Mohlerina basiliensis (Mohler, 1938): a Middle Jurassic–Early Cretaceous facultative (?) epilithic benthic foraminifer

摘要

Mohlerina basiliensis (Mohler, 1938) represents a common, cosmopolitan, shallow-water Middle Jurassic–Early Cretaceous trochospiral foraminifer. Given the numerous illustrations from thin-section specimens in the literature displaying tests dispersed within the matrix (micritic and sparitic), a free, vagile benthic mode of life is generally suggested. As an exceptional case, specimens are found with their tests attached to a variety of hard substrates, thus creating a special elevated microhabitat. The fixation is due to a calcitic cement. With its facultative sessile mode of life, Mohlerina can be compared with several modern calcareous trochospiral rotaliacean foraminifera (e.g., Ammonia, Cibicides, Discorbis). The rare preservation of fixed Mohlerina in situ is most likely due to physical taphonomic degradation (e.g., breakage). Tests of Mohlerina attached to hard substrates were found in both low- and high-energy paleoenvironments. The high test variability of Mohlerina might be influenced by the different settling strategies and substrate surface topographies within different paleohabitats.