[9] In Case’s description of the Platyhystrix holotype, he initially classified it as part of a new reptile specimen, but still noted tubercles along the neural spines which were similar to the projections found on amphibian skulls.

Large ridges and tubercle-like processes are present along the dorsal half of the orbital rim, edges of the skull table, and areas which adjoin the cheek.

Based on marginal dentition and preserved portions of the premaxilla, Platyhystrix may have had upwards of 65 teeth on either side of the upper jaw, in the form of simple, pointed pegs.

[6][10] However, the reassignment of Platyhystrix to the armored Dissorophidae clade and the blade’s extensive ornamentation led Vaughn in 1971 to reinterpret this feature as an osteoderm that was fused to the true neural spine instead.

Platyhystrix had a compact body, reaching 1 metre (3.3 ft) long including the tail, and its short, sturdy legs indicate a mainly terrestrial life.

The part of the formation in which the specimens were collected were confidently identified as belonging to the Wolfcampian age of the Early Permian, with the sediment composition denoting the presence of an ancient lake or river.

[2][3] Vaughn further describes one of the most productive regions of the Early Permian Cutler Formation as the “Platyhystrix pocket” during his field work there in 1962, due to the diversity and number of well preserved specimens found in the red sandstone.

New Mexico, and other states in the Rocky Mountain regions, were situated about ten degrees north of the equator, on the western edge of Pangea during the Early Permian.

The rivers that deposited the Abo Formation were made of fine silt beds, and were up to 8 m deep and 50 m wide, and reflect semi-arid and semi-humid conditions suggested by paleosols found on adjacent floodplains.

The presence of large ectotherms, assuming that these extant reptiles are similar to modern day species, hints at a daytime temperature range between 25-41 °C, and not dropping below 5 °C in the winter season.

Carroll and DeMar spent the 1960s attempting to explain the relationships amongst the wide variety of genera within the family, and while their phylogenies depicted differing conclusions, they had reached a general consensus when it came to the basal versus advanced groupings.

[17] Carroll’s logic (based on vertebral armor evolution) placed P.rugosus at a more basal position amongst Permian dissorophids, with the closest sister taxa being Aspidosaurus of the Late Pennsylvanian.

[5] More recently, new phylogenetic analyses have been produced in order to better understand the evolution of modern day Lissamphibaians, due to the increasing consensus that their monophyletic group is derived from Temnospondyli.

Based on the characters used in parsimony analysis, Platyhystrix was noted as having a much more basal position relative to Schoch’s findings, as a sister taxon to the Olsoniformes clade.