Fossil megaspores of Marsileales and Selaginellales from the upper Coniacian to lower Santonian (Upper Cretaceous) of the Tamagawa Formation (Kuji Group) in northeastern Japan

Bulk sieving of sedimentary samples from upper Coniacian to lower Santonian (Upper Cretaceous) of the Tamagawa Formation (Kuji Group) in northeastern Japan has yielded more than 600 fossil megaspores, which comprise the first megaspore assemblage to be described from the Cretaceous of Japan. Megaspo res were studied in detail with scanning electron microscopy, including fra ctures that allow examination of the wall structure. Molaspora (Marsileales ) is the most distinctive component of the assemblage, with a spirally twis ted acrolamella. The other megaspores share three laesurae and a granular e xospore structure that is ordered to varying degrees. The most abundant meg aspores are Erlansonisporites and Verrutriletes, followed by Bacutriletes a nd Trileites. The regular orientation of exospore granules in Erlansonispor ites suggests a selaginellalean affinity. Evidence from the new assemblage indicates that the Marsileales and Selaginellales were components of the la te Cretaceous paleoflora on the eastern side of Eurasia and expands previou s knowledge of the Cretaceous vegetation of this region.