MEANING: Huayang lizard
PERIOD: Middle Jurassic
CONTINENT: Asia
Huayangosaurus is a stegosaurian dinosaur from the Middle Jurassic of China. It was one of the smallest known stegosaurians, at just 4 m in length and 500 kg in body mass. Like other stegosaurians, Huayangosaurus was a quadrupedal herbivore with a small skull and a spiked tail. It bore the distinctive double row of plates that characterize all the stegosaurians. In Huayangosaurus, the plates were spike-like. Unique to the Huayangosaurus were the broader skull and premaxillary teeth in the front of its mouth. All later stegosaurians lost these teeth.
Huayangosaurus is from the Jurassic. The Jurassic is a geologic period that spanned from the end of the Triassic, 201 million y ears ago, to the beginning of the Cretaceous, 145 million years ago. It is the middle period of the Mesozoic Era. The start of the Jurassic was marked by the major Triassic-Jurassic extinction event. The end, however, has no clear boundary with the Cretaceous. By the beginning of the Jurassic, Pangea had begun rifting into two landmasses: Laurasia and Gondwana, and the climate was warm with no ice caps. Life on land was dominated by dinosaurs, and the first birds appeared, evolving from a branch of theropods. The oceans were inhabited by marine reptiles, while pterosaurs were the dominant flying vertebrates.
Huayangosaurus is a stegosaurian. Stegosauria is a group of herbivorous ornithischian dinosaurs that lived mainly during the Jurassic period, though there are some members known from the early Cretaceous. Stegosaurian fossils have been found mostly in the Northern Hemisphere.
Stegosaurians were armored dinosaurs; together with the ankylosaurs, they make up a larger group known as the thyreophorans. An early evolutionary innovation was the development of spikes as defensive weapons. Over time, these developed into much larger plates and spikes as the species within the group grew to larger size. These plates usually tend to run in two rows down the back, and end as spikes, known as thagomizers, at the tip of the tail.