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Giant mosasaur species discovered with strange screwdriver-like teeth

In a surprising twist of paleontological discovery, scientists have unearthed a new species of mosasaur, an enormous sea-dwelling lizard that thrived during the dinosaur era. The research is published in the journal Fossils.

This new specimen, named Stelladens mysteriosus, is intriguing not just for its size, about double that of a dolphin, but for its peculiar tooth structure, unlike any known reptile.

Very unique set of teeth

Residing in the Late Cretaceous era in what is now Morocco, Stelladens boasted a unique dental configuration. Its teeth displayed blade-like ridges, assembled in a pattern reminiscent of a star or a cross-head screwdriver. 

Contrary to the typical mosasaur tooth structure that includes two bladelike, serrated ridges to slice through prey, Stelladens displayed an astonishing four to six of these blades on each tooth.

Dr. Nick Longrich from the Milner Centre for Evolution at the University of Bath, who spearheaded the study, expressed his amazement: “It’s a surprise,” he shared. “It’s not like any mosasaur, or any reptile, even any vertebrate we’ve seen before.”

Dr. Nathalie Bardet, a marine reptile expert from the Museum of Natural History in Paris, shared a similar sentiment: “I’ve worked on the mosasaurs of Morocco for more than 20 years, and I’d never seen anything like this before – I was both perplexed and amazed!”

These teeth were no fluke

The consistent shape found in several of Stelladens’ teeth implies that this odd structure wasn’t a pathology or a mutation but a feature of the species. These teeth, likely facilitating a specialized feeding strategy or diet, open up a mystery about Stelladens’ food habits.

“We have no idea what this animal was eating, because we don’t know of anything similar either alive today, or from the fossil record,” said Dr. Longrich. The teeth, he noted, look like the tip of a Phillips-head screwdriver or maybe a hex wrench. “So what’s it eating? Phillips head screws? IKEA furniture? Who knows.”

Although small, the mosasaur teeth were robust and showed signs of wear at their tips, suggesting that soft-bodied prey were unlikely targets. However, the teeth weren’t sturdy enough to handle heavily armored animals like clams or sea urchins.

“That might seem to suggest it’s eating something small, and lightly armoured – thin-shelled ammonites, crustaceans, or bony fish – but it’s hard to know,” said Longrich. 

“There were weird animals living in the Cretaceous- ammonites, belemnites, baculites – that no longer exist. It’s possible this mosasaur ate something, and occupied a niche, that simply doesn’t exist anymore, and that might explain why nothing like this is ever seen again.”

Despite their imposing size, mosasaurs were not dinosaurs. They were giant lizards, akin to Komodo dragons, snakes, and iguanas, designed for an aquatic lifestyle. They evolved around 100 million years ago and diversified until 66 million years ago, when a catastrophic asteroid struck the Yucatan Peninsula in Mexico, instigating a mass extinction event.

This extinction led to the demise of the mosasaurs, dinosaurs, and around 90 percent of all species on Earth. However, the discovery of Stelladens, along with other recent finds from Morocco, hints that mosasaurs and other marine reptiles were evolving rapidly up to their extinction, suggesting they disappeared at their zenith rather than slowly fading away.

Still many unknowns left to be discovered

The constant discovery of new species in the Cretaceous of Morocco underscores the fact that our understanding of this era is still evolving. Most species are rare, and in a highly diverse ecosystem, finding all of the rare species may take several decades. The authors of the study anticipate many more surprises in the coming years.

“We’re not even close to finding everything in these beds,” said Dr. Longrich. “This is the third new species to appear, just this year. The amount of diversity at the end of the Cretaceous is just staggering.”

Nour-Eddine Jalil, a professor at the Natural History Museum and a researcher at University Cadi Ayyad in Morocco, also echoed the sentiment. He highlighted the astounding number of surprising discoveries, including mosasaurs with teeth arranged like a saw, a turtle with a snout fashioned as a snorkel, a myriad of vertebrates of various shapes and sizes, and now, a mosasaur with star-shaped teeth.

Jalil likened the myriad of discoveries to the “works of an artist with an overflowing imagination.” He stressed that Morocco’s sites provide an unparalleled glimpse into the extraordinary biodiversity that existed just before the catastrophic end of the Cretaceous period.

The discovery of Stelladens mysteriosus, alongside other recent finds, paints an evolving picture of the Late Cretaceous, offering a tantalizing glimpse into a world that vanished 66 million years ago. This continuing exploration underscores the dynamism of scientific discovery and the endless surprises that the past still holds for the future.

More about mosasaurs

Mosasaurs were a group of large, sea-dwelling reptiles that lived during the Late Cretaceous period, approximately 92 to 66 million years ago. 

Despite their often dinosaur-like portrayal in popular culture, mosasaurs were not dinosaurs but were actually more closely related to modern-day lizards and snakes. Their closest living relatives include the Komodo dragon and monitor lizards.

Here’s a broad overview of mosasaurs:

Size and Appearance

Mosasaurs ranged greatly in size, with the smallest species measuring about 3 feet (1 meter) long and the largest, such as Mosasaurus, reaching lengths of up to 50 feet (15 meters) or more. They had elongated, streamlined bodies with paddle-like limbs, a tail fluke similar to that of a shark for propulsion, and a long, powerful jaw filled with sharp teeth.


These reptiles were marine creatures, and their fossils have been discovered all around the globe, indicating that they inhabited a wide range of marine environments. Some species likely preferred near-shore environments, while others may have ventured into the open ocean.


Mosasaurs were predators and their diet primarily consisted of other marine creatures. They ate fish, cephalopods like ammonites and squids, other reptiles including smaller mosasaurs, and even birds.


Like modern marine reptiles, mosasaurs gave birth to live young, rather than laying eggs. Fossil evidence suggests that they may have given birth in warm, shallow waters.


Mosasaurs, along with many other species, went extinct during the Cretaceous-Paleogene (K-Pg) extinction event about 66 million years ago. This mass extinction is believed to have been caused by a combination of volcanic activity and a large asteroid or comet impact near what is now the Yucatan Peninsula in Mexico.

Fossil Discoveries

Mosasaur fossils have been found worldwide. Some of the most notable discoveries include well-preserved specimens with soft-tissue outlines, contents of their last meal, and even embryos, providing valuable information about their biology and ecology.


Mosasaurs had several notable adaptations for life in the ocean. Their limbs evolved into flippers, they developed a tail fluke to aid in swimming, and their lungs were adapted to allow them to dive deeply. Some species also had a double-hinged jaw and flexible skull (similar to snakes), which allowed them to eat prey larger than their head.


There were many different species of mosasaurs, exhibiting a wide range of sizes and adaptations. Some had long, slender bodies with needle-like teeth for catching fish, while others were robust with powerful jaws and sharp, conical teeth for tackling larger prey.

Paleontological Importance

Mosasaurs are considered important indicators of the health and diversity of Late Cretaceous marine ecosystems. Studying them provides valuable insight into prehistoric marine life and the effects of the K-Pg extinction event.

Image Credit: Nick Longrich


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