In 2017, an international team of researchers joined archaeologist Dennis Jenkins at Oregon’s Paisley Caves. Their aim? To reexamine the site’s sediments and coprolites, or ancient fecal remains, in hopes of resolving a longstanding debate about when people first arrived in North America.
The results of their study, published in July in Science Advances, confirm Jenkins’ earlier finding that people were living at the site a thousand years before the appearance of the Clovis people, long thought to be the continent’s first. That culture was named for the distinctive spear points first discovered near Clovis, New Mexico.
Jenkins, a senior archaeologist at the UO’s Museum of Natural and Cultural History, first uncovered the coprolites nearly two decades ago. Since then, radiocarbon dating has firmly established their antiquity, with some specimens dating back as far as 14,400 years.
Further examination by University of Copenhagen geneticist Eske Willerslev revealed that the coprolites were of human origin based on the mitochondrial DNA they contain. Still, questions about the coprolites remained, with researchers from Boston to Milan challenging the specimens’ human attribution.
“Critics pointed to the fact that DNA can be mobile in sediments,” Jenkins said, “so theoretically some of the DNA present in the coprolites could have been the result of contamination from overlying layers.”
The new study was a direct response to these questions. Co-authored by University of Newcastle archaeologists Lisa-Marie Shillito and John Blong along with Jenkins, UO archaeologist Tom Connolly and University of Bristol chemists Helen Whelton and Ian Bull, it zeroed in on fecal lipids, organic substances like bile acids and sterols that are far less likely than DNA to move around in sediments and can reliably identify the species of the organism that produced a particular poop.
The researchers analyzed the lipids found in 21 samples taken from the Paisley Caves coprolites. All 21 had been identified as human through earlier mitochondrial DNA analysis, and all but two had previously been radiocarbon dated. The analysis confirmed that three of six coprolites identified as human by mitochondrial DNA were in fact of human origin.
“The study demonstrates that while there probably was some degree of DNA movement from younger human occupations into older sediments, people were indeed living at Paisley Caves as much as 14,200 years ago,” Jenkins said.
To further confirm the age of one of the coprolites, the authors also radiocarbon dated a bulrush fiber artifact, likely a fragment of a basket or mat, found in the cave sediments.
“The fragment was dated to roughly 14,000 years before present, giving us a direct radiocarbon age on a pre-Clovis cultural artifact and confirming the stratigraphic integrity of the cave sediments,” said Connolly, director of archaeological research at the Museum of Natural and Cultural History and an expert in the fiber artifacts of the northern Great Basin.
Together, the results confirm that the Paisley coprolites are the oldest directly dated human remains in the Western Hemisphere.
Connolly said that the study is an example of how the dialogue of science operates.
“Our understanding is driven forward by skepticism,” he said. “When some questioned the attribution of human to the coprolites, DNA studies confirmed the source. When some questioned the accuracy of the DNA findings, scientists pursued novel approaches to confirm them. When multiple studies point to the same result, we gain much greater confidence in our findings.”
—By Kristin Strommer, Museum of Natural and Cultural History