The water those camels are drinking is black with their own dung, and four crocodiles are watching them from the back of the pool.
This is Guelta d'Archei in Chad's Ennedi Plateau. The closest other crocodile population is 700 kilometers north in the Tibesti, too far for any crocodile to walk, which means the four still living here have been genetically isolated since the Sahara was green, somewhere between 5,000 and 15,000 years ago.
DNA from a specimen pulled from this pool in 1997 confirmed them as Crocodylus suchus, the smaller West African cousin of the Nile crocodile. The lineage split from the Nile species 8 to 13 million years ago. Four females, all that's left here.
The food web is wild. Hundreds of camels water here every day. The dung and urine load fertilizes algae in the still water, which is why it's black. Algae feeds the fish. Fish feed the crocodiles. The apex predators at the top of this canyon survive on the waste of the camels that come in to drink. Without the herders, the crocodiles starve.
The water itself is a fossil. Ennedi sits on the Nubian Sandstone Aquifer System, the largest fossil aquifer ever found. 150,000 cubic kilometers of groundwater, roughly 500 years of Nile River discharge stored underground. Carbon-14 dating puts most of it at 4,000 to 30,000 years old, deposited during Pleistocene pluvials when this entire region was savanna.
You're looking at camels drinking 20,000-year-old water in a canyon where four prehistoric reptiles are waiting for an algae bloom fed by the camels' own waste.
Crocodiles used to live across the entire Sahara. They went extinct guelta by guelta through the 20th century. This pool is the most isolated relict population left on the planet.
Aseel Swaid (@aseelswaid9)
Republic of Chad
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