Stegosaurids are defined by their back armor: rows of large, flat bony plates running along the spine, typically paired with defensive spikes toward the end of a heavy, muscular tail (a structure informally nicknamed the "thagomizer"). Their skulls were small and low, with weak, leaf-shaped teeth suited to low-growing vegetation rather than tough browse -- a puzzle given the animals' large body size, one that paleontologists suspect was solved by gut fermentation rather than dental processing.
The family was widespread in the Late Jurassic, with fossils found across North America, Africa, Europe, and Asia, and a handful of genera persisting into the Early Cretaceous. Stegosaurus, from North America's Morrison Formation, is the largest and best-known member; Kentrosaurus, from East Africa, was considerably smaller but carried a similar plate-and-spike arrangement, while more basal genera like Huayangosaurus help trace how the family's armor evolved.