American Alligator ( Alligator mississippiensis )
The Sauropsida are a taxon ( a systematic group) of land vertebrates ( Tetrapoda ), the traditional classes of birds ( Aves) and reptiles ( Reptilia ) together with representatives of extinct sums ( other dinosaurs, pterosaurs, and Plesiosauria ). However, the reptiles themselves are within the meaning of cladistics no taxon, but a paraphyletic group because some representatives ( the crocodiles ) are more closely related to birds than with the other reptiles.
Synapomorphies ( shared derived characteristics) of the sauropsids include the missing or largely reduced Tabulare ( a skull bone) and the involvement of foramina ( openings ) or windows in the palate region.
Developmentally, they told the sauropsids earlier based on skull openings in the cheek region (Tempo Ralf ester) in the Anapsida (without tempo Ralf Rochester ) and the Diapsida (with two pace Ralf Star). It turned out, however, that the Anapsiden not a natural group (that is not a community of descent ) constitute, as some of sauropsids were more closely related to windowless skull like the Captorhinidae with the Diapsiden than other primitive sauropsids as the Pareiasauria, Mesosauria and Procolophonoidea that one summarized as Parareptilia in a row. It was also found that close relatives of the Para Reptiles groups with no speed Ralf Rochester convergent trained to Diapsiden skull openings in the cheek region (such as the Bolosauridae ). The turtles have a windowless skull are traditionally the only surviving group of Anapsiden or para reptiles. However, molecular studies lead to the conclusion that they are closely related to the archosaurs and the skull windows have secondary lost. Their systematic classification is still controversial.
Within the Diapsiden among other extinct Ichthyosauria, which also extinct Sauropterygia (the present-day lizards and snakes) and the Archosauromorpha distinguished (a group meeresbewohnender animals, including the Plesiosauria and Placodontia ), the Lepidosauria. Probably Lepidosauria and Sauropterygia are closely related to each other and are therefore summarized as Lepidosauromorpha.
The Archosauromorpha include not only some basal representatives such as the Protorosauria the Archosauria. The Archosauria share in the Crurotarsi ( the crocodiles and their extinct ancestors ) and the Ornithodira. Within the Ornithodira it came to the development of pterosaurs and dinosaurs that birds evolved from theropods, a group of mostly carnivorous dinosaurs.
A possible cladogram, which takes into account only the better-known taxa, is as follows:
Parareptilia (including turtles? )
? Ichthyosauria †
Sphenodontia ( now represented only by the tuatara )
Squamata ( Squamata, " lizard ", and snakes )
Basal Archosauromorpha †
Crurotarsi ( crocodiles and extinct relatives)
Dinosaurs (including extant birds)
As the sister group of the sauropsids the synapsids, which are characterized by only a skull window and include the mammals, including their extinct ancestors are. Synapsids and sauropsids together form the taxon of amniotes.