The Upper Ordovician Katian Stage Bryozoans from the Dzheromo Formation of the Moyerokan River Section (Northern Siberian Platform) and Their Paleogeographical Significance

In the upper part of the Dzheromo Formation (Dolborian Regional Stage, Katian Stage, Upper Ordovician) along the Moyerokan River (Northern Siberian Platform), seventeen bryozoan species were revealed, seven from which, owing to the poor preservation of the colonies, were identified in an open nomenclature. The bryozoans belong to ten genera from four orders: Cystoporata ( Constellaria vesiculosa (Modzalevskaya in Modzalevskaya et Nekhoroshev), Lunaferamita ? sp.), Trepostomata ( Calloporella sp. 1, Calloporella sp. 2, Stigmatella sp., S. convestens Astrova in Ivanova et al., Batostoma varians (James), Orbignyella moyerokanensis sp. nov., Leptotrypa sp.), Fenestrata ( Parachasmatopora sp.), and Cryptostomata ( Phaenopora plebeia Nekhoroshev in Modzalevskaya et Nekhoroshev, P. pennata Nekhoroshev, P. erecta Nekhoroshev in Modzalevskaya et Nekhoroshev, P. carinata Nekhoroshev, P. viluensis Nekhoroshev in Modzalevskaya et Nekhoroshev, Phaenoporella sp., and Ph. multipora Nekhoroshev). The genera Lunaferamita , Orbignyella , and Parachasmatopora were first found in the Ordovician of the Siberian Platform, and the genus Calloporella was found in the Dolborian Regional Stage. The species O. moyerokanensis sp. nov. is endemic to Northern Siberia, while the majority of the species have a wide geographic distribution. The studied bryozoan complex demonstrates some connection with bryozoan assemblages from the Taimyr Peninsula, Kotelny Island, the Sette-Daban Ridge, and Mongolia at the species level. At the generic level, it is close to the bryozoan assemblages from Laurentia, Baltica, the Argentine Precordillera, and China.