T. rex tooth leads scientists to make a shocking discovery about brute that ate dinosaurs

Mosasaurs, an extinct group of aquatic squamate reptiles, adapted to a very different environment during the Late Cretaceous period, as discovered by a group of scientists. These marine predators have been known to hunt in the salty oceans, but now they have found that these mammoths adapted to a freshwater environment and even fed on dinosaurs. IFL Science reported that when Trissa Ford came across a Tyrannosaurus rex tooth in Hell Creek, North Dakota, in 2022, the careful digging led the group to another tooth. Dig leader Dr Clint Boyd knew it didn't belong to a T. rex, and reached out to marine reptile expert Dr Nathan Van Vranken of Eastern West Virginia Community and Technical College. He confirmed that it had come from a mosasaur of the Prognathodontini subfamily.

This was strange since Hill Creek had never had an ocean, nor a salty lake. Hell Creek is almost 2,000 kilometres from the ocean, and Dr Melanie During, of Uppsala University, who helped the team solve the mystery, says the tooth had remained in the same place. There had also never been any saltwater source in the region. Her analysis revealed that this mosasaur was a descendant of a species that had adapted to living in river water. The study is published in BMC Zoology.

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Mosasaurs adapted to live in rivers

Scientists have always believed that mosasaurs lived in salty waters. This is because the Western Interior Seaway, which divided North America into two parts, was connected to both the Arctic Ocean and the Gulf of Mexico, and was presumably salty. Mosasaurs inhabited this waterway, which meant they were thriving in saltwater. However, it underwent a huge change at the end of the dinosaur era. Dr Melanie told the publication that mountains were forming at this time and the San Andreas fault was very active, leading the continent to lift upwards. The Seaway got blocked from both sides, cutting off access to the oceans. Gradually, rainwater flushed out all the salt, effectively turning the Hill Creek region into a network of rivers. This shows the mosasaurs underwent a major adaptation.

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She compared the mosasaurs to Australia’s giant saltwater crocodiles, which adapted to freshwater. Since the latter moved to also being able to live on land, could the mosasaurs also have done the same? She thinks it is possible.