| Pareiasauria | |
|---|---|
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| Skeleton ofScutosaurus karpinskii in theAmerican Museum of Natural History | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | †Parareptilia |
| Order: | †Procolophonomorpha |
| Clade: | †Ankyramorpha |
| Suborder: | †Procolophonia |
| Clade: | †Pareiasauromorpha |
| Superfamily: | †Pareiasauroidea |
| Clade: | †Pareiasauria Seeley, 1888 |
| Genera | |
Pareiasaurs (meaning "cheek lizards") are an extinct clade of large, herbivorousparareptiles. Members of the group were armoured withosteoderms which covered large areas of the body. They first appeared in southernPangea 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 contemporarytherapsids. Pareiasaurs became extinct in thePermian–Triassic extinction event.
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-sizedBunostegos 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 bonyscutes calledosteoderms 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 ofiguanas, indicating a herbivorous diet.[6] The body probably housed an extensivedigestive 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]
Pareiasaurs appear very suddenly in the fossil record. It is clear that these animals areparareptiles.[9][10] As such, they are closely related tonycteroleterids.[11] Pareiasaurs filled the large herbivoreniche (orguild) that had been occupied early in the Permian period by thecaseid pelycosaurs and, before them, thediadectid reptiliomorphs.[8] They are much larger than the diadectids, more similar to the giant caseid pelycosaurCotylorhynchus. 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]
Some paleontologists considered that pareiasaurs were direct ancestors of modernturtles. 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 asPumiliopareia.[14] However, the discovery ofPappochelys argues against a potential pareisaurian relationship to turtles,[15] and DNA evidence indicates that living turtles are more closely related to livingarchosaurs thanlepidosaurs, and therefore cladisticallydiapsids.[16]
Hallucicrania (Lee 1995): This clade was coined by MSY Lee forLanthanosuchidae + (Pareiasauridae +Testudines). Lee's pareiasaur hypothesis has become untenable due to the diapsid features of the stem turtlePappochelys and the potential testudinatan nature ofEunotosaurus. Recent cladistic analyses reveal that lanthanosuchids have a much more basal position in theProcolophonomorpha, and that the nearest sister taxon to the pareiasaurs are the rather unexceptional and conventional lookingnycteroleterids (Müller & Tsuji 2007, Lysonet al. 2010) the two being united in the clade Pareiasauromorpha (Tsujiet 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 placeSclerosaurus 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.
Below is acladogram from Tsujiet al. (2013):[17]
| Pareiasauria | |
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