Araeoscelidia or Araeoscelida is a

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

of extinct

tetrapods A tetrapod (; from Ancient Greek τετρα- ''(tetra-)'' 'four' and πούς ''(poús)'' 'foot') is any four- limbed vertebrate animal of the clade Tetrapoda (). Tetrapods include all extant and extinct amphibians and amniotes, with the lat ...

(traditionally classified as

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 earliest traditionally identified diapsids, the araeosc ...

reptiles Reptiles, as commonly defined, are a group of tetrapods with an ectothermic metabolism and Amniotic egg, amniotic development. Living traditional reptiles comprise four Order (biology), orders: Testudines, Crocodilia, Squamata, and Rhynchocepha ...

) superficially resembling

lizards Lizard is the common name used for all squamate reptiles other than snakes (and to a lesser extent amphisbaenians), encompassing over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The ...

, extending from the Late

Carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...

to the Early

Permian The Permian ( ) is a geologic period and System (stratigraphy), 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 251.902 Mya. It is the s ...

. The group contains the

genera Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...

'' Araeoscelis'', ''

Petrolacosaurus ''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 (holes at the rear part of the ...

'', the possibly aquatic '' Spinoaequalis'', and less well-known genera such as ''Kadaliosaurus'' and '' Zarcasaurus''. This clade is usually 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 ( Greek for "lizard faces") is a clade of amniotes, broadly equivalent to the class Reptilia, though typically used in a broader sense to also include extinct stem-group relatives of modern reptiles and birds (which, as theropod dino ...

s by their slender limbs, their elongated tail, and of course by the presence of two temporal openings, the feature defining the

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

Genera

Araeoscelidia includes well-known genera such as '' Araeoscelis'' 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 ( Cisuralian), roughly 299 to 270 million years ago. Mesosaurs were the first known aquatic reptiles, having apparently returned to a ...

s. New specimens have been discovered in the United States state of

Oklahoma Oklahoma ( ; Choctaw language, Choctaw: , ) is a landlocked U.S. state, state in the South Central United States, South Central region of the United States. It borders Texas to the south and west, Kansas to the north, Missouri to the northea ...

, but lack a scientific description as of 2023.

Phylogeny

The majority of historical phylogenetic studies recovered araeoscelidians as the most basal group of diapsids: Cladogram after Bickelmann ''et al.'', 2009 and Reisz ''et al.'', 2011:However, Simões ''et al.'' (2022) recover them as

stem Stem or STEM most commonly refers to: * Plant stem, a structural axis of a vascular plant * Stem group * Science, technology, engineering, and mathematics Stem or STEM can also refer to: Language and writing * Word stem, part of a word respon ...

amniote Amniotes are tetrapod vertebrate animals belonging to the clade Amniota, a large group that comprises the vast majority of living terrestrial animal, terrestrial and semiaquatic vertebrates. Amniotes evolution, evolved from amphibious Stem tet ...

s instead, as the sister group to the clade including

Captorhinidae Captorhinidae is an extinct family of tetrapods, traditionally considered primitive Reptile, reptiles, known from the late Carboniferous to the Late Permian. They had a cosmopolitan distribution across Pangea. Description Captorhinids are a cl ...

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, Halgaitosaurus''). Apart from araeoscelidans, only one other diapsid is known before the

Late Permian Late or LATE may refer to: Everyday usage * Tardy, or late, not being on time * Late (or the late) may refer to a person who is dead Music * ''Late'' (The 77s album), 2000 * Late (Alvin Batiste album), 1993 * Late!, a pseudonym used by Dave Groh ...

: ''

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 o ...

'' from the Early Permian of Oklahoma.

References

Bibliography

* * * * * * * * * * * * * * * * * * * {{Taxonbar, from=Q136663 Pennsylvanian first appearances Cisuralian extinctions Taxa named by Samuel Wendell Williston