Some 66 million years ago, when the land was ruled by dinosaurs, the oceans used to be infested with giant marine predators called mosasaurs. And, now, researchers have discovered the fossil of a new species of mosasaurs named Thalassotitan atrox. Mosasaurs were like giant marine lizards that could grow up to 12 metres in length. They were distant relatives of modern monitor lizards and iguanas and looked similar to a Komodo dragon. While they were marine, mosasaurs did not have a shark-like fin, instead, they had flippers. These reptiles evolved to grow bigger and more specialised in the last 25 million years of the Cretaceous period. While some species went on to feed on smaller fishes and squids, the Thalassotitan atrox ruled the seas devouring every other marine creature.

The fossil was unearthed outside the city of Casablanca in Morocco. According to researchers, Thalassotitan measured nearly 9 metres in length while just its skull was 1.4 meters long. Most mosasaurs had long jaws and slender teeth that were effective in catching small fish, but Thalassotitan was found to have a short, wide muzzle and massive teeth having a conical structure like those seen in an orca. They enabled the predator to tear apart huge prey.

These features, according to researchers, suggested that Thalassotitan was an apex predator and was positioned at the top of the food chain. They had the same ecological niche as the killer whales and the great white sharks found today.

The broken and worn-out condition of the Thalassotitan’s teeth suggested that it didn’t prey on fishes but hunted other marine reptiles breaking, chipping, and grinding its teeth in the process.

“Thalassotitan was an amazing, terrifying animal. Imagine a Komodo Dragon crossed with a great white shark crossed with a T. rex crossed with a killer whale,” said Dr Nick Longrich Senior Lecturer from the Milner Centre for Evolution at the University of Bath. He is the lead author of the study published in Cretaceous Research.

Besides the Thalassotitan fossil, researchers believe that they have also stumbled upon the remains of the predator’s prey. Fossils from the same bed where the Thalassotitan was found have damage from acids and their bone and teeth were observed to have eaten away. These fossils are of large predatory fish, a half-metre long plesiosaur head, a sea turtle, and skulls and jaws of three different mosasaur species.

According to Dr Longrich, while they cannot confirm who ate other mosasaurs, they at least have the bones of marine reptiles killed by large predators. He added that Thalassotitan was found in the same location and also fits the profile of the killer. “It’s a mosasaur specialised to prey on other marine reptiles. That’s probably not a coincidence,” Dr Longrich said.