Final answer:
Stegosaurs had evolutionary novelties such as plates and spikes along their back for protection and temperature regulation. Huayangosaurus is an example of a stegosaur that had these features and a unique hip structure that allowed it to adopt a semi-erect posture.
Step-by-step explanation:
Evolutionary Novelties of Stegosaurs:
Stegosaurs were a group of herbivorous dinosaurs known for their distinctive plates and spikes along their back. These plates and spikes were evolutionary novelties that provided protection and possibly helped regulate body temperature. Stegosaurs also had a unique arrangement of bones in their hind limbs, which allowed for an unusual posture. This adaptation may have helped them browse vegetation at different heights.
Huayangosaurus:
Huayangosaurus is an example of a stegosaur that exemplifies these evolutionary novelties. It had the characteristic plates and spikes on its back, which likely served as a form of defense against predators. Additionally, Huayangosaurus had a unique hip structure that allowed it to adopt a semi-erect posture. This posture, combined with its long front legs and shorter hind legs, is thought to have helped it reach vegetation at different heights.