The tetrapod fauna of the upper Permian Naobaogou Formation of China: a new mid‐sized pareiasaur <i>Yinshanosaurus angustus</i> and its implications for the phylogenetic relationships of pareiasaurs

Abstract Pareiasauria are a specialized clade of herbivorous tetrapods that existed throughout Pangaea during the middle–late Permian period. The phylogenetic relationships of Chinese pareiasaur species have remained controversial for several decades, primarily due to the poor preservation of the known specimens. For example, until the report of Shihtienfenia completus in 2019, no complete skull had been documented for Chinese pareiasaurs. The present study describes a mid‐sized pareiasaur, Yinshanosaurus angustus gen. et sp. nov., based on a nearly complete skull and an articulated partial postcranial skeleton collected from the Naobaogou Formation in 2018. It presents several significant new morphological features such as the narrowest skull of all pareiasaurs, with skull length more than twice skull width at the lateral edges of the cheeks (quadratojugals), a forked nasal posterior projection, a notch on the tabular posterior margin, and a unique combination of characters: U‐shaped paraoccipital process, snout as wide as high, long frontal with a length‐to‐width ratio greater than 2.0, and maxillary teeth oriented vertically. Although the phylogenetic framework of pareiasaurs still requires further refinement, the current analysis yields three distinct phylogenetic positions for the Chinese pareiasaurs and establishes a new clade including S . completus and Y . angustus .