Microstructure Of Reproductive Organs Of Several Gymnosperms From The Middle Jurassic Of Hami, Xinjiang And Their Geoglogical Significances

Sandaoling in Turpan-Hami Basin of Xinjiang Uygur Autonomous Region has yielded abundant fossils of various taxa, and it is one of the best regions for the development of the terrestrial Jurassic strata in China, even in the world. However, the previous studies of these plant fossils only stay in the identification and morphological description, and the micro structure is very poor. Compared with the stems, leaves and other vegetative organs, the reproductive organs of plants are difficult to be preserved. The reproductive organs, usually as an important basis of identification of plants taxa, are very valuable and significant to explore their phylogenetic relations. The present paper researches the leaves and reproductive organs of the conifer and Ginkgo in detailed. And these two reproductive organs are reported for the first time.The present paper researches the macro-morphology and microstructure of the conifer fossils. A new conifer fossil species, named as Elatides sandaolingensis sp. nov., consists of compressions with well-preserved leafy shoots, pollen cones and seed cone. Leaves are characterized by long triangular or lanceolate shapes, with straight apex and entire margins, and two stomatal bands with mostly parallel or obliquely oriented stomata, on the abaxial surface. Pollen cones are terminally disposed on the ultimate leafy shoots, borne 3-5 in clusters. Pollen sacs are long-oval shaped, with three pollen sacs fused together, and each pollen sac can produce more than 24 pollen grains. Pollen grains are spherical and have small germinal papilla and wrinkles. The seed cone is oblong, with more than 35 helically arranged bract-scale complexes, which are characterized by long-oval shape and triangular apex. Compared with the extant nine genera of Taxodiaceae on the morphology of seed cone and pollen cones, the present fossil consistently shares many characteristics with the extant genus Cunninghamia, but differs from other aspects. From the similarity between the present fossil and Cunninghamia, it can be inferred that there may be a genetic relationship between these two genera. By researching of the geological history and geographical distribution of Elatides, the earliest record of this genus was found in Sweden from the Late Triassic. The genus expanded to the south part of the Northern Hemisphere during the Middle Jurassic, such as northern Europe, Siberia and northern China. During the Early Cretaceous, its distribution was further expanded and became widespread in western Europe, eastern Asia and northern America. The earliest fossil record of the genus in China would be Elatides sandaolingensis sp. nov. from Sandaoling in Xinjiang Uygur Autonomous Region. So Tarim should be the adaptive way that Elatides was transported from Siberia to China. Furthermore, the most likely path for Elatides coming into China should be from Europe to the Ural Mountains and then to Xinjiang Uygur Autonomous Area, then into Qinghai Province, Gansu Province and lastly into the South China.The present Ginkgo fossils are preserved as male cones. From the macro-morphology and micro-structures, they are identified as Ginkgo. The present fossils are compared with the known fossil species of Ginkgo, and then identified as a new species, Ginkgo sandaolingensis sp. nov. The identification and classification of Ginkgo fossils always relay on the vegetative organs, because of the reproductive organs are very rare or preserved badly, which limited to the deep research for Ginkgo plants. The present reproductive organs of Ginkgo fossils can provide many valuable materials for studying of Ginkgo plants. The leaf shapes of the Jurassic Ginkgo plants are different from the extant leaves, as well as shortages of the reproductive organs, most researchers insist that these Mesozoic leaf fossil should be classified as Ginkgoites. The discovery of the present male cones of Ginkgo fossils can provide an important evidence for the existence of Ginkgo in the Middle Jurassic of Hami, Xinjiang.In addition, the cuticle characters of the plant fossils can restore the living environment of plants. The present Elatides has thin cuticles, without trichomes and possesses slightly sunken stomata, and coupled with the living environment and distribution of its recent relative species Cunninghamia, we can conclude that the paleoclimate of Turpan-Hami Basin in the Middle Jurassic might live under the warm and humid subtropic climate zone.