Elasmosaurus platyurus

Cruising the warm waters of the Late Cretaceous Western Interior Seaway, Elasmosaurus used four robust, paddle-like flippers to generate steady propulsion beneath the waves. Its extraordinarily elongated neck, supported by 72 individual cervical vertebrae, allowed it to sweep through schools of fish and cephalopods without alerting them to the bulk of its approaching body. Like many marine reptiles of its era, it swallowed smooth river stones known as gastroliths to help grind down food and assist with underwater buoyancy control.