{{short description|Genus of amphibians (fossil)}} {{Speciesbox | fossil_range = Latest Pennsylvanian (Late Gzhelian) - Early Permian, {{fossil range|299|279.5}} | image = Platyhystrix BW.jpg | image_caption = Life reconstruction | genus = Platyhystrix | parent_authority = Williston, 1911 | species = rugosus | authority = (Case, 1910) | synonyms = *''Zatrachys apicalis'' <small>Case, 1910</small> }}
'''''Platyhystrix''''' (from Greek: πλατύς ''platús'', 'flat' and Greek: ῠ̔́στρῐξ ''hústrix'', 'porcupine') is an extinct temnospondyl amphibian with a distinctive sail along its back, similar to the unrelated synapsids, ''Dimetrodon'' and ''Edaphosaurus''. It lived during the boundary between the latest Carboniferous and earliest Permian periods throughout what is now known as the Four Corners, Texas, and Kansas about 300 million years ago.
Not much is known about ''Platyhystrix'', with a majority of the fossils found composed of the distinct neural spines, and fractured skull fragments.<ref name=":0">{{Cite journal |last=Case |first=E.C. |date=1910 |title=New or little known reptiles and amphibians from the Permian (?) of Texas |journal=Bulletin of the American Museum of Natural History |volume=28 |pages=163–181}}</ref><ref name=":5">{{Cite journal |last1=Berman |first1=David S. |last2=Reisz |first2=Robert R. |last3=Fracasso |first3=Michael A. |date=1981-12-18 |title=Skull of the Lower Permian dissorophid amphibian Platyhysthx mgosiis |journal=Annals of the Carnegie Museum |volume=50 |pages=391–416 |doi=10.5962/p.214500 |issn=0097-4463|doi-access=free }}</ref><ref name=":6">{{Cite journal |last=Vaughn |first=Peter Paul |date=1962 |title=Vertebrates from the Halgaito Tongue of the Cutler Formation, Permian of San Juan County, Utah |journal=Journal of Paleontology |volume=36 |issue=3 |pages=529–539 |jstor=1301085 |issn=0022-3360}}</ref> There is only one species within the genus, '''''Platyhystrix rugosus'''''. Its phylogenetic relationships to other members of the family Dissorophidae have been debated in recent years, due to its unique cranial features, and recent discoveries as to the origins of modern day lissamphibians.<ref name=":7">{{Cite journal |last1=Atkins |first1=Jade B. |last2=Reisz |first2=Robert R. |last3=Maddin |first3=Hillary C. |date=2019-03-22 |title=Braincase simplification and the origin of lissamphibians |journal=PLOS ONE |volume=14 |issue=3 |article-number=e0213694 |doi=10.1371/journal.pone.0213694 |pmid=30901341 |issn=1932-6203|pmc=6430379 |doi-access=free }}</ref><ref name=":1">{{Cite journal |last=Schoch |first=Rainer R. |date=August 2012 |title=Character distribution and phylogeny of the dissorophid temnospondyls |url=http://www.foss-rec.net/15/121/2012 |journal=Fossil Record |language=en |volume=15 |issue=2 |pages=121–137 |doi=10.1002/mmng.201200010|doi-access=free }}</ref> Synonyms and alternate spellings include: ''Zatrachys apicalis, Ctenosaurus rugosus, Platyhystryx, Platyhistryx''.<ref name=":2">{{Cite book |last=Williston |first=Samuel Wendell |title=American Permian vertebrates |date=1911 |publisher=The University of Chicago Press |location=Chicago, Ill.|doi=10.5962/bhl.title.54741 }}</ref><ref>{{Cite journal |date=January 1920 |title=I. The structure, evolution and origin of the amphibia. - The "orders' rachitomi and stereospondyli |journal=Philosophical Transactions of the Royal Society of London. Series B, Containing Papers of a Biological Character |volume=209 |issue=360–371 |pages=1–73 |doi=10.1098/rstb.1920.0001 |issn=0264-3960|doi-access=free }}</ref><ref name=":3">{{Cite journal |last=Williston |first=S.W. |date=1916 |title=Synopsis of the American Permo-Carboniferous Tetrapoda |journal=Contributions of the Walker Museum |volume=1 |pages=193–236}}</ref><ref name=":0" />
== History of discovery == The holotype of ''Platyhystrix'' (AMNH FARB 4785) was first discovered in the Early Permian Cutler formation in Rio Arribas Co, New Mexico in 1881 by American paleontologist, E.D. Cope.<ref name=":4">{{Cite web |title=The Dog Days of Dissorophids, Week 3: Platyhystrix |url=http://bryangee.weebly.com/2/post/2019/08/the-dog-days-of-dissorophids-week-3-platyhystrix.html |access-date=2023-03-03 |website=Bryan Gee, Ph.D. |language=en}}</ref> The holotype consisted of a few fragmented neural spines, and was initially listed under the species name, ''Zatrachys apicalis''.<ref name=":4" /> In 1910, American paleontologist E.C. Case reclassified the neural spines as belonging to a new species of the pelycosaurian reptile ''Ctenosaurus'', ''Ctenosaurus rugosus'' (the specific name means "wrinkled, shriveled"), since they resembled spines from Texas belonging to ''C. koeneni'', described by Friedrich von Huene.<ref name=":4" />
In Case's description of the ''Platyhystrix'' holotype, he initially classified it as part of a new reptile specimen, but still noted tubercles along the neural spines which were similar to the projections found on amphibian skulls.<ref name=":4" /> It was S.W. Williston who created the genus in 1911, and placed it within the Temnospondyli order once fractured skull elements were described in 1916.<ref name=":3" /><ref name=":2" />
== Description ==
=== Skull === Compared to other dissorophid temnospondyls, ''Platyhystrix'''s skull is rather large (over 19 cm long along midline), as well as long and narrow when analyzed in dorsal view. There is a wide variety in dermal sculpturing which occurs along the dorsal and lateral portions of the skull. Large ridges and tubercle-like processes are present along the dorsal half of the orbital rim, edges of the skull table, and areas which adjoin the cheek. Nodular-like processes are most pronounced on the posterior portion of the skull roof, on the postorbital, squamosal, supratemporal, and tabular.<ref name=":5" /> The central dorsal portion of the skull is characterized by a reticulated pitting pattern, which becomes finer as it extends towards the nasals. These kinds of dermal ornamentation are what diagnose ''Platyhystrix'' from other members of Dissorophidae. Based on marginal dentition and preserved portions of the premaxilla, ''Platyhystrix'' may have had upwards of 65 teeth on either side of the upper jaw, in the form of simple, pointed pegs.<ref name=":5" />
Other diagnostic features of the skull include: long and narrow nasals, whose length is equivalent to approximately one third of the midline length of the skull; posteriorly closed otic notch; parietal is large and extends anteriorly beyond margin of orbit; parietals are longer than the frontals; postfrontal length is greater than twice its width and equal to the length of the supratemporal; cheek is steeply inclined and meets the skull table at nearly right angle.<ref name=":5" />
=== Dorsal Blades === The most notable characteristic of ''Platyhystrix'' is its elongated neural spines. Initially, these "spines" were thought to be an extension of the neural arch above the transverse process.<ref name=":2" /><ref name=":8">{{Cite journal |last1=Lewis |first1=G.E. |last2=Vaughn |first2=P.P. |last3=Baird |first3=Donald |date=1965 |title=Early Permian vertebrates from the Culter Formation of the Placerville area, Colorado, with a section on footprints from the Cutler Formation |journal=Professional Paper |doi=10.3133/pp503c |issn=2330-7102|doi-access=free }}</ref> However, the reassignment of ''Platyhystrix'' to the armored Dissorophidae clade and the blade's extensive ornamentation led Vaughn in 1971 to reinterpret this feature as an osteoderm that was fused to the true neural spine instead.<ref>{{Cite journal |last=Vaughn |first=Peter Paul |date=1971 |title=A Platyhystrix-like Amphibian with Fused Vertebrae, from the Upper Pennsylvanian of Ohio |journal=Journal of Paleontology |volume=45 |issue=3 |pages=464–469 |jstor=1302692 |issn=0022-3360}}</ref> This reclassification suggested a superficial convergence with the neural spines present in synapsids. Histological analysis revealed that the dorsal blades of ''Platyhystrix'' do indeed share histological features and were likely homologous with the internal osteoderm series present in other dissorophids.<ref name=":9">{{Cite journal |last1=Bowler |first1=Neven |last2=Sumida |first2=Stuart S. |last3=Huttenlocker |first3=Adam K. |date=2022-12-21 |title=Histological evidence for dermal-endochondral co-ossification of the dorsal blades in the late Paleozoic amphibian ''Platyhystrix rugosus'' (Temnospondyli: Dissorophidae) |journal=Journal of Vertebrate Paleontology |volume=42 |issue=2 |doi=10.1080/02724634.2022.2144338 |issn=0272-4634}}</ref> This evidence points to the blades being of dermal origin, and are a novel example of dermal-endochondral co-ossification in a Paleozoic tetrapod.<ref name=":9" />
It is estimated that the notable sail was made up of a range of 11-15 laterally compressed and distally expanded blades.<ref name=":5" /><ref>{{Cite journal |last1=Lucas |first1=Spencer G. |last2=Krainer |first2=Karl |last3=Voigt |first3=Sebastian |last4=Berman |first4=David S. |last5=Henrici |first5=Amy |date=2014 |title=The Lower Permian Abo Formation in the northern Sacramento Mountains, southern New Mexico |journal=Geology of the Sacramento Mountains Region |pages=287–302 |publisher=New Mexico Geological Society |doi=10.56577/ffc-65.287|isbn=978-1-58546-100-4 }}</ref> Most of the distal length of these dorsal blades is covered with ridges and pustules, similar to the dermal ornamentation seen on the skull.<ref name=":9" /> Similar to ''Edaphosaurus'', a paired set of lateral tubercles can be found proximally on the blade, and while some spines curve anteriorly, the rest exhibit severe curving toward the pelvis.<ref name=":4" />
The purpose of the blades still remains unknown, although many theories have been postulated over the years. The use of the sail for thermoregulation, sexual dimorphism, and species identification are all hypotheses that have been applied to other sail-bearing taxa.<ref name=":4" /> A speculation more specifically related to ''Platyhystrix'' is that these neural spines could have served to stiffen the vertebral column in order to adapt to a more terrestrial lifestyle.<ref name=":9" />
==Paleobiology== [[Image:EdaphosaurusDB.jpg|thumb|left|''Platyhystrix'' (small, foreground) and ''Edaphosaurus'']] ''Platyhystrix'' may have been preyed upon by larger temnospondyls such as ''Eryops'', or by larger carnivorous reptiles, which were becoming more common and diverse in the drier climate of the Permian. The skull was large and strongly built, with a frog-like face. ''Platyhystrix'' had a compact body, reaching {{convert|1|m|ft}} long including the tail, and its short, sturdy legs indicate a mainly terrestrial life.<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= 52|isbn= 1-84028-152-9}}</ref>
''Platyhystrix'' appeared rather unusual: the dorsal vertebrae were extraordinarily lengthened, and in life they probably formed a skin-covered sail. This structure was possibly for thermal regulation, as in other animals of similar appearance, such as the pelycosaurs ''Dimetrodon'' and ''Edaphosaurus''. The back of ''Platyhystrix'' was also covered with thick hard plates, similar to those of its near relative, ''Cacops''.<ref name=EoDP/>
== Stratigraphic and geographic range == ''Platyhystrix'' is primarily known from Early Permian formations from the southwestern United States. They are the most common rhachitomous amphibian fossils found in Wolfcampian age formations (~295-280 mya.), with one exception being El Cobre Canyon in north-central New Mexico, which has been debated as being dated around the early Permian or late Pennsylvanian (a stage of the Late Carboniferous).<ref name=":5" />
The best casting of neural spines comes from the Cutler Formation in southwestern Colorado. The part of the formation in which the specimens were collected were confidently identified as belonging to the Wolfcampian age of the Early Permian, with the sediment composition denoting the presence of an ancient lake or river.<ref name=":8" />
Additional neural spines have been found in sites scattered around New Mexico, southeastern Utah, and southwestern Colorado.<ref name=":5" /><ref name=":6" /> Vaughn further describes one of the most productive regions of the Early Permian Cutler Formation as the "''Platyhystrix'' pocket" during his field work there in 1962, due to the diversity and number of well preserved specimens found in the red sandstone. Although this site was named for the fossil, only a few neural spines and a rib bone were discovered.<ref name=":6" />
The best cranial specimen was found by David Baldwin near Rio Puerco, New Mexico in 1881. The presence of a fragmented neural spine on the skull's ventral surface indicated that it did indeed belong to a ''Platyhystrix'' specimen.<ref name=":5" /> Although found in the 19th century, it would take another 100 years for the specimen to be described by David Berman in 1981.
== Paleoecology == New Mexico, and other states in the Rocky Mountain regions, were situated about ten degrees north of the equator, on the western edge of Pangea during the Early Permian.<ref name=":10">{{Cite journal |last=Mack |first=Greg H. |date=2003 |title=Lower Permian terrestrial Paleoclimatic indicators in New Mexico and their comparison to paleoclimate models |journal=Geology of the Zuni Plateau |pages=231–240 |publisher=New Mexico Geological Society |doi=10.56577/ffc-54.231|isbn=978-1-58546-089-2 }}</ref> Throughout the Wolfcampian stage, most of northern and central New Mexico was composed of rivers which emptied into a shallow sea. The rivers that deposited the Abo Formation were made of fine silt beds, and were up to 8 m deep and 50 m wide, and reflect semi-arid and semi-humid conditions suggested by paleosols found on adjacent floodplains. These river size estimations infer a yearly precipitation rate between 30–100 cm/year.<ref name=":10" />
The vertebrate and plant fossil composition of these areas also provide insights as to the relative paleoclimate which supported these communities. The infrequent paleoflora (conifers, seed ferns, and Walchia) found in these areas are all species known to be adapted to xerophytic (dry) conditions.<ref name=":10" /> It is also believed that these kinds of plants began to dominate the American Southwest as the Early Permian climate trended toward drier and more seasonal conditions.<ref>{{Cite journal |last1=DiMichele |first1=William A. |last2=Aronson |first2=Richard B. |date=June 1992 |title=The Pennsylvanian-Permian Vegetational Transition: A Terrestrial Analogue to the Onshore-Offshore Hypothesis |journal=Evolution |volume=46 |issue=3 |page=807 |doi=10.2307/2409648 |jstor=2409648 |issn=0014-3820}}</ref> Vertebrate fossils found at these Wolfcampian sites consist of fish, amphibians, and reptiles, including charismatic pelycosaur reptiles such as ''Edaphosaurus''. The presence of large ectotherms, assuming that these extant reptiles are similar to modern day species, hints at a daytime temperature range between 25-41 °C, and not dropping below 5 °C in the winter season.<ref name=":10" />
== Phylogeny == ''Platyhystrix'''s relationship within and amongst the Dissorophidae family has been highly contested since its discovery and description. Carroll and DeMar spent the 1960s attempting to explain the relationships amongst the wide variety of genera within the family, and while their phylogenies depicted differing conclusions, they had reached a general consensus when it came to the basal versus advanced groupings.<ref name=":5" /> While the skull described by Berman in 1981 was able to provide better context, DeMar's logic placed ''Platyhystrix'' as more structurally advanced than other Wolfcampian dissorophids.<ref>{{Cite book |last=De Mar |first=Robert Eugene |title=The phylogenetic and functional implications of the armor of the Dissorophidae / Robert E. DeMar -- |date=1966 |publisher=Field Museum of Natural History |location=[Chicago] |doi=10.5962/bhl.title.5351 }}</ref> Carroll's logic (based on vertebral armor evolution) placed ''P. rugosus'' at a more basal position amongst Permian dissorophids, with the closest sister taxon being ''Aspidosaurus'' of the late Pennsylvanian.<ref>{{Cite book |last=Carroll |first=Robert L. |title=Early evolution of the dissorophid amphibians. |date=1964 |publisher=The Museum |oclc=4425765}}</ref>
In 2012, Schoch produced the most comprehensive dissorophid temnospondyl phylogeny to date, analyzing 25 taxa and 70 characters in total. The result of this analysis placed ''Platyhystrix'' and ''Aspidosaurus'' as successive sister taxa of all other dissorophids.<ref name=":1" /> ''Platyhystrix'' was separated from ''Aspidosaurus'' using two osteoderm characters, and this placement additionally agrees with the stratigraphy of fossil discovery.<ref name=":1" />
More recently, new phylogenetic analyses have been produced in order to better understand the evolution of modern day lissamphibians, due to the increasing consensus that their monophyletic group is derived from Temnospondyli.<ref name=":7" /> In 2019, Atkins, Reisz, and Maddin used characters relating to braincase simplification over time to construct a new phylogeny of lissamphibian origin. Based on the characters used in parsimony analysis, ''Platyhystrix'' was noted as having a much more basal position relative to Schoch's findings, as a sister taxon to the Olsoniformes clade.<ref name=":7" />
Cladogram produced by Schoch (2012):<ref name=":1" />
{{clade|{{clade |label1=Micromelerpetontidae |1={{clade |1=''Micromelerpeton''}} |2={{clade |label1=Amphibamidae |1={{clade |1=''Platyrhinops'' |2=''Doleserpeton''}} |label2=Olsoniformes |2={{clade |label1=Trematopidae |1={{clade |1=''Ecolsonia'' |2=''Fedexia'' |3={{clade |1=''Tambachia'' |2=''Anconastes'' |3={{clade |1=''Phonerpeton'' |2=''Acheloma''}} }} }} |label2='''Dissorophidae''' |2={{clade |1=''Platyhystrix'' |2={{clade |1=''Aspidosaurus'' |2={{clade |1=''Conjunctio'' |label2=Dissorophinae |2={{clade |1=''Dissorophus'' |2=''Broiliellus texensis'' |3=''Broiliellus brevis'' |4=''Broiliellus olsoni''}} |label3=Eucacopinae |3={{clade |1=''Brevidorsum'' |2={{clade |1=Admiral taxon (''Scapanops'') |2=Rio Arriba taxon (''Conjunctio'') |3={{clade |1=''Cacops morrisi'' |2=''Cacops aspidephorus'' |3={{clade |1=''Kamacops'' |2=''Zygosaurus'' }} }} }} }} }} }} }} }} }} }}|style=font-size:100%;line-height:100%|label1=Dissorophoidea}}
==References== {{Portal|Paleontology}} {{Reflist}} {{Refbegin}} * Vertebrate Palaeontology by Michael J. Benton and John Sibbick * The Simon & Schuster Encyclopedia of Dinosaurs and Prehistoric Creatures: A Visual Who's Who of Prehistoric Life by Barry Cox, Colin Harrison, R.J.G. Savage, and Brian Gardiner * Bibliography Of Fossil Vertebrates 1934-1938 by C. I. Camp {{Refend}}
{{Euskelia|D.}} {{Taxonbar|from=Q135586}}
Category:Dissorophidae Category:Carboniferous temnospondyls of North America Category:Cisuralian temnospondyls of North America Category:Permian geology of Texas Category:Prehistoric amphibian genera Category:Cutler Formation Category:Fossil taxa described in 1910