Famennian and Tournaisian recoveries of shallow water Rugosa following late Frasnian and late Strunian major crises, southern Belgium and surrounding areas, Hunan (South China) and the Omolon region (NE Siberia)

The Rugosa remained almost totally absent from the platform environments of southern Belgium and surrounding areas, Hunan and Omolon during the long time interval between the end-Frasnian crisis and the early part of the late Famennian (marginifera Zone), probably owing to cool climatic conditions. They first reappear in the Upper marginifera Zone, but are uncommon and poorly diversified. Few of them belong to pre-Famennian genera. It is only near the beginning of Strunian time that rugose corals radiated and became common. Their morphological and allometric variabilities were very large, indicating their high potential for adaptation to free niches. This first radiation was abruptly terminated by an extinction event, and a second radiation quickly began, mainly from new taxa and only from a few previously known ones. In western Europe and in Hunan, this second radiation was also stopped abruptly, while species were evolving, by the Hangenberg event at the end of the Strunian. In Omolon, where the position of the Devonian–Carboniferous boundary is doubtfull, the second radiation may have been completed before the end of the Strunian, and probably the corals affected by the end-Famennian event were new ones, resulting from a third radiation. In the three regions and at each recovery, the rugose corals are endemic, indicating that marine connections were poor. After the Hangenberg event, surviving Rugosa reappeared almost immediately (except in South China) and were widespread, indicating good marine connections. However, they remained poorly diversified, sometimes until the late Tournaisian. The two major extinctions (end-Frasnian and end-Famennian) and the Strunian ones were responsible for the major taxonomic differences between pre-Famennian and post-Famennian Rugosa.