overlap, or even pre-date Clovis point makers likely means that Clovis peoples were not the sole founding population of the Americas."
The crafting of sharp stone tips with shafts to be attached to a dart or spear is believed to have originated thousands of years earlier in Asia, but the method found in the northwestern US state of Oregon is not the same.
"This is a technology that has apparently developed in North America, and we have an entire assemblage that we recognise as the Western Stem tradition," said lead author Dennis Jenkins of the University of Oregon.
Other Western Stemmed points have been found at sites in Idaho and Nevada.
The points in Oregon appear to be about the same age as Clovis artifacts, but are made differently in the stem part where they attach to the shaft.
"The big a-ha here... is that we have demonstrated that these Western Stemmed tradition points are the same age as Clovis," Jenkins told reporters.
"There is no evidence of Clovis or any precursor to Clovis in the caves currently, and so that suggests that you've got here, at the exact same time, at least two technologies, or cultures if you want to call them that."
There are multiple possibilities for how such a divide could have occurred, and the findings could imply that there were at least two genetically separate populations in North America, though DNA analysis has not yet proven that.
Jenkins said it is possible that explorers may have crossed from Siberia into Alaska and then branched off into separate groups, one heading to the American west and the other east before eventually coming back together.
Traces of past cultures in the Paisley Caves were first discovered in the late 1930s, when Luther Cressman from the department of anthropology at the University of Oregon found camel, bison and horse remains as well as obsidian artifacts.
The latest study was authored by Paula Campos, Eske Willerslev and Thomas Stafford from the Centre for GeoGenetics at the University of Copenhagen, Denmark.