Overview
- An international team reports in BMC Zoology that a large mosasaur tooth from North Dakota carries freshwater oxygen and strontium signatures, with isotope work conducted at Vrije Universiteit Amsterdam.
- The tooth, recovered in 2022 from fluvial deposits near Bismarck alongside a Tyrannosaurus rex tooth and a crocodylian jaw, is dated to about 66 million years ago with no clear sign of post-burial transport.
- Morphology attributes the specimen to a prognathodontine mosasaur approaching 11 meters in length, and two slightly older North Dakota teeth show comparable freshwater isotope values.
- The researchers propose that late-stage freshening of the Western Interior Seaway created haloclines and riverine niches that some large marine mosasaurs could exploit.
- The interpretation rests on a limited number of teeth and includes tentative behavioral inferences, so the authors emphasize the need for additional fossils and geochemical tests.