Pareiasaurs ranged in size from 60 to 300 centimetres (2.0 to 9.8 ft) long, with some species estimated to exceed 1,000 kilograms (2,200 lb) in body mass.

[11] Pareiasaurs filled the large herbivore niche (or guild) that had been occupied early in the Permian period by the caseid pelycosaurs and, before them, the diadectid reptiliomorphs.

Pareiasaur skulls have several turtle-like features, and in some species the scutes have developed into bony plates, possibly the precursors of a turtle shell.

Lee's pareiasaur hypothesis has become untenable due to the diapsid features of the stem turtle Pappochelys and the potential testudinatan nature of Eunotosaurus.

More recent cladistic studies place Sclerosaurus in the procolophonid subfamily Leptopleuroninae (Cisneros 2006, Sues & Reisz 2008), which means the similarities with pareiasaurs are the result of convergences.

Below is a cladogram from Tsuji et al. (2013):[17] "Bradysaurus" seeleyi Bradysaurus baini Nochelesaurus Embrithosaurus Bunostegos Deltavjatia Parasaurus Nanoparia Provelosaurus Anthodon Pumiliopareia Shansisaurus Shihtienfenia Pareiasuchus peringueyi Pareiasuchus nasicornis Arganaceras Elginia Obirkovia Pareiasaurus Sanchuansaurus Scutosaurus