The marine contemporary of the T. rex and Triceratops

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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