Huayangosaurus

*Huayangosaurus taibaii*

***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*.

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.

## 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.

## JPInstitute.com Description

Huayangosaurus is a very important member of the same family to which Stegosaurus belongs. It is the oldest known member of the stegosaur family and it seems to demonstrate how these dinosaurs evolved the plates along their backs. Huayangosaurus was less than half the size of its later family members.

This dinosaur is considered one of the most important fossils to be discovered in China. It is one of only two stegosaurs to be found with an associated skull. Huayangosaurus exhibits many characteristics of an evolutionarily transitional species. The plates along its back become more spike-like the closer they are to the tail. This supports the theory that stegosaur plates evolved from spikes. The skull and teeth are also more primitive than later stegosaurs, as this species still had premaxillary teeth, which disappeared in later stegosaurs.

## Links

http://web.archive.org/web/20040606014902fw\_/http://www.jpinstitute.com/dinopedia/dinocards/dc\_huaya.html
https://web.archive.org/web/20080723141410/http://kids.yahoo.com/dinosaurs/140--Huayangosaurus

## References

1. ↑ Dong, Z., Tang, Z. and Zhou, S.W. (1982). ["Note on the new Mid-Jurassic stegosaur from Sichuan Basin, China"] (in Chinese). *Vertebrata PalAsiatica* 20 (1) :83-87
2. ↑ Sereno, P & Z-M Dong (1992). The skull of the basal stegosaur *Huayangosaurus taibaii* and a cladistic diagnosis of Stegosauria. *Journal of Vertebrate Paleontology* 51: 318-343