Silurian and pre-Upper Devonian bio-events

Boucot, A. J.

doi:10.1007/bfb0011140

Cited by 27 publications

(22 citation statements)

References 15 publications

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“…lacking morphological di¡erentiation into roots, stems, and leaves: Thomas & Spicer 1987;Beerbower et al 1992;Strother et al 1996). Vascular (tracheid-bearing) plants evolved and began to diversify during the Late Silurian and Early Devonian (Gensel & Andrews 1984Gray 1985Gray , 1993Boucot 1990;Edwards & Berry 1991), but these forms were small, non-rooted or shallowly rooted, and con¢ned to moist, lowland habitats, thus having little e¡ect on their physical environment (¢gure 1a). Plant^substrate interactions are likely to have increased substantially with the appearance and spread of arborescent vegetation between the Pragian and Givetian (¢gure 1b), and with the development of seed plants (¢gure 1c;Banks 1980;Thomas & Spicer 1987;Beerbower et al 1992).…”

Section: Evolutionary Innovations Among Early Vascular Land Plantsmentioning

confidence: 99%

Terrestrial-marine teleconnections in the Devonian: links between the evolution of land plants, weathering processes, and marine anoxic events

Algeo

Scheckler

1998

Phil. Trans. R. Soc. Lond. B

613

347

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The Devonian Period was characterized by major changes in both the terrestrial biosphere, e.g. the evolution of trees and seed plants and the appearance of multi-storied forests, and in the marine biosphere, e.g. an extended biotic crisis that decimated tropical marine benthos, especially the stromatoporoid-tabulate coral reef community. Teleconnections between these terrestrial and marine events are poorly understood, but a key may lie in the role of soils as a geochemical interface between the lithosphere and atmosphere/ hydrosphere, and the role of land plants in mediating weathering processes at this interface. The e¡ective-ness of terrestrial £oras in weathering was signi¢cantly enhanced as a consequence of increases in the size and geographic extent of vascular land plants during the Devonian. In this regard, the most important palaeobotanical innovations were (1) arborescence (tree stature), which increased maximum depths of root penetration and rhizoturbation, and (2) the seed habit, which freed land plants from reproductive dependence on moist lowland habitats and allowed colonization of drier upland and primary successional areas. These developments resulted in a transient intensi¢cation of pedogenesis (soil formation) and to large increases in the thickness and areal extent of soils. Enhanced chemical weathering may have led to increased riverine nutrient £uxes that promoted development of eutrophic conditions in epicontinental seaways, resulting in algal blooms, widespread bottomwater anoxia, and high sedimentary organic carbon £uxes. Long-term e¡ects included drawdown of atmospheric pCO 2 and global cooling, leading to a brief Late Devonian glaciation, which set the stage for icehouse conditions during the Permo-Carboniferous. This model provides a framework for understanding links between early land plant evolution and coeval marine anoxic and biotic events, but further testing of Devonian terrestrial^marine teleconnections is needed.

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Section: Evolutionary Innovations Among Early Vascular Land Plantsmentioning

confidence: 99%

Terrestrial-marine teleconnections in the Devonian: links between the evolution of land plants, weathering processes, and marine anoxic events

Algeo

Scheckler

1998

Phil. Trans. R. Soc. Lond. B

613

347

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“…On land, megafossil plant assemblages, such as Cooksonia and Cooksonia-like forms spread across lands during the latter part of the Silurian. Boucot (1990) sees no extinctions among shelf-dwelling brachiopods in the Late Wenlock-Ludlow interval.…”

Section: Graptolite Habitatsmentioning

confidence: 96%

Late Wenlock (Middle Silurian) global Bioevent: Possible chemical cause for mass graptolite mortalities

Quinby-Hunt

Berry

1991

Historical Biology

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Graptolites nearly became extinct in the latest Wenlock in all preserved stratigraphic sequences of this age. Graptolite mortalities occurred along the western coast of Laurentia and at sites that surrounded the ProtoTethys. Graptolite mass mortalities took place among deep-water, open ocean dwelling organisms. After the mass mortalities, only the Pristiograptus dubius group and retiolids, surface or near-surface dwellers, survived. For a period of time, little speciation or diversification occurred. The base of the Ludlow is marked by diversification, with appearances of S. colonus, M. nilssoni, and other groups which occur in near surface waters. None of the extensive plate movements postulated for the Silurian readily explain the mass extinctions that occurred. During the Silurian, global temperatures were warmer than present and atmospheric oxygen concentrations were lower, creating extensive oceanic anoxia. Below the oxygenated surface layers of the ocean, was an anoxic, non-sulfidic zone (i.e. nitrate-reducing) above a sulfidic zone. Graptolites lived over a range of depth from the oxygenated zone to either near or in the nitrate-reducing zones. As the oxygen concentration declined through the Silurian, the depth of the oxic zone would have become shoaler with expanding anoxia. Late Wenlock graptolites that were unable to migrate to shallower depths, living in borderline oxygen conditions, could have been killed, resulting in the mortalities of the late Wenlock. Only those graptolites that were surface dwellers survived, adapted and reradiated.

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“…Boucot (1990) proposed a certain ordering, based on the taxonomic level of extinct taxa: the highest ranking, i.e. The impact of global environmental events on the biota' ranges from only mild disturbances to an extensive mass extinction.…”

Section: Prefacementioning

confidence: 99%

“…1. The extinctions produce open niches (vacuums, according to Boucot, 1990) within the affected and strongly disturbed ecosystems or biotopes, respectively. According to the main phases it is named extinctionradiation (E-R) sequence.…”

Section: The Extinction-radiation (E-r) Sequencementioning

confidence: 99%

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Global Events and Event Stratigraphy in the Phanerozoic

Walliser¹

1996

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Silurian and pre-Upper Devonian bio-events

Cited by 27 publications

References 15 publications

Terrestrial-marine teleconnections in the Devonian: links between the evolution of land plants, weathering processes, and marine anoxic events

Terrestrial-marine teleconnections in the Devonian: links between the evolution of land plants, weathering processes, and marine anoxic events

Late Wenlock (Middle Silurian) global Bioevent: Possible chemical cause for mass graptolite mortalities

Global Events and Event Stratigraphy in the Phanerozoic

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