Amniotoek artikulatuaren (behe-mailakoaren atzeko hezur txiki bat) eta laukiaren (goiko maxilaren atzeko hezur txiki bat) osatutako masaileko bat zuten. Ez-mammiferoen tetrapodo guztiek sistema hau erabiltzen dute, besteak beste anfibioek, dortokek, liztorrek, sugeek, krokodiloek, dinosauroek, ikthyosauroek, pterosauroek eta terapsuroek. Baina ugaztunek masaileko desberdin bat dute, behe-maxilarreko hezurra (squob squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squib squ
artikulatua