Wikipedia considers Orobates an anamniote (not a reptile = amniote) close to Diadectidae, which are also considered anamniotes. So does a recent paper by Nyakatura et al. 2015 who un-deformed the MNG 10181, the holotype, using CT scans and software (Fig. 1).
From the Nyakaturs et al. 2015 introduction
“Orobates pabsti (Holotype MNG 10181) is one of the most basal diadectids, from the lower Permian of Germany (Bromacker quarry, Tambach Formation, Tambach-Dietharz, Thuringia). Because of its phylogenetic position, this nearly complete, articulated, comparatively well-preserved specimen can be considered a key fossil. Additionally, fossil trackways from the ichnospecies Ichnotherium sphaerodactylum of the same locality were unequivocally produced by Orobates pabsti rendering this combination of body fossil and fossil trackways the oldest known track-trackmaker association and offering direct evidence of its locomotor behavior.”
It appears that Nyakatura et al. did everything right
to produce a good virtual model of Orobates.
Their only fault
was trusting an old cladogram that gave them a mistaken nesting outside the Reptilia. The large reptile tree nests Orobates inside the Reptilia, inside the Lepidosauromorpha, with the clade Diadectidae derived from the undisputed reptile, Millleretta (Fig. 2). No stem (=pre) amniotes more closely match the morphology.
an old, traditional sour matrix seems to be at fault.
Berman, DS et al. 2004. A new diadectid (Diadectomorpha), Orobates pabsti, from the Early Permian of Central Germany. Bulletin of Carnegie Museum of Natural History 35 :1-36. doi: 10.2992/0145-9058(2004)35[1:ANDDOP]2.0.CO;2
Nyakatura JA, Allen VR, Lauströer J, Andikfar A, Danczak M, Ullrich H-J, et al. 2015. A Three-Dimensional Skeletal Reconstruction of the Stem Amniote Orobates pabsti (Diadectidae): Analyses of Body Mass, Centre of Mass Position, and Joint Mobility. PLoS ONE 10(9): e0137284. doi:10.1371/journal.pone.0137284