Overview
- A peer-reviewed paper in BMC Zoology published December 11 reports multi-proxy isotope evidence that a large prognathodontine mosasaur inhabited freshwater near the end of the Cretaceous.
- The tooth, recovered in 2022 from a fluvial deposit in the Bismarck area alongside a T. rex tooth and a crocodylian jawbone of similar age, shows no signs of postmortem transport.
- Oxygen and strontium ratios in the enamel align with freshwater, and carbon values point to shallow-water behavior that may have included scavenging drowned dinosaurs.
- Two additional, slightly older teeth from nearby North Dakota sites display comparable freshwater signatures, suggesting multiple individuals used riverine habitats.
- The authors propose that freshening of the Western Interior Seaway created a halocline with a freshwater surface layer, a view supported by contrasting isotope patterns in gill-breathing versus air-breathing animals.