Remember the urban legend about crocodiles thriving in New York City's sewers? A team of German zoologists has stumbled upon a population of Nile crocodiles in an equally improbable setting: the middle of the Sahara desert.
Wolfgang Böhme of the Zoologisches Forschungsinstitut und Museum Alexander Koenig in Bonn, Germany, and his team found the population during a 3-month, 6500-kilometer expedition to study reptiles in the Western Sahara. Hearing rumors of a mysterious crocodile colony in southern Mauritania, the team sped to the site, a large rocky plateau pocked with crevices and cavities. Peeping through the crevices, the researchers spotted some puddles and a 20-meter-wide pond some 5 meters below the surface of the plateau. Next to the puddles, they saw an African Nile crocodile (Crocodylus niloticus) sunning itself in the rays that beamed through the crevice. It was a bit of a pipsqueak, about 2 meters long, says Böhme; full-grown African crocodiles can measure up to 6 meters. When Böhme caught sight of a smaller beast, he lowered himself down a crevice and captured the 85-centimeter juvenile with his bare hands to examine it more closely. He couldn't tell which of the four subspecies of Nile crocodile it belonged to. The team spotted a total of four crocs, although they suspect that more lurk in the caverns. Böhme returned unscathed and announced the find at a press conference in Bonn last month.
"Finding a new, isolated population of large animals is sensational," says zoologist Steven Perry of the University of Bonn. Because of their isolation, he says, "these animals are a [rare] model of a new species in the process of being formed." The Mauritanian crocodiles have survived thousands of years totally isolated from other crocodile populations, says Böhme. Only 10,000 years ago most of the Sahara was fertile savanna. When the desert expanded, it cut off some groups in refuges like the underground water system that Böhme's team found. Nile crocs have been found in only one other unexpected location, a mountain range in Chad.
Much remains to be learned about the lifestyle of the newly discovered crocs. "Given that Nile crocodiles are highly territorial," Perry wonders, "how do they manage to [get along with each other] in such a confined area?" Böhme hopes to fit some of the animals with radio transmitters to find out more about these tropical relics.