[1] The interclavicle described and figured by Fraas had originally been noted by him as Labyrinthodon sp.

The taxon was reassigned to the newly named genus Plagiosuchus in 1922 by von Huene, who described new material that permitted him to differentiate it from Plagiosternum granulosum; this was also when the specific epithet was grammatically modified.

However, its most defining feature is its greatly enlarged orbit, which forms a massive orbitotemporal fenestra with the loss of several post-orbital bones, including the postfrontal and the postorbital, and the reduction of several others.

The subtemporal vacuity on the palate is also correspondingly long, while the tooth rows are short, confined to the anterior portion of the skull.

Ornamentation varies across the skeleton, with the distinct pustules found in many other plagiosaurids found on the pectoral elements, more typical temnospondyl ridging on the mandible, and more irregular large tubercles on the skull.