Life restoration of Petrolacosaurus kansensis, the earliest known diapsid, from the Late Carboniferous of Kansas. Illustration by Nobu Tamura (Wikipedia)
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Abbreviated Dendrogram
Amniota
├─Synapsida
└─Sauropsida
├─Anapsida
└─Eureptilia
└─○Diapsida
╞═○Araeoscelida
│ ├─Spinoaequalis (probably
│ └─┬─Petrolacosaurus paraphyletic)
│ └─Araeoscelis
└─○Neodiapsida
╞═"Younginiformes"
└─┬?─Ichthyosauria (in Sauria?)
└─○Sauria
├─Lepidosauromorpha
└─Archosauromorpha |
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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?
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, drawing by David Peters Reptile Evolution. |
Araeoscelis Araeoscelis gracilis
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, from the Late Pennsylvanian of Kansas. Drawing from Diapsid characters, from Benton 2000. |
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, 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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