Coincidence in the first appearance of land plant fossils and formative shifts in atmospheric oxygen and CO2 are an artefact of the paucity of earlier terrestrial rocks. There can be no doubt that early land plant evolution transformed the planet but, until recently, how and when this was achieved was unclear. Thus, the Hanadir Member specimens present what we interpret as the earliest evidence of simultaneous meiosis occurring inside a sporangium that possessed an active tapetum. Isometric, tetrahedral tetrads, like Cryptotetras and Tetrahedraletes, which dominate the Hanadir Member assemblage, express a geometry that reflects simultaneous cytokinesis during sporogenesis. Therefore, lamellate spore walls appear to be have evolved in algal (charophytic) lineages well in advance of the first plants that possessed an upright axial sporophyte. Lamellated walls occur in cryptospore dyads found in Siluro-Devonian cryptophytes (as well as fragments of presumed cryptophytes as old as the Ordovician), but this type of wall is also common in Cambrian cryptospores. This implies that these Ordovician cryptospores developed within a sporangium, although fossilized sporangia of this antiquity are not known. Homogeneous walls are characteristic of extant embryophyte sporoderm, which is actively secreted by a tapetum. The lamellated wall structure of a single Hanadir Member monad is also described. laevigata Johnson, possess the homogeneous wall type, matching that seen in younger, Silurian species of Tetrahedraletes from Laurentia. A recently described tetrad from the Hanadir Member, Cryptotetras erugata Strother, Traverse & Vecoli, and the dyad, Pseudodyadospora sp. Our study also suggests that ancestral streptophyte algae started to adapt to subaerial life in several separated regions and probably earlier than the Epoch 2 of the Cambrian.Ĭryptospores from the Hanadir Member, Qasim Formation (Darriwilian) examined with transmission electron microscopy (TEM), show two distinct kinds of walls: homogeneous and lamellated. Palynomorphs from the ZPA are comparable with those from roughly coeval sequences in North America and other areas. The ZPA shows the earliest record of Cambrian cryptospore or spore-like palynomorphs and sheds light on the TAP occurring in the Cambrian of northern China. The Zhushadong palynological assemblage (ZPA) is proposed and composed of cryptospores (15.4%), clustered forms (31.5%), acritarchs (20.1%), filaments (30.3%) and indeterminate specimens (2.7%). In this study, we recognize a Cambrian (Epoch 2, Age 4) palynological assemblage from the Zhushadong Formation of Shandong Province, northern China, which show more diversity than previously reported from the same section. Cambrian cryptospore, though its concept and affinity remain controversial, shows indispensable evidence of algal ancestor preceding occurrence of land plants. You hereby agree that we are not providing our own opinions, advice, or recommendations.Pre-Darriwilian (Middle Ordovician) spore-like palynomorphs are significant in understanding the plant origination and the evolutionary transition from algae to land plants (TAP). While we endeavor to publish and maintain accurate information on external listings, we do not guarantee the accuracy, completeness, or usefulness of any information on this site, nor do we adopt nor endorse, nor are we responsible for, the accuracy or reliability of any information submitted by other parties. The brands and the logos appearing on this website are registered trademarks by their respective brand owners. may not offer certain products, features and/or services on the App in certain jurisdictions due to potential or actual regulatory restrictions. Please note that the availability of the products and services on the App is subject to jurisdictional limitations. You may obtain access to such products and services on the App. It is not intended to offer access to any of such products and services. The purpose of this website is solely to display information regarding the products and services available on the App.
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