Amniote

From the egg hatching turtle

Amniotes ( Amniota ), amniotes or navel Animals are a major group of land vertebrates ( Tetrapoda ) whose representatives are mainly characterized by the ability to, in contrast to amphibians completely independent breed, from the water. Instead of a short embryonic followed by wild fully aquatic larval stage their Frühontogenese runs over a long embryonic without larval stage. The embryos develop in an Amniota with amniotic fluid ( amniotic fluid ) filled amniotic cavity by a Embryonalhülle ( amnion ) is surrounded.

The Amniota are considered monophyletic taxon, ie, all its kinds and went back to a single common Ursprungsart. The recent sub-groups of amniotes are the scales of lizards ( Lepidosauria ), turtles ( Testudines ), crocodiles ( Crocodylia ), birds ( Aves) and mammals ( Mammalia).

Evolution

Being able to propagate out of the water, had for early anamniotische land vertebrates the potential to open up new habitats and to be able to avoid competition from other anamnischer species. With development of the covered by a shell amniotes ice cream, as it occurs in reptiles, birds and mammals mono treme today, this potential could be used. The land vertebrates were spread now in a position, even in very dry regions and to colonize the continents across the board. The uterus of the placental mammal is a further development of this strategy, wherein the maturation of the embryos takes place completely within the body. Inside the egg shell or the uterus is the embryo in a fluid-filled bladder, called the amnion, which protects it from drying out.

System

The term was first introduced in 1866 by Ernst Haeckel ( " Amnionthiere " ) for the higher classes of vertebrates " Reptiles" ( paraphyletic ), birds and mammals - the delineation of the Anamnia ( fish and amphibians). In the modern, kladistisch embossed systematics of extant land vertebrates is as Amphibia (also Lissamphibia ) designated clade of anurans ( Anura ), newts ( Urodela ) and caecilians ( Gymnophiona ) the sister group of the amniotes.

Outer systematics

The amniotes developed not in the core group of today's amphibians, but from early, anamnischen representatives of a group known as Reptiliomorpha. The latter includes in modern systematics also the amniotes with. In particular, in the anatomy of the vertebrae, the similarity between early Reptiliomorphen and amniotes is greater than between early Reptiliomorphen and the earliest land vertebrates, or the presumed fossil relatives alive today amphibians.

The possible family relationships illustrated by the following highly simplified cladogram:

Lissamphibia ( Today's amphibians)

† Lepospondyli

† Seymouriamorpha

† Diadectomorpha

Amniota

Inside systematics

As geologically oldest amniotes are Hylonomus lyelli, Protoclepsydrops haplous, Paleothyris acadiana and Archaeothyris florensis, four rather small, lizard -like animals from the Upper Carboniferous of Cape Breton Island ( Nova Scotia ). Probably the amniotes split before the appearance of these four types into two main lines:

• The synapsids ( Synapsida ), from which emerged the mammals, and
• The sauropsids ( Sauropsida, Reptilia ) from which emerged the modern reptiles and birds.

Hylonomus and Paleothyris were representatives of sauropsids line. Archaeothyris is the oldest Synapside. Which of the two lines is Protoclepsydrops belongs still unclear.

The family relationships illustrated by the following, highly simplified cladogram:

Different basal

Synapsidentaxa extinct († " Pelycosaurier ", including † Archaeothyris )

Different basal

Extinct Therapsidentaxa (among Gorgonopier †, † Dinocephalier, † Dicynodontier )

Different basal

Extinct Cynodontiertaxa ( inter alia † † Procynosuchus or Thrinaxodon )

Mammals

† Parareptilia

Different basal

Extinct Eureptilientaxa (among Hylonomus †, † Paleothyris, † Captorhiniden )

† Araeoscelidia

† Avicephala

† Younginiformes ( paraphyletic? )

† Ichthyopterygia

Lepidosauromorpha (among Squamata, tuatara, † Sauropterygia )

Archosauromorpha (? Turtles, crocodiles, † pterosaurs, dinosaurs including birds)

Footnotes: 1) " Sauria " here in the sense of Gauthier et al. (1988 ) Diapsiden the crown group and is not to be confused with the similarly " Sauria " said subtaxon lizards (also Lacertilia ) of the Lepidosauromorpha.