SOUTHWESTERN SIBERIA — Researchers reported evidence of an invasive dental procedure performed on a Neanderthal molar dating to about 59,000 years ago that was unearthed at Chagyrskaya Cave in southwestern Siberia. The findings were published in the journal PLOS One and describe a depression on the tooth that the authors attribute to drilling with a stone tool to treat a cavity.

Excavations at the cave have produced stone and bone tools along with fossils from the easternmost known population of Neanderthals. During a rainy month and a half in the summer of 2016, a research team scraped away dirt and rock from the cave floor with scalpels and small knives, recovering Neanderthal finger and toe bones and teeth.

After cleaning, archaeologist Ksenia Kolobova noticed a deep hole on the biting surface of an adult Neanderthal upper third molar and showed it to dental anthropologist Alisa Zubova. Kolobova said of the fossil collection at the site: "It is the richest collection in this part of the Eurasia." She said her colleague flagged the anomaly early on: "At the very beginning, she suspected that the cavity inside the tooth — it's not very natural."

The team examined the molar using micro-CT scanning, scanning electron microscopy and Raman spectroscopy. The hole extended through the volume of the pulp chamber and contained numerous microscopic radial grooves. To test their interpretation, the researchers produced a replica perforator stone drill and used it on three modern human teeth, including an untreated upper left third molar donated by one of the researchers, duplicating the geometry and abrasion observed on the ancient tooth. Subsequent wear on the Neanderthal molar suggests the individual lived after the intervention.

"This [hole] was created by a stone tool handled by a Neanderthal between the thumb and the forefinger," said John Olsen, an archaeologist at the University of Arizona. He described the intervention as "Basically a root canal." and said, "We think this is an open and shut case."

Cavities were rare among Neanderthals, and the authors describe the molar as the oldest known evidence of dentistry or any direct medical treatment. Rachel Kalisher, a bioarchaeologist at UC San Diego, said the analysis was thorough but not conclusive. "They did a lot of great work and they have beautiful data presented," she said. "It's certainly believable. But I'm not sure that the evidence that they provide is necessarily the smoking gun." Kalisher added: "They are thinking broadly about what could be causing these appearances. And then they use a bunch of deductive reasoning and experiments to scratch things off one by one."