A NEW SPECIES OF PTERIDOSPERM FROM THE UPPER MESOZOIC OF XIZANG(TIBET)
【Abstract in Chinese】 描述发现于西藏拉萨晚中生代林布宗组的种子蕨化石,确定为新种——西藏叉羽叶Ptilozamites tibeticus Yang sp.nov.。该种有别于其它叉羽叶各种:叶二次羽状;末二次羽轴较粗,具斜向纵纹或瘤状突起;末次羽片披针形,在羽轴上互生;末次羽轴的表面具斜的纵条纹;小羽片在末二次羽轴和末次羽轴上互生至对生,排列规则而紧密。中生代种子蕨类植物主要发现于晚三叠世至早侏罗世地层,新种的发现表明种子蕨类植物在青藏高原可一直延续到早白垩世。
【Abstract】 The Mesozoic seed fern groups are especially significant,as it was believed that the progenitors of the angiosperms can be found in one of these groups(Taylor et al.,2009).Most records of the Mesozoic pteridosperms in China are from the Upper Triassic to the Lower Jurassic.While carrying on the field work on the Mesozoic in Xizang(Tibet)some new fossil materials were collected from the Linbuzong Formation in Lhasa,Xizang and a new species of pteridosperm was recognized.The plant revealed unusual forked,its pinnate morphology indicating a closer relationship with the genus Ptilozamites Nathorst,1878.Ptilozamites was initially considered as a typical genus for the Rhaeto-Liassic(Late TriassicEarly Jurassic)of Sweden(Nathorst,1978).Up to now it is known to occur throughout the Northern Hemisphere and has also been reported from the Lower Triassic to the Middle Jurassic.Ctenozamites was erected for species similar in epidermal characters to Ptilozamites,but presenting a typical bipinnate character,rarely or never unipinnate(Nathorst,1886).Harris(1964)emended it and pointed out that the only difference between them is that the one is bipinnate,the other simply pinnate.Schweitzer and Kirchner(1998)suggested a close relationship between Ptilozamites and Ctenozamites based on the fact that the leaves are often terminally forked in both taxa.A recent study on new Greenland material shown both genera are very strongly related anatomically,therefore it was proposed that Ctenozamites Nathorst,1886 is a synonym of Ptilozamites Nathorst,1878(Popa and McElwain,2009).The present study shows that Ptilozamites has a much younger geological record and could extend to the Lower Cretaceous in Tibetan Plateau.
【Key words】 Ptilozamites； pteridosperm； Early Cretaceous； Xizang(Tibet)；
- 【Source】 古生物学报 ,Acta Palaeontologica Sinica , Editorial E-mail ,2016(04)
- 【CLC code】Q914