Incredible Fossil Reveals Giant Lizard That Ruled The Sea With Teeth And Terror

The discovery of incredible fossils of a giant sea lizard reveals how this ancient extinct beast would have ruled the sea 66 million years ago.

The beast is a recently discovered species of mosasaur, giant marine reptiles that hunted the oceans during the Late Cretaceous.

It’s called Atrox thalassotitaniumand the wear of its teeth along with other remains found at its dig site suggest that this intimidating animal was no gentle giant – but feasted on tough prey such as sea turtles, plesiosaurs and other mosasaurs.

Other mosasaurs sought out smaller prey, like fish or ammonites (which weren’t actually always that small).

Thalassotitan skull fossil
One of Thalassotitan’s skulls. (University of Bath)

This means Thalassotitanium probably occupied a place at the very top of the food web, maintaining ecosystems by controlling other predators.

Thalassotitanium was an amazing and terrifying animal,” says paleontologist and evolutionary biologist Nick Longrich from the University of Bath in the UK. “Imagine a Komodo dragon crossed with a great white shark crossed with a T. rex crossed with a killer whale.”

artistic impression of a thalassotitanium
artistic reconstruction of Thalassotitan Astrox. (André Atuchin)

There are no reptiles alive today that are on the scale of mosasaurs, which could reach lengths of 12 meters (40 feet) – twice the size of the largest modern reptiles, crocodilians. But mosasaurs are related, somewhat and remotely, to modern snakes and iguanas.

Mosasaurs were better adapted to an all-aquatic lifestyle than the Galapagos marine iguanas. They had a reptilian head, but fins instead of clawed feet, and a tail sporting shark-like fins.

Different species of mosasaurs could also specialize in different prey, given their different teeth. Some teeth were small and sharp, good for fish and squid; others had duller teeth and crushing jaws, perfect for shelled creatures.

But, since the animals don’t seem to have a good sense of smell, it’s likely that they were primarily predators rather than scavengers.

Analyzes suggest that mosasaurs feasted on fish, cephalopods, turtles, molluscs, other mosasaurs, and even birds. Thalassotitanium seems to have been among the fiercest.

The fossils were discovered in the phosphate fossil beds of Morocco, an area rich in diverse and perfectly preserved Cretaceous and Miocene fossils.

The remains include skulls, vertebrae, limb bones and phalanges. Together they have enabled a full description of Thalassotitanium skull, jaw and teeth, as well as the skeleton, shoulders and forelimbs.

The animal, discovered by Longrich and his team, could probably reach a length of around 9 to 10 meters, slightly longer than an orca. However, its skull was almost twice as long as that of the orca, reaching around 1.5 meters in length.

size chart comparing thalassotitan to an orca and a human
Map showing the impressive size of Thalassotitan. (University of Bath)

Unlike other mosasaurs which had slender snouts, Thalassotitanium the jaw was wide and short, with large conical teeth that would have been perfect for grabbing and tearing prey. And those teeth held another clue to the animal’s diet: Many of them are broken and worn, damage that wouldn’t occur with a diet of mostly soft prey.

According to the researchers, this suggests that Thalassotitanium has chipped and broken its teeth on hard surfaces, such as turtle shells and the bones of other, possibly more timid mosasaurs.

This is supported by other fossils found near the Thalassotitanium remains: the bones of large predatory fish, a sea turtle shell, a plesiosaur skull, and the bones of at least three different mosasaur species.

These remains all show signs of acid wear, as you would expect from digestive acids in the belly of a giant beast, before being regurgitated. This is circumstantial evidence, the researchers note; but it’s still quite interesting.

wear on the teeth of a small thalassotitan
Wear on the teeth of a small Thalassotitan. (Longrich et al., Cretac. Res., 2020)

“We can’t say for sure what species of animal ate all those other mosasaurs,” says Longrich.

“But we have bones of marine reptiles killed and eaten by a large predator. And in the same place we find Thalassotitanium, a species that fits the killer’s profile – it’s a mosasaur that specializes in preying on other marine reptiles. It’s probably not a coincidence.”

During the last 25 million years of the Cretaceous, mosasaurs became increasingly specialized and diverse. The discovery of Thalassotitanium suggests that mosasaurs were even more diverse than we thought – and that their ecosystem was alive and thriving, with enough prey diversity to support this predator diversification.

In turn, this has interesting implications for the times leading up to the Cretaceous-Paleogene mass extinction event 65 million years ago. This implies that, rather than declining and making the world vulnerable, as some have thought, biodiversity was running amok, possibly as a result of a smaller extinction event in the middle of the Cretaceous.

Further excavations in the fossil beds of Morocco should clarify this intriguing possibility.

“There’s so much more to do,” Longrich says.

“Morocco has one of the richest and most diverse marine faunas known from the Cretaceous. We are just beginning to understand the diversity and biology of mosasaurs.”

The paper was published in Cretaceous research.

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