The Sahara was once a green and moist savanna. Our ancestors could even catch fish there. These apparently played an important role on the menu of the Sahara people for a long time, as fossil finds from Libya now prove. But at some point that changed: people changed their diet and ate more and more mammals. Because fish became increasingly rare in their environment. The size of the animals and the composition of the fish communities also changed significantly. The reason for this was the onset of climate change, which ultimately caused the Sahara to dry out completely, the researchers report.
Apart from the ice deserts of the polar regions, the Sahara is the largest desert on earth – and it is getting bigger, as studies show. The Sahara has expanded by around ten percent in the past 100 years. Only animals and plants that can cope with arid and dry conditions can survive in the growing sea of stone, rubble and sand. But that was not always the case: Around 10,000 years ago there was a green savannah with numerous rivers in the place of today’s dry desert. At that time, the Sahara was a heavenly habitat for a diverse flora and fauna. Archaeological finds show that people also settled there. Insights into the life of the former Sahara people can be obtained, for example, at the famous Takarkori site. This rock overhang in the Tadrart-Acacus Mountains in Libya offered our ancestors welcome protection and was inhabited for thousands of years. Only a change in climate allowed the Sahara to dry up more and more, and also meant a drastic change for the people and animals living in it.
Change in the menu
New findings from Takarkori now impressively illustrate the consequences of the transformation from green paradise to the hostile desert. Wim Van Neer from the Royal Belgian Institute of Natural Sciences in Brussels and his colleagues unearthed animal remains from the period from 10,200 to 4,650 years ago. The exciting thing: Of the total of over 17,000 fossils discovered, almost 80 percent were fish. Traces of cuts and burns show that they served the people of that time as food. In this region, our ancestors once lived mainly from such garbage carriers. “These findings reflect the more humid conditions that prevailed in southwestern Libya during the early and middle Holocene,” the scientists state.
In the waters around Takarkori, it was evidently catfish and representatives of the tilapia, a genus of cichlids, that were at the time most abundant. Based on their analyzes, Van Neer and his colleagues assume that the fish migrated westwards from the Nile and that they passed the Ennedi and Tibesti river systems and the primeval Lake Mega-Chad until they finally reached the Takarkori region. Alternatively, the fish could also come from rivers from the Sahel and Mega Chad, from where they moved north towards the Tadrart-Acacus Mountains. “It is unclear which routes the colonization of the Takarkori area took. In all scenarios, however, Mega Chad probably played an important role in the spread of the aquatic species, ”explains the team. This primeval lake in the Chad basin occupied an area of 360,000 square kilometers 6000 years ago.
Cichlids disappeared first
Regardless of where the fish came from, the most interesting thing is how their population has changed over time. The fossil finds suggest that the fish became fewer and fewer. If they made up 90 percent of all the animals found at the beginning, their share was only 40 percent at the end of the period examined. At the same time, the amount of mammalian fossils increased – clearly they are remains of human meals, as the researchers report. They see this development as an indication of the impending climate change: increasing heat and drought are gradually driving the fish away, making fishing more and more difficult. “Hydrological and geomorphological data show that conditions became more unstable during the Middle Holocene,” Van Neer and his colleagues report. The number and extent of the waters decreased and many of them only carried water seasonally. As a result, our ancestors had to look for alternative food sources. They increasingly hunted out of the water and may have already started domesticating cattle.
The gradual deterioration of the climatic conditions can also be seen from the composition of the fish communities. Because, according to the results, the tilapia in particular initially disappeared. The catfish, however, were less affected by the loss. An obvious explanation: Fish like the gill bag catfish cope better with adverse environmental conditions. They can survive in shallow water, tolerate low oxygen levels and high temperatures, as the scientists explain. The last tilapia also changed optically – they became smaller. “This may be the result of stunted growth called stunting. We know that this phenomenon occurs in these fish when the water is small, ”explains the team. These striking changes in fish fauna are thus a further indication that the environment has become increasingly hostile to fish due to increasing aridity.
“This study provides important information about the dramatic climatic changes that have contributed to the formation of the largest arid desert on earth,” the researchers concluded. “Once again, the Takarkori rock overhang has proven to be a treasure for African archeology and beyond: it is a place where the complex dynamics between early human groups and their environment can be reconstructed in a changing climate.”
Source: Wim Van Neer (Royal Belgian Institute for Natural Sciences, Brussels) et al., PLOS ONE, doi: 10.1371 / journal.pone.0228588