Article: All change at the Cretaceous–Tertiary boundary? Echinoids from the Maastrichtian and Danian of the Mangyshlak Peninsula, Kazakhstan

The Maastrichtian and Danian echinoid fauna of the Mangyshlak Peninsula, Kazakhstan is revised on the basis of new collections from three localities representing both a shallow water calcarenite facies and a deeper water chalk facies. The two chalk sections sampled have no biostratigraphically detectable breaks across the Cretaceous-Tertiary boundary.Sixteen species in 11 genera are recognized, including one new species, Cycluster galei. Of these, 13 species are found only in Maastrichtian strata. The remaining three are found only in the Danian giving an apparent species extinction rate of 100 per cent, across the Cretaceous-Tertiary boundary in Mangyshlak. However, inspection of occurrence data from localities outside Kazakhstan shows that many of these species are in fact longer ranging than the Mangyshlak occurrences alone suggest. If this global data is taken into account the species extinction rate drops to 60 per cent, and the generic extinction rate to 25 per cent. This pattern of local extinction and replacement is repeated in other Cretaceous-Tertiary sections (e.g. in Denmark and at Maastricht).The Maastrichtian chalk of Mangyshlak contains a diverse echinoid fauna and includes some taxa indicative of shallower water conditions. In contrast, the Danian contains only a small number of exclusively deep water forms. This change in local faunal content may be explained either in terms of a facies shift from shallower to deeper water conditions or by the recolonization of shelf habitats by surviving deep water clades.