More than 100,000 years ago in a Siberian cave there lived a child with a loose tooth. One day her molar fell out, and fossilized over many millenniums, keeping it safe from the elements and the tooth fairy.

But she wasn’t just any child. Scientists say she belonged to a species of extinct cousins of Neanderthals and modern humans known today as the Denisovans. And in a paper published Friday in the journal Science Advances, a team of paleoanthropologists reported that she is only the fourth individual of this species ever discovered.

“We only have relatively little data from this archaic group, so having any additional individuals is something we’re very excited about,” said Viviane Slon, a doctoral candidate at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and lead author of the study.