NEW OBSERVATIONS ON THE SPECIMEN ATTRIBUTED TO ZOSTEROPHYLLUM LONGHUASHANENSE FROM THE LOWER DEVONIAN OF QUJING,YUNNAN,SOUTHWESTERN CHINA
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Abstract:
Zosterophyllum longhuashanense was established from the Lower Devonian of Qujing,Yunnan Province(Li and Cai, 1977). Its establishment was based on only one specimen that was not well illustrated. Some authors(Gerrienne,1988;Hao et al.,2007;Edwards et al.,2015)thought that the sporangia of Z.longhuashanense were two-rowed arranged,rather than being spirally arranged as originally described by Li and Cai(1977).The present study reobserves the type specimen of Z.longhuashanense and indicates a zosterophyll spike with spirally arranged sporangia. According to the morphological features,the specimen previously attributed to Z.longhuashanense is transferred to Zosterophyllumcf.myretonianum.Class Zosterophyllopsida Banks,1975 Order Zosterophyllales Banks,1968 Family Zosterophyllaceae Banks,1968 Genus Zosterophyllum Penhallow,1892 Type species Zosterophyllum myretonianum Penhallow,1892Zosterophyllumcf.myretonianumPenhallow,1892(Text-figs.1-A—F,2)1977 Zosterophyllum longhuashanense,Li and Cai,pp 17,pl.Ⅱ,fig.21,21 a;Text-fig.1.Specimen PB6463(original Type specimen),deposited at the Nanjing Institute of Geology and Palaeontology,Chinese Academy of Sciences.Description A part of zosterophyll spike,without apical or basal part,is preserved up to 35 mm long and 7 mm in maximum width.The spike consists of an axis with sporangia loosely and spirally arranged.The spike axis is about 1.8 mm wide.A vertical ribbon-like band is seen on the surface of the axis,which might represent the vascular strand inside the axis.More slender bands are seen to depart from the central one,extending to individual sporangia(Text-figs.1-F,2).At least twelve sporangia are recognized from the spike.Sporangia are arranged in lateral or sub-lateral positions relative to the central axis,none is seen in face view(Text-figs.1-A,2).In the description of the sporangium,the up or down refers to their positions shown in the text-figure.The high or low refers to the sporangial positions relative to the observer. The higher sporangium means that the sporangium is closer to the observer under microscope.The sporangia 3,5,9 are directly attached on the surface of the axis,but the attached angles of stalks vary.The sporangium 12 attached to the middle part of the spike axis(Text-fig.1-E)can be seen by the broken axis in the lower position.The sporangium 11 breaks from the axis in the basal portion and can be seen lower than the axis.These sporangia,though being preserved as compression,can be recognized helically arranged on the spike axis.The sporangium is roughly triangular or elliptical shaped in lateral view,2.2—3.1 mm in height( =2.7,n=8),1.3—2.8 mm in lateral width( =1.9,n=7).The upper sporangia,probably near the apex of spike,appear subcircular(11,12 in text-fig.2),whilst the lower ones have acuminate apices(text-fig.1-C, D, F). The distance between neighboring sporangia becomes wider from the up spike to the down.Sporangium stalk is 0.3—0.8 mm in width( =0.6,n=7)and 1.3—2.7 mm in length( =1.9,n=7).The stalk departs from the axis in narrow angles(30°—60°),with a slight extending then curve adaxially as C-shaped.The sporangium appears to grow paralleled with the spike axis. The junction between the stalk and the sporangium is not clear.The sporangium dehiscence line is seen from the adaxial side of the sporangium,up to 0.1 mm wide along the distal margin(text-fig.1-B,F).The sporangium dehisces into two equal valves.Two dehisced but still connected valves are seen from the sporangium 4(text-fig.1-C,D).The two valves are overlapped but are seen in different heights to the observer.Locality and horizon Qujing, Yunnan.Xujiachong Formation(Pragian—Emsian).
