The Discovery of “Sacred Crocodile” (Crocodylus suchus)

The Discovery of “Sacred Crocodile” (Crocodylus suchus)

In the darkness of the Akeley Hall of Mammals, swarms of kids gawk at beautifully staged dioramas of Africa’s wildlife. The stuffed safari, nestled in the American Museum of Natural History (AMNH) in New York, includes taxidermied leopards stalking a bush pig, preserved ostriches strutting in front of warthogs, and long-dead baboons cautiously considering a viper. In one corner, in a display marked “Upper Nile Region,” a lone hippo grazes next to a herd of lechwe, roan antelope, and a comically stern shoebill stork.

“This is my favourite one,” says Evon Hekkala, pointing to the display. “There’s a taxidermied crocodile tucked away down there.”
It takes a while to spot it and I have to crane my head to do so, but yes, there it is—a large crocodile, in the back, mouth agape, next to the hippo. It’s mostly hidden from view, and until recently, it was hidden from science, too.

Five years ago, scientists would have classified it as a Nile crocodile (Crocodylus niloticus)—one of the largest of the family, and among the most feared. But in 2011, after extracting DNA from this specimen and dozens of others, Hekkala proved that the iconic species is actually two species. One had been disguised as its more widespread cousin all this time. Hekkala called it Crocodylus suchus—the sacred crocodile. It’s the species in the diorama.
Hekkala, a geneticist at Fordham University, is an evangelist for natural history museums and the many secrets that are still locked within their drawers and dioramas. In 1985, as an undergraduate volunteer at McGill University’s Redpath Museum, she was asked to re-label a set of spears collected from the Congo Basin, one of which said: Thought to have killed eleven pygmy elephants. “At the time, I thought it was kooky and sad. But then I realized that this was a piece of forensic evidence in a crime scene,” she says. These inert objects, now in her hand, were once buried deep in the flanks of living creatures. “It really changed my perspective on what museum collections could tell us.

It’s easy to view such collections as soulless stashes, examples of humanity’s hoarding instinct unleashed upon the natural world, turning vibrant menageries into dead zoos, and living, breathing, mating, hunting, fighting creatures into mere specimens, dissembled and dissected, posed in dioramas, pinned in drawers, crammed into cabinets, and stuffed into jars. But to Hekkala and many other scientists, these hoards are full of riches still. They are time capsules that contain records of past ecosystems that are rapidly changing or disappearing. They are archives that provide clues about raging epidemics, environmental pollution, and hidden extinctions. And they are full of unknown species—like the sacred crocodile.

Hekkala stumbled across it while sequencing DNA from Nile crocodile samples collected all over Africa, in a bid to understand differences between the various populations of this majestic reptile. “Because I’m a museum geek, I thought: Oh, I can get tons of Nile croc specimens from museum collections,” she says. She found 16 in the AMNH alone, collected almost a century ago, and dozens more from other institutions. From each specimen, she picked off fragments of dessicated tissue, still clinging to bones or skin and still rich in viable DNA. She even managed to sequence DNA from seven mummified crocodiles from the National Museum of Natural History in Paris. “The collections manager there let us take a little piece from their tails,” she says. The mummies are around two millennia old and DNA typically degrades in hot humid conditions, but Hekkala still found enough intact helices, thanks to the Egyptians’ skill at preservation.
Together, the hard-won samples corroborated Hekkala’s suspicions: The Nile crocodile was indeed two separate species. The Eastern one has two fewer chromosomes than the Western sacred crocodile, and is actually more closely related to crocodiles in the Caribbean. The sacred crocodile is also reportedly more docile than its belligerent Nile cousin, and digs caves in which it shelters. The Egyptians seemed to know the difference: The mummies that Hekkala studied were all sacred crocs. At that time, both species used to co-exist along the full length of the Nile. Today, they mostly stick to different parts of Africa. They only share space in museums.
“It’s maybe not an intuitive thing that anyone should take dead animals and plants and lock them in a cabinet and keep them there for years, decades, even centuries,” he adds. “But that’s the business natural history museums are in. And it’s an extraordinary pursuit.”