The tetrapod fauna of the upper Permian Naobaogou Formation of China: a new mid-sized pareiasaur Yinshanosaurus angustus gen. et sp. nov. and its implication for the phylogenetic relationship of pareiasaurs

Pareiasauria is a specialized clade of herbivorous tetrapods that existed throughout Pangaea during the mid to late Permian period. The phylogenetic relationships of Chinese pareiasaur species remain controversy for several decades, primarily due to the poor preservation of known specimens. 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 high and narrow skull, with the length of the skull table exceeding the width between the two quadratojugals; snout dimension as high as wide; long frontal with a length-to-width ratio of [~]3.0; U-shaped paraoccipital process in occipital view; and maxillary teeth oriented vertically, with only 7-9 cusps. Although the phylogenetic framework of pareiasaurs still requires further refinement, the current analysis yields distinct phylogenetic positions for Chinese pareiasaurs and establishes a new monophyletic clade that includes S. completus and Y. angustus.