Nick Carne
If you still have doubts that the Sahara was once a lot wetter, a new study by Belgian and Italian researchers should dispel them.
Catfish and tilapia make up a fair chunk of the animal remains uncovered in the Takarkori rock shelter in southwestern Libya, according to a paper published in the journal PLOS ONE.
Overall, aquatic remains comprised almost 80% of the entire find of 17,551 faunal remains. Mammals made up 19% and birds, reptiles, molluscs and amphibian the rest.
All of the fish and most of the other remains were determined to be human food refuse, due to cut marks and traces of burning.
The research was led by Wim Van Neer from Belgium’s Natural History Museum and Savino di Lernia from Sapienza University of Rome.
Fossil records show that for much of the early and middle Holocene (10,200 to 4650 years ago), the region around the Tadrart Acacus mountains was humid and wet, with evidence of multiple human settlements and diverse fauna. Rock shelters preserve significant floral and faunal remains, as well as cultural artefacts and rock art.
In their recent study, the authors worked with the Libyan Department of Antiquities in excavating parts of the Takarkori rock shelter to identify and date animal remains and investigate shifts in their abundance and type over time.
They found that the quantity of fish decreased over time (from 90% of all remains 10,200-8000 years ago versus to only 40% of all remains 5900-4650 years ago) as the number of mammal remains increased, suggesting the locals gradually focussed more on hunting/livestock.
In particular, the proportion of tilapia decreased, which, the researchers suggest, may have been because catfish have accessory breathing organs allowing them to breathe air and survive in shallow, high-temperature waters.
If that is the case, it likely provides further evidence that this now-desert environment became less favourable to fish as the aridity increased.
The authors also suggest that the presence of crocodiles and the aquatic turtle (Pelusios adansonii), as well as fish, indicates that connections must have existed in the early Holocene that allowed aquatic animals to colonise the area, starting from places where populations were present in late Pleistocene times.
“The species may have come from the Nile, migrating westwards through the eastern Sahara along the hydrographic networks of the Ennedi and Tibesti and the Lake Mega-Chad,” they write.
“Alternatively, the aquatic species may have come from rivers in the Sahel and the Lake MegaChad, propagating northwards towards the Hoggar-Tassili hydrographic network and from there towards the Tadrart Acacus area through the palaeotributary of the Niger River.”
Either way, they say, it is clear that Lake Mega-Chad played an important role in the propagation of aquatic species, and that that the reconstructed palaeohydrographic networks were not permanently flowing.
“Colonisation may have been a gradual process whereby a series of catchments were active that may have communicated with each other when conditions were periodically, or even seasonally, more humid allowing fish to be ‘decanted’ from one catchment to the next,” they suggest.”
