Diversity of late Ordovician rugose corals in Baltoscandia: role of environmental changes and comparison with other areas

Regional biodiversity curves are controlled environmentally and reveal details that can be correlated with stable isotope data, sea level curves, etc. This paper uses such ties for better understanding of the environmental background of certain palaeobiological events. The first appearance of rugose corals in the shelf seas of Baltica in the Middle Caradoc s eems to be linked to the warming of sea water and climate due to the drift of the continent closer to the equator. The same factor also favoured a further biodiversity rise in which both biology and ecology should be considered. The general diversity rise was slowed down by repeated coolings in the late Caradoc and early Ashgill and caused a diversity low within the early Ashgill. Along with a favourable temperature regime, changes in oceanic circulation, nutrient flow, and availability of suitable habitats were of great importance. The Hirnantian glaciation, accompanied by a pronounced sea level fall, brought about favourable conditions for coral evolution on many subequatorial cratonic shelves, which helped corals to survive the severe conditions of the end-Ordovician glacial time. The Baltoscandian rugose coral assemblage is the most diverse by comparison with those of Australasia and Laurentia thanks to the abundance of old lambelasmatids living in relatively cooler and deeper habit.