Planktic propagules as a potential long-distance dispersal mechanism of Cretaceous serial rotaliid benthic foraminifera

Abstract Conventionally, foraminifera were divided into two separate planktic and benthic taxonomic groups. However, more recent molecular studies call this paradigm into question, showing that mode of life of foraminifera is not diagnostic of their taxonomic affiliation. Our study shows that some Cretaceous benthic foraminifera might be more ecologically flexible than traditionally believed. World-wide paleogeographic range along with a bimodal distribution of Mg/Ca ratio for Cretaceous benthic foraminifera with serially arranged chambers suggest their propagule dispersal mechanism and a tychopelagic mode of life (i.e. the ability to occupy both planktic and benthic domains). The studied taxa possess a poremound ornamentation and/or delicate pustules that are relatively rare in benthic species and more common in planktics. It is inferred that pore-mounded test texture might have been an exceptional morphological advantage, which evolved in rotaliid foraminifera during the Mesozoic and Cenozoic. This adaptation had likely enhanced the ability to float and became a bridge between a benthic and planktic foraminiferal mode of life.