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1. The internal anatomy and the cell movement of Lower Cambrian gastrula | |||
YAO Xiaoyong,ZHENG Yajuan,GUO Junfeng,HAN Jian | |||
Earth Science 29 March 2017 | |||
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Abstract:The extraordinarily well-preserved fossil embryos recovered from the Lower Cambrian are known from both cleavage and gastrula stages and, consequently, it has the potential to yield vital insights into developmental evolution at that time. However, they are not generally accepted as gastrula fossils because of the gastrulation processes and internal structures in these embryos are poorly characterized. Here we show rare gastrula specimens in which internal anatomical features preserved. The yolk consumed in the endoderm formation and the pharynx was appeared after the archenteron formed indicates our embryo fossils are most probably 'direct-developing' animals; although the epibolic gastrulation and radial symmetry suggest a cnidaria Sea anemone affinity, the precise phylogenic position of them is still uncertain because of lacking reliable later stages in development; we also present the cell movement of epibolic gastrulas, the embryonic mechanisms have been compared with modern pattern: enveloping layer extension were observed in our fossils; and similar with purse-string-like contraction of marginal cells, the zigzag margin contraction of the epibolic frontier to reduce their perimeter that push the margin forward, all of which hint that the embryonic mechanisms of the modern embryos had evolved in Lower Cambrian. | |||
TO cite this article:YAO Xiaoyong,ZHENG Yajuan,GUO Junfeng, et al. The internal anatomy and the cell movement of Lower Cambrian gastrula[OL].[29 March 2017] http://en.paper.edu.cn/en_releasepaper/content/4723528 |
2. A unique gymnosperm from the latest Permian of China, and its ecophysiological implications | |||
Feng Zhuo,Wang Jun,RÖßLE Ronny | |||
Earth Science 03 October 2010 | |||
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Abstract:A unique probably coniferalean gymnospermous woody stem Shenoxylon mirabile gen. nov. et sp. nov. is described from the very late Late Permian Changhsingian (Lopingian) Sunjiagou Formation of the Shitanjing coalfield, northern China. It is anatomically preserved and is characterized by a regularly arranged sclerenchymatous intramedullary sheath surrounding the wide homogenous central pith, and dense development of the secondary xylem with helically arranged leaf traces. The broad eustelic vascular system consists of the heterogeneous pith and endarch primary xylem, the tracheid elements from the protoxylem to metaxylem showing annular to scalariform/reticulate thickenings. The secondary xylem is pycnoxylic; uniseriate bordered pits are continuous or individually separated present on the radial walls of tracheids, with partially biseriate, alternate or opposite on the tracheid walls; the cross-fields show one or two cupressoid pits; ray cells are parenchymatous with smooth walls; axial parenchyma is also developed. Growth-rings are present and false rings are frequently developed throughout the secondary xylem; resin canals are absent. The leaf traces are comprised of monarch vascular bundles, of circular to longitudinally elongate shape in cross section; they originate from the periphery of the pith and pass through the whole xylem cylinder nearly horizontally. The special anatomical structure of the pith and the large amount of false rings are interpreted as ecophysiological responses of the plant to the serious environmental disturbulences during the latest Permian terrestrial ecosystem. | |||
TO cite this article:Feng Zhuo,Wang Jun,RÖßLE Ronny. A unique gymnosperm from the latest Permian of China, and its ecophysiological implications[J]. |
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