Revisiting the Great Ordovician Diversification of land plants: Recent data and perspectives

Abstract

Recent molecular clock data suggest with highest probability a Cambrian origin of Embryophyta (also called land plants), indicating that their terrestrialization most probably started about million years ago. The fossil record of the 'Cambrian explosion' was limited to marine organisms and not visible in the plant fossil record. The most significant changes in early land plant evolution occurred during the Ordovician. For instance, the earliest bryophytelike cryptospores and the oldest fragments of the earliest land plants come from the Middle and Late Ordovician, respectively. Organic geochemistry studies on biomarker compositions hint at a transition from green algae to land plants during the 'Great Ordovician Biodiversification Event' (GOBE). The colonization of the terrestrial realms by land plants clearly had an impact on marine ecosystems. Interactions between the terrestrial and marine biospheres have been proposed and the radiation of land plants potentially impacted on CO2 and O2 concentrations and on global climate. In addition, the shift of strontium isotopes during the Ordovician is probably linked to changing terrestrial landscapes, affected by the first massive land invasion of eukaryotic terrestrial life. The land plants seem unaffected by the first global mass extinction at the end of the Ordovician that eliminated many marine invertebrate taxa.

Genome-scale phylogenetic analyses confirm Olpidium as the closest living zoosporic fungus to the non-flagellated, terrestrial fungi

“…These findings are consistent with a Precambrian origin of the non-flagellated fungi 6 , 44 , 45 , and that they experienced their first radiation in Neoproterozoic (Fig. 2 ), concurrent with Ediacaran fauna (625–539 Ma) 46 and predating the earliest evidence of land plants in the late Ordovician and Silurian (450–420 Mya) 47 . While animal phyla likely diversified in early marine environments, the loss of flagellum and concurrent ages of the MRCA of Zoopagomycota, Mucoromycota and Dikarya suggest that these lineages likely diversified in early terrestrial environments.…”

Genome-scale phylogenetic analyses confirmOlpidiumas the closest living zoosporic fungus to the non-flagellated, terrestrial fungi

“…These findings are consistent with a Precambrian origin of the non-flagellated fungi 5,42,43 , and that they experienced their first radiation in Neoproterozoic (Fig. 2), concurrent with Ediacaran fauna (625-539 Ma) 44 and predating the earliest evidence of land plants in the late Ordovician and Silurian (450-420 Mya) 45 . While animal phyla likely diversified in early marine environments, the loss of flagellum and concurrent ages of the MRCA of Zoopagomycota, Mucoromycota and Dikarya suggest that these lineages likely diversified in early terrestrial environments.…”

Dynamics of Silurian Plants as Response to Climate Changes

“…Early land/polysporangiate plants diversified and colonized continents during Silurian-Devonian “terrestrial radiation” [ 51 ]. Recent analysis convincingly indicates a possibility that a great land plant radiation had already occurred in the Ordovician and argues that land plants were possibly not affected by the end-Ordovician extinction event [ 52 ]. Servais et al [ 53 ] stated the importance of environmental factors, including atmospheric composition and the geochemical carbon cycle [ 54 , 55 ], as major influencers of the evolutionary dynamics of early plants.…”