This primitive stegosaurid is known from complete adult skeletons found in the Dashanpu quarries, China, in the early 1980s. It was re-described in 1992. The arrangement of teeth, and the fact that its front legs are long for a stegosaurid put it so far from later stegosaurids that it is placed in a family of its own.
Name: Huayangosaurus, meaning ‘lizard from Huayang’
Size: about 4m long and 1.5m high
Food: soft, juicy plants
Lived: 162-148 million years ago in the Middle Jurassic in China
Huayangosaurus has a double row of heart-shaped plates on the neck that are replaced by long, narrow, spine-like plates on the back. They become smaller on the tail, ending about half-way down. The tip of the tail is furnished with two pairs of spines. It had extra spikes on its shoulders, which would have been very off-putting to a predator. The skull has teeth at the front of the mouth – something that was lost in later stegosaurids – and there is a pair of horns near the eyes.
This stegosaur had many primitive features. For example, its skull had a small opening in front of each eye, and there was another small opening in each half of the lower jaw. Both of these openings closed off in later stegosaurs. At the front of its snout, Huayangosaurus had 14 teeth (seven on each side). Later stegosaurs did not have these teeth. Huayangosaurus had long front limbs three-quarters longer than the back limbs. Later stegosaurs had forelimbs that were much shorter. Finally, the armour plates that ran in two rows along the back of Huayangosaurus were more narrow and much thicker than the plates on the backs of its later relatives. All these features are clues to the stegosaurs’ place in the dinosaur family tree.
Huayangosaurus lived in a land of lakes, rivers, and lush vegetation. By looking at its teeth, scientists can tell it was a herbivore. Its spiky, upstanding armour plates and shoulder spines could have protected it from predators, but they could also have been for show, perhaps to attract a mate. They may also have been used to regulate its body temperature. The plates seem too thick, however, to have been very good for this. Certainly, the animal’s tail spikes would have kept its enemies away.