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Evolutionary lineages within the conical agglutinated family Orbitolinidae are mainly evidenced by the increased complexity of their inner structure. In this respect, gradual changes in the exoskeleton resulting in the evolution of beams and rafters in the marginal zone refer above all to lineages within the subfamily Dictyoconinae. In contrast hereto, the increasing size and complexity of the simple megalospheric embryo as well as the reduction of the initial spiral stage defines lineages within the subfamily Orbitolininae (e.g.,  Praeorbitolina-Mesorbitolina ). The case of the upper Aptian–middle Albian  Simplorbitolina  lineage, the ancestor-descendant relationship of the three species  S. aquitanica, S. manasi , and  S. conulus  represents a rare example of the Dictyoconinae displaying a successive reduction of the initial spiral stage along with an increase of both embryo size and complexity of the marginal zone. This process, which is known as spiral reduction or nepionic acceleration, is well recorded from other groups of Larger Benthic Foraminifera (fossil and extant) such as the calcareous Rotaliida. The occurrences and palaeogeographic distributional pattern of Simplorbitolinas are reviewed. The present study is preliminary based on a well-preserved assemblage of megalospheric specimens of  Simplorbitolina aquitanica  (Schroeder) from the upper Aptian Reocín Formation of northern Spain (Cantabria).

The upper Aptian–middle Albian Simplorbitolina lineage: an example of nepionic acceleration in Lower Cretaceous Orbitolinidae (Foraminifera)