Advanced features that ties it in with the amniote rather than amphibian group is unfused ankle bones , lack of labyrinthodont infolding of the dentine in teeth , a lack of an otic notch and a generally small skull . Advanced features that ties it in with the reptilian rather than amphibian group is unfused ankle bones , lack of labyrinthodont infolding of the dentin , a lack of an otic notch and a generally small skull .