While most temnospondyls are aquatic in early stages of life , most metoposaurids appear to have been terrestrial in their juvenile stage . Like other Mesozoic temnospondyls , adult metoposaurids were adapted to a semiaquatic lifestyle . Their bones are not highly developed for movement on land . The cross @-@ sectional thickness of limb bones in adult metoposaurids shows that they could not withstand the stress of terrestrial locomotion . Juvenile individuals have bones that are thick enough to withstand this stress , and could probably move about on land . To maintain a terrestrial lifestyle , a temnospondyl 's limb bones would have to thicken with positive allometry , meaning that they would grow at a greater rate than the rest of the body . This is not the case in metoposaurids , meaning that as their bodies grew larger they became less adapted toward a terrestrial lifestyle .