<p>A 66-million-year-old tooth discovered in North Dakota suggests mosasaurs—gigantic marine reptiles that could reach 12 metres—may have hunted in rivers as well as seas. These extinct lizard-like creatures, recently featured in Jurassic World Rebirth, were apex marine predators during the Late Cretaceous period.</p>.<p>The finding represents potential first evidence of mosasaurs hunting freshwater prey in Hell Creek. While mosasaurs dominated shallow seas and various marine environments, remains in estuarine and freshwater settings challenge their traditional classification as strictly marine animals.</p>.<p>Researchers from both sides of the Atlantic examined the fossilized tooth, discovered in 2022 in the Hell Creek Formation’s river-like area, formerly connected to the ancient Western Interior Seaway. Melanie During from Uppsala University, Nathan Van Vranken from Eastern West Virginia Community and Technical College, and colleagues determined the tooth belongs to the Prognathodontini mosasaur group, based on surface texture similarities with other members. Previous research indicates prognathodontids possessed bulky skulls and powerful jaws for ocean hunting.</p>.Massive search for missing radioactive isotopes in China.<p>Isotope analysis of the tooth’s enamel revealed oxygen and strontium signatures associated with freshwater environments. This suggests the mosasaur preyed on freshwater animals, indicating it could live and hunt away from the sea. The researchers found no evidence of transport, meaning the tooth’s owner lived and died in Hell Creek—unprecedented for mosasaur teeth from this period in the region.</p>.<p>Additional analyses of older mosasaur teeth and other Western Interior Seaway animals revealed isotope concentrations more consistent with freshwater than seawater habitats. This indicates salt levels gradually decreased over time, with rainwater becoming predominant. “The isotopic evidence suggests the tooth was formed while the mosasaur lived in a freshwater setting, reflecting a broader trend of mosasaurs adapting to decreasing salinity in the basin,” the researchers reported.</p>.<p>The authors hypothesise that Prognathodontini members were opportunistic predators occupying a niche similar to modern saltwater crocodiles. They likely adapted to freshwater environments responding to declining Western Interior Seaway salinity, subsequently entering Hell Creek’s river channels as the seaway receded.</p>.<p>The study appeared in BMC Zoology on Friday.</p>
<p>A 66-million-year-old tooth discovered in North Dakota suggests mosasaurs—gigantic marine reptiles that could reach 12 metres—may have hunted in rivers as well as seas. These extinct lizard-like creatures, recently featured in Jurassic World Rebirth, were apex marine predators during the Late Cretaceous period.</p>.<p>The finding represents potential first evidence of mosasaurs hunting freshwater prey in Hell Creek. While mosasaurs dominated shallow seas and various marine environments, remains in estuarine and freshwater settings challenge their traditional classification as strictly marine animals.</p>.<p>Researchers from both sides of the Atlantic examined the fossilized tooth, discovered in 2022 in the Hell Creek Formation’s river-like area, formerly connected to the ancient Western Interior Seaway. Melanie During from Uppsala University, Nathan Van Vranken from Eastern West Virginia Community and Technical College, and colleagues determined the tooth belongs to the Prognathodontini mosasaur group, based on surface texture similarities with other members. Previous research indicates prognathodontids possessed bulky skulls and powerful jaws for ocean hunting.</p>.Massive search for missing radioactive isotopes in China.<p>Isotope analysis of the tooth’s enamel revealed oxygen and strontium signatures associated with freshwater environments. This suggests the mosasaur preyed on freshwater animals, indicating it could live and hunt away from the sea. The researchers found no evidence of transport, meaning the tooth’s owner lived and died in Hell Creek—unprecedented for mosasaur teeth from this period in the region.</p>.<p>Additional analyses of older mosasaur teeth and other Western Interior Seaway animals revealed isotope concentrations more consistent with freshwater than seawater habitats. This indicates salt levels gradually decreased over time, with rainwater becoming predominant. “The isotopic evidence suggests the tooth was formed while the mosasaur lived in a freshwater setting, reflecting a broader trend of mosasaurs adapting to decreasing salinity in the basin,” the researchers reported.</p>.<p>The authors hypothesise that Prognathodontini members were opportunistic predators occupying a niche similar to modern saltwater crocodiles. They likely adapted to freshwater environments responding to declining Western Interior Seaway salinity, subsequently entering Hell Creek’s river channels as the seaway receded.</p>.<p>The study appeared in BMC Zoology on Friday.</p>
