Nile crocodile in Madagascar. Photo by: Rhett A. Butler.
DNA has shown that the Nile crocodile is in fact two very different species: a bigger, more aggressive crocodile and a smaller, tamer species that today survives only in West Africa. While the taxonomy of the Nile crocodile has been controversial for over a century, the new study points out that the ancient Egyptians recognized the differences in the species and avoided the big crocodile for its rituals.
While it is not uncommon for DNA to overturn long-established taxonomy, in this case the DNA results of over a hundred living crocodiles across Africa and over fifty museum specimens—including mummified crocodiles from ancient Egypt—found that what has long been considered one species is two distantly related species. In fact the larger Nile crocodile (Crocodylus niloticus) is more closely related to Caribbean crocodiles than it is to the new cryptic species, dubbed Crocodylus suchus.
At first researchers were dumbfounded by these results.
“I kept on sequencing it because I was convinced I was 100 percent wrong,” Evon Hekkala, lead author, told Nature. “It wasn’t even remotely related to the Nile crocodile samples I had been working on.”
Greek historian, Herodotus, actually pointed this out nearly two thousand years five hundred ago after visiting Egypt. The researchers write that according to Herodotus, who has been dubbed the Father of History, “ancient Egyptian priests were cognizant of two forms [of Nile crocodile] and selectively used the smaller, more tractable form in temples and ceremonies”. DNA tests of mummified specimens bore this out: all of them were of the more docile Crocodylus suchus.
At one time the Nile crocodile and its cryptic species used to share some of the same habitats, including the Nile River, according to the scientists. Now, however, the smaller Crocodylus suchus survives only in West Africa with researchers speculating that the bigger, fiercer crocodile outcompeted it.
The Nile crocodile is listed as Least Concern by the IUCN Red List, meaning it is currently safe from extinction. In some countries it is legal to kill the animal for its skin. However, according to the authors, if the new cryptic species is accepted such trade laws will have to be reconsidered. The new species is likely threatened due to overharvesting, bushmeat trade, and habitat loss.
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