Amniotes are the reptiles, birds, and mammals.
It is found in all amniotes and also in sharks, bony fishes, and some amphibia. It is composed of splanchnic lateral plate mesoderm and endoderm . In general, splanchnic mesoderm forms blood vessels and somatic mesoderm usually does not. The next most primitive extraembryonic membranes are the amnion and the chorion . Besides appearing in all amniotes, primitive forms of these membranes are found in some bony fishes and in some amphibia.