Devonian explosion

Artist interpretation of a Devonian swamp forest scene. Artwork by Eduard Riou from The World Before the Deluge 1872

The Devonian explosion was a period of rapid plant diversification that occurred 359-419 million years ago during the Devonian. This diversification of terrestrial plant life had vast impacts on the biotic composition of earth's soil, its atmosphere, its oceans, and for all plant and animal life that would follow it.[1] Through fierce competition for light and available space on land, phenotypic diversity of plants increased greatly, comparable in scale and effect to the explosion in diversity of animal life during the Cambrian explosion, especially in vertical plant growth, which allowed for photoautotrophic canopies to develop, and forever altering plant evolutionary floras that followed. This Devonian flora was significantly different in appearance, reproduction, and anatomy to most modern flora. Much of this flora had died out in extinction events including the Devonian mass extinction and the Carboniferous Rain Forest Collapse.[2]

## Contents

* 1 Devonian life
* 2 Effect on atmosphere, soil, and climate
* 3 Devonian evolution
* 4 References

## Devonian life

The earliest radiations of the first land plants were embryophytes, such as bryophytes and vascular plants, which began to transform terrestrial environments. Plants from ancestral floras that survived to the present day include ferns, ginkoes, cycads, and early conifer-like plants. Devonian swamp forests were dominated by giant horsetails (Equistales), club mosses, ancestral ferns (Pteridophytes), and large Lycophyte vascular plants such as Lepidodendrales, referred to as scale trees for the appearance of scales on their photosynthetic trunks, and could grow up to 40 m high. These Lycophytes grew in great numbers around swamps along with tracheophytes. This increase in terrestrial plant matter in swamplands explains the deposits of coal and oil that would later characterize the Carboniferous.[2] Conifer-like spore producing trees with the first ever display of solid wood trunks developed in the Late Devonian. Seed ferns and true leaf-bearing plants such as progymnosperms also appeared at this time and became dominant in many habitats. Most flora in Devonian coal swamps would have seemed alien in appearance when compared with modern flora, such as giant horsetail (Equisetales) which could grow up to 30 m in height. Devonian ancestral plants of modern plants that may have been very similar in appearance are ferns (Polypodiopsida), although many of them are thought to have been epiphytes rather than grounded plants. True gymnosperms like Ginkgo (Ginkophyta) and Cycads (Cycadophyta) would appear slightly after the Devonian in the Carboniferous.[2]

## Effect on atmosphere, soil, and climate

Deep-rooted vascular plants had drastic impacts upon soil, atmosphere, and oceanic oxygen composition. The Devonian Plant Hypothesis is an explanation about these effects upon biogeomorphic ecosystems of climate and marine environments.[1] A climate/carbon/vegetation model could explain the effects of plant colonization during the Devonian. Land plant expansion of Devonian flora modified soil properties and there is evidence that atmospheric CO
2 levels fell from around 6300 to 2100 ppmv, while oxygen levels rose as a direct result of plant expansion.[3] The Devonian explosion had global consequences on oceanic nutrient content and sediment cycling, which had led to the Devonian mass extinction. The altering of soil composition created anoxic sedimentation (or black shales), oceanic acidification, and global climate changes. This led to harsh living conditions for oceanic and terrestrial life.[4]

## Devonian evolution

The evolution of trees was the most prominent feature of the Devonian and is linked to global carbon sequestration as a result. These tree types were archeopteridaleans (likely related to conifers), pseudosporochnaleans (related to palms and tree ferns), and lycopsids.[5] Archeopteridaleans had likely developed extensive root systems, making them resistant to drought, and meaning they had a more significant impact on Devonian soil environments than pseudosporochnaleans.[6] Vascular plant lineages of sphenoids, fern, progymnosperms, and seed plants evolved laminated leaves during the Devonian. The seed plants of earth's flora today originated during the Devonian. Plants that possessed true leaves appeared during the Devonian, though they may have many independent origins with parallel trajectories of leaf morphologies. Morphological evidence to support this diversification theory appears in the Late Devonian or Early Carboniferous when compared with modern leaf morphologies. The marginal meristem also evolved in a parallel fashion through a similar process of modified structures around this time period.[7]

In a 1994 study Richard M Bateman and William A Dimechele of the evolutionary history of heterospory in the plant kingdom, researchers found evidence of 11 origins of heterospory events that had occurred independently in the Devonian within Zosterophyllopsida, Sphenopsida, Progymnospermopsida. The effect of this heterospory was that it presented a primary evolutionary advantage for these plants in colonizing land.[8]

## References

1. ↑ 1.0 1.1 Pawlik, Łukasz; Buma, Brian; Šamonil, Pavel; Kvaček, Jiří; Gałązka, Anna; Kohout, Petr; Malik, Ireneusz (June 2020). "Impact of trees and forests on the Devonian landscape and weathering processes with implications to the global Earth's system properties - A critical review" (in en). Earth-Science Reviews 205: 103200. doi:10.1016/j.earscirev.2020.103200. Bibcode: 2020ESRv..20503200P.
2. ↑ 2.0 2.1 2.2 Cruzan, Mitchell (2018). Evolutionary Biology A Plant Perspective. New York: Oxford University Press. pp. 37–39. ISBN 978-0-19-088267-9.
3. ↑ Le Hir, Guillaume; Donnadieu, Yannick; Goddéris, Yves; Meyer-Berthaud, Brigitte; Ramstein, Gilles; Blakey, Ronald C. (October 2011). "The climate change caused by the land plant invasion in the Devonian" (in en). Earth and Planetary Science Letters 310 (3–4): 203–212. doi:10.1016/j.epsl.2011.08.042. Bibcode: 2011E&PSL.310..203L. https://linkinghub.elsevier.com/retrieve/pii/S0012821X11005061.
4. ↑ Becker, R. T.; Königshof, P.; Brett, C. E. (2016). "Devonian climate, sea level and evolutionary events: an introduction" (in en). Geological Society, London, Special Publications 423 (1): 1–10. doi:10.1144/SP423.15. ISSN 0305-8719. Bibcode: 2016GSLSP.423....1B. http://sp.lyellcollection.org/lookup/doi/10.1144/SP423.15.
5. ↑ Berry, Christopher M.; Marshall, John E.A. (December 2015). "Lycopsid forests in the early Late Devonian paleoequatorial zone of Svalbard" (in en). Geology 43 (12): 1043–1046. doi:10.1130/G37000.1. ISSN 1943-2682. Bibcode: 2015Geo....43.1043B. http://pubs.geoscienceworld.org/geology/article/43/12/1043/131717/Lycopsid-forests-in-the-early-Late-Devonian.
6. ↑ Meyer-Berthaud, B.; Soria, A.; Decombeix, A.-L. (2010). "The land plant cover in the Devonian: a reassessment of the evolution of the tree habit" (in en). Geological Society, London, Special Publications 339 (1): 59–70. doi:10.1144/SP339.6. ISSN 0305-8719. Bibcode: 2010GSLSP.339...59M. http://sp.lyellcollection.org/lookup/doi/10.1144/SP339.6.
7. ↑ Boyce ; Knoll, C, A. (2002). "Evolution of developmental potential and the multiple independent origins of leaves in Paleozoic vascular plants". Paleobiology 28 (1): 70–100. doi:10.1666/0094-8373(2002)028<0070:EODPAT>2.0.CO;2. https://dash.harvard.edu/handle/1/3117930?show=full.
8. ↑ Bateman, Richard M.; DiMICHELE, William A. (August 1994). "Heterospory: The Most Iterative Key Innovation in the Evolutionary History of the Plant Kingdom" (in en). Biological Reviews 69 (3): 345–417. doi:10.1111/j.1469-185X.1994.tb01276.x. ISSN 1464-7931. http://doi.wiley.com/10.1111/j.1469-185X.1994.tb01276.x.

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