Thalassotitan atrox, a species of mosasaur that swam in the Cretaceous oceans 66 million years ago, shows that these specialized marine creatures evolved to fill the marine apex predator niche, a niche occupied by orcas and white sharks today, and that they continued to diversify and fill new niches until their extinction at the end of the Cretaceous period.
Life reconstruction of Thalassotitan atrox. Image credit: Andrey Atuchin.
Mosasaurs are members of Mosasauridae, a family of lizards that became highly specialized for marine life in the Cretaceous period.
Their diversity peaked in the Maastrichtian age of the Cretaceous, between 72 and 66 million years ago, with the most diverse faunas known from Morocco.
By the end of the Cretaceous, these creatures had undergone an adaptive diversification, and showed a wide range of body sizes, movement styles, and diets. Some evolved to eat small prey like fish and squid. Others crushed ammonites and clams.
The newly-identified mosasaur species, Thalassotitan atrox, evolved to prey on all the other marine reptiles.
The marine animal had an enormous skull measuring 1.4 m (5 feet) long and grew to nearly 9 m (30 feet) long, the size of a killer whale.
While most mosasaurs had long jaws and slender teeth for catching fish, Thalassotitan atrox had a short, wide muzzle and massive, conical teeth like those of an orca. These let it seize and rip apart huge prey.
These adaptations suggest Thalassotitan atrox was an apex predator, sitting at the top of the food chain.
“Thalassotitan atrox was an amazing, terrifying animal,” said University of Bath paleontologist Nick Longrich.
“Imagine a Komodo Dragon crossed with a great white shark crossed with a T. rex crossed with a killer whale.”
Dr. Nick Longrich with the Thalassotitan atrox fossil. Image credit: Nick Longrich.
The animal’s fossilized remains were found in the phosphatic beds of the Oulad Abdoun Basin in Khouribga Province, Morocco.
“The teeth of Thalassotitan atrox are often broken and worn, however eating fish wouldn’t have produced this sort of tooth wear,” Dr. Longrich and colleagues said.
“Instead, this suggests that the giant mosasaur attacked other marine reptiles, chipping, breaking, and grinding its teeth as it bit into their bones and tore them apart.”
“Some teeth are so heavily damaged they have been almost ground down to the root.”
Remarkably, the paleontologists also found the possible remains of Thalassotitan atrox’s victims.
“Fossils from the same beds show damage from acids, with teeth and bone eaten away,” they said.
“Fossils with this peculiar damage include large predatory fish, a sea turtle, a 0.5-m- (1.6-foot) long plesiosaur head, and jaws and skulls of at least three different mosasaur species.”
“They would have been digested in Thalassotitan atrox’s stomach before it spat out their bones.”
Along with recent discoveries of mosasaurs from Morocco, Thalassotitan atrox suggests that mosasaurs weren’t in decline before the asteroid impact that drove the end-Cretaceous mass extinction. Instead, they flourished.
“The phosphate fossils of Morocco offer an unparalleled window on the paleobiodiversity at the end of Cretaceous,” said Professor Nour-Eddine Jalil, a paleontologist at the Museum of Natural History in Paris.
The team’s paper appears in the journal Cretaceous Research.
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Nicholas R. Longrich et al. Thalassotitan atrox, a giant predatory mosasaurid (Squamata) from the Upper Maastrichtian Phosphates of Morocco. Cretaceous Research, published online August 24, 2022; doi: 10.1016/j.cretres.2022.105315
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