Taxonomic use of the exoskeleton in the family Orbitolinidae (Foraminifera): Aplea for a uniform Cretaceous/Paleogene approach

Abstract

Based on the distinctly higher number of species of Orbitolinidae in the Cretaceous compared to the Paleogene, the former have witnessed much more taxonomic analyses. Although, there has been a "lively" debate among specialists working on Cretaceous taxa, it is rather broad consensus that the presence/absence of horizontal partitions (= rafters; part of exoskeleton) in the marginal zone is a criterion of specific rank. Recently, however, another taxonomic concept has been used for Paleogene Orbitolinidae by giving this trait generic rank (Fallotella vs. Pseudofallotella). If applied to the Cretaceous, this approach would result in artificial groups and the creation of several new genera for currently used species that both include species with and without rafters (Coskinolinella, Heterocoskinolina, Montseciella, Paracoskinolina, Praedictyorbitolina, Simplorbitolina, Valserina). The present contribution is a plea for a uniform taxonomic approach, preferring the simpler, longer, wider and more natural usage of the "Cretaceous approach". Further difficulties on the taxonomical ranking of Orbitolinidae features are due to their fossil nature (extinct group), as no modern representatives are available for comparisons. This fact also speaks for the use of a pragmatic and uniform approach.