Early Evolution of Primitive Angiosperms in Cretaceous

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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