Acerosodontosaurus piveteaui (Currie 1980, Bickelmann, Müller and Reisz 2009) Late Permian. The later study by Bickelmann et al. (2009) determined that a bone considered to be quadratojugal (in red) 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 present study. In any case that questionable bone fits perfectly into a reconstruction as a quadratojugal. Here Acerosodontosaurus descended from a sister to Petrolacosaurus and phylogenetically preceded Adelosaurus, Hovasaurus, Claudiosaurus and Thadeosaurus.
Distinct from Petrolacosaurus, the skull of Acersodontosaurus was slightly longer with larger temporal fenestrae. The maxilla rose to block lacrimal contact with the naris. The jugal extended further anteriorly to the anterior orbit. The postorbital was higher on the skull, even with the upper rim of the orbit. The squamosal was narrower. The mandible was deeper.
The cervicals were not so elongated and they were smaller than the dorsals. The neural spines of the more robust dorsals were taller. The dorsal ribs were longer, enclosing a wider than tall torso.
The humerus had a greatly expanded distal end. This contributed to enlarging the space between the radius (which had a convex bow) and ulna. Metacarpal 4 was no longer than mc 3. The phalanges of digits 2-4 lined up parallel to the metacarpal base line. The digit length disparity was not as great.
The pelvis was more robust with all three elements similar in size to one another.