EARLY EVOLUTION OF PRIMITIVE ANGIOSPERMS IN CRETACEOUS

本文初步描述了日本本州东北部福岛县神北町出露的阿希泽组(上白垩统科尼亚西统下部)Asamigawa组中的一组新的植物化石(Kamikitaba Mesofossil植物群)。这些化石很小，是三维的，木炭化或木质化(中化石)，扫描电子显微镜研究时会产生精致的结构细节。Kamikitaba组合包括东亚白垩纪这种类型的植物化石保存的第一个记录。植物群补充和扩展了日本白垩纪植物化石的现有知识，并为与北美东部和欧洲类似的中化石组合进行比较提供了基础。化石组合包括保存完好的被子植物花、果实、种子、树叶碎片和木材，以及树枝、树叶、花粉球果、球果鳞片和针叶树种子。现有的可暂时识别的分类群包括：樟科、金缕梅科、壳斗科、山茱蒲科、鸡冠花科，可能还有杜鹃花科、木兰科、睡莲科和杉科。蕨类植物的叶和轴碎片、具有原位孢子的孢子囊和大孢子也证明了卷柏和五倍子科的存在。

A preliminary description is provided of a new assemblage of plant fossils(the Kamikitaba mesofossil flora) from the Asamigawa Member of the Ashizawa Formation(lower Coniacian, Upper Cretaceous) exposed in Kamikitaba, Fukushima Prefecture, northeastern Honshu, Japan. The fossils are small, three-dimensional and charcoalified or lignitized(mesofossils) and yield exquisite structural details when studied with scanning electron microscopy. The Kamikitaba assemblage comprises the first record of this style of fossil plant preservation from the Cretaceous of eastern Asia. The flora complements and extends current knowledge of Cretaceous fossil plants from Japan and provides a basis for comparison with similar mesofossil assemblages from eastern North America and Europe. The fossil assemblage contains well-preserved angiosperm flowers, fruits, seeds, leaf fragments and wood, as well as shoots, leaves, pollen cones, cone scales and seeds of conifers. Extant taxa that can be recognized provisionally include : Lauraceae, Hamamelidaceae, Fagaceae, Cornales, Combretaceae, and probably Ericales, Magnoliaceae, Nymphaeales and Taxodiaceae. Leaf and rachis fragments of ferns, sporangia with in situ spores, and megaspores also document the presence of Selaginellaceae and Schizaeaceae.