Perforated sea shells found at the Cueva de los Aviones site in Spain. (PNAS)

The discovery of painted shells used as jewelry by Neanderthals suggests the homonids were capable of advanced and symbolic thought, scientists say.

Joao Zilhao of the University of Bristol, U.K., and colleagues at European universities analyzed sea shells, found in what is now Murcia, Spain, that were painted and perforated, suggesting they were almost certainly used as pendants.

The researchers say this is the first time that body ornamentation has been conclusively recognized in Neanderthals.

Archeologists consider jewelry to be evidence of symbolic thinking and modern behaviour in early humans, Homo sapiens.

An oyster shell found at the Cueva de los Aviones site in Spain. The residue of a pigment used as a cosmetic is indicated on the right-hand side. (PNAS)

"This is the first secure evidence that, some 50,000 years ago — 10 millennia before modern humans are first recorded in Europe — the behaviour of Neanderthals was symbolically organized," said Zilhao, in a statement.

As well, an oyster shell found at the same site as the shell pendants contained a mixture of iron compounds that suggests it was used as a container for a cosmetic.

The reddish pigment on the oyster shell was made of the iron mineral lepidocrocite, mixed with ground hematite and pyrite. The researchers say that such a mixture, when fresh, would be black and shiny.

Yellow pigments found at another Neanderthal site were found to be natrojarosite, a iron compound used as a cosmetic in Ancient Egypt.

This isn't the first time that pigmented shells have been found associated with Neanderthals, but it is the first time that the possibility that the artifacts were made by modern humans can be ruled out.

A collection of decorated bone tools was found at a Neanderthal site near Châtelperron, France, for example, but it was dated to a time — 40,000 to 45,000 years ago — when modern humans were also in the area.

Zilhao argues that both the French tools and the Spanish pendants are evidence of sophisticated and symbolic behaviour in Neanderthals.

"The evidence from the Murcian sites removes the last clouds of uncertainty concerning the modernity of the behaviour and cognition of the last Neanderthals and, by implication, shows that there is no reason any more to continue to question the Neanderthal authorship of the symbolic artifacts of the Châtelperronian culture," he said.

The age of the artifacts was determined using carbon dating techniques. Thomas Higham of England's University of Oxford's Radiocarbon Accelerator Unit said the age of the samples approached the limit of the technique's abilities.

"We used the most refined methods of pre-treatment chemistry to obtain accurate dates for the sites involved by removing small amounts of more modern carbon contamination to discover that the shells and charcoal samples were as early as 50,000 years ago," said Higham.

The research appears this week in the Proceedings of the National Academy of Sciences.