Well-preserved Ginkgo pollen organs are analyzed from the Middle Jurassic Xishanyao Formation of the Turpan–Hami Basin, Xinjiang Uygur Autonomous Region, northwestern China, and are described as a new species, Ginkgo hamiensis Z.X. Wang et B.N. Sun sp. nov. The immature male cones are cylindrical and catkin-like, with two longitudinal stripes on the stalk. The pollen sacs are shaped like a long oval with two pollen sacs fused together for each microsporophyll, and the microsporophyll tip is a triangular cystidium. The pollen grains are oblong or fusiform and monocolpate; both ends are blunt or sharp. By comparison with previously reported fossil records of Ginkgo plants, we determined that the current fossils are different from all other reported species; thus, the present fossil is referred to as a new species of Ginkgo. The reproductive organs of the Ginkgo fossils described herein can provide valuable information for the study of Ginkgo plants. Further, there are two probable evolutionary trends in the Ginkgo pollen cones. One trend is that the number of pollen sacs changed from three or four during the Jurassic and Cretaceous to two at the present day; the other is that the number of pollen sacs has remained two from the Middle Jurassic to the present day. In addition, the pollen cones described herein are similar to the pollen cones of the extant Ginkgo, which strongly indicates that the morphology of Ginkgo plants may have remained highly conserved over millions of years.
WANG ZixiSUN FankaiJIN PeihongCHEN YingquanCHEN JingweiDENG PengYANG GuolinSUN Bainian
对福建永安市下白垩统坂头组保存较好的真蕨类营养叶化石枝脉蕨Cladophlebis进行了叶片形态及角质层微细构造特征的分析,该化石至少二次羽状分裂,末二次羽轴粗,小羽片小,全缘,排列紧密,中脉明显,侧脉密集,多数一次分叉;上表皮无气孔器,细胞轮廓不清晰,偶见表皮毛;下表皮具气孔器,呈纵向带状排列;表皮细胞长方形或呈条带状;垂周壁加厚,较直;平周壁波状突起;气孔器近圆形,具明显拱盖,保卫细胞弱角质化,副卫细胞分化不明显.对当前化石小羽片解剖学特征的分析填补了该属植物化石叶片角质层微细构造特征的空白,进一步将其与现生紫萁Osmunda joponsica以及部分真蕨类化石的表皮特征进行对比,结合宏观形态和角质层特征的分析及其与相似种类的比较,将永安的标本命名为一新种,永安枝脉蕨Cladophlebis yonganensis Dai et B.N.Sun,sp.nov.,并且推断当前化石代表了某一类已经灭绝的真蕨类植物.
