230 / 2025-04-15 15:38:40

The Chinese pareiasaurs Revised: Taxonomical validity and phylogenetic framework of late Permian pareiasaurs.

Permian, Pareiasauria, Chinese pareiasaurs, phylogenetic relationship.

Theme 3: Earth-Life Co-evolution Through Time > Session 3i: Terrestrial Extinction Events and Their Driving Mechanisms in Earth History

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 have remained controversial for several decades, primarily due to the poor preservation of the known specimens. Since the 1960s, eight Chinese pareiasaur species have been described, including Shihtienfenia permica and Shihtienfenia completus from Baode, Shanxi (Young and Yeh 1963; Wang et al. 2019); Shansisaurus xuecunensis, Huanghesaurus liulinensis, and Sanchuansaurus pygmaeus from Liulin, Shanxi (Cheng 1980; Gao 1983, 1989); Honania complicidentata and Tsiyuania simplicidentata from Jiyuan, Henan (Young 1979); and Elginia wuyongae from Baotou, Inner Mongolia (Liu and Bever 2018). Among these species, only Shihtienfenia completus is based on a complete skull, the other species were established based on either postcranial material or incomplete skulls or mandibles (Benton 2016). Therefore, it is not surprising that the taxonomy and phylogenetic relationships of Chinese pareiasaurs have remained controversial.

The latest study describes a mid-sized pareiasaur, Yinshanosaurus angustus from the Naobaogou Formation. The skeleton of Y. angustus provides the complete cranial and articulated postcranial details of Chinese pareiasaurs for the first time. In phylogeny, Y. angustus and S. completus form a monophyletic clade characterized by a unique combination of features, including the extremely pointed snout, orbit dorsoventrally expanded to form an ellipse shape, the presence of a prominent postfrontal horn, a pineal foramen located midway along the interparietal suture, and tabular sutures in the midline that encircle the postparietal. Furthermore, the postorbital region of the skull is shorter than the preorbital region. This newly identified monophyletic group forms a sister clade to Pumiliopareiasauria, distinguishing it from other pareiasaurs.

This analysis yields three distinct phylogenetic positions for the Chinese pareiasaurs and establishes a new clade including S. completus and Y. angustus. Although the newly discovered complete skull has enhanced the framework, the controversy surrounding the phylogenetic relationships of Chinese pareiasaurs, which is attributed to the indirectly compared elements still needs improvement.

In this study, extensive additional preparations were conducted on the holotype of Huanghesaurus and Shihtienfenia. Comprehensive cranial and postcranial description of Chinese pareiasaurs is provided, the autapomorphies of the named species are revised. The abundant disassociated postcranial elements from Baode locality can be categorized into two morphotype respectively, one represents Honania and Yinshanosaurus, another represents S. permica and S. completus. Additionally, Shansisaurus and Sanchuansaurus are classified as Shansisaurus, while Huanghesaurus is retained for the unique osteoderms. The proposed phylogenetic framework supports a stable monophyly that includes all mid-sized Chinese pareiasaurs. The closer relationship between African and Chinese pareiasaurs is confirmed.