Devonian

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This article is about the geological period. Devonian_sentence_0

For the residents of the UK county, see Devon. Devonian_sentence_1

For other uses, see Devonian (disambiguation). Devonian_sentence_2

Devonian_table_infobox_0

DevonianDevonian_header_cell_0_0_0
ChronologyDevonian_header_cell_0_1_0
EtymologyDevonian_header_cell_0_2_0
Name formalityDevonian_header_cell_0_3_0 FormalDevonian_cell_0_3_1
Nickname(s)Devonian_header_cell_0_4_0 Age of FishesDevonian_cell_0_4_1
Usage InformationDevonian_header_cell_0_5_0
Celestial bodyDevonian_header_cell_0_6_0 EarthDevonian_cell_0_6_1
UsageDevonian_header_cell_0_7_0 Global (ICS)Devonian_cell_0_7_1
Time scale(s) usedDevonian_header_cell_0_8_0 ICS Time ScaleDevonian_cell_0_8_1
DefinitionDevonian_header_cell_0_9_0
Chronological unitDevonian_header_cell_0_10_0 PeriodDevonian_cell_0_10_1
Stratigraphic unitDevonian_header_cell_0_11_0 SystemDevonian_cell_0_11_1
Time span formalityDevonian_header_cell_0_12_0 FormalDevonian_cell_0_12_1
Lower boundary definitionDevonian_header_cell_0_13_0 First appearance of the Graptolite Monograptus uniformisDevonian_cell_0_13_1
Lower boundary GSSPDevonian_header_cell_0_14_0 Klonk, Prague, CzechiaDevonian_cell_0_14_1
GSSP ratifiedDevonian_header_cell_0_15_0 1972Devonian_cell_0_15_1
Upper boundary definitionDevonian_header_cell_0_16_0 First appearance of the Conodont Siphonodella sulcata (discovered to have biostratigraphic issues as of 2006).Devonian_cell_0_16_1
Upper boundary GSSPDevonian_header_cell_0_17_0 La Serre, Montagne Noire, FranceDevonian_cell_0_17_1
GSSP ratifiedDevonian_header_cell_0_18_0 1990Devonian_cell_0_18_1
Atmospheric and Climatic DataDevonian_header_cell_0_19_0
Mean atmospheric O 2 contentDevonian_header_cell_0_20_0 c. 15 vol %

(75 % of modern level)Devonian_cell_0_20_1

Mean atmospheric CO 2 contentDevonian_header_cell_0_21_0 c. 2200 ppm

(8 times pre-industrial level)Devonian_cell_0_21_1

Mean surface temperatureDevonian_header_cell_0_22_0 c. 20 °C

(6 °C above modern level)Devonian_cell_0_22_1

Sea level above present dayDevonian_header_cell_0_23_0 Relatively steady around 189m, gradually falling to 120m through periodDevonian_cell_0_23_1

The Devonian (/dɪˈvoʊ.ni.ən, də-, dɛ-/ dih-VOH-nee-ən, də-, deh-) is a geologic period and system of the Paleozoic, spanning 60 million years from the end of the Silurian, 419.2 million years ago (Mya), to the beginning of the Carboniferous, 358.9 Mya. Devonian_sentence_3

It is named after Devon, England, where rocks from this period were first studied. Devonian_sentence_4

The first significant adaptive radiation of life on dry land occurred during the Devonian. Devonian_sentence_5

Free-sporing vascular plants began to spread across dry land, forming extensive forests which covered the continents. Devonian_sentence_6

By the middle of the Devonian, several groups of plants had evolved leaves and true roots, and by the end of the period the first seed-bearing plants appeared. Devonian_sentence_7

Various terrestrial arthropods also became well-established. Devonian_sentence_8

Fish reached substantial diversity during this time, leading the Devonian to often be dubbed the Age of Fishes. Devonian_sentence_9

The placoderms began dominating almost every known aquatic environment. Devonian_sentence_10

The ancestors of all four-limbed vertebrates (tetrapods) began adapting to walking on land, as their strong pectoral and pelvic fins gradually evolved into legs. Devonian_sentence_11

In the oceans, primitive sharks became more numerous than in the Silurian and Late Ordovician. Devonian_sentence_12

The first ammonites, species of molluscs, appeared. Devonian_sentence_13

Trilobites, the mollusc-like brachiopods, and the great coral reefs were still common. Devonian_sentence_14

The Late Devonian extinction which started about 375 million years ago severely affected marine life, killing off all placodermi, and all trilobites, save for a few species of the order Proetida. Devonian_sentence_15

The palaeogeography was dominated by the supercontinent of Gondwana to the south, the continent of Siberia to the north, and the early formation of the small continent of Euramerica in between. Devonian_sentence_16

History Devonian_section_0

The period is named after Devon, a county in southwestern England, where a controversial argument in the 1830s, over the age and structure of the rocks found distributed throughout the county was eventually resolved by the definition of the Devonian period in the geological timescale. Devonian_sentence_17

The Great Devonian Controversy was a long period of vigorous argument and counter-argument between the main protagonists of Roderick Murchison with Adam Sedgwick against Henry De la Beche supported by George Bellas Greenough. Devonian_sentence_18

Murchison and Sedgwick won the debate and named the period they proposed as the Devonian System. Devonian_sentence_19

While the rock beds that define the start and end of the Devonian period are well identified, the exact dates are uncertain. Devonian_sentence_20

According to the International Commission on Stratigraphy, the Devonian extends from the end of the Silurian 419.2 Mya, to the beginning of the Carboniferous 358.9 Mya – in North America, at the beginning of the Mississippian subperiod of the Carboniferous. Devonian_sentence_21

In nineteenth-century texts the Devonian has been called the "Old Red Age", after the red and brown terrestrial deposits known in the United Kingdom as the Old Red Sandstone in which early fossil discoveries were found. Devonian_sentence_22

Another common term is "Age of the Fishes", referring to the evolution of several major groups of fish that took place during the period. Devonian_sentence_23

Older literature on the Anglo-Welsh basin divides it into the Downtonian, Dittonian, Breconian, and Farlovian stages, the latter three of which are placed in the Devonian. Devonian_sentence_24

The Devonian has also erroneously been characterised as a "greenhouse age", due to sampling bias: most of the early Devonian-age discoveries came from the strata of western Europe and eastern North America, which at the time straddled the Equator as part of the supercontinent of Euramerica where fossil signatures of widespread reefs indicate tropical climates that were warm and moderately humid but in fact the climate in the Devonian differed greatly during its epochs and between geographic regions. Devonian_sentence_25

For example, during the Early Devonian, arid conditions were prevalent through much of the world including Siberia, Australia, North America, and China, but Africa and South America had a warm temperate climate. Devonian_sentence_26

In the Late Devonian, by contrast, arid conditions were less prevalent across the world and temperate climates were more common. Devonian_sentence_27

Subdivisions Devonian_section_1

The Devonian Period is formally broken into Early, Middle and Late subdivisions. Devonian_sentence_28

The rocks corresponding to those epochs are referred to as belonging to the Lower, Middle and Upper parts of the Devonian System. Devonian_sentence_29

Devonian_description_list_0

The Early Devonian lasted from ± 2.8 to ± 2.5 and began with the Lochkovian stage ± 2.8 to ± 2.5, which was followed by the Pragian from ± 2.8 to ± 2.5 and then by the Emsian, which lasted until the Middle Devonian began, ± 2.7 million years ago. Devonian_sentence_30

During this time, the first ammonoids appeared, descending from bactritoid nautiloids. Devonian_sentence_31

Ammonoids during this time period were simple and differed little from their nautiloid counterparts. Devonian_sentence_32

These ammonoids belong to the order Agoniatitida, which in later epochs evolved to new ammonoid orders, for example Goniatitida and Clymeniida. Devonian_sentence_33

This class of cephalopod molluscs would dominate the marine fauna until the beginning of the Mesozoic era. Devonian_sentence_34

Devonian_description_list_1

The Middle Devonian comprised two subdivisions: first the Eifelian, which then gave way to the Givetian ± 2.7 million years ago. Devonian_sentence_35

During this time the jawless agnathan fishes began to decline in diversity in freshwater and marine environments partly due to drastic environmental changes and partly due to the increasing competition, predation, and diversity of jawed fishes. Devonian_sentence_36

The shallow, warm, oxygen-depleted waters of Devonian inland lakes, surrounded by primitive plants, provided the environment necessary for certain early fish to develop such essential characteristics as well developed lungs, and the ability to crawl out of the water and onto the land for short periods of time. Devonian_sentence_37

Devonian_description_list_2

Finally, the Late Devonian started with the Frasnian, ± 2.8 to ± 2.5, during which the first forests took shape on land. Devonian_sentence_38

The first tetrapods appeared in the fossil record in the ensuing Famennian subdivision, the beginning and end of which are marked with extinction events. Devonian_sentence_39

This lasted until the end of the Devonian, ± 2.5 million years ago. Devonian_sentence_40

Climate Devonian_section_2

The Devonian was a relatively warm period, and probably lacked any glaciers. Devonian_sentence_41

The temperature gradient from the equator to the poles was not as large as it is today. Devonian_sentence_42

The weather was also very arid, mostly along the equator where it was the driest. Devonian_sentence_43

Reconstruction of tropical sea surface temperature from conodont apatite implies an average value of 30 °C (86 °F) in the Early Devonian. Devonian_sentence_44

CO 2 levels dropped steeply throughout the Devonian period. Devonian_sentence_45

The newly evolved forests drew carbon out of the atmosphere, which were then buried into sediments. Devonian_sentence_46

This may be reflected by a Mid-Devonian cooling of around 5 °C (9 °F). Devonian_sentence_47

The Late Devonian warmed to levels equivalent to the Early Devonian; while there is no corresponding increase in CO 2 concentrations, continental weathering increases (as predicted by warmer temperatures); further, a range of evidence, such as plant distribution, points to a Late Devonian warming. Devonian_sentence_48

The climate would have affected the dominant organisms in reefs; microbes would have been the main reef-forming organisms in warm periods, with corals and stromatoporoid sponges taking the dominant role in cooler times. Devonian_sentence_49

The warming at the end of the Devonian may even have contributed to the extinction of the stromatoporoids. Devonian_sentence_50

Paleogeography Devonian_section_3

The Devonian period was a time of great tectonic activity, as Euramerica and Gondwana drew closer together. Devonian_sentence_51

The continent Euramerica (or Laurussia) was created in the early Devonian by the collision of Laurentia and Baltica, which rotated into the natural dry zone along the Tropic of Capricorn, which is formed as much in Paleozoic times as nowadays by the convergence of two great air-masses, the Hadley cell and the Ferrel cell. Devonian_sentence_52

In these near-deserts, the Old Red Sandstone sedimentary beds formed, made red by the oxidised iron (hematite) characteristic of drought conditions. Devonian_sentence_53

Near the equator, the plate of Euramerica and Gondwana were starting to meet, beginning the early stages of the assembling of Pangaea. Devonian_sentence_54

This activity further raised the northern Appalachian Mountains and formed the Caledonian Mountains in Great Britain and Scandinavia. Devonian_sentence_55

The west coast of Devonian North America, by contrast, was a passive margin with deep silty embayments, river deltas and estuaries, found today in Idaho and Nevada; an approaching volcanic island arc reached the steep slope of the continental shelf in Late Devonian times and began to uplift deep water deposits, a collision that was the prelude to the mountain-building episode at the beginning of the Carboniferous called the Antler orogeny. Devonian_sentence_56

Sea levels were high worldwide, and much of the land lay under shallow seas, where tropical reef organisms lived. Devonian_sentence_57

The deep, enormous Panthalassa (the "universal ocean") covered the rest of the planet. Devonian_sentence_58

Other minor oceans were the Paleo-Tethys Ocean, Proto-Tethys Ocean, Rheic Ocean, and Ural Ocean (which was closed during the collision with Siberia and Baltica). Devonian_sentence_59

During the Devonian, Chaitenia, an island arc, accreted to Patagonia. Devonian_sentence_60

Life Devonian_section_4

Marine biota Devonian_section_5

See also: Evolution of fish § Devonian: Age of fishes Devonian_sentence_61

Sea levels in the Devonian were generally high. Devonian_sentence_62

Marine faunas continued to be dominated by bryozoa, diverse and abundant brachiopods, the enigmatic hederellids, microconchids and corals. Devonian_sentence_63

Lily-like crinoids (animals, their resemblance to flowers notwithstanding) were abundant, and trilobites were still fairly common. Devonian_sentence_64

Among vertebrates, jawless armored fish (ostracoderms) declined in diversity, while the jawed fish (gnathostomes) simultaneously increased in both the sea and fresh water. Devonian_sentence_65

Armored placoderms were numerous during the lower stages of the Devonian Period and became extinct in the Late Devonian, perhaps because of competition for food against the other fish species. Devonian_sentence_66

Early cartilaginous (Chondrichthyes) and bony fishes (Osteichthyes) also become diverse and played a large role within the Devonian seas. Devonian_sentence_67

The first abundant genus of shark, Cladoselache, appeared in the oceans during the Devonian Period. Devonian_sentence_68

The great diversity of fish around at the time has led to the Devonian being given the name "The Age of Fish" in popular culture. Devonian_sentence_69

The first ammonites also appeared during or slightly before the early Devonian Period around 400 Mya. Devonian_sentence_70

Reefs Devonian_section_6

A now dry barrier reef, located in present-day Kimberley Basin of northwest Australia, once extended a thousand kilometres, fringing a Devonian continent. Devonian_sentence_71

Reefs in general are built by various carbonate-secreting organisms that have the ability to erect wave-resistant structures close to sea level. Devonian_sentence_72

Although modern reefs are constructed mainly by corals and calcareous algae, the main contributors of the Devonian reefs were different: They were composed of calcareous algae, coral-like stromatoporoids, and tabulate and rugose corals, in that order of importance. Devonian_sentence_73

Terrestrial biota Devonian_section_7

By the Devonian Period, life was well underway in its colonisation of the land. Devonian_sentence_74

The moss forests and bacterial and algal mats of the Silurian were joined early in the period by primitive rooted plants that created the first stable soils and harbored arthropods like mites, scorpions, trigonotarbids and myriapods (although arthropods appeared on land much earlier than in the Early Devonian and the existence of fossils such as Protichnites suggest that amphibious arthropods may have appeared as early as the Cambrian). Devonian_sentence_75

By far the largest land organism at the beginning of this period was the enigmatic Prototaxites, which was possibly the fruiting body of an enormous fungus, rolled liverwort mat, or another organism of uncertain affinities that stood more than 8 metres (26 ft) tall, and towered over the low, carpet-like vegetation during the early part of the Devonian. Devonian_sentence_76

Also the first possible fossils of insects appeared around 416 Mya, in the Early Devonian. Devonian_sentence_77

Evidence for the earliest tetrapods takes the form of trace fossils in shallow lagoon environments within a marine carbonate platform / shelf during the Middle Devonian, although these traces have been questioned and an interpretation as fish feeding traces (Piscichnus) has been advanced. Devonian_sentence_78

The greening of land Devonian_section_8

Many Early Devonian plants did not have true roots or leaves like extant plants although vascular tissue is observed in many of those plants. Devonian_sentence_79

Some of the early land plants such as Drepanophycus likely spread by vegetative growth and spores. Devonian_sentence_80

The earliest land plants such as Cooksonia consisted of leafless, dichotomous axes and terminal sporangia and were generally very short-statured, and grew hardly more than a few centimetres tall. Devonian_sentence_81

By the Middle Devonian, shrub-like forests of primitive plants existed: lycophytes, horsetails, ferns, and progymnosperms had evolved. Devonian_sentence_82

Most of these plants had true roots and leaves, and many were quite tall. Devonian_sentence_83

The earliest-known trees appeared in the Middle Devonian These included a lineage of lycopods and another arborescent, woody vascular plant, the cladoxylopsids. Devonian_sentence_84

(See also: lignin.) Devonian_sentence_85

These are the oldest-known trees of the world's first forests. Devonian_sentence_86

By the end of the Devonian, the first seed-forming plants had appeared. Devonian_sentence_87

This rapid appearance of so many plant groups and growth forms has been called the "Devonian Explosion". Devonian_sentence_88

The 'greening' of the continents acted as a carbon sink, and atmospheric concentrations of carbon dioxide may have dropped. Devonian_sentence_89

This may have cooled the climate and led to a massive extinction event. Devonian_sentence_90

See Late Devonian extinction. Devonian_sentence_91

Animals and the first soils Devonian_section_9

Primitive arthropods co-evolved with this diversified terrestrial vegetation structure. Devonian_sentence_92

The evolving co-dependence of insects and seed-plants that characterised a recognisably modern world had its genesis in the Late Devonian period. Devonian_sentence_93

The development of soils and plant root systems probably led to changes in the speed and pattern of erosion and sediment deposition. Devonian_sentence_94

The rapid evolution of a terrestrial ecosystem that contained copious animals opened the way for the first vertebrates to seek out a terrestrial living. Devonian_sentence_95

By the end of the Devonian, arthropods were solidly established on the land. Devonian_sentence_96


Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Devonian.