Neodiapsida is a cladistic term for basically all Diapsids apart from a few unfortunate primitive ones lumped under the Araeoscelida. In the opinion of the present author, the Araeoscelida are a grade of early diapsids, all of which were pretty similar. One of these however was more successful than its fellows, and gave rise to the huge diapsid phylogenetic radiation, including ichthyosaurs and plesiosaurs, lizards and snakes, phytosaurs and crocodilians, prolacertifoms and pterosaurs, dinosaurs and birds, as well as other assorted forms.
Ther ancestors of this glorious evolution were agile long-legged, long-necked, lizard like forms, very much like their araeoscelidan ancestors, and differing only in minor details of the skull and skeleton (and presumably, of teh soft body physiology that isn't fossilsed).
Until recently, the earliest neodiaspids were known exclusively from the latest Permain and early Triassic. This changed with the recent discovery of two new early and middle Permian forms, Orovenator and Lanthanolania, which bridge the morphologiocal and temporal gap between the permocarbonifderous araeoscelidians and petralacosaurs and the Permo-Triassic younginiforms or eosuchians MAK111116
Neodiapsida: defined: younginiforms + crown diapsids [C97a], or Sauria > Araeoscelida ToL
Range: from the Middle Permian.
Phylogeny: Diapsida: Araeoscelida + * : Orovenator + (Lanthanolania + (Tangasauridae + (Claudiosaurus + Weigeltisauridae + (Ichthyopterygia + Sauria)))).
Characters: lacrimal reduced or absent [R89]; descending flange of parietal participates in UTF [R89]; quadrate laterally exposed (not covered by squamosal in lateral view) [R89]; quadrate embayed posteriorly [R89]; retroarticular process present [R89]; caniniform teeth absent [R89]; parasphenoid without teeth [R89, dubitante]; olecranon absent [R89]; femur slender & sigmoid [R89]; femoral distal condyles not projecting markedly beyond shaft [R89]; $ femoral ventral ridge system reduced (without prominent ventral adductor crest for, e.g. m. caudofemoralis); $ proximal carpals and tarsals small.
Links: Neodiapsida; Autapomorphies of Diapsid Clades.
References: Callaway (1997a) [C97a]; Rieppel (1989) [R89]. ATW070113. Phylogeny revised MAK111116
Orovenator: O. mayorum Reisz et al., 2011
Phylogeny: Neodiapsida : (Lanthanolania + (Tangasauridae + (Claudiosaurus + Weigeltisauridae + (Ichthyopterygia + Sauria)))) + *
From the abstract: The initial stages of evolution of Diapsida (the large clade that includes not only snakes, lizards, crocodiles and birds, but also dinosaurs and numerous other extinct taxa) is clouded by an exceedingly poor Palaeozoic fossil record. Previous studies had indicated a 38 Myr gap between the first appearance of the oldest diapsid clade (Araeoscelidia), ca 304 million years ago (Ma), and that of its sister group in the Middle Permian (ca 266 Ma). Two new reptile skulls from the Richards Spur locality, Lower Permian of Oklahoma, represent a new diapsid reptile: Orovenator mayorum n. gen. et sp. A phylogenetic analysis identifies O. mayorum as the oldest and most basal member of the araeoscelidian sister group. As Richards Spur has recently been dated to 289 Ma, the new diapsid neatly spans the above gap by appearing 15 Myr after the origin of Diapsida. The presence of O. mayorum at Richards Spur, which records a diverse upland fauna, suggests that initial stages in the evolution of non-araeoscelidian diapsids may have been tied to upland environments. This hypothesis is consonant with the overall scant record for non-araeoscelidian diapsids during the Permian Period, when the well-known terrestrial vertebrate communities are preserved almost exclusively in lowland deltaic, flood plain and lacustrine sedimentary rocks. (original url)
References: Reisz et al 2011 .
Lanthanolania: L. ivakhnenkoi Reisz & Modesto, 2003
Phylogeny: Neodiapsida : Orovenator + ((Tangasauridae + (Claudiosaurus + Weigeltisauridae + (Ichthyopterygia + Sauria))) + *)
Comments: Known from the holotype and only specimen PIN 162/56, a partial skull with an incomplete lower temporal bar from the Glyadnaya Shchelya locality, Mezen river in Mesen District, recently discovered to be a very primitive neodiapsid. Interpreted as possible stem lepidosauromorph by Evans & Jones 2010, reinterpreted as very primitive (basal) neodiapsid by Reisz et al 2011
References: Reisz et al 2011 .
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