Araeoscelidia

Petrolacosaurus ("rock lake lizard") is an extinct genus of diapsid reptile from the late Carboniferous period. It was a small, long reptile, and one of the earliest known reptiles with two temporal fenestrae. This means that it was near the base of Diapsida (it may have been the basal taxon), the largest and most successful radiation of reptiles that would eventually include all modern reptile groups, as well as dinosaurs (which survived to the modern day as birds) and other famous extinct reptiles such as plesiosaurs, ichthyosaurs, and pterosaurs. However, Petrolacosaurus itself was part of

Araeoscelidia or Araeoscelida is a clade of extinct tetrapods (traditionally classified as diapsid reptiles) superficially resembling lizards, extending from the Late Carboniferous to the Early Permian. The group contains the genera Araeoscelis, Petrolacosaurus, the possibly aquatic Spinoaequalis, and less well-known genera such as Kadaliosaurus and Zarcasaurus. This clade has historically been considered to be the sister group to all (currently known) later diapsids, though studies from the early 2020s onwards have found it much closer to the base of Sauropsida unrelated to other diapsid rept

Araeoscelis (from , 'thin' and , 'ribs of beef') is an extinct genus of tetrapods from the Early Permian of what is now Texas. Fossils have been found in the Nocona, Arroyo and Waggoner Ranch Formations. Two species have been described, A. casei and A. gracilis.

Spinoaequalis is an extinct genus of lizard-like araeoscelidian. It is known from a single species, S. schultzei based on fossils found in Kansas, United States. About 30 cm (1 ft), long it is one of the earliest known amniotes to have returned to the water. Spinoaequalis was not fully aquatic, frequently returning to dry land. It probably swam using its laterally flattened, fanned tail. Its name means "symmetrical spine" referring to its deep, laterally compressed tail. Spinoaequalis was described and named by Michael deBraga and Robert Reisz in 1995.