The land plant cover in the Devonian: a reassessment of the evolution of the tree habit
B. Meyer-Berthaud, A. Soria, A.-L. Decombeix, 2010. "The land plant cover in the Devonian: a reassessment of the evolution of the tree habit", The Terrestrialization Process: Modelling Complex Interactions at the Biosphere–Geosphere Interface, M. Vecoli, G. Clément, B. Meyer-Berthaud
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This paper reviews information on the Devonian trees that evolved in the euphyllophyte clade with special focus on the Middle Devonian Pseudosporochnales. The morphology of pseudosporochnalean trees shows analogies with that of extant tree ferns, including the possession of an adventitious root system of limited extent at the base of the trunk. Direct evidence on how these trees were constructed is scarce. We propose a growth model integrating information from younger representatives of the same class known to reach large diameters. According to this model, trunk width in its aerial part results from the large size of its primary body where living tissues are abundant, a condition reached early during growth. Secondary xylem contributes little to trunk diameter. This model sharply diverges from that of the Late Devonian archaeopteridalean trees characterized by an extended root system and where trunk diameter and mechanical support are achieved by the substantial development of secondary vascular tissues. These differences suggest that pseudosporochnalean trees may have had a lesser impact on Devonian environments than the Archaeopteridales. The important investment in living tissues in the Pseudosporochnales probably made them vulnerable to drought and cold.
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The Terrestrialization Process: Modelling Complex Interactions at the Biosphere–Geosphere Interface
The invasion of the land by plants (‘terrestrialization’) was one of the most significant evolutionary events in the history of life on Earth, and correlates in time with periods of major palaeoenvironmental perturbations. The development of a vegetation cover on the previously barren land surfaces impacted on the global biogeochemical cycles and the geological processes of erosion and sediment transport. The terrestrialization of plants preceded the rise of major new groups of animals, such as insects and tetrapods, the latter numbering some 24 000 living species, including ourselves. Early land-plant evolution also correlates with the most spectacular decline of atmospheric CO2 concentration of Phanerozoic times and with the onset of a protracted period of glacial conditions on Earth. This book includes a selection of papers covering different aspects of the terrestrialization, from palaeobotany to vertebrate palaeontology and geochemistry, promoting a multidisciplinary approach to the understanding of the co-evolution of life and its environments during Early to Mid-Palaeozoic times.