Stegosauria

The Stegosaurs were a group of dinosaurs in the suborder Thyreophora. They have small heads, peg-like teeth and vertical bony plates and spines on their back and tail. They flourished from the Upper Jurassic to the Lower Cretaceous.
Classification.
The Stegosauria was originally named as an order by O.C. Marsh in 1877. Now it is treated as an infraorder or suborder (or simply a clade) within the armoured dinosaurs, the Thyreophora. The Stegosauria includes the families Huayangosauridae and Stegosauridae.
The Huayangosauridae were an early family of stegosaurs from the Middle Jurassic. They were smaller than later stegosaurs and had shorter and higher skulls. The type genus is "Huayangosaurus" of China. The poorly-known remains of "Regnosaurus" from England suggest it also could be a member. Its lower jaw is very similar to that of the former. 
The vast majority of stegosaurs being in the Stegosauridae. They lived in the later part of the Jurassic and the early Cretaceous. The group includes the well-known "Stegosaurus". The family is widespread, with fossils found in the Northern Hemisphere and Africa. Their decline coincides with that of the Cycadophyta.
Suborder Thyreophora
Infraorder Stegosauria