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