Fossil footprints and detailed studies of its anatomy have proven that Stegosaurus didn’t drag its tail on the mud, but actually walked erect, like an elephant, with its tail held horizontally, parallel to the ground. Its back wasn’t as arched as they had us believe, and the neck was not carried horizontally as usually depicted, but upright, like a bird’s.
Also, the tail spike cluster (known among paleontologists as the “thagomizer”) didn’t actually point upwards, but sideways. This made the tail a much deadlier and more efficient weapon; to stab an attacking predator, Stegosaurus only had to swing its tail horizontally; punctures matching the Stegosaurus’ tail spikes have been found in the bones of predatory dinosaurs from the same age and place, proving once and for all that Stegosaurus wasn’t any less dangerous than the ankylosaurs that would evolve later.
And that's just the first of ten dinosaurs we once thought we knew. Link -via the Presurfer