Skull found in a Greek cave is 286,000 years old, but its identity has been a mystery since 1960

A skull belonging to an unknown hominin, found in 1960 inside Petralona Cave in northern Greece, has finally given up one of its biggest secrets.

New measurements of the mineral crust that formed directly on the bone show the skull is at least 286,000 years old.

This anchors it firmly in the Middle Pleistocene and contributes to a debate that has stretched for decades.

The cave sits in Chalkidiki, about 31 miles (50 kilometers) from Thessaloniki.

In this cave, the chambers are lined with slow-growing cave minerals. Those minerals turned out to be the timekeeper that earlier studies could not find.

The skull was discovered without reliable layers of sediment around it. This means that estimates of its age have ranged wildly from 170,000 to 700,000 years.

Petralona skull is a true puzzle

The latest work was led by Christophe Falguères of the Institute of Human Paleontology, National Museum of Natural History, in Paris (IHPNMNH).

He has spent years refining radiometric methods on difficult fossils in caves.

His team sampled the calcite crust that began forming when moisture exposed the cranium to the cave air, then read the clock inside the rock.

The Petralona skull is clearly human-like, but it does not match either Homo sapiens or Neanderthals.

Its features point to an older European group that lived alongside the Neanderthal lineage during the later Middle Pleistocene.

That alone makes its age and context matter for how we tell the story of Europe.

The skull’s history in the Petralona Cave is complicated. The team also dated nearby formations to bracket when the cranium could have arrived and when its coating began to grow.

That broad view helps separate the age of the skull from the age of unrelated cave features that happen to sit near it.

How the calcite clock works

In cave settings, U-series dating measures how uranium in dripping water becomes part of calcite layers, then decays into thorium at a known half-life.

Because thorium does not dissolve easily in water, the thorium that appears later, inside that calcite, forms as uranium decays. This means that the ratio between the two elements can act as a clock.

A speleothem is a cave deposit, like a stalagmite, stalactite, or thin mineral curtain on a wall. When these deposits form in a closed system, they lock in uranium with almost no initial thorium.

This is exactly the condition needed to convert isotope ratios into ages.

The approach has matured with better mass spectrometry and careful protocols. It is now possible to test whether a sample behaved like a closed system after it formed.

A recent review outlines how these improvements allow precise age estimations, from a few years up to more than 500,000 years for the right carbonate materials.

What the Petralona skull dates say

“The results yield a finite age suggesting that the Petralona cranium has a minimum age of 286 ± 9 ka,” said Falguères, citing the team’s results. That number comes from the white inner calcite layer that first formed on the skull.

Other measurements show the stalagmitic veil on the nearby Mausoleum wall started forming far earlier. The top layers were dated at 510 ± 29 thousand years, while the deeper parts were older than 650 thousand years.

Those older wall coatings mean the skull’s calcite is not the same generation as the wall. This implies that the skull’s minimum age reflects when its own coating began to form.

Stratigraphy in the corridor leading to the chamber indicated no stalagmitic floor older than about 410 ± 6 thousand years.

A younger surface was, however present. It was dated at 228 ± 1 thousand years and tied to Marine Isotope Stage 7 (MIS 7) in warmer phases.

Taken together, the most reasonable windows are about 539-277 thousand years, if the cranium was once attached to the wall, or about 410-277 thousand years if it was not. There was a firm minimum of 286 ± 9 thousand years.

Fitting into the human family tree

“From a morphological point of view, the Petralona hominin forms part of a distinct and more primitive group than Homo sapiens and Neanderthals,” said Falguères.

He described a population that likely lived alongside an evolving Neanderthal lineage in Europe.

This position fits a growing view that the later Middle Pleistocene was busy, with several distinct hominin species co-existing. Hominin evolution was not a simple hand-off from one species to another.

A separate study directly dated the Broken Hill, or Kabwe, skull from Zambia to 299 ± 25 thousand years. This is much younger than many had assumed.

Kabwe often gets grouped with the European material, sometimes called Homo heidelbergensis, and its age coincides well with the Petralona minimum.

Work on Spanish fossils from Sima de los Huesos adds more context.

An extensive mandibular analysis indicates that European Middle Pleistocene hominins separated into at least two lineages, one with clear Neanderthal traits and another without them.

This mirrors the idea that the Petralona skull represents a more primitive group that was not Neanderthal.

Further studies of the Petralona skull

The new Petralona skull dates remove a major stumbling block by establishing a clear floor for its age. That minimum places the skull squarely within a period when multiple hominin groups shared the continent.

Now, discussion about its shape and its relationships can proceed without a fog of incompatible chronologies.

Future progress will come from more direct dating of materials that are physically attached to fossils and from integrating those ages with careful anatomical studies.

Non-destructive sampling and tighter checks on whether a sample stayed closed after it formed will keep pushing uncertainties down while avoiding damage to irreplaceable specimens.

For Europe, the picture looks less like a straight line and more like a set of hominin branches living side-by-side.

The Petralona skull now sits on one of those branches with a firm timestamp. That helps narrow which scenarios still make sense for how Neanderthals emerged and how other groups faded.

The study is published in the Journal of Human Evolution.

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