Lower Cretaceous sediments from an unexplored area of Tunisia have yielded the fossilized remains of a 10-meter-long marine crocodile – the largest ocean-dwelling croc ever discovered. Researchers named the new extinct species Machimosaurus rex, and it’s described in Cretaceous Research this week.

The articulated remains of the giant crocodylomorph were unearthed in December of 2014 during a prospecting trip at the Touil el Mhahir locality of Tataouine Governorate in southern Tunisia. The body was lying belly down with the head curved to the right side. After sorting through the sandy and clayish sediments, Federico Fanti of Università di Bologna and colleagues were able to identify skull fragments, teeth, vertebrae, ribs, a partial humerus, and osteoderms (the bony plates in the skin) of a never-before-seen species.

Its skull alone was up to 1.55 meters (5 feet) long – giving it an estimated body length of at least 9.6 meters (31.5 feet). The team named the species after the Latin word for “king,” a reference to its majestic size. Two views of the skull are pictured to the right.

M. rex belongs to a lineage called the thalattosuchian teleosaurids, marine crocodylomorphs that were thought to have gone extinct at the end of the Jurassic, before the Cretaceous. But at about 120 million to 130 million years old, M. rex is evidence that teleosauroids crossed the Jurassic-Cretaceous boundary.

This giant croc was likely an ambush predator in a lagoon-like environment that characterized this part of Africa during the early Cretaceous. Its ecology would have been similar to today’s semi-aquatic crocodilians that hunt both aquatic and terrestrial prey. Short, rounded teeth, like those of other members of the Machimosaurus genus, indicate that it fed on hard-shelled vertebrates.

Lots of turtle remains, including some that were a meter long, were also found in the same quarry – suggesting that turtles made up a large part of the M. rex diet. Additionally, Machimosaurus bite marks have previously been found on a sauropod dinosaur bone.

For comparison, the biggest freshwater “super croc,” called Sarcosuchus imperator, lived 110 million years ago, and it grew up to 12 meters (39 feet) long.

Image in the text: F. Fanti et al., 2016 Cretaceous Research