JPR SYMPOSIUM Palaeobotany: Old but new stories on plant diversity Palynofloras from the upper Barremian-Aptian Nishihiro Formation (Outer Zone of southwest Japan) and the appearance of angiosperms in Japan Julien Legrand • Toshihiro Yamada • Harufumi Nishida Received: 31 July 2013 / Accepted: 18 November 2013 Ó The Botanical Society of Japan and Springer Japan 2013 Abstract Palynomorphs are reported for the first time from the Nishihiro Formation (Wakayama Prefecture, Outer Zone of southwest Japan). The Nishihiro Formation consists of brackish to shallow marine deposits, dated as late Barremian to Aptian from geological correlations. Spores prevail in the assemblage, representing Filicopsida (mainly Cyatheaceae and Anemiaceae), Marchantiopsida and Lycopsida. The pollen assemblage is dominated by Coniferales, whereas Gnetales and Bennettitales/Cycadales are only rarely observed. Moreover, we report angiosperm pollen grains of the genus Retimonocolpites for the first time in the Early Cretaceous sediments of Japan. Pollen grains of the Retimonocolpites Group are typical of early angiosperms and commonly found in assemblages from the early to mid-Cretaceous of all paleofloristic provinces. Until this paper, the oldest angiosperm fossils in Japan were represented by a single seed and a wood reported from the Albian of Hokkaido. The oldest reliable angio- sperm pollen grains were reported in Hokkaido from the Cenomanian, and in Honshu from the Coniacian. Thus, Retimonocolpites pollen grains reported in the present study represent the oldest record of angiosperms in Japan. They indicate an appearance of the angiosperms in Japan older than thought until now, which is consistent with that proposed elsewhere in eastern Asia. Keywords Early angiosperms pollen Á Japan Á Lower Cretaceous Á Nishihiro Formation Á Retimonocolpites Á Ryoseki-type Palynoflora Introduction The developmental history of the Japanese archipelago still remains unsolved. For some authors, the Japanese Islands were mainly in two parts before the opening of the Sea of Japan (Miocene, 28 My), the Inner Zone of present-day Japan (northwestern part, along the Sea of Japan) being connected to the east of the Korean Peninsula and the Outer Zone (southeastern part, along the Pacific Ocean) of southwest Japan interpreted as oceanic islands located further to the south. These moved northwards by sinistral strike-slip movements along the Median Tectonic Line (MTL) to reach their present latitude and collide with the Inner Zone during the late Hauterivian (Hirooka et al. 1983, 1985; Matsukawa and Fukui 2009; Matsukawa and Obata 1993; Matsuoka et al. 1997; Otoh 1998; Otoh and Sasaki 1998; Yaskawa 1975). However, other authors have suggested that Japan was formed by accretion tectonics between the Asian continent and Pacific Ocean (Isozaki 1996, 1997; Isozaki et al. 2010; Maruyama et al. 1997). Paleofloras of the Inner and Outer Zones show differences in their composition from the Upper Jurassic to Lower Cretaceous, reflecting their paleoenvironment and climate. The paleoflora of the Inner Zone is called ‘‘Tetori-(Sibe- rian-)type’’ flora; it is characterized by an abundance of ferns, ginkgos and macrophyllous conifers, and supposed to have flourished under a warm temperate climate. The paleoflora of the Outer Zone is called ‘‘Ryoseki-(Gondw- anian-) type’’, and is widely accepted as having flourished J. Legrand (&) Á H. Nishida Department of Biological Sciences, Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan e-mail: legrand@kc.chuo-u.ac.jp T. Yamada Division of Life Sciences, Graduate School of Natural Science and Technology, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan 123 J Plant Res DOI 10.1007/s10265-013-0619-6