Huayangosaurus

Phylogeny: Dinosauria > Ornithischia > Genasauria > Thyreophora > Thyreophoroidea > Eurypoda > Stegosauria > Huayangosauridae

Overview: Back in the late 1970’s, in what is now the Chinese province of Sichuan, remains of a few armored dinosaurs were discovered. Chinese researchers would publish a description of the animal in 1982, naming it Huayangosaurus, deriving its name from the Mandarin term “Huayang”, which can historically be applied as a name for the region of Sichuan. It was found in some of the deeper layers of the Shaximiao Formation, dated to the Middle Jurassic. The discovery proved quite significant, as Huayangosaurus was at that time one of the oldest known members of the clade Stegosauria, to which the famous Stegosaurus belonged. In many respects, the two dinosaurs were very similar. Both possessed twin rows of enlarged osteoderms growing along their backs and long spines on the end of the tail. They walked on all fours and are assumed to have largely lived on low-level plant life. Huayangosaurus, however, was smaller than Stegosaurus.

Length estimates for Huayangosaurus put it at maybe four meters long at most, with it being much lighter than Stegosaurus as well. These weren’t the only differences. Huayangosaurus had far more robust forelimbs, comparatively, than its famous cousin, as well as a proportionately larger skull. Even more notable, Huayangosaurus retained teeth towards the front of its mouth, which among later stegosaurs, were absent (though they retained teeth farther back in the mouth). Most agree it was, fitting for its age, one of the most basal of the known stegosaurs, probably belonging to a family separate from that of Stegosaurus. Said family is referred to as the Huayangosauridae and may contain other notable Chinese stegosaurs like Chungkingosaurus. Huayangosaurus had rather narrow dorsal plates and possibly a set of long spikes on the shoulders. These spines were likely used to ward off predators, such as Gasosaurus or the larger Yangchuanosaurus.