Erpetonyx arsenaultorum (Modesto et al. 2015, Latest Pennsylvannian, 298 Mya) was originally considered a bolosaurid due to its similarity to Eudibamus, which the authors mistakenly considered a sister to Bolosaurus and Belebey, both closer to Diadectes. Here Erpetonyx is a basal diapsid. The authors thought 3 sacrals were present, but the third sacral could not reach the ilium. Distinct from Milleropsis and Broomia the manus is not quite as large as the pes.

Acerosodontosaurus piveteaui (Currie 1980, Bickelmann, Müller and Reisz 2009; Late Permian). Acerosodontosaurus is a larger, later relative of Erpetonyx.

Bickelmann et al. (2009) determined that a bone considered to be quadratojugal (in purple) was instead a portion of rib. Because of that reasssessment the authors considered Acerosodontosaurus a phylogenetic enigma in which the phylogenetic position was poorly understood. That is not the case when the rest of the anatomy also supports a basal diapsid nesting in the LRT.

Bickelmann C, Müller J and Reisz RR 2009. The enigmatic diapsid Acerosodontosaurus piveteaui (Reptilia: Neodiapsida) from the Upper Permian of Madagascar and the paraphyly of “younginiform” reptiles. Canadian Journal of Earth Sciences 46:651-661.

Broom, R. 1921. On the structure of the reptile tarsus. Proceedings of the Zoological Society, London 1921:143–155.

Currie PJ 1980. A new younginid (Reptilia: Eosuchia) from the Upper Permian of Madagascar. Canadian Journal of Earth Sciences 17(4):500-51.

Modesto SP, Scott DM, MacDougall MJ, Sues H-D, Evans DC, Reisz RR 2015. The oldest parareptile and the early diversification of reptiles. Proceedings of the Royal Society B 282: 20141912. online

wiki/Acerosodontosaurus
wiki/Erpetonyx