dMummy and Modern DNA Analysis at Sackler Institute Reveals Two Nile Crocodile Species

DNA from mummified crocodiles helped reveal that the Nile crocodile is really two distinct species. 
Photo courtesy of John Thorbjarnarson, Wildlife Conservation Society. 

The Nile crocodile, one of Egypt’s most famous icons, is in fact two distinct species, according to recent genetic analyses of mummified crocodiles from ancient Egyptian temples.

Evon Hekkala, an assistant professor at Fordham University, conducted a DNA analysis at the Museum’s Sackler Institute for Comparative Genomics by extracting the DNA of 57 specimens—some of them mummies—from museums around the world and 123 modern crocodiles, which she then sequenced at the Sackler Institute.

The study found that the two species are not even each others’ closest relatives. Crocodylus niloticus, known for being the more aggressive of the two, is more closely related to four Caribbean species than to the previously unacknowledged Crocodylus suchus, an animal considered sacred by some of its human neighbors.

George Amato, director of the Sackler Institute and one of the study’s co-authors, says that the finding will have a direct impact on efforts to manage the iconic crocodiles’ conservation. The discovery that the Nile crocodile is really two species means both of the groups’ ranges are far smaller than previous conservation literature estimated. Crocodylus suchus is especially threatened, most likely due to its habitat drying out.

Genetic analysis continues to shape scientists' views of even familiar species. 
Photo courtesy of Matthew Shirley, University of Florida, Gainesville.

Hekkala’s discovery shows how DNA analysis can change scientists’ views of seemingly well-known animals. “It’s incredible how little we still know about large, familiar wildlife,” says Dr. Amato.

The study also debunks the long-held view that crocodiles are literal living fossils, or species that are no different from specimens in the fossil record. Modern crocodiles, it turns out, are relatively recent descendants of an older lineage that lived alongside the dinosaurs. Though the long-term success of the crocodilian body plan makes the modern animals look similar to their ancient relatives, crocodiles have evolved over millennia. As Amato explains, “They’re as modern as any other species alive today.”