Huayangosaurus

Huayangosaurus is a genus of extinct stegosaurian dinosaur from the Middle Jurassic of China. The name derives from "Huayang", an alternate name for Sichuan (the province where it was discovered), and "saurus", meaning "lizard". It lived during the Bathonian to Callovian stages, around 165 million years ago, some 20 million years before its famous relative, Stegosaurus appeared in North America. At only 4.5 metres long, it was also much smaller than its famous cousin. Found in the Lower Shaximiao Formation, Huayangosaurus shared the local Middle Jurassic landscape with the sauropods Shunosaurus, Datousaurus, Omeisaurus and Protognathosaurus, the ornithopod Xiaosaurus and the carnivorous Gasosaurus.

Description
Like other stegosaurians, Huayangosaurus was a quadrupedal herbivore with a small skull and a spiked tail. Like its more famous relative, Stegosaurus, Huayangosaurus bore the distinctive double row of plates that characterize all the stegosaurians. These plates rose vertically along its arched back. In Huayangosaurus, the plates were more spike-like than in Stegosaurus. Like Stegosaurus, however, it bore two pairs of long spikes extending horizontally near the end of its tail.

Huayangosaurus was one of the smallest known stegosaurians, at just 4.5 meters in length.

Discovery and species
Huayangosaurus remains from twelve individual animals were recovered from the Dashanpu Quarry near Zigong in Sichuan, and named by Dong, Tang, and Zhou in 1982. The type species is H. taibaii.

Classification
As it is the most basal stegosaurian, it is placed in within its own family Huayangosauridae. It is also morphologically distinct from later (stegosaurid) forms. Its skull was broader and had premaxillary teeth in the front of its mouth. All later stegosaurians lost these teeth.

Palaeobiology
Like many other stegosaurians, it had plates all down its back and spikes on its tail. Two large spikes were above its hips, and may have been used for deterring an attack from above (considering as it was a fairly short in height compared to later stegosaurians). Its plates were smaller than those of Stegosaurus, with much less surface area. Thus they would have been much less effective heat regulators, one of the postulated functions of plates.

Popular culture
Mounted skeletons of Huayangosaurus are on display at the Zigong Dinosaur Museum in Zigong and the Municipal Museum of Chongqing in Sichuan Province in China.