noun
- any vertebrate of the group Amniota, comprising the reptiles, birds, and mammals, characterized by having an amnion during the embryonic stage.
noun
- any vertebrate animal, such as a reptile, bird, or mammal, that possesses an amnion, chorion, and allantois during embryonic developmentCompare anamniote
- Any of the vertebrates that have an amnion during embryonic development. Reptiles, birds, and mammals are amniotes.