The tetrapod fauna of the upper Permian Naobaogou Formation of China: a new species of Elginia (Parareptilia, Pareiasauria)

The pareiasaur fossil record in China is poor compared to that of Russia or South Africa. A new pareiasaur specimen is here reported from the upper Permian Naobaogou Formation of the Daqing Mountains, Nei Mongol, China. It is recognized as a new species of Elginia, a taxon otherwise known only from the upper Permian Cutties Hillock Sandstone of Scotland. Diagnostic features include a moderately developed cheek flange; prominent otic notch (formed between squamosal and quadratojugal at the posterior margin of the temporal plate); enlarged supraorbital bosses on prefrontal, postfrontal, and postorbital; a hypertrophied supratemporal horn, and squamosal horn prominently projecting posteriorly from caudal margin of temporal plate. The new taxon is differentiated from E. mirabilis by a well-developed and crescentic postfrontal boss, which is the largest among a series of circumorbital bosses; upper orbital border distinctly domed with a smooth rather than angled anterodorsal margin; lesser developed cranial bosses, basal confluence of the transverse process and postzygapophysis produces at horizontal flange in some dorsal vertebrae. The new discovery significantly extends the geographic distribution of Elginia and Elginiidae.

相较于俄罗斯与南非的副爬行类（pareiasaur）化石记录，中国该类群的化石记录较为匮乏。本次研究报道了一件产自中国内蒙古大青山地区上二叠统脑包沟组（Naobaogou Formation）的副爬行类新标本。该标本被归入埃尔加蜥属（Elginia）的一个新物种，该属此前仅发现于苏格兰上二叠统的卡蒂希尔砂岩（Cutties Hillock Sandstone）中。该新种的鉴别特征如下：具中等发育的颊突（cheek flange）；显著的耳凹（otic notch，由颞板（temporal plate）后缘的鳞骨（squamosal）与方轭骨（quadratojugal）共同围成）；前额骨（prefrontal）、后额骨（postfrontal）及眶后骨（postorbital）上具膨大的眶上隆脊（supraorbital bosses）；特化膨大的颞上角（hypertrophied supratemporal horn），以及从颞板后缘显著向后突出的鳞骨角（squamosal horn）。该新类群与奇异埃尔加蜥（E. mirabilis）的区别在于：其一，具发育良好的新月形后额骨隆脊，该隆脊为眶周隆脊系列中最大的一个；其二，眶上缘明显隆起，其前背缘平滑而非棱角状；其三，颅顶隆脊发育程度较弱；其四，部分背椎的横突（transverse process）与后关节突（postzygapophysis）在基部愈合，形成水平突缘。此次新发现极大地扩展了埃尔加蜥属（Elginia）及埃尔加蜥科（Elginiidae）的地理分布范围。