What's more, the researchers have done "exquisite" radiocarbon dating.
"It's clearly older than Clovis," Grayson said.
Covering All the Bases
It's not the first claim to fame for Oregon's Paisley 5 Mile Point Caves, which in the 1930s were the site of extensive excavation. At the time, archaeologists claimed to have found secure evidence of human artifacts alongside the remains of extinct mammals.
No one believed it, and they were right not to, Grayson said, because the methodology was flawed.
"Jenkins and his group went back to Paisley to see if there was still material worth excavating, and to do the job right," he said.
Jenkins said that in the past, researchers had made several claims about pre-Clovis sites, but "they were all proven wrong."
"I wanted to be really cautious, because this site is simply too important," he said.
To verify that that the coprolites they found were human and date accurately, Jenkins enlisted DNA experts to conduct multiple tests on the samples.
Results indicated that the people in those caves were of the Native American founding genetic groups, or haplogroups, A2 and B2.
This means researchers must recalibrate when humans first migrated to the New World, Jenkins said.
Ideal For Study
In his lab in Eugene, Oregon, Jenkins opens a drawer to show one of the samples. The plastic bag is labeled with a bunch of numbers and letters—a meticulous coding system for tracking which cave the sample came from and where and from what depth it was excavated.
The coprolite itself looks like a hardened clump of brown mud of a, uh, familiar shape.
For archaeology, coprolites are ideal remains, Jenkins said. Bones can be controversial, because indigenous people may take offense to excavation. Bones also calcify over time, making it difficult to extract viable DNA.
In contrast, no one takes offense to examining stool samples, which are filled with cellular material shed by the harsh environment of the colon.
"You don't think of it," Jenkins said, "but you're leaving behind genetic signatures every morning."
The University of Washington's Grayson added: "No one would have predicted that the next Monte Verde would be based on turds."
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