Researchers found a 66 million-year-old giant sea lizard that ruled the oceans

It occupied the place of the mega predator in the food chain, revealing fossil evidence.
Ameya Paleja
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Thalassotitan atrox grew up to 12 metres (40 feet) and was at the top of the food chain.

University of Bath 

Researchers at the University of Bath have discovered fossilized remains of a colossal mosasaur, a marine contemporary of the Tyrannosaurus rex (T.rex) and Triceratops, a university press release said. The remains were found in Morocco.

66 million years ago, near the end of the Cretaceous period, the Atlantic flooded northern Africa, and nutrient-rich waters gave rise to plankton blooms. Small fish consumed the plankton and became prey for bigger fish, then consumed by marine reptiles such as mosasaurs and plesiosaurs. While the T.rex occupied the position on top of the food chain on land, a similar predator was missing in the seas. So, a mosasaur evolved to occupy this spot.

What are mosasaurs?

Mosasaurs weren't dinosaurs but giant marine lizards that grew up to 40 feet (12 m) in length. Distant relatives of modern-day monitor lizards and iguanas, mosasaurs looked much like a Komodo dragon but had flippers instead of feet and even had a tail fin, much like a shark.

In the last 25 million years of the Cretaceous era, the press release said that mosasaurs grew larger and specialized in taking up niches that were once occupied by plesiosaurs and ichthyosaurs. Some of the mosasaurs preyed on small fish, some ate clams and ammonites, while others evolved to eat other marine reptiles. One such predator was dug up recently in Morocco and has been dubbed, Thalassotitan atrox.

What we know about Thalassotitan atrox?

Researchers found a 66 million-year-old giant sea lizard that ruled the oceans

Thalassotitan had an enormous skull measuring five feet (1.5 m) long and at 30 feet (9 m) grew to a size of a killer whale. While other mosasaurs had long jaws and slender teeth for catching fish, Thalassotitan had a short wide muzzle and housed inside are massive conical teeth, much like an orca.

The fossil reveals that the Thalassotitan teeth are worn and broken, something that would not be the result of eating small fish. It is, therefore, likely that the mosasaur attacked other marine reptiles, and as it tore them apart and bit into their bones, its teeth chipped and broke away, while some were even ground to the root.

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Fossils found in the same beds include large predatory fish, sea turtles, plesiosaur heads, and jaws and skulls of at least three mosasaur species, likely victims of the Thalassotitan. The remains show damage from acids and teeth and bone eaten away, which researchers suggest are signs that were digested in the giant reptile's stomach.

Thalassotitan was not just a threat to marine animals but also other Thalassotitans since the fossils show injury marks that were likely sustained during fights for feeding grounds or over mates.

“Thalassotitan was an amazing, terrifying animal,” said Nick Longrich, a senior lecturer at the University of Bath and one who led the research on the fossil. “Imagine a Komodo Dragon crossed with a great white shark crossed with a T. rex crossed with a killer whale."

The researchers have just begun looking into mosasaurs. "Morocco has one of the richest and most diverse marine faunas known from the Cretaceous. We’re just getting started understanding the diversity and the biology of the mosasaurs,” Longrich added.

The research was published in the journal Cretaceous Research


The Cretaceous-Paleogene (K-Pg) transition saw mass extinctions in terrestrial and marine ecosystems. Terrestrial vertebrate diversity patterns across the K-Pg boundary have seen extensive study, but less is known about marine vertebrates. We describe a new mosasaurid from the latest Maastrichtian phosphatic beds of Morocco, showing how mosasaurids evolved to become apex predators in the latest Cretaceous. Thalassotitan atrox n. gen. et sp., from the Oulad Abdoun Basin of Khouribga Province, Morocco is characterized by large size, a broad skull, massive jaws, and reduced cranial kinesis, suggesting it was highly adapted for carnivory. Teeth resemble those of killer whales in their robust, conical shape, and show heavy wear and damage. Phylogenetic analysis recovers Thalassotitan as a close relative of Prognathodon currii and P. saturator within the Prognathodontini. Among the associated fauna, three genera of mosasaurids, elasmosaurid plesiosaur, chelonioid turtle, and enchodontid fish show acid damage, and could be prey ingested by mosasaurids, likely Thalassotitan. Thalassotitan shows mosasaurids evolved to fill the marine apex predator niche, a niche occupied by orcas and white sharks today. Mosasaurs continued to diversify and fill new niches until their extinction at the end of the Cretaceous.

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