what is an amniote

Amniotes are a group of tetrapod vertebrates that comprise the vast majority of living terrestrial vertebrates. They evolved from amphibian ancestors during the Carboniferous period and further diverged into two groups, sauropsids (including all reptiles and birds) and synapsids (including mammals and extinct ancestors like "pelycosaurs" and therapsids). The term "amniote" comes from the amnion, which is a membrane that surrounds a fetus. One of the key features of amniotes is the amniotic egg, which is able to withstand dry conditions and allows for reproduction on land. The egg has a sturdy but porous leathery or hard shell, and a series of fluid-filled membranes that permit the embryo to survive, including the amnion, allantois, yolk sac, and chorion. Amniotes can reproduce on dry land by either laying shelled eggs (reptiles, birds, and monotremes) or nurturing fertilized eggs within the mother (marsupial and placental mammals).