Late Cretaceous Orbitolinidae (Larger Benthic Foraminifera): Taxonomy, determination, biostratigraphy and palaeobiogeography

Abstract

Agglutinated larger benthic foraminifera with conical tests of the families Orbitolinidae and Coskinolinidae (not treated herein) underwent several periods of diversification and successive extinctions within the Lower Cretaceous (upper Berriasian)-Oligocene (Chattian) stratigraphical interval. Bounded by two extinctions events that affected severely most of the larger benthic foraminifera at the base (Cenomanian-Turonian boundary) and top (Maastrichtian-Paleogene or K-Pg boundary), the Orbitolinidae represents a distinct, but only marginal group within the so-called Late Cretaceous community maturation cycle. Compared to the greatest diversification encountered in the Lower-middle Cretaceous, the taxonomic diversity is reduced to ten genera in the Late Cretaceous (Turonian-Maastrichtian), most of which are monospecific including a total of 14 taxa with two of them treated in open nomenclature. Only the genus Dictyoconus Blanckenhorn survived the K-Pg boundary mass extinction event, being subsequently recorded in the Eocene of the Tethyan Realm. Out of the three subfamilies, only the Dictyoconinae and Dictyorbi-tolininae occur in the Upper Cretaceous, whereas the representatives of the Orbitolininae (with complex embryo) are absent. Marginal apertures, which were traditionally considered a characteristic feature of the Paleogene Orbitolinidae are recorded already during the Late Cretaceous (e. g. genus Dictyoconus). The stratigraphic ranges of the different taxa appear well-constrained only for a relatively small number of them, but in most cases are poorly known and therefore, reduce their applicability in biostratigraphic studies. Late Cretaceous Orbitolinidae are exclusively restricted to the Tethyan Realm including both margins; they are seemingly absent in the Pacific and American-Caribbean realms. Lineages that have been recorded within