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

Recent molecular clock data suggest with high probability a Cambrian origin of Embryophyta (also called land plants), indicating that their terrestrialization most probably started about 500 Ma. 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 bryophyte-like cryptospores and the oldest fragments of the earliest land plants are 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 O-2 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.