Biodiversity of the upper Ordovician Bol'shaya Kos'yu reef (Northern Urals)

In the structure of the Bol'shaya Kos'yu reef, four intervals corresponding to the phases/ stages of growth are established. The highest biodiversity of the reef ecosystem is typical for interval III, while for the final stage IV - it is the lowest. The frame-building organisms are dominated by stromatoporoids, tabulates and sphinctozoan. For the first time, a wide distribution and taxonomic diversity of sphinctozoan in the Upper Ordovician reefs of the Urals is recognized. They were mostly cryptobionts, lived in environments conducive to other Metazoa, and had, thus, their own ecological niche. However, with the deterioration of living conditions, they quickly adapted to changing environmental conditions and became one of the dominant groups among frame-building organisms.