The Crocodile Color So Rare You've Probably Never Seen It

Crocodiles are a fascinating species. Known as living fossils, these ancient-looking reptiles share a common heritage with dinosaurs, and have changed very little since their emergence almost 250 million years ago. It might go without saying, then, that they are remarkably hardy creatures. Their cold-blooded state and adaptability also allows them to live in a variety of environments that would be detrimental to other species, including polluted water full of heavy metals and radiation, or even a subterranean cave suspended in perpetual darkness and packed with thousands of bats.

A group of cave-dwelling crocodiles has been isolated in such a habitat for 3,000 years, but their choice of living quarters isn't the most surprising thing about them. This unique species of African dwarf crocodile, discovered in central Africa, has been underground so long that not only have they branched off into their own species, some of them have developed a whole new skin color. Among this particular group of crocs, several have turned orange, initially stunning researchers who had never seen such coloration on a crocodile before. This distinctive skin, though striking, actually arises for a fairly repulsive reason that has to do with the crocodiles' underground habitat and the creatures they share it with.

The African dwarf crocodile is one of the smallest crocodile species in the world, reaching lengths of just 5 feet. One of the most interesting animals of West Africa, the small crocodiles live among the rainforests, swamps, and rivers of the region and spend most of their time in the water, though they may leave to soak up sun rays. However, the dwarf crocodiles discovered in the central African country of Gabon rarely, if ever, see the sunlight.

These cave crocs were first discovered in 2008 by archaeologist Richard Oslisly, who ventured into the Abanda Caves in Gabon with a completely different intention. Oslisly was actually looking for rock paintings made by ancient humans, but instead came across what he told The Guardian was a "great room ... filled with water." That room was also filled with a unique species of crocodiles that proved to be even more remarkable than Oslisly originally realized.

In 2010, the archaeologist returned to the caves with scientist Olivier Testa and crocodile specialist, Matthew Shirley. Together, the trio managed to capture one of the crocs, only to discover once they got outside that they had a truly remarkable species on their hands.

You might think that a whole group of crocodiles that live in perpetual darkness is unique enough already. But once Richard Oslisly and his colleagues removed one of the cave-dwelling dwarf crocodiles (Osteolaemus tetraspis) from its habitat, they were struck to see that it did not have the typical blue/grey coloration of an African dwarf crocodile. Instead, while the body parts of the crocodile were typical of the dwarf species, the cave-dweller had orange skin.

Researchers have since theorized the crocodiles' unique skin color is due to the reptiles existing in an alkaline mix of water and bat guano, which over time turns their skin orange. Indeed, while a Texas cave is currently home to the largest bat colony in the world, the Abanda cave system hosts a considerable number of bat colonies itself, made up of Egyptian fruit bats (Rousettus aegyptiacus), Noack's roundleaf bats (Hipposideros aff. ruber), and Giant leaf-nosed bats (Hipposideros aff. Gigas). In total, there are thought to be more than 100,000 bats in the cave system, providing more than enough sustenance for the dwarf crocodiles that have made Abanda their home.

The cave-dwelling dwarf crocodiles survived in the caves by feasting on these bats, as well as cave crickets, but sitting in the bat guano-filled water of the caves is what gives the reptiles their distinct color. As Matthew Shirley told National Geographic, bat guano contains large amounts of urea. The herpetologist explained, "When [the crocodiles are] sitting in this bat guano slushie, we think the highly basic pH water is tanning their skin."

After discovering the orange crocs of the Abanda cave system, researchers carried out genetic analyses on samples taken from several of the reptiles in 2010. The results were surprising in that they showed the cave-dwelling crocodiles appeared to be mutating into their own species.

The samples revealed a significant genetic difference between the cave crocs and the dwarf crocodiles that exist above ground. Specifically, one of the sets of genes, known as a haplotype, found in the cave crocs is not found in their above-ground counterparts, confirming that the cave-dwellers had split off from standard African dwarf crocodiles thousands of years ago. As Richard Oslisey told The Guardian in 2018, "The [crocodiles in the] caves of Abanda stand out as an isolated genetic group."

This also confirmed that the cave crocs had been there for quite some time, as it would take a few hundred generations of the animals to create a new genetic signature. The orange skin, however, is not thought to be part of this genetic picture, with researchers maintaining that the bat guano is the reason for their unique hue.

Aside from revealing what is very likely to be a new species of crocodile, the cave discovery is significant for one other big reason. We know crocodiles are ectothermic, which means they rely on external sources such as the sun and warm water to regulate their internal temperatures. But in the caves of Gabon, these subterranean reptiles have no access to sunlight, though it is thought that a handful of the animals are able to somehow enter and exit the caves.

But the fact that an entire species of crocodile has been able to survive underground presents an intriguing opportunity; to study the hardiness of these animals and their ability to adapt to certain environments. Crocs are already known to be incredibly adaptable, but existing for thousands of years without sunlight amid pools of bat guano, while subsisting on a diet of only bats and insects, is a whole new thing entirely. As more research is conducted, this new species of croc is sure to reveal even more insights into this already fascinating creature.