Araeoscelidia or Araeoscelida is a clade of extinct

diapsid Diapsids ("two arches") are a clade of sauropsids, distinguished from more primitive eureptiles by the presence of two holes, known as temporal fenestrae, in each side of their skulls. The group first appeared about three hundred million years ...

reptiles Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates (lizards and snakes) and rhynchocephali ...

superficially resembling

lizards Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia a ...

, extending from the Late Carboniferous to the Early

Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Pale ...

. The group contains the

genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial ...

Araeoscelis ''Araeoscelis'' (from el, αραιά , 'thin' and el, σκελίς , 'ribs of beef') is an extinct genus of reptile, and one of the earliest diapsids. Fossils have been found in the Nocona, Arroyo and Waggoner Ranch Formations in Texas, datin ...

'', ''

Petrolacosaurus ''Petrolacosaurus'' ("rock lake lizard") is an extinct genus of diapsid reptile from the late Carboniferous period. It was a small, long reptile, and the earliest known reptile with two temporal fenestrae (holes at the rear part of the skull) ...

'', the possibly aquatic '' Spinoaequalis'', and less well-known genera such as '' Kadaliosaurus'' and '' Zarcasaurus''. This clade is considered to be the

sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

to all (currently known) later diapsids.

Description

Araeoscelidians were small animals (less than one meter in length) looking somewhat like lizards, though they are only distantly related to true lizards. They differ from other, earlier

sauropsid Sauropsida ("lizard faces") is a clade of amniotes, broadly equivalent to the class Reptilia. Sauropsida is the sister taxon to Synapsida, the other clade of amniotes which includes mammals as its only modern representatives. Although early s ...

s by their slender limbs, their elongated tail, and of course by the presence of two

temporal opening The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...

s, the feature defining the

condition. In ''

'', only the upper temporal opening remains, thus resulting in a derived euryapsid condition.

Genera

Araeoscelidia includes well-known genera such as ''

'' Williston 1910, ''

'' Lane 1945 and '' Spinoaequalis'', known from virtually complete skeletons. '' Zarcasaurus'', '' Aphelosaurus'' and '' Kadaliosaurus'' belong to this clade, but are known only from post-cranial remains and a mandible fragment for ''Zarcasaurus''. The genus '' Dictybolos'' has been included in Araeoscelidia by Olson (1970) but this inclusion has been criticized e.g. by Evans (1988), especially since Olson also included distantly related groups such as protorosaurs and

mesosaur Mesosaurs ("middle lizards") were a group of small aquatic reptiles that lived during the early Permian period, roughly 299 to 270 million years ago. Mesosaurs were the first known aquatic reptiles, having apparently returned to an aquatic lif ...

s. New specimens have been discovered in Oklahoma, United States but so far lack a scientific description.

Phylogeny

Phylogenetic relationships: The majority of phylogenetic studies recover araeoscelidians as

basal Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''. Science * Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure * Basal (medicine), a minimal level that is nec ...

diapsids; however, Simões ''et al.'' (2022) recover them as

stem Stem or STEM may refer to: Plant structures * Plant stem, a plant's aboveground axis, made of vascular tissue, off which leaves and flowers hang * Stipe (botany), a stalk to support some other structure * Stipe (mycology), the stem of a mushr ...

- amniotes instead, as the sister group to the clade including

Captorhinidae Captorhinidae (also known as cotylosaurs) is an extinct family of tetrapods, traditionally considered primitive reptiles, known from the late Carboniferous to the Late Permian. They had a cosmopolitan distribution across Pangea. Description ...

and ''

Protorothyris ''Protorothyris'' is an extinct genus of Early Permian protorothyridid known from Texas and West Virginia of the United States. It was first named by Llewellyn Ivor Price in 1937 and the type species is ''Protorothyris archeri''. ''P. archeri'' ...

archeri''.

Stratigraphic and geographic distribution

Araeoscelidia are known from the Late Carboniferous in the United States (''Petrolacosaurus'', ''Spinoaequalis'') to the Early Permian in France (''Aphelosaurus''), Germany (''Kadaliosaurus'') and the United States (''Dictybolos'', ''Zarcasaurus'', ''Araeoscelis''). Apart from araeoscelidans, only one other diapsid is known before the

Late Permian Late may refer to: * LATE, an acronym which could stand for: ** Limbic-predominant age-related TDP-43 encephalopathy, a proposed form of dementia ** Local-authority trading enterprise, a New Zealand business law ** Local average treatment effect, ...

: ''

Orovenator ''Orovenator'' is an extinct genus of diapsid from Lower Permian (Artinskian stage) deposits of Oklahoma, United States. It is known from two partial skulls from the Richards Spur locality in Oklahoma. The holotype OMNH 74606 consists of ...

'' from the Early Permian of Oklahoma.

Description

Genera

Phylogeny

Stratigraphic and geographic distribution

References

Further reading