Researchers discover fossilized giant sea lizard that ruled the ocean 66 million years ago

Scientists discover fossils of giant sea lizards that ruled the ocean 66 million years ago

Artist’s rendering of Thalassotitan atrox.Credit: Andrei Artuchin

Researchers have discovered a giant new mosasaur called Thalassotitan atrox in Morocco that fills a top predator niche. With jaws and teeth as large as killer whales, Thalassotitan hunted other marine reptiles – plesiosaurs, turtles and other mosasaurs.


Sea monsters did exist at the end of the Cretaceous period, 66 million years ago. While dinosaurs flourished on land, the oceans were ruled by the giant marine reptile mosasaurs.

Mosasaurs were not dinosaurs, but giant sea lizards up to 12 meters (40 feet) long. They are distant relatives of modern iguanas and monitor lizards.

The mosasaur looked like a Komodo dragon, with flippers instead of legs, and a shark-like tail. During the last 25 million years of the Cretaceous period, mosasaurs became larger and more specialized, occupying niches once occupied by marine reptiles such as plesiosaurs and ichthyosaurs. Some evolved to eat small prey, such as fish and squid. Others smashed ammonites and clams. The new mosasaur, named Thalassotitan atrox, evolved to prey on all other marine reptiles.

The remains of the new species were dug up in Morocco, about an hour’s drive from Casablanca. Here, at the end of the Cretaceous period, the Atlantic Ocean flooded North Africa. Nutrient-rich waters gushing from the depths nourish plankton blooms. Those that fed small fish, fed big fish, fed mosasaurs and plesiosaurs — and so on, these marine reptiles became food for giant carnivorous marine marine animals.

Researchers discover fossilized giant sea lizard that ruled the ocean 66 million years ago

Nick Longridge and Mosasaurus fossils.Credit: Nick Longridge

Thalassotitan had a massive 1.4-meter (5-foot-long) skull that grew to nearly 30 feet (9 meters) long, about the size of a killer whale. While most mosasaurs had long jaws and slender teeth for fishing, sea dragons had a short, wide muzzle and huge, tapered teeth, like those of an orca whale. These allow it to grab and tear apart huge prey. These adaptations suggest that seaweed is an apex predator, at the top of the food chain. The giant mosasaur occupied the same ecological niche as today’s killer whales and great white sharks.

Thalassotitan’s teeth are often broken and worn, but eating fish does not produce this kind of tooth wear. Instead, it suggests the giant mosasaur attacked other marine reptiles, shattering, breaking and grinding its teeth as it bit into their bones and ripped them apart. Some teeth are so badly damaged that they are almost ground to the root.

fossil remains of prey

Notably, the remains of possible marine life victims have been found. Fossils from the same bed showed acid damage, with teeth and bones eroded away. Fossils with this particular damage include large predatory fish, a sea turtle, a half-meter-long plesiosaur head, and the jaws and skulls of at least three different mosasaurs. They digest it in the Thalassotitan’s stomach before spitting out their bones.

Researchers discover fossilized giant sea lizard that ruled the ocean 66 million years ago

Size comparison of Thalassotitan atrox.Credit: Nick Longridge

“This is circumstantial evidence,” said Dr Nick Longrich, senior lecturer at the Milner Centre for Evolution at the University of Bath and lead author of the study, which was published in Cretaceous studies.

“We can’t be sure which animal ate all the other mosasaurs. But we have bones from marine reptiles that were killed and eaten by large predators.

“In the same place, we found Thalassotitan, a species that fits the killer profile — a mosasaur that specialized in preying on other marine reptiles. It’s probably no coincidence.”

Thalassotitan is a threat to everything in the ocean – including other Thalassotitans. The giant mosasaur was injured in the fierce battle with other mosasaurs, and the face and jaw were injured in the battle. Other mosasaurs have similar scars, but in Thalassotitan these scars are unusually common, indicating frequent, intense competition for feeding ground or mates.

“Thalassotitan is an amazing, terrifying animal,” said Dr. Nick Longrich, who led the study. “Imagine a Komodo dragon interbreeding with a great white shark with a Tyrannosaurus rex and a killer whale.”

The new mosasaur lived in the last million years of the age of dinosaurs and was contemporary with animals such as Tyrannosaurus rex and Triceratops. Together with the recent discovery of mosasaurs in Morocco, this suggests that mosasaurs did not decline before the asteroid impact caused the mass extinction in the Cretaceous. Instead, they thrive.

Researchers discover fossilized giant sea lizard that ruled the ocean 66 million years ago

Thalassotitan distribution map.Credit: Nick Longridge

Professor Nour-Eddine Jalil, co-author of the paper at the Musée Natural History de Paris, said: “Phosphate fossils from Morocco provide an unparalleled window into the paleontological diversity of the late Cretaceous.

“They tell us how rich and diverse life was before the end of the ‘Dinosaur Age’, an era in which animals had to specialize to have a place in their ecosystems. Thalassotitan came to the rescue by taking on the role of giant predators at the top of the food chain. Finish the painting.”

“There’s still a lot of work to do,” Longreach said. “Morocco has one of the richest and most diverse marine fauna since the Cretaceous. We are just beginning to understand the diversity and biology of mosasaurs.”


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More information:
Nicholas R. Longrich et al., Thalassotitan atrox, a giant predatory mosasaur (Squamata) from the phosphate region of Upper Maastricht, Morocco, Cretaceous studies (2022). DOI: 10.1016/j.cretres.2022.105315

Dr. Longrich blogged about the research here: https://www.nicklongrich.com/blog/thalassotitan-the-killer-mosasaur

Provided by the University of Bath

Citation: Scientists discover fossil of giant sea lizard that ruled the oceans 66 million years ago (24 Aug 2022), 24 Aug 2022 from https://phys.org/news/2022-08-scientists-fossils- giant-sea-lizard retrieved .html

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