A Fordham University professor has published evidence that shatters the long-thought belief that the Nile crocodile (Crocodylus niloticus) found throughout Africa is a single species of crocodile.
A team of researchers led by Evon Hekkala, Ph.D., assistant professor of biology at Fordham, and Matt Shirley of University of Florida, Gainsville, discovered a second cryptic, or hidden, lineage of crocodiles through DNA analyses of modern crocodiles and ancient mummy crocodile hatchlings.
Hekkala and her team collected contemporary crocodile samples from throughout Africa as well as from museum specimens, including some from Thebes, Egypt that are currently housed in the Museé National d’Histoire Naturelle (MNHN) in Paris. Although the modern Nile crocodile (C. niloticus) is found throughout Africa, there have long been reports that it is larger and more aggressive in the Eastern and Southern African regions and smaller and more docile in the Congo and West Africa.
The reason, Hekkala’s research suggests, is because the Eastern and Western crocodiles are in reality different crocodile lineages, which shared the Nile river as recently as 100 years ago.
Hekkala’s analysis showed that several of the MNHN mummy samples, collected during Napoleon’s expedition to Egypt in the early 1800s and estimated to be up to 2,000 years old, belong to a species once described as Crocodylus suchus.
Although the cryptic C. suchus lineage had been recognized and described (as the smaller and gentler “sacred” crocodile) by the scientist Geoffroy Saint-Hilaire back in 1807, his contemporaries discounted his theory of a separate species. Among scientists, the taxonomic status of the Nile crocodile has been disputed ever since.
Hekkala and her team analyzed DNA from eight crocodile mummies from the same collections as the specimen corresponding to Saint Hilaire’s description of C. suchus.
“Saint Hilaire was very prescient in understanding the very detailed behavioral ecological differences between these two species,” said Hekkala. “But the scientific community called him crazy and,Crocodylus suchus was never recognized. We hope to change that with our research.”
Although the Nile crocodile was once worshipped in ancient Egypt, today it sits on the International Union for Conservation of Nature (IUCN) red list as a species of Least Concern. Because of the value of its skins, some governments allow it to be hunted under sustainable-use-based management policies and programs.
But with the discovery that two different species—not just one—are being hunted, Hekkala said that any new conservation agreements producing sustainable harvesting of the Nile crocodile should be “re-evaluated.” In their paper, Hekkala and her team call for the new C. Suchus lineage to be recognized, and for the IUCN to review its status.
“Our research showed that the habitat range of C. Suchus has seriously declined since the turn of the century,” said Hekkala. “Without proper recognition of this second cryptic species and proper management of it, we may lose it altogether.”
Hekkala added that she could not have made the discovery without the use of ancient museum archival specimens—an area of research in which she has a special interest.
“Our success emphasizes the utility of non-traditional archival specimens in contributing to our understanding of evolutionary relationships and biogeographic history,” she said.
The findings were published on September 9th in an article in the journal Molecular Ecology. Hekkala’s co-collaborators included scientists from the University of Florida, the Sackler Institute for Comparative Genomics at the American Museum of Natural History, the San Diego Zoo, Tulane University and the Wildlife Conservation Society.