Abstract
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. Megaspores were studied in detail with scanning electron microscopy, including fractures that allow examination of the wall structure. Molaspora (Marsileales) is the most distinctive component of the assemblage, with a spirally twisted acrolamella. The other megaspores share three laesurae and a granular exospore structure that is ordered to varying degrees. The most abundant megaspores are Erlansonisporites and Verrutriletes, followed by Bacutriletes and Trileites. The regular orientation of exospore granules in Erlansonisporites suggests a selaginellalean affinity. Evidence from the new assemblage indicates that the Marsileales and Selaginellales were components of the late Cretaceous paleoflora on the eastern side ...
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