Discovery O F Bipinnate Ptilophyllum Leaves (Bennettitales) from The

No. 101 Proc. Japan Acad., 60, Ser. B (1984) 385

99. Discovery of Bipinnate Ptilophyllum Leaves (Bennettitales) from the Upper Jurassic Tochikubo Formation, Fukushima Prefecture, Northeast Japan*'

By Tatsuaki KIMURA and Masanori TsuJii Tokyo Gakugei University, Koganei, Tokyo 184 (Communicated by Teiichi KOBAYASHI, M. J. A., Dec. 12, 1984)

During 1983-4 we made a good collection of fossil plants from the Tochikubo Formation of the Somanakamura Group distributed along the Pacific coast in Fukushima Prefecture. According to Mori (1963) who studied the Somanakamura Group in detail, the geological age of the Tochikubo Formation is Oxf ordian. This paper deals with our proposal of a new genus based on the Ptilophyllum leaves of bipinnate habit found in our collection and with their description. Genus Nipponoptilophyllum Kimura et Tsujii nov. For diagnosis and discussion, see below. The prefix of its generic name is after Nippon (meaning Japan in Japanese). Type species : Nip ponoptilophyllum bipinnatum.

Nipponoptilophyllum bipinnatum Kimura et Tsujii sp, nov. Figs. 1-10 Material : Holotype ; ARA-875. Paratypes ; ARA-391, 432, 456, 573, 576, 773. Other specimens ; ARA-177 and other 42 specimens. Stratum typicum : Tochikubo Formation (Oxf ordian), Somanakamura Group. Locus typicus : Aratozawa, Haranomachi-City, Fukushima Prefecture. Derivatio nominis : From bipinnate leaf. Diagnosis : Leaf bipinnate. Main rachis rather slender, 2.5 mm wide or more, giving alternately off penultimate pinnae at an angle of 60 degrees and typically at an interval of 1.4 cm. (Whole leaf unknown.) Penultimate pinnae varied in form and size; elongate- oblanceolate in outline, more than 10 cm long and 3.5 cm wide, or elongate-obovate, 7.5 cm long including petiole of 1 cm long and up to 3 cm wide. Penultimate pinna axis rather slender ; lower expanded end of petiole forming pulvinus, 2.5 mm wide. Pinnae imparipinnate, set closely, consisting at least of 20 pairs, attached alternately by whole base to the upper surface of pinna axis at an angle of 60-90

' Supported by the Grant-in-Aids for the Scientific Research from the Ministry of Education, Science and Culture of Japan (no. 59540499). 386 T. KIMURA and M. TsUJII [Vol. 60(B),

Figs. 1-10 (natural size unless otherwise indicated). 1: A bipinnate leaf- fragment (la) and a detached penultimate pinnae (lb) (ARA-875, Holo- type, X1/2). 2: Drawn from la. 3: Drawn from lb. 4: Basal part of a detached penultimate pinna (4a) and detailed venation (4b, X2) drawn from a pinna of 4a (ARA-456, Paratype). 5 : Basal part of a detached penultimate pinna (ARA-773, Paratype). 6 : Ditto, showing the mode of attachment of pinnae ( ARA-391, Paratype, X2). 7-9: Distal portions of detached penultimate pinnae (7; ARA-573, Paratype. 8; ARA-531. 9; ARA-389). 10: Middle portion of a detached penultimate pinna (ARA-576, Paratype).

degrees. Pinna axis concealed but sometimes partially exposed; lower portion of pinna axis devoid of pinnae for about 1 cm from base, thus forming a petiole. Pinnae nearly parallel-sided for the most part, No. 10] Bipinnate Ptilophyllum Leaves from NE-Japan 387 then suddenly narrowing to the obtusely pointed or rounded apex, or gradually narrowing to apex, typically 1.5-2 cm long and 3-3.5 mm wide, but those of two or three pairs of both distal and proximal regions shorter in length and triangular in form. Pinna base asymmetrical; acroscopic basal margin contracted and forming a rounded angle, and basiscopic basal margin mostly decurrent or occasionally straight, sometimes concealed by the acroscopic margin of pinna below. Veins arising from whole region of attachment, typically 7 in number at pinna base, mostly simple but one or two of them forked once, parallel, not divergent and ending with the distal margin of pinna. (Cuticle not preserved and reproductive organs unknown.) Distribution and occurrence : Nipponoptilophyllum bipinnatum is locally abundant at Aratozawa locality where its detached penultimate pinnae or their fragments are thickly massed and appressed. Discussion and comparison : Among a good number of specimens examined, only one shows a leaf of bipinnate habit although it is faintly preserved on the bedding plane of medium-grained sandstone together with many detached penultimate pinnae. Several detached penultimate pinnae are still with their pulvinus petioles. Judging from their occurrence, the penultimate pinnae appear to be easy to shed from the main rachis, but unfortunately we could not make their very point of attachment clear. Our penultimate pinnae are undoubtedly of Ptilophyllum-type, because the pinnae show asymmetrical base and are attached to the upper surface of pinna axis. Among about 60 Ptilophyllum species hitherto described, so far as we know, this is the first record of Ptilophyllum of bipinnate habit. Thus we here propose a new generic name Nipponoptilophyllum for it, we, however, don't think that in all other Ptilophyllum species hitherto known, their leaves are of bipinnate habit, because Bose and Kasat (1972) illustrated P. cutchense Morris showing singly pinnate leaves attached terminally to a Bucklandia-type stem (their fig. 114 of p1. 13) and P. acuti f olium Morris showing an apical crown of singly pinnate leaves (their fig. 116 of p1. 14). In size and form of pinnae (ultimate pinnae), our penultimate pinnae resemble the leaves of the following species: Ptilophyllum amarjolense Bose,1953 (Upper Jurassic of Rajmahal Hills), P, distans (Feistmantel) Jacob et Jacob, 1954 (Bose and Kasat, 1972) (Jurasso- Cretaceous Jabalpur Series), P. pectinoides (Phillips) Morris (Harris, 1942, 1969) (Middle Jurassic of Yorkshire) and P. vasekgahense Barnard et Miller, 1976 (Middle Jurassic of Iran). But they can externally be distinguished from ours. Further detailed comparison will be mentioned in our separate paper. 388 T. KIMURAand M. Tsuaii [Vol. 60(B),

So far as we know no matched leaf with ours has been described and thus we here propose Nipponoptilophyllum bipinnatum sp, nov. Another bennettitalean leaf of bipinnate habit has already been described by Kimura and Kim (1982) from the Upper Triassic Daedong Supergroup, Korea as Coreanophyllum variisegmentum bear- ing Pterophyllum-type ultimate pinnae. Nipponoptilophyllum bipinnatum differs from any pteridosper- mous Ctenozamites species hitherto known in the reason mentioned previously by Kimura and Kim (1982). Acknowledgements. We express our sincere gratitude to Pro- fessor Emeritus Teiichi Kobayashi, M. J. A., of the University of Tokyo for giving us the facilities to publish this paper. Our thanks are extended to our students of the Tokyo Gakugei University for their help in collecting the material here described.

References

Barnard, P. D. W., and Miller, J. C. (1976) : Palaeontographica, B, 155, 31-117, pls. 1-15. Bose, M. N. (1953) : Proc. Natn. Inst. Sci. India, 19(5), 605-612, pls. 26-28. Bose, M. N., and Kasat, M. L. (1972) : Palaeobotanist, 19(2), 115-145, pls. 1-14. Harris, T. M. (1942) : Ann. Mag. Nat. Hist., (11), 9, 568-587. (1969) : Brit. Mus. (Nat. Hist.), vi+186 pp., 7 pls. Jacob, K., and Jacob, C. (1954) : Palaeont. Indica, N. S., 33(1), 1-34, pls. 1-10. Kimura, T., and Kim, B.-K. (1982) : Proc. Japan Acad., 58B, 152-155. Mori, K. (1963) : Sci. Rep., Tohoku Univ., (2), 35(1), 33-65, pls. 21-23.