The iconic Nile crocodile actually comprises two different species only distantly related. The large east African Nile crocodile (Crocodylus niloticus) is in fact more closely related to four species of Caribbean crocodile than to its small west African neighbour, which has been named Crocodylus suchus.

Evon Hekkala of Fordham University in New York and her colleagues revealed evidence for the existence of the second species by sequencing the genes of 123 living Nile crocodiles and 57 museum specimens, including several 2,000-year-old crocodile mummies.

For years, people have been looking at what they considered to be the Nile crocodile and they didn’t really have much material to compare across Africa. In the 1970s, the industry that was involved in tanning crocodile hides was looking for ones with fewer bony scutes. A man called Fuchs did an analysis of the scutes to identify stocks that have fewer of them. He proposed some of these subspecies but the crocodile researchers threw out his work and said this guy doesn’t know what he’s talking about.

That’s the earliest sign of a morphological difference. People had been looking and looking and they just couldn’t see these differences. There had been all this evidence throughout the years about some extreme differences but most of the anecdotes were about their behaviour. Crocodiles are generally very hard to tell apart from their exterior features.

We can now revisit the morphological data to see what springs out. There’s an unpublished preliminary analysis of skulls by Chris Brochu that does pull apart the two species based on just skull morphology. We’re working together to write a description of the new species to pull together the behavioural, genetic and morphological data.