Overview
- The peer-reviewed study, published December 12 in BMC Zoology, analyzes three mosasaur teeth from North Dakota’s Hell Creek Formation.
- The first tooth, excavated in 2022 from a river deposit alongside a Tyrannosaurus rex tooth and a crocodylian jawbone, showed freshwater oxygen and strontium isotope signatures; two slightly older teeth from nearby sites matched this pattern.
- Carbon isotope values were higher than in typical ocean-diving mosasaurs, indicating shallow foraging and raising the possibility of scavenging or feeding on animals such as drowned dinosaurs.
- The authors propose that the Western Interior Seaway became increasingly fresh and stratified, with a freshwater surface layer; comparisons show gill-breathers retained saline signals while lung-breathers, including mosasaurs, align with the surface layer.
- Morphology points to a prognathodontine mosasaur, likely related to Prognathodon, with tooth-based estimates suggesting an animal around 11 meters long in a riverine setting where such fossils are rare.