Scientists discover fossils of a Giant Sea Lizard, Thalassotitan Atrox, that existed 66 million years ago in the oceans.

Thalassotitan Atrox, a huge new mosasaur from Morocco discovered by researchers, fits the apex predator niche.

Mosasaurs resembled a Komodo dragon with flippers in place of legs and a shark-like tail fin.

Mosasaurs, which could reach a length of 12 meters (40 feet), were not dinosaurs but rather huge sea lizards. They were distant relatives of monitor lizards and modern iguanas.

Thalassotitan had an enormous skull measuring 1.4 meters (5 feet long), that grew to nearly 30 feet (9 meters) long, the size of a killer whale.

Artist's representation of Thalassotitan atrox. Credit: Andrey Atuchin

Using gigantic jaws and teeth similar to those of killer whales, Thalassotitan used to hunted other marine reptiles like plesiosaurs, ichthyosaurs, sea turtles, and other mosasaurs.

Size comparison of Thalassotitan atrox. Credit: Nick Longrich

Thalassotita had a short, broad muzzle and enormous, conical teeth similar to those of an orca, while other mosasaurs had long jaws and thin teeth for hunting fish. These enable it to grasp and dismember large prey.

Nick Longrich with the mosasaur fossil. Credit: Nick Longrich

These adaptations suggest that Thalassotitan was in the top position in the food chain as an apex predator. The giant mosasaur shared the same ecological niche as the killer whale and great white shark of today.

The teeth of Thalassotitans are frequently broken and worn, although this sort of tooth loss wouldn't have resulted from eating fish.

This instead shows that the huge mosasaur attacked other marine reptiles, biting into their bones and tearing them apart while chipping, breaking, and grinding its teeth.

Some teeth have been so badly destroyed that they have almost been ground down to the root.

Remarkably, probable remains of Thalassotitan's victims have been discovered. Fossils from the same layers show damage from acids, with teeth and bone eaten away.

Large predatory fish, a sea turtle, a plesiosaur head that is half a meter long, and the jaws and skulls of at least three different mosasaur species are among the fossils that have this peculiar damage.

Thalassotitan's stomach would have digested them before it spat out their bones.

According to Dr. Nick Longrich, lead author of the study published in Cretaceous Research and from the Milner Center for Evolution at the University of Bath,  "It's circumstantial evidence."

He said, "We can't say for certain which species of animal ate all these other mosasaurs. But we have the bones of marine reptiles killed and eaten by a large predator."

"And it is probably not a coincidence that the killer's species, Thalassotitan, a mosasaur specialized to prey on other marine reptiles, is also found in the same place."

Map of distribution of Thalassotitan. Credit: Nick Longrich

"Everything in the oceans, even other Thalassotitan, was under threat from Thalassotitan."

The giant mosasaurs have injuries sustained in violent combat with other mosasaurs, including injuries to their faces and jaws.

Similar wounds are present in other mosasaurs,  but in Thalassotitan, these wounds were extremely common, indicating frequent, violent conflicts over eating grounds or mates.

Dr. Nick Longrich, who led the study, said, "Thalassotitan was an amazing and terrible animal. The new mosasaur coexisted with creatures like T. rex and Triceratops that lived in the last million years of the Age of Dinosaurs.

Recent discoveries of mosasaurs from Morocco show that mosasaurs weren't in decline before the asteroid impact. They instead thrived.

He said, "It boasts one of the richest and most diversified marine faunas. Understanding the diversity and biology of the mosasaurs is still in its infancy. There's so much more to be done."

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