Pantelosaurus saxonicus (Credner 1888, Spindler 2016, RS 14752, Early Permian) nests at the base of the Pelycosauria in the large reptile tree. It greatly resembles Haptodon. Palaeohatteria may be a juvenile of Pantelosaurus.

Below, the illustration of Haptodon saxonicus is an early representation of Pantelosaurus saxonicus, shown to scale with the smaller valid Haptodon specimens.

Haptodus longicaudatus (Credner 1888, H. garnettenis Currie 1977) lived ~305 mya, Kasimovian (Late Carboniferous) , 60 cm long, was similar in size to its predecessor, Archaeothyris and was a sister to the other pelycosaurs, Ophiacodon, Edaphosaurus, Haptodus and Dimetrodon. Haptodus specimens started off small in the Late Carboniferous and continued to grow into the Early Permian. H. garnettensis most closely resembled Ophiacodon. H. saxonicus most closely resembles Sphenacodon and Dimetrodon.

Distinct from Ophiacodon the skull of Haptodus was short, like that of Archaeothyris. The maxilla was deeply convex ventrally but beneath the lateral emporal fenestra the jawline was deeply concave as the quadrate dropped below the jawline. The lateral temporal fenestra was enlarged, approaching the jaw line. The quadratojugal was reduced to a nearly invisible vestige at the tip of the quadrate. The mandible developed a reflected lamina, a thin sheet of bone that projected posteriorly off the angular.

The cervicals were slightly longer. The neural spines were slightly shorter. The ilium developed an anterior process.

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A sister to Haptodus, Stenocybus nests at the base of the Therapsida.

Credner H 1888. Die Stegocephalen un d'Saurier aus dem Rothliegnden des Plauen'schen Grudes bei Dresden: Zeitschrift der Deutschen Geologischen Gesellschaft, v. 40, p. 490-558.

Currie PJ 1977. A new Haptodontine Sphenacodont (Reptilia: Pelycosauria) from the Late Pennsylvanian of North America: Journal of Paleontology, v. 51, n. 5, p. 927-942.

Huene F von 1925. Ein neuer Pelycosaurier aus der unteren Permformaiton Sachens: Geologische und Palaeontologische Abhandlungen, Jena., v. 18, NF 14, p. 215-264.

Romer AS and Price LW 1940. Review of the Pelycosauria. Geological Society of America Special Papers 28: 1-538.

Spindler F 2016. Morphological description and taxonomic status of Palaeohatteria and Pantelosaurus (Synapsida: Sphenacodontia). Paläontologie, Stratigraphie, Fazies (23), Freiberger Forschungshefte, C 550: 1– 57; Freiberg.

wiki/Haptodus
wiki/Pantelosaurus