Pareiasaur

Pareiasaurs (meaning "cheek lizards") were a clade of parareptiles comprising the family Pareiasauridae. They were large herbivores that flourished during the Permian period. Parareptiles form a sister clade to reptiles and birds.

Pareiasaurs ranged in size from 60 to 300 centimetres (2.0 to 9.8 ft)
long, and may have weighed up to 600 kilograms (1,300 lb). They were
stocky, with short tails, small heads, robust limbs, and broad feet. The
 cow-sized species Bunostegos, which lived 260 million years ago, is the earliest known example of a tetrapod with a fully erect posture as its legs were positioned directly under its body. Pareiasaurs were protected by bony scutes called osteoderms
 that were set into the skin. Their heavy skulls were ornamented with
multiple knobs and ridges. The leaf-shaped multi-cusped teeth resemble
those of iguanas, caseids, and other reptilian herbivores. This dentition, together with the deep body, which may have housed an extensive digestive tract,
 are evidence of a herbivorous diet. Most authors have assumed a
terrestrial lifestyle for pareiasaurs, but bone microanatomy suggests a
more aquatic, plausibly amphibious lifestyle.

Pareiasaurs appear very suddenly in the fossil record. It is clear that these animals are parareptiles. As such, they are closely related to Nycteroleterids. Like Rhipaeosaurs, they may have 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 amphibians and Edaphosaur reptiles. They are much larger than the diadectids, more similar to the giant caseid pelycosaur Cotylorhynchus
 . Although the last Pareiasaurs were no larger than the first types
(indeed, many of the last ones became smaller), there was a definite
tendency towards increased armour as the group developed .

Some paleontologists considered that pareiasaurs were direct ancestors of modern turtles.
 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. Jalil and Janvier, in a large analysis of
 pareiasaur relationships, also found turtles to be close relatives of
the "dwarf" pareiasaurs, such as Pumiliopareia. However, the discovery of Pappochelys argues against a potential pareisaurian relationship to turtles.
Associated clades
Hallucicrania (Lee 1995): This clade was coined by MSY Lee for Lanthanosuchidae + (Pareiasauridae + Testudines).
 Lee's pareiasaur hypothesis has become untenable due to the diapsid
features of the stem turtle Pappochelys and the potential testudinatan
nature of Eunotosaurus. Recent cladistic analyses reveal that lanthanosuchids have a much more basal position in the Procolophonomorpha, and that the nearest sister taxon to the pareiasaurs are the rather unexceptional and conventional looking nycteroleterids (Müller & Tsuji 2007, Lyson et al. 2010) the two being united in the clade Pareiasauromorpha (Tsuji et al. 2012).
Pareiasauroidea
 (Nopcsa, 1928): This clade (as opposed to the superfamily or suborder
Pareiasauroidea) was used by Lee (1995) for Pareiasauridae +
Sclerosaurus. 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.
Pareiasauria (Seeley, 1988): If neither
Lanthanosuchids or Testudines are included in the clade, the
Pareiasauria only contains the monophyletic family Pareiasauridae. It's a
 traditional linnaean term.
Phylogeny