The Vertebrates Araeoscelida

Diapsida: Araeoscelida

Abbreviated Dendrogram
Amniota ├─Synapsida └─Sauropsida ├─Anapsida └─Eureptilia └─○Diapsida ╞═○Araeoscelida │ ├─Spinoaequalis (probably │ └─┬─Petrolacosaurus paraphyletic) │ └─Araeoscelis └─○Neodiapsida ╞═"Younginiformes" └─┬?─Ichthyosauria (in Sauria?) └─○Sauria ├─Lepidosauromorpha └─Archosauromorpha


Taxa on this Page

  1. Araeoscelida *
  2. Araeoscelis X
  3. Petrolacosaurus X
  4. Spinoaequalis X

Life restoration of Petrolacosaurus kansensis, the earliest known diapsid, from the Late Carboniferous of Kansas. Illustration by Nobu Tamura (Wikipedia)

* Traditionally a monophyletic clade, the present author considers that, on stratigraphica nd morphological grounds, the Araeoscelida are better understood as a grade of early diapsids. In which case, phylogenetically and cladistically speaking, Aeroscelida = Diapsida.


Araeoscelida: Aphelosaurus, Araeoscelis, Kadaliosaurus, Petrolacosaurus, Spinoaequalis, Zarcasaurus. Most basal diapsids?

Late Carboniferous to Early Permian.

Diapsida: Neodiapsida + * : Spinoaequalis + (Araeoscelis + Petrolacosaurus)

Lizard-like; some euryapsid (upper temporal fenestra only), but jugal still bifurcated; long necks, with great elongation of neck in some; gracile, presumably cursorial, limbs.

Comments: a number of poorly known very forms have been placed here, making the group something of a "wastebasket taxon". Most certainly a paraphyletic basal assemblage; also spelt "Araeoscelidia", here we are using Williston (1913)'s original spelling.

Links: Palaeocritti, Paleobiology database, Wikipedia, UCMP - Basal Diapsids (only a paragraph), MAK101001.

Araeoscelis gracilis
Araeoscelis gracilis, drawing by David Peters Reptile Evolution.

Araeoscelis Araeoscelis gracilis

Early Permian.

Araeoscelida : Spinoaequalis + (Petrolacosaurus + *)

euryapsid (upper temporal fenestra only).

Comments: At one time considered to be the ancestor of sauropterygia, because of the euryapsid style openings.

Links: Palaeocritti, Wikipedia, About com Dinosaurs MAK101001

Petrolacosaurus kansensis
Petrolacosaurus kansensis, from the Late Pennsylvanian of Kansas. Drawing from Diapsid characters, from Benton 2000.


Late Carboniferous

Araeoscelida : Spinoaequalis + (Araeoscelis + *)

Comments: The earliest known diapsid. Unlike the closely related Araeoscelis, it shows the typical diapsid condition with two temporal fenestrae in the skull.

Links: Palaeocritti, Wikipedia, Prehistoric Land Reptiles - Planet Dinosaur, David Peters - Reptile Evolution MAK101001

References: Reisz 1977, 1981

Spinoaequalis schultzei
Spinoaequalis schultzei, from the Late Pennsylvanian of Kansas. Note the deep (laterally compressed) tail, which would have been used as a swimming organ, the animal moving side to side in a sinuous motion. Drawing from deBraga & Reisz 1995.


Late Carboniferous (Virgilian - Late Pennsylvanian) of N Am

Araeoscelida : (Araeoscelis + Petrolacosaurus) + *

deep, laterally compressed tail.

Comments: The earliest known aquatic reptile. It probably swam using its flattened, fanned tail. Found in association with marine fish..

Links: Wikipedia

checked ATW031003, revised MAK111116

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