A mystery in human evolution may be close to being solved, thanks to a new study by the Insтιтut de Paléontologie Humaine in France. A nearly complete cranium discovered in 1960 inside the Petralona Cave in northern Greece has defied all efforts at identification and precise dating for several decades. The new study, published in the Journal of Human Evolution, has applied advanced isotopic techniques to place limits on its age, offering a precious insight into one of Europe’s most enigmatic fossils.

Petralona skull covered by stalagmite. Credit: Nadina / CC BY-SA 3.0

The skull was first found by a villager from a local village about 22 miles southeast of Thessaloniki. Embedded in a wall and without its lower jaw, the fossil drew the scientific community’s attention. Clearly from the Homo genus, it looked neither like Neanderthals nor modern humans. Its age remained unknown for decades, with speculation ranging anywhere from 170,000 to 700,000 years.

The new research employs uranium-series (U-series) dating, a method that measures the rate of decay of uranium isotopes into thorium. It is not a reliable method in open soil deposits because uranium is constantly supplied by the environment. But caves are a closed system: as water seeps through rock and evaporates, it leaves behind calcite deposits containing uranium but not thorium. Over time, uranium within these calcite layers decays into thorium, allowing scientists to calculate when the mineral layer first formed.

Researchers sampled calcite directly from the coating on the skull, as well as from several cave formations, including the Mausoleum chamber where the cranium was reportedly cemented. The results show that the calcite coating over the cranium began to form at least 286,000 years ago, with a margin of error of about 9,000 years. Depending on where it is precisely located in the cave’s stratigraphy, the fossil might actually date to anywhere between 277,000 and 539,000 years ago, or even between 410,000 and 277,000 years if it was not attached to the wall deposits.

This speleothem is covered by younger layers, the youngest of which is dated to 228 ± 1 ka (PE05a), contemporaneous with MIS 7. Credit: Falguères et al., Journal of Human Evolution (2025)

This finding produces a more precise chronology than previously available, yet one that continues to admit argument regarding the fossil’s broader evolutionary context. “ᴀssigning an age to the Petralona cranium is of outstanding importance because this fossil has a key position in European human evolution,” the authors noted in their study.

Morphologically, the Petralona skull appears to represent a more primitive population than both Homo sapiens and Neanderthals. The new age range is consistent with the view that this hominin coexisted with early Neanderthal lineages within Europe during the Middle Pleistocene, a period of significant evolutionary change.

Petralona Cave. Credit: Carlstaffanholmer / CC BY-SA 3.0

Despite warnings from scientists that the cranium can never be firmly ᴀssigned to any specific ancestor group, the new analysis is an important step towards learning its position in human history.

More information: Falguères, C., Shao, Q., Perrenoud, C., Stringer, C., Tombret, O., Garbé, L., & Darlas, A. (2025). New U-series dates on the Petralona cranium, a key fossil in European human evolution. Journal of Human Evolution, 206(103732), 103732. doi:10.1016/j.jhevol.2025.103732