Giant lizards were thriving during the age of dinosaurs

A team of experts led by the University of Bath is describing a previously unknown lizard species, Pluridens serpentis, that was thriving during the the end of the Cretaceous period in Morocco. 

The giant mosasaur, which reached up to eight metres in length, was wiped out by the asteroid impact that killed the dinosaurs 66 million years ago.

“It’s a new species of a large predator which, with its eight meter length, comes to confirm the diversity of the faunas of the seas just before the Cretaceous crisis,” said study co-author Dr Nour-Eddine Jalil.

“Pluridens serpentis highlights the importance of the paleontological heritage of Morocco to help illustrate the history of life.”

Pluridens represents the third new mosasaur species to be described from the region in less than a year, bringing the total number up to 13. These massive marine reptiles were related to snakes and Komodo dragons. 

The fossils found in Morocco have revealed that mosasaurs were extremely diverse. Some had small teeth for preying on fish and squid, some had blunt teeth for crushing clams and crustaceans, and some had teeth that could rip apart marine animals, including other mosasaurs.

“The diversity in these fossils is just astonishing. Far from declining in diversity, the mosasaurs seem to be peaking just before they went extinct,” said study lead author Dr. Nick Longrich.

“We’re not seeing any evidence that this group was struggling before they went extinct – From an evolutionary standpoint, they were succeeding, they did everything right- but nothing can prepare you for an asteroid.”

According to the researchers, Pluridens had long, slender jaws with over a hundred sharp teeth. The ancient lizard had small eyes, which indicates that it also had poor vision. 

However, the experts discovered that Pluridens had a snout with dozens of openings for nerves, possibly representing the ability to hunt by sensing water movements. These nerves may have been sensitive to tiny variations in water pressure, which is an adaptation found in sea snakes.

“Typically, when animals evolve small eyes, it’s because they’re relying more heavily on other senses,” said Dr. Longrich.

“If it wasn’t using the eyes, then it’s very likely that it was using the tongue to hunt, like a snake. Many aquatic snakes and lizards – sea snakes, filesnakes, water monitors- flick their forked tongues underwater, using chemical cues to track their prey.” 

“Mosasaurs would have resembled whales and dolphins, so it’s tempting to assume they lived like them. But they’re very different beasts – they’re huge lizards – so they probably acted like them.”

Along with its massive size, Pluridens had thick, heavily built jawbones. “It’s possible that big males were fighting with these jaws,” said Dr. Longrich. 

“In some beaked whales, the males have massive jaws they use to fight with, and male sperm whales can be highly aggressive. Some Pluridens jaws show healing injuries, which suggests some violent fights.”

Dr. Nathalie Bardet is an expert on mosasaurs, particularly those from the Phosphates of Morocco at the Muséum National d’Histoire Naturelle of Paris.

“Working on this group of marine reptiles since more than 20 years, I never stop being surprised by the incredible diversity of these predators, who all lived there and shared the available space and food resources,” said Dr. Bardet.

“These latest discoveries show perfectly that the list of species present here is far from being closed and that the future still holds great surprises and discoveries!”

The study is published in the journal Cretaceous Research.

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By Chrissy Sexton, Earth.com Staff Writer