A dvinosaurian temnospondyl from the Carboniferous-Permian boundary of Germany sheds light on dvinosaurian phylogeny and distribution

A complete skull and well-preserved postcranium of a dvinosaurian temnospondyl from the Carboniferous-Permian boundary of Germany is referred to a new genus and species, <i>Trypanognathus remigiusbergensis</i>. The skull closely resembles that of the early Permian dvinosaurian genus <i>Trimerorhachis</i> in outline and suture topology, but the occiput and the palate differ substantially. Derived states are the penetration of vomerine tusks through the splenial and symphyseal tusks through the premaxilla. <i>Trypanognathus</i> shares with dvinosauroids the lack of a squamosal embayment, an elongated basipterygoid process, a foreshortened palatine ramus exclusively reaching the ectopterygoid, the absence of pterygoid denticles, and enlarged palatal tusks. The body is elongate with well-ossified, but small limbs, the presacral count is ca. 28, and the pleurocentra are large and reached ventrally almost as far as the intercentrum. The new taxon nests within Dvinosauria above the trimerorhachid clade and <i>Erpetosaurus</i>, at the base of the broad-skulled dvinosauroids. <i>Trypanognathus</i> occurs in a tetrapod fauna that closely resembles early Permian assemblages of western North America, with which it shares sphenacodontid and edaphosaurid synapsids, as well as eryopid temnospondyls.

一件产自德国石炭纪-二叠纪界线（Carboniferous-Permian boundary）地层的完整头骨及保存完好的颅后骨骼（postcranium），被归入新属新种**瑞米根刺颌螈（Trypanognathus remigiusbergensis）**，该类群属于双椎螈类（dvinosaurian）离片椎类（temnospondyl）。该头骨在轮廓与骨缝拓扑结构（suture topology）上，与早二叠世双椎螈类的**三叠螈属（Trimerorhachis）**高度相似，但枕区（occiput）与腭部（palate）结构差异显著。其演化衍生特征（derived states）包括：犁骨獠牙（vomerine tusks）穿透夹板骨（splenial），下颌联合獠牙（symphyseal tusks）穿透前颌骨（premaxilla）。**刺颌螈属（Trypanognathus）**与双椎螈超科（dvinosauroids）共享以下共有特征：无鳞骨凹（squamosal embayment）、基翼突（basipterygoid process）延长、腭骨支（palatine ramus）缩短且仅延伸至外翼骨（ectopterygoid）、无翼骨小齿（pterygoid denticles），以及增大的腭齿（palatal tusks）。该类群躯体修长，四肢骨化良好但体型小巧；荐椎前椎骨（presacral）数目约为28枚；侧椎体（pleurocentra）硕大，腹侧延伸范围几乎与间椎体（intercentrum）持平。该新分类群（taxon）隶属于双椎螈类（Dvinosauria），处于三叠螈科支系（trimerorhachid clade）与**蛇颈螈属（Erpetosaurus）**之上，位于宽头骨双椎螈超科（broad-skulled dvinosauroids）的基部位置。**瑞米根刺颌螈（Trypanognathus remigiusbergensis）**所在的四足动物群（tetrapod fauna）与北美西部早二叠世的四足动物组合群（assemblages）高度相似，二者共享楔齿龙科（sphenacodontid）、基龙科（edaphosaurid）合弓类（synapsids）以及离螈科（eryopid）离片椎类类群。