Parioxys

The type species, Parioxys ferricolus, was named in 1878 by American paleontologist Edward Drinker Cope based on two badly preserved skulls that were collected from the early Permian Texas red-beds.[1] Egyptian paleontologist, Youssef S. Moustafa, described new material of P. ferricolus from other localities in Texas.[2][3] Moustafa also described another species, P. romeri, on the basis of an isolated humerus, but this was regarded as being indeterminate. A second definitive species, P. bolli, was described by Canadian paleontologist Robert Carroll in 1964.[4] This taxon is only known from postcranial material.

Parioxys was historically considered to be closely related to eryopoids, more specifically the well-known Eryops megalocephalus, which was collected from the same locality as the type material of P. ferricolus. Cope himself listed P. ferricolus as a species of Eryops,[5][6] possibly because he considered it to be a juvenile specimen of Eryops.[7] It was shortly revived as a distinct genus[8] with a suggestion that the original specimen's described by Cope might have been inadvertently described as other taxa by other authors,[9] but its affinities continued to be debated, with some suggestions that it might instead belong to the Trematopidae.[10][11] Moustafa (1955a) placed Parioxys in its own family and suggested that it was related to the Dissorophidae.[3] Schoch & Milner (2014) placed Parioxys within Dissorophidae based on personal observations of further preparation of historic material, although this has not been tested in a phylogenetic analysis due to the poor quality of much of the material.[12]