Pteropods (Mollusca, Euthecosomata) from the Early Eocene of Rotterdam (The Netherlands)

A borehole was drilled at Rotterdam in 1955 as a demonstration during the E55 exhibition. Holoplanktonic molluscs (pteropods) were found to be present in the interval 504.5-655.0 m below rotary table (= RT). The upper sample of Middle Eocene (Lutetian) age yielded just a few unidentifiable limacinids. The section between 507.5-607.0 m, of Early Eocene (Ypresian) age, yielded poorly preserved pteropods and demonstrated that the complete interval belongs to pteropod zone 9. Apart from the most abundant species, Camptoceratops priscus, which is the index taxon of pteropod zone 9, the section yielded Heliconoides mercinensis and Limacina taylori, which are known to accompany the index species. Two further limacinid species are described as new to science, viz. Limacina erasmiana sp. nov. and L. guersi sp. nov., to date not known from elsewhere in the North Sea Basin. The occurrence of L. pygmaea in a restricted interval (569.0-574.0 m-RT) is remarkable; it is generally considered to be of Lutetian age, but also is found in the Ypresian of Gan, southwest France. Its occurrence in the E55 section is explained as a ‘sealevel related molluscan plankton event’, allowing species of oceanic distribution to enter the basin during sea level high stands, as was recently also demonstrated for several Oligocene pteropods.