While marine reptiles swam in the Jurassic seas, dinosaurs roamed the land. Where Peterborough is today was under the Jurassic seas, so dinosaur bones are rarely found. Some however may have washed down to the coast. These bones are thought to belong to a Stegosaurus were found in the Fletton brick pits. Stegosaurus was a large, plant-eating dinosaur that had two rows of bony plates along its back that end with a double pair of spikes.