America’s crocodiles came out of Africa, study finds

– The several species of crocodiles plying rivers and brackish byways in the Americas – from Florida to Peru – all came from Africa, according to a study published on Thursday.

They may have descended, researchers speculate, from a single pregnant specimen that bobbed along Atlantic Ocean currents to the New World at least five million years ago, probably longer.

Based on the high-tech analysis of a skull fragment unearthed from the Libyan desert in 1939, the findings are bolstered by genetic evidence pointing in the same direction, they reported in the journal Scientific Reports.

“This is a really exciting discovery,” said lead authors Massimo Delfino from the University of Turin and Dawid Iurino, a palaeontologist at Sapienza University in Rome.

“It supports the results of molecular biologists that proposed the origin of American crocodiles had to be found in Africa.”

The out-of-Africa narrative is based on the re-examination of the skull and upper jaw of a sevenmillion-year-old fossil that had been tucked away for decades in a university museum drawer. It belonged to an extinct species called Crocodylus checchiai.

Using CT scans and 3D-modelling, the scientists identified a tell-tale protrusion in the middle of the animal’s snout not found in any other African crocodile, living or extinct, but present in all four species currently found in the Americas.

In the world of paleontology, this is close to a smoking gun.

Four other fossils dug up in Libya at the same time – including a complete skull and jaw – were either destroyed during World War II or lost.

C. checchiai rewrites the story of how crocodiles spread across the planet in at least two ways. It lays to rest the already fading hypothesis that the giant, flesh-ripping reptiles – which first emerged from Asia – arrived in the Americas before moving on to Africa.

The long-neglected fossil also supplants another contender from Africa – Crocodylus niloticus, aka the Nile crocodile – as the closest forebear of the American species.

That such a voyage is possible has been demonstrated by a present-day cousin, Australia’s saltwater crocodile, which satellite tracking has shown can travel 500km in about a month while passively transported by ocean currents.

More closely related to birds than dinosaurs, egg-laying crocodiles have been around for about 55 million years.