Уear of publication: 2026

The Katian is a critical stage that witnessed the last acme of the Great Ordovician Biodiversification Event (GOBE), marked by the diversification and provincialism of shallow-water brachiopod faunas in the tropical and temperate regions. The knowledge of brachiopods from the Qilian Mountains, northern Qinghai-Xizang (Tibet) Plateau, was limited due to the difficulty of access to the fossil site. In this study, a shallow-water Altaethyrella brachiopod fauna from the Qilian Mountains was collected and identified, revealing totally 15 genera and 15 species. The brachiopods Sulcatospira qinghaiensis (Xu in Jin et al., 1979) and Altaethyrella gentilis (Xu in Jin et al., 1979) are the two most abundant and representative species in this fauna. Statistical analyses (i.e., cluster analysis, principal co-ordinates analysis, and network analysis) of late Katian (Ka4) shallow-water brachiopod faunas from China, Mongolia, Russia, Kazakhstan, and eastern Europe imply that the fauna from the Qilian Mountains has the highest affinity with faunas from the Tarim paleoplate of Northwest China, South China, and Kazakhstan. The studied fauna can be distinguished from the contemporaneous faunas from Mongolia, Siberian Platform, and Altai Mountains. Mid-Boda cooling enhanced the thermohaline ocean circulation, contributing to the wide distribution of the Altaethyrella fauna in the tropical Proto-Tethys. The complexity of the environmental settings and regional lithofacies fostered diverse brachiopods, making these communities evolutionary hot spots prior to the Late Ordovician Mass Extinction (LOME).