Mosasaur Discovery Reveals Terrifying New Details About Ancient Sea Monsters
Mosasaurs were formidable predators that ruled the oceans alongside dinosaurs, but recent research has uncovered surprising evidence that they also thrived in freshwater environments.
A team of researchers from Sweden, the US, and the Netherlands conducted an analysis of isotopes found in mosasaur teeth from various sites in North Dakota. The results confirmed that these prehistoric sea monsters were not confined to saltwater habitats.
Uncovering New Insights
The discovery of a mosasaur tooth in an inland floodplain shed light on a group of mosasaurs that could have reached lengths of up to 11 meters (36 feet). This finding suggests that these creatures were not only lurking in the oceans but also in rivers, presenting a new level of danger for terrestrial dinosaurs.
Per Ahlberg, a vertebrate paleontologist at Uppsala University in Sweden, remarked, “The size of these mosasaurs would have rivaled that of the largest killer whales, making them formidable predators in riverine environments previously unassociated with such massive marine reptiles.”
Ancient Predators
Mosasaur were carnivorous reptiles that inhabited the late Cretaceous period, with some species growing to immense sizes that allowed them to dominate the ancient seas. The presence of a mosasaur tooth in a freshwater environment alongside a Tyrannosaurus rex tooth and a crocodylian jawbone raised questions about their habitat preferences.
By analyzing isotopes in the enamel of the mosasaur tooth, researchers could determine the creature’s diet and living environment. Oxygen, strontium, and carbon isotopes provided valuable insights into the freshwater signatures present in the tooth, indicating that mosasaurs adapted to riverine environments.
A Chilling Revelation
Further analysis of carbon isotopes revealed that the mosasaur in question had a higher 13C value than other known specimens, suggesting a unique feeding behavior. Melanie During, another vertebrate paleontologist at Uppsala University, explained, “This distinct carbon isotope ratio indicates that this mosasaur may have occasionally preyed on drowned dinosaurs, unlike its deep-diving counterparts.”
The transition of mosasaurs from saltwater to freshwater habitats may have been a late adaptation in the final million years before their eventual extinction, coinciding with the demise of the dinosaurs.
This groundbreaking research, published in the journal BMC Zoology, provides new insights into the behavior and ecology of these ancient sea monsters.

