Image copyright Gabriel Hernández Image caption The Iberus alonensis snail has been part of gastronomy in Spain for more than 30,000 years

Palaeolithic humans in Spain began eating snails 10,000 years earlier than their Mediterranean neighbours, study reveals.

Snails were an extra food source for ancient humans, important for their survival and adaptation.

The findings revealed that Homo sapiens living in the Benidorm area were the first recorded group to include snails in their diet, some 30,000 years ago.

The paper is published in the journal Plos One.

Archaeologists working in Cova de la Barriada have found large and concentrated amounts of snail shells among stone tools and other animal remains in pits that were used for cooking during the early Gravettian era - 32,000 to 26,000 years ago.

Lead author Dr Javier Fernández-López de Pablo, from the Catalan Insitute of Human Palaeoecology and Evolution, told BBC News: "What this suggests is that these groups [of humans] had already opted for a strategy of diet diversification that allowed them to increase their population."

Image copyright J.Fernández-López de Pablo/IPHES Image caption The snail shells were found among stone tools and animal remains

Diet has been changing throughout human evolution.

In contrast to traditional ideas about the diets of earlier human species, Homo sapiens is known to have broadened its diet to include plants, freshwater fish, molluscs and land snails.

Dr Alex Pryor from the University of Southampton, who was not involved in the latest study, explained: "Humans evolved in Africa and then spread out and colonised the whole of Eurasia, and in each of these new environments they were moving in and adapting.

"They were experimenting with things that had not been done before. The paper also refers to the period when an explosion of art is going on, which is another aspect of people experimenting."

He added: "You see people beginning to use more of the smaller resources… I see the land snail as another example of catching small animals."

However, it is still unclear exactly when and how this happened.

Homo sapiens living along the Mediterranean coast of northern Africa, France, Italy, Greece and the Middle East are also known to have eaten snails, but started eating them 10,000 years later.

Dr Fernández-López de Pablo said the new fossils are "clearly the oldest record [of snail consumption] we have so far".

Molluscs and snails are considered intrusive in archaeological sites because other animals also eat them and can transport and accumulate the remains.

"It is one of the most difficult elements to interpret," explained Dr Fernández-López de Pablo.

"Here we find huge amounts, very concentrated and very well selected, next to clear evidence of human activity."

Image copyright J.Fernández-López de Pablo/IPHES Image caption Early humans selected only large snails that corresponded to adult specimens

The researchers are sure that the snail remains were produced by humans because of the similarity and composition of the shells.

The 112 samples of Iberus alonensis that have been excavated at the site were relatively large and of similar size, indicating that the ancient humans carefully picked adult snails in order to conserve the species.

Further analysis using high-resolution microscopes showed that the shells' levels of aragonite - a mineral based on calcium, carbon and oxygen - are consistent with those after roasting the shells for a prolonged time.

A delicacy

The Iberus alonensis snail is indigenous to the Iberian Peninsula and lives in dry terrains among rosemary, lavender and thyme.

Romans were already known to harvest snails, which were considered as elite food 2,000 years ago.

Nowadays, snails are regarded as a delicacy in Spain and are part of the country's gastronomy, used in dishes like paella.

They even have their own yearly festival in Lleida, Catalonia, where people meet to celebrate and eat tonnes of snails.

"Next time you come to Spain and eat snails, you'll have a nice story to tell," said Dr Fernández-López de Pablo.