Plesiosaurs are marine reptiles that lived during the time of the dinosaurs. They often had longer necks than some of their fellow sea creatures like mosasaurs and ichthyosaurs, but even among plesiosaurs, there’s a lot of diversity.

Plesiosaurs can be split into two groups– plesiosauromorphs, which had long, thin necks and slender jaws, and pliosauromorphs, which had shorter necks and bigger heads. Even though the plesiosauromorphs look sleek and streamlined, they probably didn’t move very quickly and hunted small prey, in part because their long necks were likely quite rigid. On the other hand, the pliosauromorphs, like this Kronosaurus, were top predators that hunted big animals.

Photo by Tim Sackton