Scientists excavating an archaeological site in southern Spain have finally gotten the real poop on Neandertals, finding that the Caveman Diet for these quintessential carnivores included substantial helpings of vegetables. Using the oldest published samples of human fecal matter, archaeologists have found the first direct evidence that Neandertals in Europe cooked and ate plants about 50,000 years ago.

The extinct Neandertals, who lived from about 230,000 to 30,000 years ago, have long been portrayed as uber-carnivores—humans at the top of the food chain who ate mostly meat to fuel their revved-up metabolisms in order to survive in the frigid climes of northern Europe and Asia. This image was based on evidence from butchered meat bones and hunting tools at archaeological sites, as well as from studies of carbon, nitrogen, and other chemicals in the fossilized teeth of Neandertals, which can reveal their diets. But a recent study of starches in the plaque of Neandertal teeth indicated that Neandertals in modern-day Iraq and Belgium ate grasses, tubers, and other plants, and that they also cooked barley grains in Iraq. This view of Neandertals gathering plants and cooking barley porridge challenged the old view that our burly cousins went extinct because they depended too much on meat, whereas versatile modern humans could survive on a broader range of plant and animal foods. But it was still unclear whether vegetables made up a significant part of the European Neandertal diet.

Now, at an open-air archaeological site called El Salt in Alicante, Spain, researchers have gathered fossilized feces in the sediment where Neandertals lived at different times between 40,000 and 60,000 years ago, before modern humans arrived in the region. By applying a powerful method that was developed for detecting fecal matter in drinking water, geoarchaeologist Ainara Sistiaga of the University of La Laguna in Tenerife and geobiologist Roger Summons of the Massachusetts Institute of Technology in Cambridge have detected the biological signature, or biomarkers, of meat and plants in the sediments containing fossilized feces from five different places at El Salt. Specifically, the team was able to detect the chemical byproducts created by bacteria in the gut in the digestion of cholesterol from meat, as well as sterols and stanols, which are lipids in plants that are similar to cholesterol. The tests revealed that the poop “clearly” contained high proportions of cholesterol and coprostanol from eating meat, but it also included significant plant sterols that “unambiguously record the ingestion of plants,” the researchers report today in PLOS ONE.

Sistiaga says this is the first “direct” evidence that the Neandertals actually ingested plants, because the biomarkers were in their feces—and not just on their teeth.

The team determined that the fecal samples were from humans because other mammals, such as wolves and lions, cannot convert cholesterol to coprostanol, as primates do when they eat meat. No other primate bones have been found at the site, which includes Neandertal tools and artifacts that date to a time before modern humans are known to have inhabited Europe. The fine shape and structure of the coprolites in the soil also resembled those of humans, and parasites in the samples also suggest they came from humans.

Other researchers would like to see the link drawn more tightly between the poop and the Neandertals. “It is notoriously difficult to identify the species of coprolites,” says paleoanthropologist Michael Richards of the University of British Columbia, Vancouver, who studies isotopes in the Neandertal diet. He adds that many animals would have used the site over the thousands of years that Neandertals were there, and that the samples could contain biomarkers from their feces, which would contaminate the results. “So, while it is a promising new line of research, I don’t think it provides direct evidence of Neandertal diet.”

Paleobiologist Amanda Henry of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, would also like to see the researchers use DNA, parasite types unique to humans, or some other means to conclusively prove that the poop came from Neandertals. However, “the study is really exciting,” says Henry, author of the earlier study of Neandertal dental plaque that showed that a Neandertal in Iraq ate plants. “If they are correct, this is one more nail in the coffin for the idea that Neandertals were obligate carnivores.”