811. 東北地方に分布する古第三系野田層群港層産の Ginkgo tzagajanica Samylina- とくにその外形と表皮系の特徴

抄録

Many fossil Ginkgo leaves with well-preserved cuticles were obtained from the Lower Palaeogene Noda Group distributed in the Pacific side of Iwate Prefecture, Northeast Japan. Judging from the occurrence, external morphology and cuticular features, these fossil leaves belong to the same species and were derived from the same population. They are referable to Ginkgo tzagajanica originally described by Samylina from the lowermost Tertiary in the Bureja Basin. In this paper, the detailed description of Ginkgo tzagajanica and its emended diagnosis were given. Variation of the external and cuticular features of these leaves were also discussed. Cuticular features of Ginkgo tzagajanica vary according to the portions of a lamina. This fact shows that careful observation of cuticular data is required when dealing with Ginkgo species by their cuticles. In addition, re-evaluation of some features, said to be diagnostic of Ginkgo leaves, were made based on our fossil and extant leaves. Decrease in development of papillae on the subsidiary and ordinary cells, since the early Tertiary, is recognized among the Tertiary Ginkgo species hitherto known.