In Gabon, known for its geological diversity and wildlife, scientists have had the incredible surprise of discovering orange-colored crocodiles, unique in the world, living in the middle of bat droppings in dark caves.

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"When I approached with the flashlight in the cave, I saw red eyes ... crocodiles!" It was in 2008. Two years later, we released a first specimen of the cave and we have noticed that it was orange, "recalls geoarchaeologist (archaeological sediment specialist) Richard Oslisly.

An exceptional double discovery made while with a team of researchers, he was trying to find traces of human traces in the caves of Abanda (south). This "orange cavernous crocodile", which can reach 1m70, is unique in the world and has been observed only in these caves of Gabon, according to Mr. Oslisly.

"At first, we thought that color could come from their diet, because we noticed that these reptiles eat bats oranges," says the French researcher. But after further studies, researchers have advanced other hypotheses: a "depigmentation" due to the lack of light in these caves or the harmfulness of "guano", a substance made of bat droppings in which these animals marinate throughout their underground life.

"The urine of bats started to attack their skin and transformed their color," explains Olivier Testa, speleologist and member of the scientific team.

Since 2010, Richard Oslisly, Olivier Testa and the American researcher Matthew Shirley have multiplied scientific expeditions to learn more about these unusual crocodiles. By mapping the caves, they have so far identified four orange crocodiles on about forty of this species "cavernicole".

Dozens of crocodiles with a "normal" color live in neighboring caves connected to the surface, explains Mr. Testa, while orange crocodiles roost in caves accessible only by vertical wells.

3.000 years old
"It is thought that these dozens of crocodiles would have settled in the caves of Abanda about 3,000 years ago, which corresponds relatively well with a period when the sea level had fallen and this coastal area became terrestrial", explains Shirley.

The orange crocodiles, stranded in the cave, "found themselves trapped after entering the corridors when they were small, then they grew," said Richard Oslisly. Several more or less narrow and interconnected corridors form a network of caves in Abanda where they sometimes become blocked with the rise of the water table.

According to Matthew Shirley, crocodiles have settled in their cave because they find their account and they may not have been stuck in it for 3,000 years. In the absolute dark, these animals survive with a particular diet. In the caves, no fish or shellfish. They feed on bats, locusts, crickets. "It’s a particularly demanding environment," says Shirley.

According to the researchers, this cavernicolous population - orange and normal-colored animals - belongs to the group of dwarf crocodiles Osteolaemus tetraspis and is "mutating". The DNA of this cavernicolous population is not different enough from its surface dwarf cousin to make it a new species, explains Matthew Shirley, but these animals have developed their own "genetic signature".

Cave crocodiles are indeed endowed with a unique group of genes transmitted from generation to generation, found the researchers, after comparing their DNA with that of their dwarf cousins living exclusively on the surface in Gabon. B

Although the crocodile is already a protected species in Gabon, Richard Oslisly is pleading for the Abanda Caves site to become a "sanctuary", "fully protected". "There is still much to discover in the caves of Abanda," said the geoarchaeologist who hopes to develop the "scientific tourism".