New species of mosasaur discovered with unique teeth

Scientists have made a remarkable discovery in the world of paleontology. They have identified a previously unknown species of mosasaur, an ancient marine reptile that thrived during the time of the dinosaurs. This newfound creature, named Stelladens mysteriosus, possessed an extraordinary feature: its teeth were unlike anything seen in any reptile before.

The researchers found the remains of Stelladens mysteriosus in the Late Cretaceous deposits of Morocco. Impressively, this mosasaur was twice the size of a dolphin, highlighting its immense stature in the ancient oceans. However, it was the peculiar arrangement of its teeth that truly captivated the scientific community.

Typically, mosasaurs exhibited two blade-like, serrated ridges on their teeth, aiding them in slicing through their prey. Stelladens, on the other hand, possessed a remarkable dental arrangement. Its teeth featured anywhere from four to six blade-like ridges, resembling the shape of a cross-head screwdriver and forming a star-shaped pattern.

Dr. Nick Longrich, leading the study at the Milner Center for Evolution at the University of Bath, expressed his astonishment at this unexpected find. He emphasized that Stelladens mysteriosus stood out not just among other mosasaurs but also among all reptiles and vertebrates known to science.

This groundbreaking discovery, coupled with other recent findings from Africa, provides compelling evidence that mosasaurs and other marine reptiles were undergoing rapid evolutionary changes until their extinction 66 million years ago. The cataclysmic event caused by an asteroid impact resulted in the demise of not only the dinosaurs but also around 90% of all species on Earth. Stelladens mysteriosus stands as a testament to the diversity and mysterious nature of the ancient marine world.

Illustration of how Stelladens mysteriosus may have looked. Credit: Dr Nick Longrich

Dr. Nathalie Bardet, a renowned expert in marine reptiles from the Museum of Natural History in Paris, expressed her astonishment at the discovery, stating, “Having studied Moroccan mosasaurs for over two decades, I have never encountered anything of this nature before. I was simultaneously perplexed and amazed.”

The presence of multiple teeth with the same distinct shape suggests that this unique dental arrangement was not a result of pathology or mutation, but rather an inherent characteristic of the species.

The extraordinary teeth indicate a specialized feeding strategy or diet; however, the precise nature of Stelladens’ food source remains uncertain. Dr. Longrich acknowledged this uncertainty, remarking, “We are clueless regarding the diet of this creature, as we have no modern or fossil references that bear resemblance to it. The teeth resemble the tip of a Phillips-head screwdriver or perhaps a hex wrench. So, what exactly was it consuming? Phillips head screws? IKEA furniture? The answer eludes us.”

Although the teeth were relatively small, they displayed sturdiness and exhibited signs of wear on the tips, suggesting that the mosasaur did not prey on soft-bodied organisms. However, the teeth were not robust enough to crush heavily armored creatures such as clams or sea urchins.

Dr. Longrich further explained, “This might indicate that the mosasaur targeted small, lightly armored prey, such as thin-shelled ammonites, crustaceans, or bony fish. Yet, it is challenging to ascertain. The Cretaceous period hosted peculiar creatures like ammonites, belemnites, and baculites, which no longer exist today. It is conceivable that this mosasaur consumed a unique and extinct food source, occupying an ecological niche that no longer exists. Such circumstances might account for the absence of similar discoveries in the fossil record.”

Highlighting the unpredictability of evolution, Dr. Longrich emphasized that sometimes it ventures into unprecedented paths, giving rise to extraordinary organisms that never reappear in subsequent evolutionary events.

Mosasaurs, though contemporaries of dinosaurs, were not classified as dinosaurs themselves. They represented giant marine lizards, akin to Komodo dragons, snakes, and iguanas, specifically adapted to an aquatic lifestyle.

Mosasaurs emerged approximately 100 million years ago and experienced diversification until their extinction around 66 million years ago, coinciding with the catastrophic impact of a massive asteroid on the Yucatan Peninsula in Mexico, which shrouded the world in darkness.

Silhouette showing the approximate size of Stelladens mysteriosus. Scale = 2 m. Credit: Fossils (2023). DOI: 10.3390/fossils1010002

The recent discovery of Stelladens and other mosasaurs in Morocco provides compelling evidence that these marine reptiles were undergoing rapid evolutionary changes until the very end of the Cretaceous period, contradicting previous debates about the role of environmental changes in their extinction. Rather than fading away, it appears that mosasaurs were thriving and evolving at their peak when they met their demise.

The study also highlights the ongoing nature of scientific exploration in the Cretaceous deposits of Morocco. Despite years of research in the region, new species continue to be unearthed, possibly due to the rarity of most species present.

Dr. Longrich expressed, “We have only scratched the surface of what lies within these fossil beds. This year alone, we have already discovered three new species. The level of diversity during the late Cretaceous is simply mind-boggling.”

Nour-Eddine Jalil, a professor at the Natural History Museum and a researcher at Univers Cadi Ayyad in Morocco, also marveled at the surprises unearthed from the Moroccan sites. He mentioned the astonishing variety, including mosasaurs with saw-like teeth, a turtle with a snorkel-shaped snout, and a plethora of vertebrates of different shapes and sizes. The extraordinary findings led him to liken the discoveries to the works of an artist with an imaginative mind.

The fossil sites in Morocco offer an unparalleled glimpse into the astonishing biodiversity that thrived just before the catastrophic events marking the end of the Cretaceous period. The ongoing revelations continue to shed light on the fascinating ancient ecosystems and the evolutionary marvels that once inhabited our planet.

Source: University of Bath

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