Sphenobaiera Coreanica Kim Et Kimura Sp. Nov., from the Bansong Group in the Danyang Coal-Field, Korea

No. 6] Prod. Japan Acad., 63, Ser. B (1987) 183

48. Sphenobaiera coreanica Kim et Kimura sp. nov., from the Bansong Group in the Danyang Coal-Field, Korea

By Jong Heon KIM and Tatsuaki KIMURA Tokyo GakugeiUniversity, Koganei,Tokyo 184 (Communicatedby TeiichiKoBAYASHI, M.J. A.,June 9, 1987)

This paper deals with the description of a new type of Sphenobaiera leaves attached to a stem (or short shoot ) in organic connection, collected from the Bansong Group in the Danyang Coal-Field, Korea. The Bansong Group in the adjacent Mungyeong Coal-Field is obviously Late Triassic in age based on its plant-assemblage (Kimura and Kim, B. K., 1984a, b, 1985) . But the geological age of the, Bansong Group distributed in the Danyang Coal-Field has not yet been settled because of insufficiency of available or effective fossils for age- determination.

Ginkgoales Genus Sphenobaiera Florin, 1936: 105 Sphenobaiera coreanica Kim et Kimura sp. nov. Figs. 1-2 Material : Holotype; YYH-016 (kept in Tokyo Gakugei University). Stratum typicum : Middle part of the Bansong Group (Hyeoncheonri For- mation) in the Danyang Coal-Field. Locus typicus : Yeonhari (roughly 128°32' 43"E, 37°11'15"N) (= C-point in Kawasaki, 1926, p. 1), Sangdong-up, Yeongweol- gun, Guangweon-do, Korea. Derivatio nominis : After Korea. Occurrence : Rare. Number o f specimens examined: Four. Known fossil plants coexisted: Annulariopsis bunkeiensis (Kobatake) Kimura et Kim (MS), Equisetites sp, cf. E. f erganensis Seward, Marattia asiatica (Kawasaki) Harris, Coniopteris sp. cf. C. neiridaniensis Kimura et Tsujii, Clado phlebis nampoensis Kawasaki, C. sp. cf. Asterotheca okafujii Kimura et Ohana, C. sp. cf. Todites denticulatus (Brongniart) Krasser, C. sp. cf. Todites yamanoi- ensis (Yokoyama) Kimura et Ohana, C. sp. cf. C. pseudodelicatula Oishi, C. sp. A, Coreanophyllum variisegmentum Kimura et Kim, Ctenis yamanarii Kawasaki, Nilssonia sp. A, Baiera sp. cf. B. f urcata (Lindley et Hutton) Braun, Eretmo- phyllum ? sp., Elatocladus spp., Pityophyllum ? sp. and Podozamites ex gr. distans (Presl) Braun. Diagnosis : Stem (or short shoot) elongated, more than 6 cm long and 9 mm wide; surface being ornamented over by helically arranged scars considered to be leaf-base shed, sending helically and terminally off leaves at a narrow angle. Leaves narrowly wedge-shaped, more than 13.5 cm long and up to 2 cm wide, consisting of two parts ; one corresponding to petiole undivided, 2.5-5 cm long and up to 2 mm wide with swollen base and another corresponding to limb. Limb-part dividing into two segments at a narrow angle; each segment further dichotomously divided by a narrow angle into narrow lobes in four times. These segments and lobes being nearly in parallel each other. Ultimate lobe 1 mm wide and more than 1 cm long. Penultimate lobe receiving two veins but ultimate one 184 J. H. KIM and T. KIMURA [Vol. 63(B),

a single vein. (Apical margin of leaf not known and cuticle not preserved.) Discussion and comparison. Our leaves do not belong to Czekanowskiales, because in czekanowskialeans foliage leaves are persistent, borne in bundles on caducous short (or dwarf) shoots surrounded with scale leaves. Our leaves do not make such a bundle and attached singly to the stem (or short shoot), and no such scale leaves are recognized at the base.

Figs. 1-2. Sphenobaiera coreanica sp. nov. 1: A probable short shoot terminally with three leaves of which one is preserved only by basal part of petiole (holotype). 2: Drawn from Fig. 1 showing the mode of attachment of leaves and visible venation near the tip of leaf-segments.

Our leaves are also different from those regarded as Baiera and Ginkgo (or Ginkgoites), because in the latter leaves the boundary between petiole- and limb- parts are generally distinctive, while in Sphenobaiera leaves, they are without a distinctive set-off petiole, narrowing wedgewise towards the base (Florin, 1936; Lundblad, 1959) like those of ours. Sphenobaiera stems preserved still with their leaves in position have rarely been recorded. So far as we know, such stems were illustrated by Leuthardt (1903) and Krausel (1943) as Baiera f urcata Heer [= Sphenobaiera f ureata (Heer) Florin] from the Upper Triassic of Neuewelt, by Sixtel et al. (1971) as Sphenobaiera aravanica Sixtel from the Permian of South Fergana and by Kimura and Tsujii (1984) as Sphenobaiera sp. cf. S. curl/basis Sze from the Lower Jurassic of Japan. They are all distinguished from ours by their leaves attached not to the stems (or short shoots) terminally but to them laterally. In addition the former two are also distinguished by their broader segments and lobes divided not in parallel but at a wider angle. Besides 22 Sphenobaiera species defined by Florin (1936), though some of them were later removed to other taxa, many Sphenobaiera species were described No. 6] Sphenobaiera eoreanica sp. nov. 185 from the Mesozoic of Europe, the Middle East, Siberia, China and Japan, mostly with their cuticles together. Of these our leaves resemble externally, especially in the width of lobes and mode of multi-division, those of the following species: Sphenobaiera longif olio (Pomel) Florin (see Harris and Millington, in Harris et al., 1974) S. pecten Harris (Harris, 1945; Harris and Millington, in Harris et al., 1974) ; Middle Jurassic of Yorkshire S. tchirvae Kiritchkova (Kiritchkova, 1985) ; Lower Cretaceous of the Lena Basin S. uninervis Samylina (Samylina, 1956, 1963) ; Lower Cretaceous of the Aldan Basin S. sp. cf. S. eurybasis Sze (Kimura and Tsujii, 1984) ; Lower Jurassic of Japan Of these Sphenobaiera pecten and S. tchirvae are distinguished by their fan-shaped leaves, and S. ion gi f olia by its broader lobes with several veins. Sphenobaiera sp. cf. S. eurybasis is distinguished by its broader lobes and some leaves are fan-shaped. Its venation is still uncertain. Sphenobaiera uninervis is most close in external leaf-form and venation to ours, but is distinguishable by its obtriangular form of leaves. Under the circumstances, we here propose Sphenobaiera coreanica as a new species to accommodate our material. Acknowledgement. We express our sincere gratitude to Professor Emeri- tus Teiichi Kobayashi, M. J. A., of the University of Tokyo for giving us the facilities to publish this paper.

References

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