Infraphylum: Gnathostomata Superclass: Tetrapoda (unranked): Amniota Haeckel , 1866 Clades Synapsida Sauropsida The amniotes are a group of tetrapod vertebrates that have a terrestrially adapted egg . They include mammals , birds and reptiles , as well as their fossil ancestors. Amniote embryos, whether laid as eggs or carried by the