Artist's representation of Thalassotitan atrox (Credit: Andrey Atuchin/ Bath University)

Researchers from the University of Bath in the United Kingdom have uncovered the fossil of a new mosasaur species that ruled the seas during the Cretaceous period. The ferocious marine lizard was an apex predator that thrived in the waters of Morocco at the same time T. rex was on land. The scientist named the creature Thalassotitan atrox (T. atrox) from the Greek words "Thalassa" and "titan," meaning "sea giant." The species name atrox translates to "cruel" or "merciless."

"Thalassotitan was an amazing, terrifying animal," said study leader Dr. Nick Longrich. "Imagine a Komodo dragon crossed with a great white shark crossed with a T. rex crossed with a killer whale."

Dr. Nick Longrich poses next to the massive T. atrox fossil (Credit: Dr. Nick Longrich/ Bath University)

Mosasaurs comprised a diverse group of giant lizards that inhabited much of the Atlantic Ocean from 135 million to 66 million years ago. The scaly-skinned reptiles grew up to 40 feet in length and used their paddle-like flippers and tail fin to glide through the water. Mosasaurs went extinct at the same time as the dinosaurs after a giant asteroid struck Earth 66 million years ago. Fortunately, their modern-day relatives — snakes, iguanas, and monitor lizards — did not evolve to be as large.

The remains of the T. atrox were unearthed in an area of Morocco that was underwater during the late Cretaceous period. The carnivorous reptile had an enormous 5-foot-long skull and measured almost 30 feet long. Unlike other mosasaur species, which had long snouts and thin teeth suitable for eating small fish, the T. atrox sported a stout muzzle and gigantic, orca-like teeth. This allowed the lizard to easily devour giant marine reptiles, like sea turtles, plesiosaurs, and even other mosasaurs. The researchers suspect the creature's chipped and broken teeth may have been damaged as it violently attacked its prey and chewed on their bones.

Size comparison of the T.atrox (Credit: Dr. Nick Longrich/Bath University)

This is not the first time a mosasaur fossil has been found in Morocco, and it likely will not be the last. The scientists, who published their findings in the journal Cretaceous Research on August 24, 2022, believe the North African country was once home to about 30 different mosasaur species.

While T. atrox is one of the largest mosasaur species, it is not the biggest. Mosasaurus hoffmanni, a different mosasaur species found in Russia in 2014, was estimated to be about 56 feet long.