{{Short description|Extinct genus of amphibians}} {{Automatic taxobox | fossil_range = {{fossil range|Ladinian|Rhaetian|[[Ladinian]]–[[Rhaetian]] (Middle–Late [[Triassic]])}} | image = Gerrothorax pustuloglomeratus.JPG | image_caption = Fossil of ''Gerrothorax'' in the [[Naturmuseum Senckenberg]] | taxon = Gerrothorax | authority = Nilsson, [[1934 in paleontology|1934]] | type_species = {{extinct}}'''''Gerrothorax pulcherrimus''''' | type_species_authority = Nilsson, 1934 }}
'''''Gerrothorax''''' ("wicker chest") is an extinct genus of [[temnospondyl]] [[amphibian]] from the [[Triassic]] period of [[Greenland]], [[Germany]], [[Poland]], [[Sweden]], and possibly [[Thailand]]. It is known from a single species, ''G. pulcherrimus'', although several other species such as ''G. pustuloglomeratus'' have been named in the past.
''Gerrothorax'' was about {{convert|1|m|ft}} long, and had a remarkably flattened body. It probably hid under sand or mud on [[Stream bed|river]] and [[Lake beds|lake bottom]]s, and in [[brackish water]]s,<ref>[https://books.google.com/books?id=tJcwEAAAQBAJ&dq=Gerrothorax+brackish+environment&pg=PT730 Vertebrate Skeletal Histology and Paleohistology]</ref> scanning for prey with its large, upward-facing eyes. ''Gerrothorax'' had an unusually shaped skull with angular protrusions on the sides. This looked vaguely similar to the skull of the earlier, unrelated, amphibian ''[[Diplocaulus]]'', but was not so developed.<ref name=EoDP>{{cite book |editor=Palmer, D.|year=1999 |title= The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals|publisher= Marshall Editions|location=London|page= 53|isbn= 978-1-84028-152-1}}</ref>
Some ''Gerrothorax'' fossils preserved [[hypobranchial]]s and [[ceratobranchial]]s (bony [[Branchial arch|gill arches]]) near the neck. This shows that ''Gerrothorax'' was [[pedomorphosis|pedomorphic]], retaining its [[larva]]l [[gill]]s as an adult. When originally described in 1946, these bones were considered to correspond to feather-like [[external gills]] similar to those of modern-day neotenic [[salamander]]s, such as the [[mudpuppy]], the [[axolotl]], and the [[olm]].<ref>{{Cite journal|last=Nilsson|first=Tage|date=13 February 1946|title=A new find of Gerrothorax rhaeticus Nilsson, a plagiosaurid from the Rhaetic of Scania|url=http://paleoarchive.com/literature/Nilsson1946-NewGerrothoraxRhaeticusScania.pdf|journal=Lunds Universitets årsskrift|volume=42|issue=10}}</ref><ref name="EoDP" />
However, a 2011 paper found that it was more likely that plagiosaurids such as ''Gerrothorax'' had internal gills, like those of fish, rather than salamander-like external gills. The authors of that study noted that plagiosaurids and other ancient amphibians which retained gills as adults had grooves on their ceratobranchials. Grooved ceratobranchials are present in both modern and ancient fish, but unknown in modern amphibians. Therefore, they were indicative of internal gills. This would have also been advantageous for survival in large animals, as internal gills would have been protected by a large skin fold and were less likely to have been damaged by the environment.<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 }}</ref> [[Image:Gerrothorax22DB.jpg|thumb|left|Life restoration of ''Gerrothorax pulcherrimus'']] A 2008 study showed that ''Gerrothorax'' lifted its head rather than dropping its jaw when catching prey, which has been compared to how a [[toilet seat]] opens.<ref>{{cite journal |author1=Farish A. Jenkins, Jr. |author2=Neil H. Shubin |author3=Stephen M. Gatesy |author4=Anne Warren |year=2008 |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 }}</ref> In 2011 the skull of ''Gerrothorax'' was scanned using [[microtomography]], revealing that the [[braincase]] and [[palatoquadrate]] regions are highly ossified.<ref>{{cite journal |author1=F. Witzmann |author2=R. R. Schoch |author3=A. Hilger |author4=N. Kardjilov |year=2011 |title=Braincase, palatoquadrate and ear region of the plagiosaurid ''Gerrothorax pulcherrimus'' from the Middle Triassic of Germany |journal=[[Palaeontology (journal)|Palaeontology]] |volume=55 |issue=1 |pages=35–50 |doi=10.1111/j.1475-4983.2011.01116.x|doi-access=free }}</ref> A 2013 study argued that ''Gerrothorax'' consumed prey using [[suction feeding]]. ''Gerrothorax'' had strong muscles capable of both raising the cranium and lowering the jaw rapidly. The robust internal gill apparatus would have expelled water through the gills during this motion, creating intense pressure in the throat that would suck in small prey items. The gill arches were also covered in small [[wikt:denticle|denticle]]s, prohibiting any prey from escaping once devoured. Although suction feeding is common in fish and modern larval amphibians, ''Gerrothorax'' differs from these animals by its lack of [[cranial kinesis]], meaning that its cranial bones had fused [[joint]]s and could not flex against each other to create more negative space or to envelop prey.<ref>{{Cite journal|last1=Witzmann|first1=Florian|last2=Schoch|first2=Rainer R.|date=27 December 2012|title=Reconstruction of cranial and hyobranchial muscles in the triassic temnospondyl ''Gerrothorax'' provides evidence for akinetic suction feeding|journal=Journal of Morphology|language=en|volume=274|issue=5|pages=525–542|doi=10.1002/jmor.20113|pmid=23280767 |s2cid=25217352 |issn=0362-2525}}</ref>
The fossil record of ''Gerrothorax pulcherrimus'' extends 35 million years from the [[Ladinian]] stage of the [[Middle Triassic]] to the [[Rhaetian]] stage of the [[Late Triassic]]. Throughout this time span, specimens of the species show few [[Morphology (biology)|morphologic]] differences, making ''G. pulcherrimus'' an extreme example of [[Punctuated equilibrium|evolutionary stasis]]. ''G. pulcherrimus'' may have remained unchanged for so long because it could tolerate a wide range of ecological conditions. Although it always needed to live in an aquatic habitat, ''G. pulcherrimus'' may have been able to live in a variety of different water bodies with a wide range of salinity.<ref name="SW11">{{cite journal|author1=R. R. Schoch|author2=F. Witzmann|year=2011|title=Cranial morphology of the plagiosaurid ''Gerrothorax pulcherrimus'' as an extreme example of evolutionary stasis|journal=[[Lethaia]]|volume=45|issue=3|pages=371–385|doi=10.1111/j.1502-3931.2011.00290.x}}</ref>
==References== {{Reflist}} {{Portal|Paleontology}} {{Stereospondyli|T.}} {{Taxonbar|from=Q134415}}
[[Category:Triassic temnospondyls of Europe]] [[Category:Late Triassic amphibians of Europe]] [[Category:Middle Triassic amphibians of Europe]] [[Category:Triassic temnospondyls of Asia]] [[Category:Late Triassic amphibians of Asia]] [[Category:Middle Triassic amphibians of Asia]] [[Category:Triassic temnospondyls of North America]] [[Category:Late Triassic amphibians of North America]] [[Category:Middle Triassic amphibians of North America]] [[Category:Plagiosauridae]] [[Category:Ladinian genus first appearances]] [[Category:Rhaetian genus extinctions]] [[Category:Norian genera]] [[Category:Carnian genera]] [[Category:Fossil taxa described in 1934]]