Almost 70 million years ago mosasaurs were nightmares. Multiple views of the top marine reptiles They lived during the Late Cretaceous period, often growing between 30 and 40 feet in length. But just as dangerous as the ancient one, the size of a great white shark Paleontologists have long believed that mosasaurs were their prehistoric ocean prey, and they lived in salt water.
A tooth recently found in a famous Hell Creek Formation in Montana says otherwise. According to findings published Dec. 11 in the journal BMC ZoologyAt least one species of mosasaurus may have foraged upstream into freshwater rivers.
Hell Creek contains some of the world's most diverse fossil hoards from the Upper Cretaceous and Lower Paleocene. In addition to land dinosaurs such as Tyrannosaurs And Triceratopsthis region was also home to aquatic species such as mosasaurs. Although there is no ocean today, the area does have rivers that flow into a long-vanished body of water called the Western Interior Seaway some 66 million years ago.
In 2022, paleontologists discovered a tooth in the sediments of one of these ancient rivers. By comparing the fossil's textured ridges with existing specimens, the researchers noticed similarities to a genus of mosasaurs. Prognathodon. Prognatodontids with massive skulls and strong jaws hunted in the oceans, but isotope analysis of tooth enamel revealed the presence of oxygen and strontium, which confirm a freshwater habitat.
Because the tooth remained in place after the owner's death, the study authors believe their aquatic mosasaurus likely lived and died in present-day landlocked North Dakota. Although no other mosasaur teeth from the same period were found there, older specimens excavated in other parts of the Western Interior Seaway also had isotopic signatures consistent with freshwater ones. Because of this, paleontologists now believe that salt levels in aquatic ecosystems are slowly decreasing over time.
If true, the team is comparing their mosasaurus to today's. Saltwater crocodiles (Crocodile porous), which are known to venture into fresh water in search of prey. It is possible that ancient predators gradually adapted to swimming in river beds as the salt content of the water decreased and the sea route became smaller. Either way, a recent discovery suggests that the only way to avoid encounters with some mosasaurs is to stay out of the water altogether.
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