👉 Plesiosaurs were a group of dinosaurs that lived during the Late Cretaceous period, approximately 69 to 65 million years ago. They were characterized by their large size, powerful jaws and strong body structure. The most well-known plesiosaur was the Dinosauria's largest member: Plesiosaurus. It was a large, reptile-like creature with a long neck, thick legs, and a powerful jaw that could open large bodies of water like rivers or