Palaeontologists searching in Tunisia made a discovery of massive proportions: the world's previously unknown largest sea-dwelling crocodile.

This prehistoric crocodile is believed to have measured more than 10m long and weighed three tonnes. The skull alone is more than1.5m long. Researchers named the new species the Machimosaurus rex and described their findings this week in the journal Cretaceous Research.

"Massive" is how lead author Federico Fanti of the University of Bologna described the crocodile. "It's almost the size of a bus.

"It definitely was at the top of the food chain at the time, at least in this particular locality," he said.


Fanti and his team, supported by the National Geographic Society committee for research and exploration, found the fossils buried below just a few centimetres of sediment on the edge of the Sahara Desert in Tunisia, a country rich with fossils.

"This one was a big surprise, not because we found fossils, but we found beautiful ones," Fanti said.

The skull took two days to uncover, and the "rest of the body was just lying there".

This particular site was likely home to a lagoon that faced the ocean. Researchers also found the remains of fish and turtles that they still need to identify.

M. rex lived way after the "hypothesised mass extinction" between the Jurassic and Cretaceous periods," Fanti said.

"That's leading us to consider the mass-extinction theory is wrong and that we should better understand what's going on at the end of the Jurassic period."