Parareptilia
Parareptiles | |
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A collage of five parareptile fossils. Clockwise from top, procolophonid )
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Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Reptilia |
Clade: | †Parareptilia Olson, 1947 |
Orders | |
Parareptilia ("near-reptiles") is a subclass or
Compared to most eureptiles, parareptiles retained fairly "primitive" characteristics such as robust, low-slung bodies and large
Like many other so-called 'anapsids', parareptiles were historically understudied. Interest in their relationships were reinvigorated in the 1990s, when several studies argued that Testudines (turtles and their kin) were members of Parareptilia.[4] Although this would suggest that Parareptilia was not extinct after all, the origin of turtles is still heavily debated. Many other morphological or genetic analyses find more support for turtles among diapsid eureptiles such as sauropterygians or archosauromorphs, rather than parareptiles.[6][7][8][3]
Description
Skull
Parareptilian skulls were diverse, from
Many amniotes have a row of small pits running along bones at the edge of the mouth, but parareptiles have only a few pits, with one especially large pit near the front of the maxilla.[4][9][7] The rest of the skull was often strongly-textured by pits, ridges, and rugosities in most parareptile groups, occasionally culminating in complex bosses or spines. The maxilla is usually low, while the prefrontal and lacrimal bones in front of the eye are both fairly large. In all parareptiles except mesosaurs, the prefrontal has a plate-like inner branch which forms a broad contact with the palatine bone of the palate.[4][7][5] A prominent hole, the foramen orbitonasale, is present at the intersection of the prefrontal, palatine, and lacrimal. Parareptilian palates also have toothless and reduced ectopterygoid bones, a condition taken to extremes in mesosaurs, which have lost the ectopterygoid entirely.[4][5]
Most parareptiles had large
Apart from the long, slender jaws of mesosaurs, most parareptile jaws were short and thick. The jaw joint is formed by the
Postcranial skeleton
There was some variation in the body shape of parareptiles, with early members of the group having an overall lizard-like appearance, with thin limbs and long tails. The most successful and diverse groups of parareptiles, the pareiasaurs and procolophonids, had massively-built bodies with reduced tails and stout limbs with short digits. This general body shape is shared with other ‘cotylosaurs’ such as captorhinids, diadectomorphs, and seymouriamorphs.[3] Another general ‘cotylosaurian’ feature in parareptiles is the ‘swollen’ appearance of their vertebrae, which have wide and convex upper surfaces.[12]
Parareptiles lacked a supraglenoid foramen on the scapula, a hole which is also absent in varanopids and neodiapsids.[5][11] Most had a fairly short and thick humerus which was expanded near the elbow. Unlike early eureptiles, the outer part of the lower humerus possessed both a small supinator process and an ectepicondylar foramen and groove.[4] The ulna generally has a poorly developed olecranon process, another trait in contrast with the earliest eureptiles.[4][5]
Most parareptiles had an ilium which was fan-shaped and vertically (rather than horizontally) oriented, an unusual trait among early amniotes.[4][9][7] The sacral ribs, which connect the spine to the ilium, were usually slender or fan-shaped, with large gaps between them.[4] The hindlimbs were typically not much longer than the forelimbs, and had thick reptilian ankle bones and short toes. There are some exceptions, such as Eudibamus, an early Permian bolosaurid with very elongated hindlimbs.[14]
History of classification
The name Parareptilia was coined by
Parareptilia's usage was revived by
Amniota |
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In contrast, several studies in the mid-to-late 1990s by
The cladogram below follows an analysis by M.S. Lee, in 2013.[23]
Amniota |
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The cladogram below follows the analysis of Li et al. (2018).[24]
Eureptilia |
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A 2020 study by David P. Ford and Roger B. J. Benson found that Parareptilia was nested within Diapsida as the sister group to
Evolutionary history
The oldest known parareptiles are the bolosaur Erpetonyx and the acleistorhinid Carbonodraco from the Late Carboniferous (Moscovian-Gzhelian) of North America, which represents the only currently known Carboniferous parareptiles, indicating that the initial diversification of the group took place in the Late Carboniferous.[1] Numerous parareptile lineages appeared during the early Permian and the group reached a cosmopolitan distribution. Parareptile diversity declined towards the end of the Permian and procolophonoids, which first appeared during the Late Permian, were the only group of parareptiles to survive the Permian–Triassic extinction event. Procolophonid diversity sharply declined beginning in the Middle Triassic, with the group becoming extinct by the end of the Triassic.[26]
References
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- ^ Gauthier JA, Kluge AG, Rowe T (1988). "The early evolution of the Amniota". In Benton MJ (ed.). The Phylogeny and Classification of the Tetrapods, Volume 1: Amphibians, Reptiles, Birds. Systematics Association Special Volume. Vol. 35A. Clarendon Press. pp. 103–155.
- ^ Rieppel O (1994). "Osteology of Simosaurus gaillardoti and the relationships of stem-group sauropterygia". Fieldiana Geology. 28 (1462): i-85.
- ^ Rieppel O (1995). "Studies on skeleton formation in reptiles: implications for turtle relationships". Zoology. 98: 298–308.
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