Stegosaurus roamed the Earth about 150 million years ago, during the Jurassic period of the Mesozoic Era, or "Age of Dinosaurs." According to the US Geological Survey, Stegosaurus had already been extinct for approximately 80 million years when Cretaceous dinosaurs such as Tyrannosaurus rex first appeared about 67 million years ago.

In short, 80 million years separated Stegosaurus from T. rex, while 67 million years separate T. rex from us — that's a pretty mind-blowing difference of 20 million years.