Arachana

{{Short description|Extinct genus of amphibians}} {{Automatic taxobox | fossil_range = [[Late Permian]] or [[Early Triassic]] | taxon = Arachana | authority = Piñeiro ''et al.'', [[2012 in paleontology|2012]] | type_species = {{extinct}}'''''A. nigra''''' | type_species_authority = Piñeiro ''et al.'', 2012 }}

'''''Arachana''''' is an [[extinct]] [[genus]] of [[rhinesuchid]]-like [[temnospondyl]] known from the [[Late Permian]] to [[Early Triassic]] [[Buena Vista Formation]] of northeastern [[Uruguay]]. ''Arachana'' was first named by Graciela Piñeiro, Alejandro Ramos and Claudia Marsicano in [[2012 in paleontology|2012]] and the [[type species]] is ''A. nigra''. It shares characteristics with both rhinesuchids and [[lydekkerinid]]s, making it a transitional form between basal and more advanced [[stereospondyl]]s.<ref name=Arachana>{{cite journal |last=Piñeiro |first= Graciela |authorlink=Graciela Piñeiro |last2=Ramos |first2=Alejandro |last3=Marsicano |first3=Claudia |name-list-style=amp |year=2012 |title=A rhinesuchid-like temnospondyl from the Permo-Triassic of Uruguay |journal=[[Comptes Rendus Palevol]] |volume=11 |issue=1 |pages=65–78 |doi=10.1016/j.crpv.2011.07.007 }}</ref>

==Description== ''Arachana'' is known from the [[holotype]] FC-DPV 1369, a three-dimensionally preserved nearly complete [[skull]] that has not been distorted. It was collected in the Colonia Orozco locality from the [[Buena Vista Formation]] of the [[Parná Basin|Norte Basin]]. The formation spans the boundary between the [[Permian]] and the [[Triassic]], and it is uncertain whether FC-DPV 1369 was found in rocks above or below the boundary.<ref name=Arachana/>

''Arachana'' shares several characters with [[rhinesuchid]]s. For example, it has a large head with [[orbit (anatomy)|orbits]] or eye sockets placed slightly behind the mid-length of the skull. The surface of the skull is deeply pitted and the margins of the cheek regions are smooth and convex. The [[basioccipital]] bone at the back of the skull is small. On the [[palate]], the [[pterygoid bone]] is connected to the [[vomer]] by a projection called the palatal ramus. The ramus separates the interpterygoid vacuities, two large holes in the palate. In many temnospondyls, the [[palatine bone|palatine]] and [[ectopterygoid bone]]s also touch the vacuities, but in ''Arachana'' and rhinesuchids, the palatine ramus excludes these bones from the vacuity margins.<ref name=Arachana/>

''Arachana'' also has characteristics of a more [[Synapomorphy|derived]] group of stereospondyls called [[lydekkerinid]]s. In both ''Arachana'' and lydekkerinids, the [[otic notch]] in the back of the skull is shallow and is not touched by the [[supratemporal bone]] as is otherwise the case in temnospondyls. Sensory [[sulci]], grooves in the skull that held a [[lateral line]] system in life, run across the [[lacrimal bone]] but are not angled sharply as in other temnospondyls. On the palates of both ''Arachana'' and lydekkerinids, rows of palatine teeth are relatively small and the main body of the pterygoid bone is covered in small projections. None of these features are present in rhinesuchids, suggesting that ''Arachana'' was a [[transitional form]] between basal stereospondyls like rhinesuchids and more advanced forms like lydekkerinids.<ref name=Arachana/>

The transitional features of ''Arachana'' place it as part of an entire transitional fauna that existed around the Permo-Triassic boundary. While it is uncertain whether ''Arachana'' lived before or after the [[Permian-Triassic extinction event]], its transitional position shows that some temnospondyls were diversifying rather than diminishing across the boundary.<ref name=Arachana/>

==Phylogeny== Below is a [[cladogram]] from the analysis of Piñeiro ''et al.'' (2012):<ref name=Arachana/>

{{clade| style=font-size:100%;line-height:100% |label1=[[Stereospondyli]] |1={{clade |1=''[[Peltobatrachus]]'' |2={{clade |1=[[Rhinesuchidae]] |2={{clade |1='''''Arachana''''' |2={{clade |1={{clade |1=''[[Watsonisuchus]]'' |2={{clade |1=''[[Benthosuchus]]'' |2=''[[Lydekkerina]]''}} }} |2={{clade |1=''[[Arcadia (genus)|Arcadia]]'' |2={{clade |1=''[[Sangaia]]'' |2={{clade |1=''[[Uruyiella]]'' |2={{clade |1=''[[Laidleria]]'' |2={{clade |1=''[[Keratobrachyops]]'' |2={{clade |1=''[[Bothriceps]]'' |2={{clade |1=''[[Pneumatostega]]'' |2=[[Plagiosauridae]] }} }} }} }} }} }} }} }} }} }} }} }}

== References == {{Reflist}}

[[Category:Stereospondyli]] [[Category:Triassic temnospondyls of South America]] [[Category:Triassic Uruguay]] [[Category:Fossils of Uruguay]] [[Category:Paraná Basin]] [[Category:Fossil taxa described in 2011]]