For thousands of years, humans have been wondering if fearsome, long-necked, flesh-eating monsters lurked in deep, dark water. But while all the stories of Nessie, Champ the Lake Champlain Monster, and sea serpents have gone unproved, in the time of the dinosaurs, animals that looked like Nessie were very real. These creatures were called plesiosaurs.

Plesiosaurs weren’t dinosaurs. Instead, they were swimming reptiles. The smallest ones were around the size of a person, while the biggest ones were the size of a bus. Elasmosaurus was 40 feet long and had a long, skinny neck, while Kronosaurus had a short neck and big, crushing jaws it used to eat its prey– including other plesiosaurs!

Illustration by Dmitry Bogdanov