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62-551: One important event in this period was the initial establishment of terrestrial life in what is known as the Silurian-Devonian Terrestrial Revolution : vascular plants emerged from more primitive land plants, dikaryan fungi started expanding and diversifying along with glomeromycotan fungi, and three groups of arthropods ( myriapods , arachnids and hexapods ) became fully terrestrialized. Another significant evolutionary milestone during

124-672: A direct result of plant expansion. With increased oxygenation came increased fire activity. Earth's atmosphere first became sufficiently high in oxygen to produce wildfires in the Pridoli, when the first charcoal evidence of wildfires is recorded. For most of the Early and Middle Devonian, the atmosphere was insufficiently oxygenated to enable significant fire activity. By the late Famennian, however, oxygen levels were high enough to enable wildfires to occur with regularity and on large scales, something which had not been previously possible due to

186-471: A diverse range of epibionts, including certain hederelloids as aforementioned. Photosymbiotic scleractinians made their first appearance during the Middle Silurian. Reef abundance was patchy; sometimes, fossils are frequent, but at other points, are virtually absent from the rock record. Silurian-Devonian Terrestrial Revolution The Silurian-Devonian Terrestrial Revolution , also known as

248-422: A drop in atmospheric carbon dioxide levels through elevated organic carbon burial brought about by the formation of wetlands. Some palaeoclimatic simulations have found that depending on the circumstances, the spread of plants could temporarily increase p CO 2 by promoting regolith growth that would hinder the ability of water containing dissolved carbon dioxide to percolate into bedrock. Oxygen levels rose as

310-405: A food web based on as-yet-undiscovered detritivores and grazers on micro-organisms. Millipedes from Cowie Formation such as Cowiedesmus and Pneumodesmus were considered as the oldest millipede from the middle Silurian at 428–430 million years ago, although the age of this formation is later reinterpreted to be from the early Devonian instead by some researchers. Regardless, Pneumodesmus

372-512: A high degree of development in relation to the age of its fossil remains. Fossils of this plant have been recorded in Australia, Canada, and China. Eohostimella heathana is an early, probably terrestrial, "plant" known from compression fossils of Early Silurian (Llandovery) age. The chemistry of its fossils is similar to that of fossilised vascular plants, rather than algae. Fossils that are considered as terrestrial animals are also known from

434-488: A large ocean occupied most of the northern half of the globe. The high sea levels of the Silurian and the relatively flat land (with few significant mountain belts) resulted in a number of island chains, and thus a rich diversity of environmental settings. During the Silurian, Gondwana continued a slow southward drift to high southern latitudes, but there is evidence that the Silurian icecaps were less extensive than those of

496-420: A minor mass extinction and associated with rapid sea-level change. Each one leaves a similar signature in the geological record, both geochemically and biologically; pelagic (free-swimming) organisms were particularly hard hit, as were brachiopods , corals , and trilobites , and extinctions rarely occur in a rapid series of fast bursts. The climate fluctuations are best explained by a sequence of glaciations, but

558-559: 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 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

620-408: A period of erosion or non-deposition. Disconformities are marked by features of subaerial erosion. This type of erosion can leave channels and paleosols in the rock record. A nonconformity exists between sedimentary rocks and metamorphic or igneous rocks when the sedimentary rock lies above and was deposited on the pre-existing and eroded metamorphic or igneous rock. Namely, if the rock below

682-420: A region or were subsequently eroded before the next deposition. The local record for that time interval is missing and geologists must use other clues to discover that part of the geologic history of that area. The interval of geologic time not represented is called a hiatus . It is a kind of relative dating . A disconformity is an unconformity between parallel layers of sedimentary rocks which represents

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744-525: A second supercontinent known as Euramerica . When the proto-Europe collided with North America, the collision folded coastal sediments that had been accumulating since the Cambrian off the east coast of North America and the west coast of Europe. This event is the Caledonian orogeny , a spate of mountain building that stretched from New York State through conjoined Europe and Greenland to Norway. At

806-452: 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. The Late Devonian saw the most rapid land plant diversification of the Devonian, largely owing to the rapid radiation of pteridophytes and progymnosperms. Cladoxylopsids continued to dominate forest ecosystems during

868-497: 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. Expansion of terrestrial Devonian flora modified soil properties, increasing silicate weathering by way of rhizosphere development as evidenced by pedogenic carbonates. This caused atmospheric CO 2 levels to fall from around 6300 to 2100 ppmv, although it also drastically reduced

930-518: Is presented by the Briançonnais realm (Swiss and French Prealps) during the Jurassic. Angular unconformities can occur in ash fall layers of pyroclastic rock deposited by volcanoes during explosive eruptions . In these cases, the hiatus in deposition represented by the unconformity may be geologically very short – hours, days or weeks. A paraconformity is a type of unconformity in which

992-560: Is still an important fossil as the oldest definitive evidence of spiracles to breath in the air. The first bony fish, the Osteichthyes , appeared, represented by the Acanthodians covered with bony scales. Fish reached considerable diversity and developed movable jaws , adapted from the supports of the front two or three gill arches. A diverse fauna of eurypterids (sea scorpions)—some of them several meters in length—prowled

1054-706: The Devonian Plant Explosion ( DePE ) and the Devonian explosion , was a period of rapid colonization , diversification and radiation of land plants and fungi on dry lands that occurred 428 to 359 million years ago (Mya) during the Silurian and Devonian periods , with the most critical phase occurring during the Late Silurian and Early Devonian. This diversification of terrestrial photosynthetic florae had vast impacts on

1116-738: The Early Cretaceous . Much of these Silurian-Devonian florae had died out in extinction events including the Kellwasser event , the Hangenberg event , the Carboniferous rainforest collapse , and the End-Permian extinction . Rather than plants, it was fungi , in particular nematophytes such as Prototaxites , that dominated the early stages of this terrestrial biodiversification event. Nematophytes towered over even

1178-585: The Rheic Ocean 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. Basal members of Euphyllophytina ,

1240-577: The South Pole until they almost disappeared in the middle of Silurian. Layers of broken shells (called coquina ) provide strong evidence of a climate dominated by violent storms generated then as now by warm sea surfaces. The climate and carbon cycle appear to be rather unsettled during the Silurian, which had a higher frequency of isotopic excursions (indicative of climate fluctuations) than any other period. The Ireviken event , Mulde event , and Lau event each represent isotopic excursions following

1302-473: The biotic composition of the Earth's surface , especially upon the Earth's atmosphere by oxygenation and carbon fixation . Their roots also eroded into the rocks, creating a layer of water-holding and mineral / organic matter -rich soil on top of Earth's crust known as the pedosphere , and significantly altering the chemistry of Earth's lithosphere and hydrosphere . The floral activities following

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1364-619: The clade that includes trimerophytes , ferns , progymnosperms, and seed plants , are known from Early Devonian fossils. Lycopsids experienced their first evolutionary radiation during the Devonian period. Early Devonian plant communities were generally similar regardless of what landmass they inhabited, although zosterophyllopsids displayed high levels of endemism. In the Middle Devonian, euphyllophytes continued to increase in diversity. The first true forest environments featuring trees exceeding eight metres in height emerged by

1426-587: The Devonian in the Carboniferous . Vascular plant lineages of sphenoids, fern, progymnosperms , 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 or Early Carboniferous when compared with modern leaf morphologies. The marginal meristem also evolved in

1488-664: The Early Devonian. Land plants probably evolved in the Ordovician. The earliest radiations of the first land plants, also known as embryophytes , were bryophytes , which began to transform terrestrial environments and the global climate in the Ordovician. Baltica was a particularly important cradle for early land plant evolution, with it having a diverse flora by the Darriwilian . ∆ Hg and ∆ Hg excursions reveal that land plants had already spread across much of

1550-803: The Earth's land surface by the Early Silurian . The end of the Homerian 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 , corresponding to the Lau event , led to a major marine regression , creating significant areas of new dry land habitat that were colonised by plants, along with cyanobacterial mats. These newly created terrestrial habitats helped facilitate

1612-619: The Llandovery and Wenlock. Trilobites started to recover in the Rhuddanian, and they continued to enjoy success in the Silurian as they had in the Ordovician despite their reduction in clade diversity as a result of LOME. The Early Silurian was a chaotic time of turnover for crinoids as they rediversified after LOME. Members of Flexibilia, which were minimally impacted by LOME, took on an increasing ecological prominence in Silurian seas. Monobathrid camerates, like flexibles, diversified in

1674-486: The Llandovery, whereas cyathocrinids and dendrocrinids diversified later in the Silurian. Scyphocrinoid loboliths suddenly appeared in the terminal Silurian, shortly before the Silurian-Devonian boundary, and disappeared as abruptly as they appeared very shortly after their first appearance. Endobiotic symbionts were common in the corals and stromatoporoids. Rugose corals especially were colonised and encrusted by

1736-905: The Middle Devonian, with the earliest known fossil forest dating to the Eifelian . The oldest known trees were members of the clade Cladoxylopsida . Devonian swamp forests were dominated by giant horsetails ( Equisetales ), clubmosses, 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. These lycophytes, which could grow up to 40 metres high, grew in great numbers around swamps along with tracheophytes. Seed ferns and true leaf-bearing plants such as progymnosperms also appeared at this time and became dominant in many habitats, particularly archeopteridaleans , which were likely related to conifers. Pseudosporochnaleans (morphologically similar to palms and tree ferns) likewise experienced

1798-595: The Order in which the Older Sedimentary Strata Succeed each other in England and Wales, which was the germ of the modern geological time scale . As it was first identified, the "Silurian" series when traced farther afield quickly came to overlap Sedgwick's "Cambrian" sequence, however, provoking furious disagreements that ended the friendship. The English geologist Charles Lapworth resolved

1860-474: The Silures show little correlation ( cf . Geologic map of Wales , Map of pre-Roman tribes of Wales ), Murchison conjectured that their territory included Caer Caradoc and Wenlock Edge exposures - and that if it did not there were plenty of Silurian rocks elsewhere 'to sanction the name proposed'. In 1835 the two men presented a joint paper, under the title On the Silurian and Cambrian Systems, Exhibiting

1922-1129: The Silurian and Devonian periods, comparable in scale and effect to the explosion in diversity of animal life during the Cambrian explosion , especially in vertical growth of vascular plants , which allowed for expansive canopies to develop, and forever altering the plant evolutions that followed. As plants evolved and radiated, so did arthropods , who became the first established terrestrial animals and some formed symbiotic coevolution with plants. Herbivory , granivory and detritivory subsequently evolved independently among terrestrial arthropods (especially hexapods such as insects , as well as myriapods ), molluscs ( land snails and slugs ) and tetrapod vertebrates , causing plants to in turn develop defenses against foraging by animals. The Silurian and Devonian terrestrial florae were largely spore -bearing plants ( ferns ) and significantly different in appearance, anatomy and reproductive strategies to most modern florae, which are dominated by fleshy seed -bearing angiosperms that evolved much later during

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1984-485: The Silurian was the diversification of jawed fish , which include placoderms , acanthodians (which gave rise to cartilaginous fish ) and osteichthyan ( bony fish , further divided into lobe-finned and ray-finned fishes )， although this corresponded to sharp decline of jawless fish such as conodonts and ostracoderms . The Silurian system was first identified by the Scottish geologist Roderick Murchison , who

2046-525: The Silurian-Devonian plant revolution also exerted significant influences on changes in the water cycle and global climate , as well as driving the biosphere by creating diverse layers of vegetations that provide both sustenance and refuge for both upland and wetland habitats , paving the way for all terrestrial and aquatic biomes that would follow. Through fierce competition for sunlight , soil nutrients and available land space, phenotypic diversity of plants increased greatly during

2108-513: The Silurian. The definitive oldest record of millipede ever known is Kampecaris obanensis and Archidesmus sp. from the late Silurian (425 million years ago) of Kerrera . There are also other millipedes, centipedes , and trigonotarbid arachnoids known from Ludlow (420 million years ago). Predatory invertebrates would indicate that simple food webs were in place that included non-predatory prey animals. Extrapolating back from Early Devonian biota, Andrew Jeram et al. in 1990 suggested

2170-591: The Tethys, the Proto-Tethys and Paleo-Tethys , the Rheic Ocean , the Iapetus Ocean (a narrow seaway between Avalonia and Laurentia), and the newly formed Ural Ocean . The Silurian period was once believed to have enjoyed relatively stable and warm temperatures, in contrast with the extreme glaciations of the Ordovician before it and the extreme heat of the ensuing Devonian; however, it is now known that

2232-525: The albedo of much of Earth's land surface, retarding the cooling effects of this greenhouse gas drawdown. The biological sequestration of so much carbon dioxide resulted in the beginning of the Late Palaeozoic Ice Age at the terminus of the Devonian, together with the tectonic uplift of the continent Gondwana . However, an alternative hypothesis holds that land plant evolution actually decreased silicate weathering rates, instead causing

2294-438: The break is igneous or has lost its bedding due to metamorphism, then the plane of juncture is a nonconformity. An angular unconformity is an unconformity where horizontally parallel strata of sedimentary rock are deposited on tilted and eroded layers, producing an angular discordance with the overlying horizontal layers. The whole sequence may later be deformed and tilted by further orogenic activity. A typical case history

2356-494: The conflict by defining a new Ordovician system including the contested beds. An alternative name for the Silurian was "Gotlandian" after the strata of the Baltic island of Gotland . The French geologist Joachim Barrande , building on Murchison's work, used the term Silurian in a more comprehensive sense than was justified by subsequent knowledge. He divided the Silurian rocks of Bohemia into eight stages. His interpretation

2418-411: The deposits of coal and oil that would later characterize the Carboniferous . Unconformity An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval of time before deposition of the younger layer, but

2480-657: The early Late Devonian. 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 ), although many of them are thought to have been epiphytes rather than grounded plants. True gymnosperms like ginkgos ( Ginkgophyta ) and cycads ( Cycadophyta ) would appear slightly after

2542-406: The edge of the continental shelf) can be identified, and the highest Silurian sea level was probably around 140 metres (459 ft) higher than the lowest level reached. During this period, the Earth entered a warm greenhouse phase, supported by high CO 2 levels of 4500 ppm, and warm shallow seas covered much of the equatorial land masses. Early in the Silurian, glaciers retreated back into

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2604-461: The end of the Silurian, sea levels dropped again, leaving telltale basins of evaporites extending from Michigan to West Virginia, and the new mountain ranges were rapidly eroded. The Teays River , flowing into the shallow mid-continental sea, eroded Ordovician Period strata, forming deposits of Silurian strata in northern Ohio and Indiana. The vast ocean of Panthalassa covered most of the northern hemisphere. Other minor oceans include two phases of

2666-504: The first deep-boring bivalves are known from this period. Chitons saw a peak in diversity during the middle of the Silurian. Hederelloids enjoyed significant success in the Silurian, with some developing symbioses with the colonial rugose coral Entelophyllum . The Silurian was a heyday for tentaculitoids , which experienced an evolutionary radiation focused mainly in Baltoscandia, along with an expansion of their geographic range in

2728-434: The form of Baragwanathia , which was an aquatic predecessor of fully terrestrialised lycophytes. Palynological 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 in

2790-513: The form of moss -like miniature forests along lakes and streams and networks of large, mycorrhizal nematophytes , heralding the beginning of the Silurian-Devonian Terrestrial Revolution. However, the land fauna did not have a major impact on the Earth until it diversified in the Devonian. The first fossil records of vascular plants , that is, land plants with tissues that carry water and food, appeared in

2852-479: The fossil record are found 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 networks. Deep-rooted vascular plants had drastic impacts upon soil, atmosphere, and oceanic oxygen composition. The Devonian Plant Hypothesis

2914-446: The global climate underwent many drastic fluctuations throughout the Silurian, evidenced by numerous major carbon and oxygen isotope excursions during this geologic period. Sea levels rose from their Hirnantian low throughout the first half of the Silurian; they subsequently fell throughout the rest of the period, although smaller scale patterns are superimposed on this general trend; fifteen high-stands (periods when sea levels were above

2976-464: The global expansion and evolutionary radiation of polysporangiophytes . A warming climate during the subsequent Pridoli epoch lent itself to further floral diversification. During the Wenlock epoch of the Silurian, the first fossils of vascular plants appear in the fossil record in the form of sporophytes of polysporangiophytes . Lycophytes first appeared during the later Ludlow epoch in

3038-532: The lack of tillites in the middle to late Silurian make this explanation problematic. The Silurian period has been viewed by some palaeontologists as an extended recovery interval following the Late Ordovician mass extinction (LOME), which interrupted the cascading increase in biodiversity that had continuously gone on throughout the Cambrian and most of the Ordovician. The Silurian was the first period to see megafossils of extensive terrestrial biota in

3100-652: The land. The Devonian explosion had global consequences on oceanic nutrient content and sediment cycling, which had led to the Devonian mass extinction . The expansion of trees in the Late Devonian drastically increased biological weathering rates and the consequent riverine input of nutrients into the ocean. 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. The increase in terrestrial plant matter in swamplands explains

3162-538: 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 of arbuscular mycorrhizae , a type of symbiosis between fungi and vascular plants, are known from

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3224-402: The late-Ordovician glaciation. The southern continents remained united during this period. The melting of icecaps and glaciers contributed to a rise in sea level, recognizable from the fact that Silurian sediments overlie eroded Ordovician sediments, forming an unconformity . The continents of Avalonia , Baltica , and Laurentia drifted together near the equator , starting the formation of

3286-553: The mass extinction's aftermath, but expanded their range afterwards. The most abundant brachiopods were atrypids and pentamerides; atrypids were the first to recover and rediversify in the Rhuddanian after LOME, while pentameride recovery was delayed until the Aeronian. Bryozoans exhibited significant degrees of endemism to a particular shelf. They also developed symbiotic relationships with cnidarians and stromatolites. Many bivalve fossils have also been found in Silurian deposits, and

3348-605: The paucity of atmospheric oxygen. The rise of trees and forests caused greater amounts of fine sediment particles to be retained on alluvial plains, increasing the complexity of meandering and braided fluvial systems. The greater complexity of terrestrial habitats facilitated the colonisation of the land by arthropods. Additionally, the increased weathering of phosphates and quantity of terrestrial humic matter increased nutrient levels in freshwater lakes, facilitating their colonisation by freshwater vertebrates. From these lakes, vertebrates would later follow arthropods in their conquest of

3410-493: The second half of the Silurian Period. The earliest-known representatives of this group are Cooksonia . Most of the sediments containing Cooksonia are marine in nature. Preferred habitats were likely along rivers and streams. Baragwanathia appears to be almost as old, dating to the early Ludlow (420 million years) and has branching stems and needle-like leaves of 10–20 centimetres (3.9–7.9 in). The plant shows

3472-400: The sedimentary layers above and below the unconformity are parallel, but there is no obvious erosional break between them. A break in sedimentation is indicated, for example, by fossil evidence. It is also called nondepositional unconformity or pseudoconformity. Short paraconformities are called diastems . A buttress unconformity also known as onlap unconformity, occurs when younger bedding

3534-514: The shallow Silurian seas and lakes of North America; many of their fossils have been found in New York state . Brachiopods were abundant and diverse, with the taxonomic composition, ecology, and biodiversity of Silurian brachiopods mirroring Ordovician ones. Brachiopods that survived the LOME developed novel adaptations for environmental stress, and they tended to be endemic to a single palaeoplate in

3596-405: The spread of drought-induced embolism . Tracheids , 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. Evidence of root structures appears for the first time during the Late Silurian. Further appearances of roots in

3658-606: The term is used to describe any break in the sedimentary geologic record . The significance of angular unconformity (see below) was shown by James Hutton , who found examples of Hutton's Unconformity at Jedburgh in 1787 and at Siccar Point in Berwickshire in 1788, both in Scotland. The rocks above an unconformity are younger than the rocks beneath (unless the sequence has been overturned). An unconformity represents time during which no sediments were preserved in

3720-600: Was examining fossil-bearing sedimentary rock strata in south Wales in the early 1830s. He named the sequences for a Celtic tribe of Wales, the Silures , inspired by his friend Adam Sedgwick , who had named the period of his study the Cambrian , from a Latin name for Wales. Whilst the British rocks now identified as belonging to the Silurian System and the lands now thought to have been inhabited in antiquity by

3782-408: Was questioned in 1854 by Edward Forbes , and the later stages of Barrande; F, G and H have since been shown to be Devonian. Despite these modifications in the original groupings of the strata, it is recognized that Barrande established Bohemia as a classic ground for the study of the earliest Silurian fossils. With the supercontinent Gondwana covering the equator and much of the southern hemisphere,

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3844-431: 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 with more elongate, complex xylem strand shapes that would have made the plant body more resistant to

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