Answer: amniote

AnswerCrossword Clue
amnioteany of a group (Amniota) of vertebrates that undergo embryonic or fetal development within an amnion and include the birds, reptiles, and mammals
amniotea vertebrate that develops an amnion during the embryonic stage
amnioteany vertebrate of the group Amniota, comprising the reptiles, birds, and mammals, characterized by having an amnion during the embryonic stage