Most heterodontosaurid fossils are found in geologic formations that represent arid to semi-arid environments, including the Upper Elliot Formation of South Africa and the Purbeck Beds of southern England. It has been suggested that heterodontosaurids underwent seasonal aestivation or hibernation during the driest times of year. Due to the lack of replacement teeth in most heterodontosaurids, it was proposed that the entire set of teeth was replaced during this dormant period, as it seemed that continual and sporadic replacement of teeth would interrupt the function of the tooth row as a single chewing surface. However, this was based on a misunderstanding of heterodontosaurid jaw mechanics. It was thought that heterodontosaurids actually did replace their teeth continually, though more slowly than in other reptiles, but CT scanning of skulls from juvenile and mature "Heterodontosaurus" shows no replacement teeth. There is currently no evidence that supports the hypothesis of aestivation in heterodontosaurids, but it cannot be rejected, based on the skull scans.