Diadectomorpha

Diadectomorpha is a clade of large tetrapods that lived in Euramerica during the Carboniferous and Early Permian periods and in Asia during Late Permian (Wuchiapingian), They have typically been classified as advanced reptiliomorphs (transitional between "amphibians" sensu lato and amniotes) positioned close to, but outside of the clade Amniota, though some recent research has recovered them as the sister group to the traditional Synapsida within Amniota, based on inner ear anatomy and cladistic analyses. They include both large (up to 2 meters long) carnivorous and even larger (to 3 meters) herbivorous forms, some semi-aquatic and others fully terrestrial. The diadectomorphs seem to have originated during late Mississippian times, although they only became common after the Carboniferous rainforest collapse and flourished during the Late Pennsylvanian and Early Permian periods.

==Anatomy== thumb|left|Life restoration of Limnoscelis Diadectomorphs possessed both amphibian-like and amniote-like characteristics. Originally these animals were included under the order Cotylosauria, and were considered the most primitive and ancestral lineage of reptiles. More recently they have been reclassified either as non-amniote reptiliomorphs lying just outside the clade Amniota, or as early-diverging synapsids (members of the amniote group containing mammals and their extinct relatives). Contrary to other non-amniote reptiliomorphs, the teeth of the Diadectomorpha lacked the infolding of the dentine and enamel that account for the name Labyrinthodontia for the non-amniote tetrapods.