Silurian-Devonian Terrestrial Revolution
   HOME

TheInfoList



OR:

The Silurian-Devonian Terrestrial Revolution, also known as the Devonian Plant Explosion (DePE) and the Devonian explosion, was a period of rapid plant and fungal diversification that occurred 428 to 359 million years ago during the
Silurian The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleozo ...
and
Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...
, with the most critical phase occurring during the Late Silurian and Early 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. 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 The Cambrian explosion, Cambrian radiation, Cambrian diversification, or the Biological Big Bang refers to an interval of time approximately in the Cambrian Period when practically all major animal phyla started appearing in the fossil recor ...
, especially in vertical plant growth, which allowed for photoautotrophic canopies to develop, and forever altering plant evolutionary floras that followed. This Silurian and 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
Kellwasser Event The Late Devonian extinction consisted of several extinction events in the Late Devonian Epoch, which collectively represent one of the five largest mass extinction events in the history of life on Earth. The term primarily refers to a major exti ...
, the
Hangenberg Event The Hangenberg event, also known as the Hangenberg crisis or end-Devonian extinction, is a mass extinction that occurred at the end of the Famennian stage, the last stage in the Devonian Period (roughly 358.9 ± 0.4 million years ago). It is usuall ...
, the Carboniferous Rainforest Collapse, and the End-Permian Extinction.


Silurian and Devonian life

Rather than plants, it was
fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
, in particular
nematophytes The Nematophyta or nematophytes are a paraphyletic group of land organisms, probably including some plants as well as algae known only from the fossil record, from the Silurian period until the early Devonian Rhynie chert. The type genus ''Nemat ...
such as ''
Prototaxites ''Prototaxites'' is a genus of terrestrial fossil fungi dating from the Middle Ordovician until the Late Devonian periods, approximately . ''Prototaxites'' formed small to large trunk-like structures up to wide, reaching in length, made up of ...
'', that dominated the early stages of this terrestrial biodiversification event. Nematophytes towered over even the largest land plants during the Silurian and Early Devonian, only being truly surpassed in size in the Early Carboniferous. The nutrient-distributing glomeromycotan mycorrhizal networks of nematophytes were very likely to have acted as facilitators for the expansion of plants into terrestrial environments, which followed the colonising fungi. The first
fossils A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in ...
of arbuscular mycorrhizae, a type of symbiosis between fungi and vascular plants, are known from the Early Devonian. Land plants probably evolved in the Ordovician. The earliest radiations of the first land plants, also known as
embryophytes The Embryophyta (), or land plants, are the most familiar group of green plants that comprise vegetation on Earth. Embryophytes () have a common ancestor with green algae, having emerged within the Phragmoplastophyta clade of green algae as sist ...
, were
bryophytes The Bryophyta s.l. are a proposed taxonomic division containing three groups of non-vascular land plants (embryophytes): the liverworts, hornworts and mosses. Bryophyta s.s. consists of the mosses only. They are characteristically limited i ...
, which began to transform terrestrial environments and the global climate in the Ordovician. The end of the
Homerian In the geologic timescale, the Homerian is an age of the Wenlock Epoch of the Silurian Period of the Paleozoic Era of the Phanerozoic Eon that is comprehended between 430.5 ± 0.7 Ma and 427.4 ± 0.5 Ma (million years ago), approximately. Th ...
glaciation, a glacial phase of the Early Palaeozoic Ice Age, and the corresponding period of global warming marked the first major diversification of plants that produced trilete spores. The later glaciation during the middle
Ludfordian In the geologic timescale, the Ludfordian is the upper of two chronostratigraphic stages within the Ludlow Series. Its age is the late Silurian Period, and within both the Palaeozoic Era and Phanerozoic Eon. The rocks assigned to the Ludfordian ...
, corresponding to the
Lau event The Lau event was the last of three relatively minor mass extinctions (the Ireviken, Mulde, and Lau events) during the Silurian period. It had a major effect on the conodont fauna, but barely scathed the graptolites, though they suffered an extin ...
, led to a major
marine regression A marine regression is a geological process occurring when areas of submerged seafloor are exposed above the sea level. The opposite event, marine transgression, occurs when flooding from the sea covers previously-exposed land. Evidence of marine ...
, creating significant areas of new dry land habitat that were colonised by plants, along with cyanobacterial mats. These newly created terrestrial habitats helped facilitate the global expansion and
evolutionary radiation An evolutionary radiation is an increase in taxonomic diversity that is caused by elevated rates of speciation, that may or may not be associated with an increase in morphological disparity. Radiations may affect one clade or many, and be rapid ...
of
polysporangiophytes Polysporangiophytes, also called polysporangiates or formally Polysporangiophyta, are plants in which the spore-bearing generation (sporophyte) has branching stems (axes) that bear sporangia. The name literally means 'many sporangia plant'. The cl ...
. A warming climate during the subsequent Pridoli epoch lent itself to further floral diversification. During the Wenlock epoch of the Silurian, the first
fossils A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in ...
of
vascular plants Vascular plants (), also called tracheophytes () or collectively Tracheophyta (), form a large group of land plants ( accepted known species) that have lignified tissues (the xylem) for conducting water and minerals throughout the plant. They al ...
appear in the fossil record in the form of
sporophytes A sporophyte () is the diploid multicellular stage in the life cycle of a plant or alga which produces asexual spores. This stage alternates with a multicellular haploid gametophyte phase. Life cycle The sporophyte develops from the zygot ...
of
polysporangiophytes Polysporangiophytes, also called polysporangiates or formally Polysporangiophyta, are plants in which the spore-bearing generation (sporophyte) has branching stems (axes) that bear sporangia. The name literally means 'many sporangia plant'. The cl ...
. Clubmosses first appeared during the later
Ludlow epoch In the geological timescale, the Ludlow Epoch (from 427.4 ± 0.5 million years ago to 423.0 ± 2.3 million years ago) occurred during the Silurian Period, after the end of the Homerian Age. It is named for the town of Ludlow in Shropshire, England ...
.
Palynological Palynology is the "study of dust" (from grc-gre, παλύνω, palynō, "strew, sprinkle" and ''-logy'') or of "particles that are strewn". A classic palynologist analyses particulate samples collected from the air, from water, or from deposit ...
evidence points to Silurian terrestrial floras exhibiting little provincialism relative to present day floras that vary significantly by region, instead being broadly similar across the globe. Plant diversification in the Silurian was aided by the presence of numerous small, rapidly changing
volcanic islands Geologically, a high island or volcanic island is an island of volcanic origin. The term can be used to distinguish such islands from low islands, which are formed from sedimentation or the uplifting of coral reefs (which have often formed ...
in the
Rheic Ocean The Rheic Ocean was an ocean which separated two major palaeocontinents, Gondwana and Laurussia (Laurentia- Baltica-Avalonia). One of the principal oceans of the Palaeozoic, its sutures today stretch from Mexico to Turkey and its closure result ...
that acted as natural laboratories accelerating evolutionary changes and enabling distinct, endemic floral lineages to arise. Silurian plants rarely reached large sizes, with heights of 13 cm, achieved by ''Tichavekia grandis'', being exceptionally large for the time. The Devonian witnessed the widespread greening of the Earth's surface, with many modern vascular plant clades originating during this period. The first true forest environments featuring trees exceeding eight metres in height emerged by the Middle Devonian. Basal members of
Euphyllophytina The euphyllophytes are a clade of plants within the tracheophytes (the vascular plants). The group may be treated as an unranked clade, a division Division or divider may refer to: Mathematics *Division (mathematics), the inverse of multiplic ...
, the
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...
that includes
trimerophytes Trimerophytopsida (or Trimeropsida) is a class (biology), class of early vascular plants from the Devonian, informally called trimerophytes. It contains genera such as ''Psilophyton''. This group is probably paraphyletic, and is believed to be th ...
,
ferns A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The polypodiophytes include all living pteridophytes except th ...
, progymnosperms, and
seed plants A spermatophyte (; ), also known as phanerogam (taxon Phanerogamae) or phaenogam (taxon Phaenogamae), is any plant that produces seeds, hence the alternative name seed plant. Spermatophytes are a subset of the embryophytes or land plants. They inc ...
, are known from
Early Devonian The Early Devonian is the first of three Epoch (geology), epochs comprising the Devonian period, corresponding to the Lower Devonian Series (stratigraphy), series. It lasted from and began with the Lochkovian Stage , which was followed by the P ...
fossils. Lycopsids experienced their first evolutionary radiation during the Devonian period. Devonian swamp forests were dominated by giant horsetails (
Equisetales Equisetales is an order of subclass Equisetidae with only one living family, Equisetaceae, containing the genus ''Equisetum'' (horsetails). Classification In the molecular phylogenetic classification of Smith et al. in 2006, Equisetales, in its ...
), clubmosses, ancestral ferns (
pteridophytes A pteridophyte is a vascular plant (with xylem and phloem) that disperses spores. Because pteridophytes produce neither flowers nor seeds, they are sometimes referred to as "cryptogams", meaning that their means of reproduction is hidden. Ferns, ...
), and large
lycophyte The lycophytes, when broadly circumscribed, are a vascular plant (tracheophyte) subgroup of the kingdom Plantae. They are sometimes placed in a division Lycopodiophyta or Lycophyta or in a subdivision Lycopodiophytina. They are one of the oldes ...
vascular plants such as
Lepidodendrales Lepidodendrales (from the Greek for "scale tree") were primitive, vascular, heterosporous, arborescent (tree-like) plants related to present day lycopsids. Members of Lepidodendrales are the best understood of the fossil lycopsids due to the vast ...
, referred to as scale trees for the appearance of scales on their
photosynthetic Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in c ...
trunks, and could grow up to 40 metres 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 The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carbonifero ...
. Seed ferns and true leaf-bearing plants such as
progymnosperm The progymnosperms are an extinct group of woody, spore-bearing plants that is presumed to have evolved from the trimerophytes, and eventually gave rise to the seed plants, gymnosperms, ancestral to gymnosperms, acrogymnosperms and angiosperms (f ...
s also appeared at this time and became dominant in many habitats, particularly archeopteridaleans (likely related to conifers). Pseudosporochnaleans (related to palms and tree ferns) likewise experienced a similar rise to dominance. 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. During the latest Devonian, the first true spermatophytes appeared, evolving as a sister group to archaeopteridaleans or to progymnosperms as a whole. Most flora in Devonian coal swamps would have seemed alien in appearance when compared with modern flora, such as giant horsetails 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 A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The polypodiophytes include all living pteridophytes except th ...
), although many of them are thought to have been
epiphyte An epiphyte is an organism that grows on the surface of a plant and derives its moisture and nutrients from the air, rain, water (in marine environments) or from debris accumulating around it. The plants on which epiphytes grow are called phoroph ...
s rather than grounded plants. True gymnosperms like ginkgos ( Ginkophyta) and cycads (
Cycadophyta Cycads are seed plants that typically have a stout and woody (ligneous) trunk (botany), trunk with a crown (botany), crown of large, hard, stiff, evergreen and (usually) pinnate leaves. The species are dioecious, that is, individual plants o ...
) would appear slightly after the Devonian in the
Carboniferous The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carbonifero ...
. Vascular plant lineages of sphenoids, fern,
progymnosperm The progymnosperms are an extinct group of woody, spore-bearing plants that is presumed to have evolved from the trimerophytes, and eventually gave rise to the seed plants, gymnosperms, ancestral to gymnosperms, acrogymnosperms and angiosperms (f ...
s, and seed plants evolved laminated leaves 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 The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, wher ...
or
Early Carboniferous Early may refer to: History * The beginning or oldest part of a defined historical period, as opposed to middle or late periods, e.g.: ** Early Christianity ** Early modern Europe Places in the United States * Early, Iowa * Early, Texas * Early ...
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. In a 1994 study by Richard M Bateman and William A. Dimechele of the evolutionary history of
heterospory Heterospory is the production of spores of two different sizes and sexes by the sporophytes of land plants. The smaller of these, the microspore, is male and the larger megaspore is female. Heterospory evolved during the Devonian period from iso ...
in the plant kingdom, researchers found evidence of 11 origins of
heterospory Heterospory is the production of spores of two different sizes and sexes by the sporophytes of land plants. The smaller of these, the microspore, is male and the larger megaspore is female. Heterospory evolved during the Devonian period from iso ...
events that had occurred independently in the Devonian within Zosterophyllopsida,
Sphenopsida Equisetidae is one of the four subclasses of Polypodiopsida (ferns), a group of vascular plants with a fossil record going back to the Devonian. They are commonly known as horsetails. They typically grow in wet areas, with whorls of needle-like ...
,
Progymnospermopsida The progymnosperms are an extinct group of woody, spore-bearing plants that is presumed to have evolved from the trimerophytes, and eventually gave rise to the gymnosperms, ancestral to acrogymnosperms and angiosperms (flowering plants). They ...
. The effect of this heterospory was that it presented a primary evolutionary advantage for these plants in colonizing land. The simultaneous colonization of dry land and increase in plant body size that many lineages underwent during this time was likely facilitated by another parallel development: the replacement of the ancestral central cylinder of
xylem Xylem is one of the two types of transport tissue in vascular plants, the other being phloem. The basic function of xylem is to transport water from roots to stems and leaves, but it also transports nutrients. The word ''xylem'' is derived from ...
with more elongate, complex xylem strand shapes that would have made the plant body more resistant to the spread of drought-induced
embolism An embolism is the lodging of an embolus, a blockage-causing piece of material, inside a blood vessel. The embolus may be a blood clot (thrombus), a fat globule ( fat embolism), a bubble of air or other gas (gas embolism), amniotic fluid (amniot ...
.
Tracheids A tracheid is a long and tapered lignified cell in the xylem of vascular plants. It is a type of conductive cell called a tracheary element. Angiosperms use another type of tracheary element, called vessel elements, to transport water through t ...
, tapered cells that make up the xylem of vascular plants, first appear in the fossil record during the Early Devonian. Woody stems evolved during the Devonian as well, with the first evidence of them dating back to the Early Devonian. Root structures appear for the first time in the fossil record in Early Devonian lycophytes, and it has been suggested that the development of roots was an adaptation for maximising water acquisition in response to the increase in aridity over the course of the Silurian and Devonian. The Early Devonian also saw the appearance of complex subterranean
rhizome In botany and dendrology, a rhizome (; , ) is a modified subterranean plant stem that sends out roots and shoots from its nodes. Rhizomes are also called creeping rootstalks or just rootstalks. Rhizomes develop from axillary buds and grow hori ...
networks.


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. 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 levels fell from around 6300 to 2100 ppmv as a result of carbon sequestration by land plants, while oxygen levels rose as a direct result of plant expansion. 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 change In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...
s. This led to harsh living conditions for oceanic and terrestrial life.


References

{{Reflist, refs= Silurian life Devonian life Evolution of plants