4.05" Plesiosaur (Trinacromerum) Vertebra - Kansas

About Plesiosaurs

Plesiosaurs were a diverse group of marine reptiles that lived during the Jurassic and Cretaceous periods, thriving in Earth’s oceans for more than 135 million years. Although they lived alongside dinosaurs, plesiosaurs were not dinosaurs; instead, they were fully aquatic reptiles adapted for life in open water. Their most recognizable features included broad, streamlined bodies, four powerful flippers used for underwater “flight,” and a wide range of neck lengths. Fossils of plesiosaurs have been found on every continent, including Antarctica, showing that they inhabited oceans across the globe.

This group included two main body types that filled very different ecological roles. Long-necked plesiosaurs had small heads and slender teeth suited for catching fish and squid, likely relying on stealth and precise strikes. Short-necked plesiosaurs, known as pliosaurs, evolved massive skulls and powerful jaws and became apex predators capable of hunting large prey, including other marine reptiles. Together, these forms made plesiosaurs one of the most successful and adaptable marine reptile groups in Earth’s history, dominating prehistoric seas until their extinction at the end of the Cretaceous.

The Smoky Hill Chalk Member of the Niobrara Chalk formation is a Cretaceous conservation Lagerstätte, or fossil-rich geological formation, known primarily for its exceptionally well-preserved marine reptiles. It outcrops in parts of northwest Kansas--its most famous localities for fossils--and in southeastern Nebraska. Large, well-known fossils excavated from the Smoky Hill Chalk include marine reptiles such as plesiosaurs, large bony fish such as Xiphactinus, mosasaurs, pterosaurs, and turtles.