Ordovician corals of the Siberian and Mongolian basins: Taxonomic diversity, morphogenesis, and occurrence

Taxonomic diversity, structural peculiarities, and occurrence of the Ordovician corals Tabulatoidea, Heliolitoidea, Rugosa, and Cyrtophyllida from the Siberian and Mongolian basins are analyzed. The corals settled in the Siberian basin almost for 1.5 million of years earlier than in the Mongolian basin. First corals in the Siberian basin were found in the lowermost Muktei Horizon (Llanvirn, i.e. Darriwilian Stage) while first corals in the Mongolian basin are known from the lower part of the Bairim Horizon (Late Caradoc, i.e. lower part of the Katian Stage). First corals in both basins belonged to the subclass Tabulatoidea