The Sahara desert was once home to several species of fish, including tilapia and catfish, which were hunted by animals and humans alike. The fossil record shows that these populations dwindled as a changing climate dried up the lakes and swamps they inhabited, which may have forced the people and animals who relied on them to change their diets.

Between 2003 and 2006, Savino di Lernia at Sapienza University of Rome and his colleagues analysed fossils from a rock shelter called Takarkori in southwestern Libya. Until about 5500 years ago, the 140-square-metre cave was close to large pond, making it ideal for ancient human occupation.

Di Lernia and his team examined fossils dating from 10,200 to 4650 years old, which were well-preserved in the shelter and arid conditions of the cave.

“During this period, the central Sahara was much more humid than it is today. It was a savannah-like environment and it supported large animals like elephants, hippos and rhinos,” he says.

Because of this, di Lernia expected to find a lot of fish bones at the site. Nevertheless, he says he was surprised at how many they found. In fossils between 10,200 and 8000 years old, around 90 per cent of the animal material they found belonged to fish, including catfish and tilapia. Cut marks on the bones suggest that the bones were human food refuse.

This number dramatically reduced when they analysed animal remains from between 5900 and 4650 years ago. At that point, fish bones only made up about 48 per cent of these remains. Much of the rest of the bones belonged to a whole host of mammals such as sheep, goats and cattle.

The fossil record also suggested that the Saharan environment began to dry out around 7400 years ago. An increasing proportion of the tilapia fossils form around that time came from a hardy species – Coptodon zillii – which can withstand drier conditions. At the same time, there was a decrease in the proportion of bones from Oreochromis niloticus, a species less suited to dry conditions.

“There are not a whole lot of sites like Takarkori that show the transition in the ways people were eating in this period of dramatic landscape change,” says David Wright at the University of Oslo in Norway. “It is just one piece of the puzzle, but an important one as we wrestle with understanding how people can adapt to extreme forms of climate change.”

Journal reference: PLOS One , DOI: 10.1371/journal.pone.0228588