What is Amniote?
{{Automatic Taxobox | name = Amniota | fossil_range = <small>[[Carboniferous]] (Middle [[Mississippian]]) to Recent</small> | image = Tortoise-Hatchling.jpg | image_width = 250px | image_caption = A baby [[tortoise]] leaves its amniotic egg. | taxon = Amniota | authority = [[Ernst Haeckel|Haeckel]], 1866 | subdivision_ranks = Living subgroups | subdivision = See [[Amniote#Taxonomy|text]] }} The '''amniotes''' are a [[Taxonomy|taxonomic]] group of [[animal]]s: all the [[tetrapod]]s except the [[amphibians]]. They are the land [[vertebrate]]s which lay [[cleidoic egg]]s.<ref>Mammalian embryos have the same structures.</ref> Two super-groups make up the amniotes: the [[Synapsida]] ([[Pelycosaur]]s, [[Theriodont]]s and [[mammal]]s) and the [[Sauropsida]] (all [[reptile]]s, including [[dinosaur]]s and [[bird]]s). The [[embryo]]s of amniotes are either laid as [[Egg (biology)|eggs]] or develop in the female. These embyros are protected by several [[membrane]]s, and have a much larger food supply than amphibian eggs. The 'invention' of the [[cleidoic egg]], and its embryonic membranes, is the main reason why the eggs of an amniote do not need to be laid in water. Thus, as distinct from the [[amphibian]]s, ''amniotes are truly terrestrial''. Secondarily, many reptiles and mammals returned to water, and mammals bear the young live, as do some reptile groups. This [[evolution]]ary flexibility is much less common in amphibians. ==Evolutionary history== The first amniotes, such as ''[[Casineria]]'', looked like small lizards. They [[evolution|evolved]] about 340 million years ago, in the [[Mississippian]] or Lower [[Carboniferous]]. Their eggs could survive out of the water. This let amniotes move into [[environment]]s that had less [[water]]. The amniotes moved across the [[Earth]]. Most vertebrates that live on land are amniotes, as are most of the air-breathing animals of the sea. Very early in the evolutionary history of amniotes, they split into two main lines, the '''[[synapsids]]''' and the '''[[sauropsids]]'