Parareptilia

Parareptiles Temporal range: Moscovian - Rhaetian, 306–201.3 Ma PreꞒ Ꞓ O S D C P T J K Pg N Survive if neodiapsids descend from them[1]
A collage of five parareptile fossils. Clockwise from top, Mesosaurus tenuidens (a mesosaur), Delorhynchus cifellii (a probable acleistorhinid), Scutosaurus karpinskii (a pareiasaur), Nyctiphruretus acudens (a nyctiphruretid), Hypsognathus fenneri (a procolophonid)
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	†Parareptilia Olson, 1947
Orders
†Mesosauria †Millerosauria †Procolophonomorpha

Parareptilia ("near-reptiles") is an extinct subclass or clade of basal sauropsids/reptiles, typically considered the sister taxon to Eureptilia (the group that likely contains all living reptiles and birds). Parareptiles first arose near the end of the Carboniferous period and achieved their highest diversity during the Permian period. Several ecological innovations were first accomplished by parareptiles among reptiles. These include the first reptiles to return to marine ecosystems (mesosaurs), the first bipedal reptiles (bolosaurids such as Eudibamus), the first reptiles with advanced hearing systems (nycteroleterids and others), and the first large herbivorous reptiles (the pareiasaurs). The only parareptiles to survive into the Triassic period were the procolophonoids, a group of small generalists, omnivores, and herbivores. The largest family of procolophonoids, the procolophonids, rediversified in the Triassic, but subsequently declined and became extinct by the end of the period.^[2][3]

Compared to most eureptiles, parareptiles retained fairly "primitive" characteristics such as robust, low-slung bodies and large supratemporal bones at the back of the skull. While all but the earliest eureptiles were diapsids, with two openings at the back of the skull, parareptiles were generally more conservative in the extent of temporal fenestration. In its modern usage, Parareptilia was first utilized as a cladistically correct alternative to Anapsida, a term which historically referred to reptiles with solid skulls lacking holes behind the eyes.^[4] Nevertheless, not all parareptiles have 'anapsid' skulls, and some do have large holes in the back of the skull. They also had several unique adaptations, such as a large pit on the maxilla, a broad prefrontal-palatine contact, and the absence of a supraglenoid foramen of the scapula.^[4][5]

Like many other so-called 'anapsids', parareptiles were historically understudied. Interest in their relationships were reinvigorated in the 1990s, when several studies argued that Testudines (turtles and their kin) were members of Parareptilia.^[4] Although this would suggest that Parareptilia was not extinct after all, the origin of turtles is still heavily debated. Many other morphological or genetic analyses find more support for turtles among diapsid eureptiles such as sauropterygians or archosauromorphs, rather than parareptiles.^[6][7][8][3]