An anapsid is an amniote whose skull lacks one or more skull openings near the temples. Traditionally, the Anapsida are considered the most primitive subclass of amniotes, the ancestral stock from which Synapsida and Diapsida evolved, making anapsids paraphyletic. It is, however, doubtful that all anapsids lack temporal fenestra as a primitive trait, and that all the groups traditionally seen as anapsids truly lacked fenestra.
Mesosaurs were a group of small aquatic reptiles that lived during the early Permian period (Cisuralian), roughly 299 to 270 million years ago. Mesosaurs were the first known aquatic reptiles, having apparently returned to an aquatic lifestyle from more terrestrial ancestors. It is uncertain which and how many terrestrial traits these ancestors displayed; recent research cannot establish with confidence if the first amniotes were fully terrestrial, or only amphibious. Most authors consider mesosaurs to have been aquatic, although adult animals may have been amphibious, rather than completely aquatic, as indicated by their moderate skeletal adaptations to a semiaquatic lifestyle. Similarly, their affinities are uncertain; they may have been among the most basal sauropsids or among the most basal parareptiles.
Archosauromorpha is a clade of diapsid reptiles containing all reptiles more closely related to archosaurs rather than lepidosaurs. Archosauromorphs first appeared during the late Middle Permian or Late Permian, though they became much more common and diverse during the Triassic period.
Neodiapsida is a clade, or major branch, of the reptilian family tree, typically defined as including all diapsids apart from some early primitive types known as the araeoscelidians. Modern reptiles and birds belong to the neodiapsid subclade Sauria.
Youngina is an extinct genus of diapsid reptile from the Late Permian Beaufort Group of the Karoo Red Beds of South Africa. This, and a few related forms, make up the family Younginidae, within the order Eosuchia. Eosuchia, having become a wastebasket taxon for many probably distantly-related primitive diapsid reptiles ranging from the Late Carboniferous to the Eocene, Romer proposed that it be replaced by Younginiformes.
Petrolacosaurus is an extinct genus of diapsid reptile from the late Carboniferous period. It was a small, 40-centimetre (16 in) long reptile, and one of the earliest known reptile with two temporal fenestrae. This means that it was at the base of Diapsida, the largest and most successful radiation of reptiles that would eventually include all modern reptile groups, as well as dinosaurs and other famous extinct reptiles such as plesiosaurs, ichthyosaurs, and pterosaurs. However, Petrolacosaurus itself was part of Araeoscelida, a short-lived early branch of the diapsid family tree which went extinct in the mid-Permian.
Parareptilia ("near-reptiles") is an extinct subclass or clade of basal sauropsids/reptiles, typically considered the sister taxon to Eureptilia. 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, the first reptiles with advanced hearing systems, and the first large herbivorous reptiles. 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.
Younginiformes is a group of diapsid reptiles known from the Permian-Triassic of Africa and Madagascar. It has been used as a replacement for "Eosuchia". Younginiformes were historically suggested to be lepidosauromorphs, but were later suggested to be basal non-saurian neodiapsids. The group is sometimes divided into two families, Tangasauridae and Younginidae. The monophyly of the group is disputed. A 2009 study found them to be an unresolved polytomy at the base of Neodiapsida, while a 2011 study recovered the group as paraphyletic. A 2022 study recovered the Younginiformes as a monophyletic group of basal neodiapsid reptiles, also including Claudiosaurus and Saurosternon as part of the group. Some younginiforms like Hovasaurus and Acerosodontosaurus are thought to have had an amphibious lifestyle, while others like Kenyasaurus, Thadeosaurus and Youngina were probably terrestrial.
Araeoscelidia or Araeoscelida is a clade of extinct amniotes 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 is usually considered to be the sister group to all later diapsids.
Drepanosaurs are a group of extinct reptiles that lived between the Carnian and Rhaetian stages of the late Triassic Period, approximately between 230 and 210 million years ago. The various species of drepanosaurs were characterized by a bird-like skull, a barrell shaped body, and a horizontally narrow tail. A number of drepanosaurs had specialized grasping limbs and often prehensile tails similar to those of chameleons. Drepanosaurs are generally thought to have been arboreal (tree-dwelling), and probably insectivores. Some studies have alternately suggested fossorial (digging) and aquatic lifestyles for some members. Fossils of drepanosaurs have been found in North America and Europe. The name is taken from the family's namesake genus Drepanosaurus, which means "sickle lizard," a reference to their strongly curved claws.
Acerosodontosaurus is an extinct genus of neodiapsid reptiles that lived during the Late Permian of Madagascar. The only species of Acerosodontosaurus, A. piveteaui, is known from a natural mold of a single partial skeleton including a crushed skull and part of the body and limbs. The fossil was discovered in deposits of the Lower Sakamena Formation. Based on skeletal characteristics, it has been suggested that Acerosodontosaurus individuals were at least partially aquatic.
Tangasauridae is an extinct family of diapsids known from fossil specimens from Madagascar, Kenya and Tanzania that are Late Permian to Early Triassic in age. Fossils have been found of numerous specimens of common members of this family such as Hovasaurus in different stages of ontogenic development. Recent material from the Middle Sakamena Formation of the Morondava Basin of Madagascar that dates back to the early Triassic period suggests that the Tangasauridae were relatively unaffected by the Permian-Triassic extinction event.
Heleosaurus scholtzi is an extinct species of basal synapsids, known as pelycosaurs, in the family of Varanopidae during the middle Permian. At first H. scholtzi was mistakenly classified as a diapsid. Members of this family were carnivorous and had dermal armor, and somewhat resembled monitor lizards. This family was the most geologically long lived, widespread, and diverse group of early amniotes. To date only two fossils have been found in the rocks of South Africa. One of these fossils is an aggregation of five individuals.
Owenetta is an extinct genus of owenettid procolophonian parareptile. Fossils have been found from the Beaufort Group in the Karoo Basin of South Africa. Although most procolophonians lived during the Triassic, Owenetta existed during the Wuchiapingian and Changhsingian stages of the Late Permian as well as the early Induan stage of the Early Triassic. It is the type genus of the family Owenettidae, and can be distinguished from other related taxa in that the posterior portion of the supratemporal bears a lateral notch and that the pineal foramen is surrounded by a depressed parietal surface on the skull table.
Heleosuchus is an extinct genus of diapsid reptile from the Late Permian of South Africa. It was originally described as a species of Saurosternon by Richard Owen. The type species is Saurosternon griesbachi. The specific name honours Carl Ludolf Griesbach. It was later recognized as a separate genus by Robert Broom.
Reptiles arose about 320 million years ago during the Carboniferous period. Reptiles, in the traditional sense of the term, are defined as animals that have scales or scutes, lay land-based hard-shelled eggs, and possess ectothermic metabolisms. So defined, the group is paraphyletic, excluding endothermic animals like birds that are descended from early traditionally-defined reptiles. A definition in accordance with phylogenetic nomenclature, which rejects paraphyletic groups, includes birds while excluding mammals and their synapsid ancestors. So defined, Reptilia is identical to Sauropsida.
Tangasaurus is an extinct genus of aquatic basal tangasaurid neodiapsid known from the Late Permian period of Tanga, northeastern Tanzania. It contains a single species, Tangasaurus mennelli.
Kenyasaurus is an extinct genus of basal tangasaurid known from the Early Triassic period of Coast Province, southeastern Kenya. It contains a single species, Kenyasaurus mariakaniensis.
Younginidae is an extinct family of diapsid reptiles from the Late Permian and Early Triassic. In a phylogenetic context, younginids are near the base of the clade Neodiapsida. Younginidae includes the species Youngina capensis from the Late Permian of South Africa and Thadeosaurus colcanapi from the Late Permian and Early Triassic of Madagascar. Heleosuchus griesbachi from the Late Permian of South Africa may also be a member of the family.
