Temporal range: Carboniferous - Permian 307–275.6 Ma
|Life restoration of Petrolacosaurus kansensis|
Araeoscelidia or Araeoscelida is a clade of extinct 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 is considered to be the sister group to all (currently known) later diapsids.
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 sauropsids by their slender limbs, their elongated tail, and of course by the presence of two temporal openings, the feature defining the diapsid condition. In Araeoscelis, only the upper temporal opening remains, thus resulting in a derived euryapsid condition.
Araeoscelidia includes well-known genera such as Araeoscelis (Williston, 1910; Vaughn, 1955; Reisz et al., 1984), Petrolacosaurus (Lane, 1945; Peabody, 1952; Reisz, 1981) and Spinoaequalis (deBraga & Reisz, 1995; deBraga & Rieppel, 1997), known from virtually complete skeletons. Zarcasaurus (Brinkman et al., 1984), Aphelosaurus (Gervais, 1859; Thévenin, 1910; Falconnet & Steyer, 2007) and Kadaliosaurus (Credner, 1889) 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 mesosaurs.
New specimens have been discovered in Oklahoma, United States (May & Hall, 2002; Swanson & Carlson, 2002) but so far lack a scientific description.
Phylogenetic relationships after deBraga and Reisz (1995) and Falconnet and Steyer (2007).
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: Orovenator from the Early Permian of Oklahoma (Reisz et al., 2011).
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