These giant sea reptiles lived in freshwater rivers, too (earthsky.org) [View all]
Posted by
Shireen Gonzaga
December 18, 2025
Chemical analysis of a mosasaur tooth reveals a surprise
Mosasaurs were giant aquatic reptiles that lived 94 to 66 million years ago. While T. rex was the dominant predator on land, mosasaurs were the apex predators of the sea. But scientists from Uppsala University in Sweden said on December 12, 2025, that they have new evidence showing mosasaurs also lived in freshwater, in inland rivers. Their diverse habitats suggest they were adapting to a changing environment.
In 2022, researchers found a mosasaur tooth at an unexpected location in North Dakota. They recovered it from ancient river deposits alongside a T. rex tooth and the jawbone of a freshwater crocodile-like (or crocodilian) reptile. Plus, the area was known for its fossilized Edmontosaurus duck-billed dinosaurs.
How did a seagoing mosasaur’s tooth end up in a freshwater river?
In this new study, scientists found answers in the mosasaur’s tooth enamel. A chemical analysis of certain elements revealed that this mosasaur had, in fact, lived in freshwater, not salt water.
The researchers published their study in the peer-reviewed journal BMC Zoology on December 12, 2025.
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more: https://earthsky.org/earth/giant-sea-reptiles-mosasaurs-freshwater-predators/?mc_cid=8062ada9aa
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