Final answer:
Stegosaurs lived during the Jurassic Period of the Mesozoic Era, approximately 145 to 201.3 million years ago.
Step-by-step explanation:
Stegosaurs lived during the Jurassic Period of the Mesozoic Era, approximately 145 to 201.3 million years ago. This period is also known as the Age of Reptiles, and it was a time when dinosaurs were abundant and diverse.