Early Evolution of Primitive Angiosperms in Cretaceous

近20年来，在欧洲、北美东部和中美洲发现了许多白垩纪中化石植物群。对这些组合中的中化石的研究，在我们对白垩纪被子植物系统分化模式的理解上取得了巨大的进展。中化石是从日本东北部福岛县双叶群露头的大量沉积物样品中分离出来的。双叶群的沉积物被认为是从早科尼亚世到晚桑托尼亚世，并通过在双叶群的某些相中也出现的海洋无脊椎动物化石来确定年代。含铂沉积物来自双叶群最低的Asamigawa段，并根据上世纪80年代的海洋化石来确定年代为早科尼亚世，大约距今8900万年。 关于我们 说谎的Obisagawa成员。朝美川段沉积物被解释为由分选不良的砂岩和粉砂岩组成的冲积扇存款。该化石组合以采样点的名称命名为“上北叶组合”，其中包含保存完好的大孢子、孢子囊、针叶树芽、圆锥鳞片以及被子植物的花、果实和种子。在蕨类植物中，裂殖科是很好的代表，针叶树包括各种各样的假定的紫杉亚科和可能的其他科。总之，Kamikitaba组合包括保存完好的早期被子植物的化石花，果实和种子。我从中化石的证据中得出结论，在以Kamikitaba组合为代表的环境中，早期的Coniacian植被在丰度方面可能是由针叶树和被子植物主导的，被子植物在物种方面可能更加多样化。现存的分类群，可以暂时承认包括：樟科，金缕梅科，壳斗科，Cornales，Combretaceae，并可能Ercales，木兰科和睡莲目。少

Over the last 20 years, many Cretaceous mesofossil floras have been discovered in Europe, eastern North America and central America. Studies of the mesogossils in these assemblages have yielded dramatic progress in our understanding of pattens of systematic differentiation during the Cretaceous history of angiosperms.In this study, I would like to present a new Cretaceous mesofossil flora from northeastern Asia and the Pacific Rim. The mesofossils were isolated from bulk sediment samples collected from an outocrop of the Futaba Group exposed in Fukushima Prefecture in northeastern Japan. The sediments of the Futaba Group are thought to range in age from early Coniacian to late Santonian, and well dated by marine invertebrate fossils that also occur in some facies of the Futaba Group.The platn-bearing sediments are from the Asamigawa Member, the lowermost within the Futaba Group, and are dated as early Coniacian, about 89 million years before present, based on marine fossils in the over … More lying Obisagawa Member. The sedeiments of the Asamigawa Member are interpreted as an alluvial fan deposit comprising poorly-sorted sand stones and siltstones.The fossil assemblage, which I call "Kamikitaba assemblage" after the name of the sampling site, contains well preserved megaspores, sporangia, conifer shoots, cone scales, and angiosperm flowers, fruits and seeds. Among the ferns, the family Schizeaceae is well represented, and the conifers include a variety of presumed Taxoideae and perhaps other familes.In summary, the Kamikitaba assemblage includes well-preserved fossil flower, fruits and seed of early angiosperms. I concluded from the evidence of mesofossils, that the early Coniacian vegetation in the environments represented by the Kamikitaba assemblage, was probably dominated, in terms of abundance, by both conifers and angiosperms, with angiosperms probably more diverse in terms of species. Extant taxa that can be recognized provisionally include: Lauraceae, Hamamelidaceae, Fagaceae, Cornales, Combretaceae, and probably Ercales, Magnoliaceae and Nymphaeales. Less