Machimosaurus rex

Machimosaurus rex grew to be about 10 metres long and hunted in the shallow seas in what is now Tunisia around 130 million years ago, during the age of dinosaurs. (Davide Bonadonna)

Scientists have discovered what may be the largest marine crocodile that ever lived, a monstrous predator as long as a bus that crunched up and ate sea turtles with blunt, bullet-shaped teeth.

The new species, named Machimosaurus rex, grew to be about 10 metres long and hunted in the shallow seas of what is now Tunisia around 130 million years ago, during the age of dinosaurs, report scientists in a new paper published in the journal Cretaceous Research.

Its powerful jaws were equipped with teeth shaped like "armour-piercing bullets," said Tetsuto Miyashita, a PhD candidate in paleontology at the University of Alberta who co-authored the study. "Those are built for crushing the bones rather than [to] slice through or pierce through flesh."

Those teeth were likely the perfect tool for crunching through the shells of turtles that were common in the tropical waters where it lived.

Machimosaurus rex skull

Tetsuto Miyashita, centre, visited Tunis in 2015 with Federico Fanti to study the skull in collaboration with some of the Tunisian researchers pictured here.

Last of its kind

Not only was the crocodile the largest of its kind, but it was also the last of its kind. Machimosaurus rex belonged to a lineage of sea-dwelling crocodiles, most of them no longer than three metres, thought to have gone extinct about 20 million years earlier.

Modern saltwater crocodiles are not part of the same lineage.

While Machimosaurus rex is the largest saltwater crocodile ever discovered, a freshwater crocodile that lived around the same time in the same region may have been larger, Miyashita said.

The researchers don't know exactly how long Machimosaurus rex was, because so far they have only been able to collect its skull.

Study leader Federico Fanti, an assistant professor at the University of Bologna in Italy, was conducting field research in the desert about 50 kilometres south of Tatouine, Tunisia, in 2014 when a member of his team spotted the tip of the croc's snout sticking out from the rock. They soon realized the animal's entire body was attached, but it was so large that they only had time to excavate the skull before returning to other obligations, such as teaching.

Fanti wanted to go back to excavate the rest of the body with a team of trained paleontologists, so he called up Miyashita. The two had met in Drumheller, Alta., in 2004 when they were both students working with Canadian paleontologist Philip Currie at the Royal Tyrell Museum. Miyashita was a high school student on exchange from Japan, while Fanti had been finishing his undergraduate degree and entering grad school.

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The crocodile's skull alone is as long as an average woman is tall — about 1.6 metres. (Marco Auditore)

Fanti send Miyashita pictures of the crocodile's skull.

"I thought, 'It's a nice specimen,'" Miyashita recalled. Then he looked more closely. "I realized that what looked to me like a toothpick was actually a hammer beside the skull. That gives you a sense of how big this animal is."

The skull alone is as long as an average woman is tall — about 1.6 metres.

Security stalls research

Fanti and Miyashita planned to go to Tunisia to excavate the rest of the crocodile's body together last March.

But due to national security issues since the Tunisian revolution in 2011, they weren't able to return to the excavation site. Instead, they remained in the capital of Tunis, where they studied the skull, which is being housed at Tunisia's national collection of rocks and minerals.

While Tunis was peaceful during their stay, 21 people were killed by two gunmen linked to the extremist Islamic State of Iraq and Syria (ISIS) at the city's National Bardo Museum just a week later.

The researchers don't know when they'll be able to return, but Miyashita is worried what will happen to the fossil in the meantime.

Powerful sandstorms regularly rip through the area where the excavation site is found. The storms can rebury fossils, making them difficult to find again. The sand whipped up by the winds can also grind up the fossils, Miyashita said.

"It's possible that if we keep postponing the return to the field site, within several years … the skeleton will be gone, all we'll have is powder of bones that used to be there."

Machimosaurus rex field team

Study leader Federico Fanti, an assistant professor at the University of Bologna, was conducting field research about 50 kilometres south of Tatouine, Tunisia, in 2014 when a member of his team spotted the tip of the croc's snout sticking out from the rock. (Andrea Cau)