The image on the left shows an orange cave crocodile, while the one on the right is a forest crocodile. Scientists captured specimens from each group and compared them to see if there were any physical differences related to their habitat. (Image credit: Olivier Testa, CC BY-SA 3.0, via Wikimedia Commons)
Name: Cave dwarf crocodiles (Osteolaemus tetraspis)
Habitat: Abanda cave system, Ogooue-Maritime province, Gabon.
Diet: cave crickets and bats.
Why it's amazing: Deep in a cave system in Gabon, there's a unique population of orange dwarf crocodiles. They live in total darkness, feed on bats, and swim in liquid guano (aka bat excrement).
The exact number of crocodiles inhabiting these caves and when they began their underground lifestyle are unknown, but they may have been there for thousands of years. Scientists speculate that they may be evolving into a new species.
Cave-dwelling crocodiles were first studied only in 2010, and a 2016 study comparing them to forest-dwelling crocodiles found a number of differences. Their diets are significantly different, with cave crocodiles relying almost entirely on the generous supply of crickets and bats that cling to the cave walls. Cave crocodiles were found to be in generally better condition than their forest-dwelling counterparts, which the team believes is likely due to the abundance of available food and the lack of predators.
Cave crocodiles are thought to lay their eggs at the entrance to caves, after which the young head into the darkness. Once they reach maturity, they are thought to rarely leave the caves.
Orange Skin and Genetic Changes
The unique orange skin color of adult crocodiles may be a result of their prolonged exposure to bat guano, which is rich in urea, lead author Matthew Shirley, a conservation biologist at Florida International University, told National Geographic in 2018. Over time, this exposure appears to result in a chemical bleaching of the crocodiles' skin, the study authors report.
Interestingly, a genetic analysis of the crocodiles, which has not yet been published, points to the possibility of mutations in orange cave crocodiles, according to a 2018 Guardian article. The researchers told the publication that one haplotype (a group of DNA variants inherited from an ancestor) found in cave crocodiles is absent from forest crocodiles. “[The crocodiles] of the Abanda caves stand out as an isolated genetic group,” commented study co-author Richard Oslisley, a research fellow at the French Institute for Development Research.
This genetic change is evidence that the cave crocodiles are evolving into a new species. “As a result of this isolation and the fact that so few individuals are coming or going, they are in the process of [forming] a new species,” Shirley told National Geographic. “When exactly that will happen is anyone’s guess.”
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