July 23 (UPI) -- Novel bone structures found on the skull of Crocodylus checchiai, an extinct African crocodile species, suggest American crocodiles originated in Africa, according to a study published Thursday in the journal Scientific Reports.
Over the last few years, molecular biologists have shown that the four crocodile species found in the Americas are close relatives of the Nile crocodile, Crocodylus niloticus.
Researchers say that Crocodylus checchiai rests somewhere between the Nile crocodile and American crocodiles on the evolutionary tree -- meaning the American crocodiles made their way across the Atlantic more than 5 million years ago.
"Some of these morphological features had been hypothesized on the basis of a few fragmented skulls, but it is the first time that these anatomical details were identified by CT images and then considered in the phylogenetic analysis," Dawid Iurino, study co-author and researcher at the Sapienza University of Rome, told UPI in an email.
To better understand the relationship between African and American crocodiles, researchers at the Sapienza University of Rome recruited a team of specialists to reexamine the "forgotten' skull of Crocodylus checchiai, a fossil found in As Sahabi, Libya, in 1939.
The skull, the most well-preserved of its kind, is part of the reptilian collection at MUST, the natural history museum at Sapienza University.
In addition to specialists in the phylogeny of crocodilians -- the study of the relationships between various species -- authors of the new study brought in experts in advanced imaging techniques and the evolution of Mediterranean vertebrates.
The analysis revealed never-before-observed bone structures on the forgotten skull, including a bump on the snout.
The feature absent on the skulls of other African crocodiles species, but present on the skulls of the four American crocodiles species, researchers say.
Scientists also found similar structures present on the snout of Crocodilus falconensis, an extinct species from Venezuela that is about 5 million years old.
"We can therefore assume that one -- a pregnant female, or some specimens of C. checchiai or of a species still unknown very close to it -- dispersed from Africa to America around 7 million years ago, for sure before 5 million years ago, the age of the oldest fossil Crocodylus from America," Iurino said.
Until now, researchers weren't sure whether crocodiles migrated from Africa to the Americas or the other way around. The new study suggests crocodiles migrated westward, from Australasia to Africa to the Americas.
"We can suppose that a few months [would be] enough for a journey from Africa to America and is compatible with the survival of a crocodile passively transported by the currents," Iurino said.
Because of the current political climate in Libya, field work isn't possible, but Iurino hopes to return to As Sahabi as soon as possible to collect and study more Crocodylus checchiai fossils.