Ariekanerpeton sigalovi (Ivakhnenko 1981, Laurin 1996; PIN 2079-1; Early Permian ~280 mya, 25cm in length) is represented by more than 900 specimens with none considered fully mature due to the paired neural arches disarticulated from the pleurocentra. More likely this genus retained juvenile traits into adulthood. No dermal scales are present. Lateral lines are present only on larvae and adults traversed arid landscapes. I did not find the ventrally expanded quadratojugal applied to the reconstruction by Laurin 1996. Rather the quadratojugal was straight.

Importantly Ariekanerpeton nests at the base of the Seymouriamorpha, between Eucritta (near the base of the reptilomorphs) and Utegenia (at the base of the lepospondyls) + Bystrowiella (at the base of the stem reptiles). This taxon, therefore, is transitional between several clades and THAT fits a pattern seen elsewhere in the cladogram of phylogenetic miniaturization and neotony at the bases of major clades.

Stegops divaricata (Cope 1885; Milner and Schoch 2005; Moodie 1916; AMNH 2559; 5.6 cm skull length; Westphalian, Late Carboniferous, 310 mya) has bounced around the family tree without settling down. Here it nests with Tersomius, not with squamosal spikes (upper right, from Moodie 1916), but with deeply excavated squamosals and elevated orbits.

Cope ED 1885. Second continuation of researches among the Batrachia of the Coal Measures of Ohio. Proceedings of the American Philosophical Society 22:405–408.

Ivakhenko MF 1981. Dscosauriidae from the Permain of Tadrzhikistan. Paleontological Journal 1981:90-102.

Laurin M 1996. A reevaluation of Ariekanerpeton, a lower Permian seymouriamorph (Vertebrata: Seymouriamorpha) from Tadzhikistan. Journal of Vertebrate Paleontology 16(4):653–665.

Milner A and Schoch R 2006. Stegops, a problematic spiky-headed temnospondyl. Journal of Vertebrate Paleontology. 26 (3, Suppl.): 101A.

Moodie RL 1916. The microsaurian family stegopidae. The coal measures amphibia of North America. Carnegie Institution of Washintion 238: 222pp.

Ruta M, Jeffery JE and Coates MI 2003. A supertree of early tetrapods. Proc. R. Soc. Lond. B (2003) 270, 2507–2516 DOI 10.1098/rspb.2003.2524 online pdf

wiki/Ariekanerpeton
wiki/Stegops