New findings about some ancient feces are the latest rejoinder in a five-year-long debate over one of the most important and controversial recent archaeological finds in USA. The debate centers around the discovery of dessicated feces, or coprolites, in a cave in south-Central Oregon, first reported by an international team of researchers in 2008.
     Found in a network of rockshelters known as the Paisley Caves, under layers laced with animal bones and a few human artifacts, the coprolites were found to contain fragments of human DNA. What's more, they were radiocarbon-dated to about 14,300 years ago - more than 1,000 years earlier than the oldest known sets of human remains in North America.
     The feces, originally analyzed by a team led by biologist Dr. M.T.P. Gilbert, recharged an ongoing debate about who the earliest Americans were and when, and by what means, humans first occupied the continent. Now, reporting in the Journal of Archaeological Science, another team of researchers says that its analysis of the oldest coprolite from the cave suggests it's from an herbivore, not a human. "The specimen under study was not excreted by a human," said Ainara Sistiaga, an archaeologist and visiting researcher at the Massachusetts Institute of Technology. "Our results show a predominance of the product of plant intake. This value is too high to represent a human origin," she added.
     Sistiaga's team used gas chromatography and mass spectrometry to scan the scat for types of sterols - fatty molecules found in both plants and animals. "Humans, because of their omnivorous diet and their high levels of cholesterol biosynthesis, will always have a predominance of coprostanol, the intestinal product of cholesterol," Sistiaga said. But while coprostanol usually makes up about 60% of the sterols in human droppings, she said, the study finds that nearly 70% of the sterols in the Paisley Cave feces are plant-based. "Even in the case of a vegetarian diet - unusual in an Upper Paleolithic society - the cholesterol and coprostanol values are too small to derive from a human," she said.
     The new study is only the latest salvo launched in the long scientific exchange over the Paisley Cave coprolites, which Sistiaga's team describes as "hotly debated." Soon after Gilbert's team published its findings in 2008, a few other researchers began drawing different conclusions about the site.

Edited from Western Digs (16 December 2013)