An ancient skull hints crocodiles swam from Africa to the Americas

A resemblance between a long-lost African crocodile and modern American crocs goes beyond the shared bump on their snouts.  

New analyses of a roughly 7-million-year old skull from the extinct Crocodylus checchiai suggest that crocodiles journeyed from Africa to the Americas millions of years ago, researchers report July 23 in Scientific Reports. Unearthed in the 1930s, the fossil came from what’s now Libya and sat for decades in a museum. With CT scanning, scientists have now mapped the skull’s structure, revealing hidden anatomical features that tie the animal closely to the four species of American crocodiles alive today.

“It really looks like an American true crocodile, but it comes from Africa,” says Massimo Delfino, a paleoherpetologist at the University of Turin in Italy.

Genetic analyses had already linked the Nile crocodile with its American kin. Though scientists suspected that crocs long ago colonized one of the locales before journeying to the other, the fossil record hadn’t painted a clear picture of which came first.

This C. checchiai specimen predates the earliest known crocodile in the Americas (from roughly 5 million years ago) by about 2 million years. The skull’s structural features place C. checchiai at the base of the American crocs’ branch of the crocodile family tree. But the animal was also a close relative of the Nile crocodile, the researchers found. As a result, the newly described fossil “fills a gap between the Nile crocodile in Africa and the four extant American species,” Delfino says.

ancient African crocodile skull
The features of this C. checchiai, excavated in the 1930s from what’s now Libya, place the animal at the base of American crocs’ branch in the crocodile evolutionary tree.Bruno Mercurio
ancient African crocodile skull
The features of this C. checchiai, excavated in the 1930s from what’s now Libya, place the animal at the base of American crocs’ branch in the crocodile evolutionary tree.Bruno Mercurio

The continents would have been in roughly the same place as now when C. checchiai or a close relative may have been on the move. So the new finding suggests that a group of crocs, or at least one pregnant female, may have made a transatlantic journey from Africa to the Americas, Delfino says. “It’s not so surprising,” he says, given today’s crocodilians’ ability to survive saltwater and travel hundreds of kilometers when helped by ocean currents.

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