The first fossil of Stegosaurus was described in 1877. Yale paleontologist Othniel Charles Marsh named the dinosaur Stegosaurus armatus after studying partial remains discovered in Colorado’s Morrison Formation.
The name Stegosaurus means “roof lizard,” reflecting Marsh’s early interpretation that its large back plates lay flat like roof tiles. Later discoveries showed that the plates were arranged upright along the back, while pairs of spikes armed the tail.
The original material was incomplete, so early reconstructions of Stegosaurus changed substantially as additional fossils were found. Scientists now recognize several species, although Stegosaurus armatus remains the type species that anchors the genus’s scientific name.
A common mix-up is confusing 1877 with the description of other famous dinosaurs. Iguanodon was named in 1825, while Tyrannosaurus was named much later, in 1905. Stegosaurus lived during the Late Jurassic, roughly late in the dinosaur age’s Jurassic chapter, about 150 million years ago.