摘要
本文报道了采自鄂西晚三叠世地层中的五种种子蕨植物,它们分别隶属于副镰羽叶(Paradrepanozamites)、丁菲羊齿(Thinnfeldia)和篦羽羊齿(Ctenozamites)三个属。由于这些植物的小羽片或羽片基部上边均明显收缩,基部下边均显著下延等,认为它们在系统发生上可能有密切的亲缘关系,并提出它们的形态结构可能朝两个方向发展:一是输导组织不断发达——叶脉从亚放射状,无中脉→有中脉但不发达→中脉发达→变成末级羽轴;二是小羽片或羽片由全缘→局部分裂→大部分裂→羽状全裂。同时,根据奇特篦羽羊齿(新种)[Ctenoza-mites difformis(sp.nov.)]同一植株上的叶呈现四种不同的形态和脉序,初步推测上述三属的演变趋势是:由 Paradrepanozamites→Thinnfeldia→Ctenozamites。
This paper deals with five fossil plants which are Paradrepanozamites dadaochangensis, Thinnfeldia elegans,T.nanzhangensis,Ctenozamites difformis sp.nov.,C.microloba.They were collected from the lower part of Late Triassic Jiuligang Formation in Western Hubei, while the sequence found in these plants is just coincident with the order of their evolution. Although the fertile parts of Paradrepanozamites,Thinnfeldia and Ctenozamites are unk- nown,the writer believes that they belong to pteridosperms,according to the present materials From Text-fig.I,it is shown that these genera have close relations in shape. From Text-fig.I,it is also revealed that these genera mentioned above have a certain law of evolution.Based on morphological variations,two directions of evolutionary trends can be recognized as follows:1.subradiat veins without midrib→midrib but undeveloped→well-deve- loped midrib→forming the ultimate rachis;2.the pinnae being undivided→only little part of every pinnae being divided→most part of every one being divided→bipinnate. As it is knoum that ontogeny is a recapitulation of phylogeny.So the original shapes in different evolutionary stages of Ctenozamites may be traced by the changes of the shapes of Ctenozamites difformis sp.nov. According to the facts related above,the writer proposes the following sequence of lineage of evolution of the genera in this paper:Paradrepanozamites→Thinnfeldia→Ctenozamites.
关键词
晚三叠世
种子蕨
演变趋势
Late Triassic
Pteridosperms
Evolutionary tendency
