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Pareiasauria; Temporal range: Middle Permian - Late Permian, 265–252 Ma PreꞒ Ꞓ O S D C P T J K Pg N
	Skeleton of Scutosaurus karpinskii in the American Museum of Natural History
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	†Parareptilia
Order:	†Procolophonomorpha
Node:	†Ankyramorpha
Suborder:	†Procolophonia
Clade:	†Pareiasauromorpha
Superfamily:	†Pareiasauroidea
Clade:	†Pareiasauria; Seeley, 1888
Genera
	†Bradysaurus; †Bunostegos; †Deltavjatia; †Embrithosaurus; †Parasaurus; †Senectosaurus; †Velosauria †Pumiliopareiasauria †Anthodon; †Nanopareia; †Provelosaurus; †Pumiliopareia; ; †Therischia †Arganaceras; †Pareiasaurus; †Sanchuansaurus; †Scutosaurus; †Shihtienfenia; †Elgininiinae †Elginia; †Obirkovia; ; ; ;

Pareiasaurs (meaning "cheek lizards") are an extinct clade of large, herbivorous parareptiles. Members of the group were armoured with osteoderms which covered large areas of the body. They first appeared in southern Pangea during the Middle Permian, before becoming globally distributed during the Late Permian. Pareiasaurs were the largest reptiles of the Permian, reaching sizes equivalent to those of contemporary therapsids. Pareiasaurs became extinct in the Permian–Triassic extinction event.

Description

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.^[1]^[2] The limbs of many parieasaurs were extremely robust, likely to account for the increased stress on their limbs caused by their typically sprawling posture.^[1]^[2] The cow-sized Bunostegos differed from other pareiasaurs by having a more upright limb posture, being amongst the first amniotes to develop this trait.^[3] Pareiasaurs were protected by bony scutes called osteoderms that were set into the skin.^[4] Their skulls were heavily ornamented with bosses, rugose ridges, and bumps.^[5] Their leaf-shaped multi-cusped teeth resemble those of iguanas, indicating a herbivorous diet.^[6] The body probably housed an extensive digestive tract.^[1] Most authors have assumed a terrestrial lifestyle for pareiasaurs. A 2008 bone microanatomy study suggested a more aquatic, plausibly amphibious lifestyle,^[7] but a later 2019 study found that the bone histology provided no direct evidence of this lifestyle.^[8]

Evolutionary history

Pareiasaurs appear very suddenly in the fossil record. It is clear that these animals are parareptiles.^[9]^[10] As such, they are closely related to nycteroleterids.^[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.^[8] 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. Pareiasaurs first appeared in the fossil record in the Middle Permian (Guadalupian) of Southern Pangaea, before dispersing into Northern Pangaea and gaining a cosmopolitan distribution during the Late Permian (Lopingian).^[12]

Classification

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.^[13] Jalil and Janvier, in a large analysis of pareiasaur relationships, also found turtles to be close relatives of the "dwarf" pareiasaurs, such as Pumiliopareia.^[14] However, the discovery of Pappochelys argues against a potential pareisaurian relationship to turtles,^[15] and DNA evidence indicates that living turtles are more closely related to living archosaurs than lepidosaurs, and therefore cladistically diapsids.^[16]

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 Lanthanosuchidae or Testudines are included in the clade, the Pareiasauria only contains the monophyletic family Pareiasauridae.

Phylogeny

Below is a cladogram from Tsuji et al. (2013):^[17]

Pareiasauria

"Bradysaurus" seeleyi

	Deltavjatia

	Parasaurus

Velosauria

Nanoparia

Provelosaurus

	Anthodon

	Pumiliopareia

Shansisaurus

Shihtienfenia

	Pareiasuchus peringueyi

	Pareiasuchus nasicornis

	Arganaceras

	Elginia

	Obirkovia

	Pareiasaurus

	Sanchuansaurus

	Scutosaurus

References

^ ^a ^b ^c Romano, Marco; Manucci, Fabio; Rubidge, Bruce; Van den Brandt, Marc J. (2021-06-17). "Volumetric Body Mass Estimate and in vivo Reconstruction of the Russian Pareiasaur Scutosaurus karpinskii". Frontiers in Ecology and Evolution. 9: 692035. doi:10.3389/fevo.2021.692035. hdl:11573/1634310. ISSN 2296-701X.
^ ^a ^b Van den Brandt, Marc Johan; Day, Michael Oliver; Manucci, Fabio; Viglietti, Pia Alexa; Angielczyk, Kenneth David; Romano, Marco (2023-02-27). "First volumetric body mass estimate and a new in vivo 3D reconstruction of the oldest Karoo pareiasaur Bradysaurus baini, and body size evolution in Pareiasauria". Historical Biology: 1–15. doi:10.1080/08912963.2023.2175211. ISSN 0891-2963. S2CID 257369904.
^ Turner, Morgan L.; Tsuji, Linda A.; Ide, Oumarou; Sidor, Christian A. (2015-11-02). "The vertebrate fauna of the upper Permian of Niger—IX. The appendicular skeleton of Bunostegos akokanensis (Parareptilia: Pareiasauria)". Journal of Vertebrate Paleontology. 35 (6): e994746. Bibcode:2015JVPal..35E4746T. doi:10.1080/02724634.2014.994746. ISSN 0272-4634. S2CID 86503874.
^ Scheyer, T. M. & Sander, P. M. (2009). "Bone microstructures and mode of skeletogenesis in osteoderms of three pareiasaur taxa from the Permian of South Africa". Journal of Evolutionary Biology. 22 (6): 1153–1162. doi:10.1111/j.1420-9101.2009.01732.x. PMID 19416416.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^ Van Den Brandt, Marc Johan; Abdala, Fernando; Rubidge, Bruce Sidney (2019). "Cranial morphology and phylogenetic relationships of the Middle Permian pareiasaur Embrithosaurus schwarzi from the Karoo Basin of South Africa". Zoological Journal of the Linnean Society. doi:10.1093/zoolinnean/zlz064.
^ Sues, Hans-Dieter; Reisz, Robert R. (1998-04-01). "Origins and early evolution of herbivory in tetrapods". Trends in Ecology & Evolution. 13 (4): 141–145. doi:10.1016/S0169-5347(97)01257-3. ISSN 0169-5347. PMID 21238234.
^ Kriloff, A.; Germain, D.; Canoville, A.; Vincent, P.; Sache, M.; Laurin, M. (2008). "Evolution of bone microanatomy of the tetrapod tibia and its use in palaeobiological inference". Journal of Evolutionary Biology. 21 (3): 807–826. doi:10.1111/j.1420-9101.2008.01512.x. PMID 18312321. S2CID 6102313.
^ ^a ^b Boitsova, Elizaveta A; Skutschas, Pavel P; Sennikov, Andrey G; Golubev, Valeriy K; Masuytin, Vladimir V; Masuytina, Olga A (2019-07-05). "Bone histology of two pareiasaurs from Russia (Deltavjatia rossica and Scutosaurus karpinskii) with implications for pareiasaurian palaeobiology". Biological Journal of the Linnean Society: blz094. doi:10.1093/biolinnean/blz094. ISSN 0024-4066.
^ Gauthier, J.A.; Kluge, A.G.; Rowe, T. (1988). "The early evolution of the Amniota". In Benton, M.J. (ed.). The Phylogeny and Classification of the Tetrapods. Vol. 1. Oxford: Clarendon Press. pp. 103–155. ISBN 978-0198577058.
^ Laurin, M.; Reisz, R.R. (1995). "A reevaluation of early amniote phylogeny". Zoological Journal of the Linnean Society. 113 (2): 165–223. doi:10.1111/j.1096-3642.1995.tb00932.x.
^ LEE, M. S. Y. (1995). "Historical burden in systematics and the interrelationships of 'parareptiles'". Biological Reviews of the Cambridge Philosophical Society. 70 (3): 459–547. doi:10.1111/j.1469-185x.1995.tb01197.x. S2CID 85790423.
^ Olroyd, Savannah L.; Sidor, Christian A. (August 2017). "A review of the Guadalupian (Middle Permian) global tetrapod fossil record". Earth-Science Reviews. 171: 583–597. Bibcode:2017ESRv..171..583O. doi:10.1016/j.earscirev.2017.07.001.
^ Lee, M.S.Y. (1997). "Pareiasaur phylogeny and the origin of turtles". Zoological Journal of the Linnean Society. 120 (3): 197–280. doi:10.1111/j.1096-3642.1997.tb01279.x.
^ Jalil, N.-E.; Janvier, P. (2005). "Les pareiasaures (Amniota, Parareptilia) du Permien supérieur du Bassin d'Argana, Maroc". Geodiversitas. 27 (1): 35–132.
^ Schoch, Rainer R.; Sues, Hans-Dieter (2015). "A Middle Triassic stem-turtle and the evolution of the turtle body plan". Nature. 523 (7562): 584–587. Bibcode:2015Natur.523..584S. doi:10.1038/nature14472. PMID 26106865. S2CID 205243837.
^ Crawford, Nicholas G.; Parham, James F.; Sellas, Anna B.; Faircloth, Brant C.; Glenn, Travis C.; Papenfuss, Theodore J.; Henderson, James B.; Hansen, Madison H.; Simison, W. Brian (February 2015). "A phylogenomic analysis of turtles". Molecular Phylogenetics and Evolution. 83: 250–257. doi:10.1016/j.ympev.2014.10.021. PMID 25450099.
^ Tsuji, L. A.; Sidor, C. A.; Steyer, J. - S. B.; Smith, R. M. H.; Tabor, N. J.; Ide, O. (2013). "The vertebrate fauna of the Upper Permian of Niger—VII. Cranial anatomy and relationships of Bunostegos akokanensis (Pareiasauria)". Journal of Vertebrate Paleontology. 33 (4): 747–763. Bibcode:2013JVPal..33..747T. doi:10.1080/02724634.2013.739537. S2CID 86097405.