{{Short description|Extinct family of temnospondyls}} {{Automatic taxobox | fossil_range = [[Early Triassic]] - [[Late Triassic]] | image = Gerrothorax pustuloglomeratus.JPG | image_caption = Fossil of ''[[Gerrothorax pustuloglomeratus]]'' | taxon = Plagiosauridae | authority = Abel, 1919 | subdivision_ranks = Genera | subdivision = *{{extinct}}''[[Gerrothorax]]'' *{{extinct}}''[[Capulomala]]'' *{{extinct}}''[[Megalophthalma]]'' *{{extinct}}''[[Plagiosternum]]'' *{{extinct}}''[[Plagiosaurus]]'' *{{extinct}}''[[Plagioscutum]]'' *{{extinct}}''[[Plagiobatrachus]]'' *{{extinct}}''[[Plagiorophus]]'' }}
'''Plagiosauridae''' is a [[clade]] of [[temnospondyl]]s of the Early to Late [[Triassic]]. Deposits of the group are most commonly found in non-marine aquatic [[depositional environment]]s from central Europe and Greenland, but other remains have been found in Russia, Scandinavia, Australia and possibly Thailand.
== Material == The majority of plagiosaurid remains are of the genus ''Gerrothorax'', which have been recovered from the Fleming Fjord Formation of [[Jameson Land]], East Greenland,<ref name=":0">{{Cite journal|last1=Jenkins|first1=Farish A.|last2=Shubin|first2=Neil H.|last3=Gatesy|first3=Stephen M.|last4=Warren|first4=Anne|date=2008-12-01|title=Gerrothorax pulcherrimus from the Upper Triassic Fleming Fjord Formation of East Greenland and a Reassessment of Head Lifting in Temnospondyl Feeding|journal=Journal of Vertebrate Paleontology|volume=28|issue=4|pages=935–950|doi=10.1671/0272-4634-28.4.935|s2cid=86523094|issn=0272-4634}}</ref> and from many localities in southern Germany.<ref name=":1">{{Cite book|title=Gerrothorax pustuloglomeratus, ein Temnospondyle (Amphibia) mit knöcherner Branchialkammer aus dem Unteren Keuper von Kupferzell (Süddeutschland): Gerrothorax pustuloglomeratus, a temnospondyle (Amphibia) with a bony branchial chamber from the Lower Keuper of Kupferzell (South Germany)|last=Hellrung|first=Hanna|publisher=Staatliches Museum für Naturkunde|year=2003}}</ref><ref name=":2">{{Cite journal|last1=Schoch|first1=Rainer R.|last2=Witzmann|first2=Florian|date=2010-06-18|title=Bystrow's Paradox - gills, fossils, and the fish-to-tetrapod transition|journal=Acta Zoologica|language=en|volume=92|issue=3|pages=251–265|doi=10.1111/j.1463-6395.2010.00456.x|issn=0001-7272}}</ref><ref>{{Cite journal|last1=WITZMANN|first1=FLORIAN|last2=SCHOCH|first2=RAINER R.|last3=HILGER|first3=ANDRÉ|last4=KARDJILOV|first4=NIKOLAY|date=2011-11-25|title=Braincase, palatoquadrate and ear region of the plagiosaurid Gerrothorax pulcherrimus from the Middle Triassic of Germany|journal=Palaeontology|language=en|volume=55|issue=1|pages=31–50|doi=10.1111/j.1475-4983.2011.01116.x|issn=0031-0239|doi-access=free}}</ref> All of this material is currently assigned to a single species, ''G. pulcherrimus''.<ref name=":0" /> ''Plagiosuchus'' material is also very abundant, though poorly preserved and has been found only from Germany.<ref name=":3">{{Cite journal|last1=Damiani|first1=Ross|last2=Schoch|first2=Rainer R.|last3=Hellrung|first3=Hanna|last4=Werneburg|first4=Ralf|last5=Gastou|first5=Stéphanie|date=2009-02-01|title=The plagiosaurid temnospondyl Plagiosuchus pustuliferus (Amphibia: Temnospondyli) from the Middle Triassic of Germany: anatomy and functional morphology of the skull|journal=Zoological Journal of the Linnean Society|language=en|volume=155|issue=2|pages=348–373|doi=10.1111/j.1096-3642.2008.00444.x|issn=0024-4082|doi-access=free}}</ref> Additional material, including the material of all other plagiosaurids, is significantly more fragmentary and less abundant than that of ''Gerrothorax.'' These additional materials are predominantly from Germany and Russia<ref name=":1" /> with some potential material also reported from Thailand<ref>{{Cite journal|last1=Suteethorn|first1=Varavudh|last2=Janvier|first2=Philippe|last3=Morales|first3=Michael|date=January 1988|title=Evidence for a plagiosauroid amphibian in the upper triassic Huai Hin Lat formation of Thailand|journal=Journal of Southeast Asian Earth Sciences|volume=2|issue=3–4|pages=185–187|doi=10.1016/0743-9547(88)90029-3|issn=0743-9547}}</ref> and Brazil.<ref name=":4">{{Cite journal|last1=Dias-Da-Silva|first1=Sérgio|last2=Milner|first2=Andrew R.|date=September 2010|title=The Pustulated Temnospondyl Revisited—a Plagiosternine Plagiosaurid from the Lower Triassic of Brazil|journal=Acta Palaeontologica Polonica|language=en|volume=55|issue=3|pages=561–563|doi=10.4202/app.2009.0131|issn=0567-7920|doi-access=free}}</ref>
== Description == Plagiosaurids are predominantly characterized by the unique structure of their skulls and the armor that lines their trunk. The heads of these animals are short and wide with an overall semi-circular layout<ref name=":0" /> and extremely large [[orbital fenestra]]e.<ref name=":0" /><ref name=":5">{{Cite journal|last1=Schoch|first1=Rainer R.|last2=Milner|first2=Andrew R.|last3=Witzmann|first3=Florian|date=2014-02-26|title=Skull morphology and phylogenetic relationships of a new Middle Triassic plagiosaurid temnospondyl from Germany, and the evolution of plagiosaurid eyes|journal=Palaeontology|language=en|volume=57|issue=5|pages=1045–1058|doi=10.1111/pala.12101|issn=0031-0239|doi-access=free}}</ref> The skull and trunk of these organisms are generally vertically compressed to varying degrees within members of the clade to form an overall flattened [[body plan]]. Some articulated, three-dimensional preservation of plagiosaurids indicates that this flattening was a feature of the animals in life and is not a [[preservation artifact]] (the animals were not flattened by fossilization). The amount of vertical compression ("flattening") in plagiosaurids varies somewhat with the most basal member, ''Plagiosuchus'', being only somewhat compressed while more derived members such as ''Gerrothorax'' and ''Megalophthalma'' being much significantly more compressed.<ref name=":0" /><ref name=":5" /><ref name=":3" /> Their skull, also vertically compressed, has dorsally oriented large orbital fenestrae and contained a battery of small teeth the curve inward.<ref name=":3" /> The trunks of these animals have shortened limbs relative their body size and the backs were generally covered in bony armor which is denser in the more derived members of the clade.<ref name=":0" />
== Ecology == Plagiosaurids are believed to have lived an almost entirely [[Aquatic animal|aquatic lifestyle]]. Much of this interpretation stems from analysis of the remains of ''Gerrothorax'' because specimens of this group are so much more abundant and well preserved than other plagiosaurid remains.<ref name=":0" /> Aside from their remains being found dominantly within aquatic settings, evidence for an aquatic lifestyle comes primarily from evidence that the clade possessed internal gills, given by the presence of [[branchial arch]]es that were lined with arteries.<ref name=":2" /> Additionally, the limbs of plagiosaurids are short relative to their body size and the size of their [[pectoral girdle]]. Coupled with their vertically compressed body plan, a popular interpretation for these organisms has been that they lived on the [[Benthic zone|floor]] of freshwater systems and were obligatorily aquatic.<ref name=":0" /><ref name=":5" /> To facilitate a bottom dwelling lifestyle these organisms possess a special jaw joint, the [[atlanto-occipital joint]], which facilitates the lifting of the [[cranium]] to open the mouth rather than lowering the [[jaw]] as would be expected in other organisms.<ref name=":0" /><ref name=":3" /> Consequently, it is presumed that the animal would lay flat on river or lake beds waiting in ambush to catch prey, such as fish.<ref name=":0" /><ref name=":5" /><ref name=":3" /> It has been proposed that they may have captured prey via [[Suction feeding|suction]] by rapidly opening their mouth and then clamping down with their curved teeth.<ref name=":0" /><ref name=":3" /> This is somewhat supported by the lateral elongation of the skull in later plagiosaurids like ''[[Gerrothorax]]'' and ''[[Plagiosternum]]'' compared to earlier members such as ''[[Plagiosuchus]]''.<ref name=":4" /> The elongation of the skull is interpreted to have facilitated muscle attachment to the back of the skull and increasing the ability and force directed toward lifting the head.
The large [[Orbit (anatomy)|orbits]] of plagiosaurids have only been extensively analyzed in a single study (Schoch et al. 2014) which put forth two plausible eye structures.<ref name=":5" /> According to this study, because of their incredibly flat and vertically compressed skulls, it is unlikely that the eyes actually filled the space of the groups large orbits because these hypothetically large eyes would permanently protrude into at least part of the [[palate]]. Thus, it is most plausible that, like many modern amphibians, the eyes of these animals were actually significantly smaller than the orbit and positioned toward the front of the skull, though there is not enough data to make conclusive judgment about their exact position. The alternate hypothesis is that the group had large, flat, [[Lens (vertebrate anatomy)|lens]]less eyes similar to a family of [[Deep-sea fish|deep sea teleost fish]], the [[Ipnopidae]] (especially the [[type genus]], ''[[Ipnops]]''). These lensless eyes would allow plagiosaurids to detect when something is moving directly above them by causing a shadow in the light detected by the [[retina]]. While not observed among modern amphibians today, this hypothesis does align with the interpreted life habit of plagiosaurids and helps to explain the abnormal space afforded to the orbits of these animals.<ref name=":5" />
Plagiosaurids also represent an interesting case of extreme [[Punctuated equilibrium|evolutionary and morphological stasis]]. The features of these animals change very little through their evolutionary history despite changes. Schoch and Witzmann analyzed the collections of ''Gerrothorax'' material and noted that, despite being recovered from multiple environments that encompass approximately 40 million years of time, the general body plan of ''Gerrothorax'' was relatively static. This was interpreted to support a relatively high degree of [[Ecological niche|biological flexibility]] in these animals despite their unique morphology.<ref>{{Cite journal|last1=SCHOCH|first1=RAINER R.|last2=WITZMANN|first2=FLORIAN|date=2011-10-13|title=Cranial morphology of the plagiosaurid Gerrothorax pulcherrimus as an extreme example of evolutionary stasis|journal=Lethaia|language=en|volume=45|issue=3|pages=371–385|doi=10.1111/j.1502-3931.2011.00290.x|issn=0024-1164}}</ref>
==References== {{Reflist}}
==External links== {{Commons category}}
* [http://palaeos.com/vertebrates/temnospondyli/plagiosauroidea.html#Plagiosauridae Plagiosauridae at Palaeos.]
{{Trematosauria|P.}} {{Taxonbar|from=Q1620129}}
[[Category:Plagiosauridae| ]] [[Category:Triassic temnospondyls]] [[Category:Temnospondyl families]]