2021 年 37 巻 p. 22-29
Thalassionema bacillare, which is a temperate and warm-water species in modern oceans, was recently revealed to have been one of the major diatom species in the subpolar North Atlantic around the Pliocene–Pleistocene boundary. In this study, the morphology of T. bacillare was examined through detailed observation of fossils collected from upper Pliocene to lower Pleistocene sediments in the subpolar North Atlantic. Although many morphological characteristics of the fossil valves examined in this study are consistent with results from previous studies of modern specimens of T. bacillare, there are some new important findings. For example, the fossil valves often have apical pores and lack spines on the tapered apex, though this is likely related to the weak silicification of the examined fossil valves. In addition, the minimum valve length is much shorter than previously reported, and external openings of rimoportulae differ slightly in shape between both poles. Fossils of T. bacillare are potential proxies for reconstructing paleoceanographic conditions because of the species’ limited modern distribution.
