A cold-water brachiopod fauna from the upper Cisuralian (lower Permian) Kharnuden Formation at the Hovsugol section, southeastern Mongolia: systematic description and biogeographical implications

Abstract This study presents a comprehensive systematic analysis of a cold-water brachiopod fauna from the upper Cisuralian (lower Permian) Kharnuden Formation, exposed at the Hovsugol section in southeastern Mongolia. Taxonomic investigation identifies 40 species belonging to 28 genera, including three newly described taxa: Paramarginifera pentagona n. sp., Linoproductus planiconvexus n. sp., and Jilinmartinia hovsugolensis n. sp. Biostratigraphic evidence tentatively indicates a Kungurian age, with possible extension down into the Artinskian. The assemblage likely originated along the southern margin of the Siberian Craton, within the Paleo-Asian Ocean (PAO). The fauna exhibits strong biogeographic affinities with contemporaneous faunas from the Beishan orogenic belt (northwestern China), Inner Mongolia, South Primorye (Russia), and selected Japanese terranes, yet differs significantly from assemblages in Transbaikal and central-northeastern Mongolia. These contrasts support the presence of the Sino-Mongolian Seaway—a transitional marine corridor within the closing PAO. The fauna is characterized by elements of the northern Boreal biogeographic realm, with a dominance of cold-adapted and endemic taxa and a complete absence of paleotropical elements. Associated paleoecological indicators suggest the influence of cool-temperate conditions at a relatively high-latitude paleogeographic position as well as geographic isolation. This paleobiogeographic pattern sheds light on the responses of Permian marine ecosystems to plate convergence, latitudinal climate gradients, and oceanic current reorganization during the final stages of the PAO closure. UUID: http://zoobank.org/67bcfb84-2b08-46a7-a117-d86b79837c75