Publication Date:
2010-09-09
Description:
This paper summarizes research on Ordovician to Lochkovian vegetation development in a palaeogeographic framework. A terrestrialization model is described. Palaeogeographic maps are modified to explain the vegetation migrations. Land plants first evolved on the Gondwana plate and colonized Avalonia and later Laurentia and Baltica when those plates were in close proximity (Ashgill-Llandovery). South America was colonized during the Llandovery following the collapse of the ice sheet centred on the southern pole which had previously been an impassable barrier for miospores. An Aeronian-Telychian event related to the global early Silurian transgression modified the vegetation by destroying biotopes where the earliest vegetation was thriving. During the regression, trilete spore-producing plants appear to have been more able to respond to environmental changes and dominated the vegetation from the Homerian. Cryptospore-producing plants could survive under a wide range of climates, which helped them to survive during the Hirnantian glaciation. On the contrary, the earliest trilete spore-producing plants were probably climatically restricted, as suggested by latitudinal variation in assemblage composition. By the end of the Silurian, there were several phytogeographic units. Information on the earliest vegetation favours palaeogeographic reconstructions where plates are in close proximity.
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