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The Devonian ( ) is a geologic period and system of the
Paleozoic The Paleozoic (or Palaeozoic) Era ( ; from the Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its popula ...
, spanning 60.3 million years from the end of the
Silurian The Silurian ( ) is a spanning 24.6 million years from the end of the Period, at million years ago (), to the beginning of the Period, Mya. The Silurian is the shortest period of the . As with other periods, the beds that define the per ...
, million years ago (Mya), to the beginning of the
Carboniferous The Carboniferous ( ) is a geologic period The geologic time scale (GTS) is a system of chronological dating that classifies Geology, geological strata (stratigraphy) in time. It is used by geologists, paleontology, paleontologists, and other ...
, Mya. It is named after
Devon Devon (, archaically known as Devonshire) is a county A county is a geographical region of a country used for administrative or other purposesChambers Dictionary The ''Chambers Dictionary'' (''TCD'') was first published by William Ch ...

Devon
, England, where rocks from this period were first studied. The first significant
adaptive radiation In evolutionary biology, adaptive radiation is a process in which organisms diversify rapidly from an ancestral species into a multitude of new forms, particularly when a change in the environment makes new resources available, alters biotic inte ...
of life on dry land occurred during the Devonian. Free-sporing vascular plants began to spread across dry land, forming extensive
forest A forest is an area of land dominated by tree In botany, a tree is a perennial plant with an elongated Plant stem, stem, or trunk (botany), trunk, supporting branches and leaves in most species. In some usages, the definition of a ...

forest
s which covered the continents. 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. The
arthropod An arthropod (, (gen. ποδός)) is an invertebrate Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This includes all animals apart fr ...
groups of
myriapods Myriapoda (Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycen ...
,
arachnids Arachnida () is a class of joint-legged invertebrate animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, co ...
and hexapods also became well-established early on in this period, after having started their expansion to land at least from the
Ordovician The Ordovician ( ) is a geologic period A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place. These periods form elements of a hierarchy of divisions i ...

Ordovician
period.
Fish Fish are aquatic Aquatic means relating to water Water (chemical formula H2O) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the ...

Fish
reached substantial diversity during this time, leading the Devonian to often be dubbed the Age of Fishes. The
placoderms Placodermi (from the Greek πλάξ = plate and δέρμα = skin, literally " plate-skinned") is a Class (biology), class of armoured prehistoric fish, known from fossils, which lived from the Silurian to the end of the Devonian period. Their hea ...
began dominating almost every known aquatic environment. The ancestors of all four-limbed vertebrates (
tetrapod Tetrapods (; ) are four-limbed animals constituting the superclass Tetrapoda (). It includes extant Extant is the opposite of the word extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a sp ...
s) began adapting to walk on land, as their strong pectoral and pelvic fins gradually evolved into legs, though they were not fully established until the
Late Carboniferous Late may refer to: * LATE, an acronym which could stand for: ** Limbic-predominant age-related TDP-43 encephalopathy, a proposed form of dementia ** Local-authority trading enterprise, a New Zealand business law ** Local average treatment effect, ...
. In the oceans, primitive
shark Sharks are a group of elasmobranch Elasmobranchii () is a subclass of Chondrichthyes or cartilaginous fish, including shark Sharks are a group of elasmobranch fish characterized by a Chondrichthyes#Skeleton, cartilaginous skeleton, ...

shark
s became more numerous than in the Silurian and
Late Ordovician The Ordovician ( ) is a geologic period A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place. These periods form elements of a hierarchy of divisions i ...
. The first
ammonites Ammonoids are a group of extinct Extinction is the termination of a kind of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Li ...

ammonites
, a subclass of molluscs, appeared.
Trilobite Trilobites (; meaning "three lobes") are a group of marine s that form the Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the of the ( ...

Trilobite
s, the mollusc-like
brachiopod Brachiopods (), phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the grammatical number, grammatical category of number. The plural of a ...
s, and the great
coral reef A coral reef is an underwater ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient c ...

coral reef
s were still common. The
Late Devonian extinction The Late Devonian extinction was one of five major extinction event An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a shar ...
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 Proetida is an order of trilobite that lived from the Ordovician to the Permian. It was the last order of trilobite to go extinct, finally dying out in the Permian extinction. Description These typically small trilobites resemble those of the o ...
. The
palaeogeography area during the Middle Devonian period. Image:Pangea animation 03.gif, upright=1.4, Animation of the break-up of the supercontinent Pangaea and the subsequent drift of its constituents, from the Early Triassic to recent (250 Ma to 0). Palaeoge ...
was dominated by the
supercontinent In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology), rocks of which it is composed, and the proces ...
of
Gondwana Gondwana () or Gondwanaland was a supercontinent In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (ge ...

Gondwana
to the south, the small continent of
Siberia Siberia (; rus, Сибирь, r=Sibir', p=sʲɪˈbʲirʲ, a=Ru-Сибирь.ogg) is an extensive geographical region, constituting all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has been a part of R ...
to the north, and the early formation of the medium-sized continent of
Euramerica Laurasia (), a portmanteau for Laurentia and Asia, was the more northern of two large landmasses (the other being Gondwana) that formed part of the Pangaea supercontinent from around (Mya (unit), Mya). It separated from Gondwana (beginning in t ...
in between.


History

The period is named after
Devon Devon (, archaically known as Devonshire) is a county A county is a geographical region of a country used for administrative or other purposesChambers Dictionary The ''Chambers Dictionary'' (''TCD'') was first published by William Ch ...

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. The Great Devonian Controversy was a long period of vigorous argument and counter-argument between the main protagonists of
Roderick Murchison Sir Roderick Impey Murchison, 1st Baronet, (22 February 1792 – 22 October 1871) was a British geologist who first described and investigated the Silurian system. Early life and work Murchison was born at Tarradale Castle, Tarradale House, M ...

Roderick Murchison
with
Adam Sedgwick Adam Sedgwick (; 22 March 1785 – 27 January 1873) was a British geologist A geologist is a scientist who studies the solid, liquid, and gaseous matter that constitutes Earth and other terrestrial planets, as well as the processes that shap ...

Adam Sedgwick
against
Henry De la Beche Sir Henry Thomas De la Beche KCB, FRS (10 February 179613 April 1855) was an English geologist and palaeontologist Paleontology, also spelled palaeontology or palæontology (), is the scientific study of life that existed prior to, and som ...
supported by
George Bellas Greenough George Bellas Greenough Fellow of the Royal Society, FRS Geological Society of London, FGS (18 January 1778 – 2 April 1855) was a pioneering English (people), English geologist. He is best known as a synthesizer of geology rather than as an ori ...

George Bellas Greenough
. Murchison and Sedgwick won the debate and named the period they proposed as the Devonian System. While the rock beds that define the start and end of the Devonian Period are well identified, the exact dates are uncertain. According to the
International Commission on Stratigraphy The International Commission on Stratigraphy (ICS), sometimes referred to unofficially as the "International Stratigraphic Commission", is a daughter or major subcommittee grade scientific daughter organization that concerns itself with stratigr ...
, the Devonian extends from the end of the Silurian Mya, to the beginning of the
Carboniferous The Carboniferous ( ) is a geologic period The geologic time scale (GTS) is a system of chronological dating that classifies Geology, geological strata (stratigraphy) in time. It is used by geologists, paleontology, paleontologists, and other ...
Mya – in
North America North America is a continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven geographical regions are commonly regarded as continen ...

North America
, at the beginning of the Mississippian subperiod of the Carboniferous. 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 The Old Red Sandstone is an assemblage of rocks in the North Atlantic region largely of Devonian The Devonian ( ) is a period (geology), geologic period and system of the Paleozoic, spanning 60.3 million years from the end of the Silurian, mil ...
in which early fossil discoveries were found. Another common term is "Age of the Fishes", referring to the evolution of several major groups of
fish Fish are aquatic Aquatic means relating to water Water (chemical formula H2O) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the ...

fish
that took place during the period. 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. The Devonian has also erroneously been characterised as a "greenhouse age", due to
sampling bias In statistics Statistics is the discipline that concerns the collection, organization, analysis, interpretation, and presentation of data. In applying statistics to a scientific, industrial, or social problem, it is conventional to begin with ...
: most of the early Devonian-age discoveries came from the
strata In geology and related fields, a stratum (plural: strata) is a layer of sedimentary rock or soil, or igneous rock that was formed at the Earth's surface, with internally consistent characteristics that distinguish it from other layers. The "str ...
of
western Europe Western Europe is the western region of Europe Europe is a continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven geographical r ...

western Europe
and eastern
North America North America is a continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven geographical regions are commonly regarded as continen ...

North America
, which at the time straddled the
Equator The Equator is a circle of latitude, about in circumference, that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the N ...

Equator
as part of the supercontinent of Euramerica where
fossil A fossil (from Classical Latin Classical Latin is the form of Latin language Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication used by humans, inc ...

fossil
signatures of widespread reefs indicate tropical
climate Climate is the long-term pattern of weather Weather is the state of the atmosphere An atmosphere (from the greek words ἀτμός ''(atmos)'', meaning 'vapour', and σφαῖρα ''(sphaira)'', meaning 'ball' or 'sphere') is a la ...

climate
s that were warm and moderately humid. In fact the climate in the Devonian differed greatly during its
epochs
epochs
and between geographic regions. 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 South America is a continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven geographical regions are commonly regarded as continent ...

South America
had a warm
temperate climate In geography Geography (from Ancient Greek, Greek: , ''geographia'', literally "earth description") is a field of science devoted to the study of the lands, features, inhabitants, and phenomena of the Earth and Solar System, plan ...
. In the Late Devonian, by contrast, arid conditions were less prevalent across the world and
temperate climate In geography Geography (from Ancient Greek, Greek: , ''geographia'', literally "earth description") is a field of science devoted to the study of the lands, features, inhabitants, and phenomena of the Earth and Solar System, plan ...
s were more common.


Subdivisions

The Devonian Period is formally broken into Early, Middle and Late subdivisions. The rocks corresponding to those
epoch In chronology 222px, Joseph Scaliger's ''De emendatione temporum'' (1583) began the modern science of chronology Chronology (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-E ...
s are referred to as belonging to the Lower, Middle and Upper parts of the Devonian System. ;Early Devonian The Early Devonian lasted from and began with the
Lochkovian The Lochkovian is one of three faunal stage In chronostratigraphy, a stage is a succession of rock strata laid down in a single age on the geologic timescale The geologic time scale (GTS) is a system of chronological dating that classifies G ...
Stage , which was followed by the
Pragian The Pragian is one of three faunal stage In chronostratigraphy, a stage is a succession of rock strata laid down in a single age on the geologic timescale The geologic time scale (GTS) is a system of chronological dating that classifies Geol ...
from and then by the
Emsian The Emsian is one of three faunal stage In chronostratigraphy, a stage is a succession of rock strata laid down in a single age on the geologic timescale The geologic time scale (GTS) is a system of chronological dating that classifies Geolo ...
, which lasted until the Middle Devonian began, . During this time, the first
ammonoids Ammonoids are a group of extinct Extinction is the termination of a kind of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Li ...

ammonoids
appeared, descending from bactritoid nautiloids. Ammonoids during this time period were simple and differed little from their nautiloid counterparts. These ammonoids belong to the order
Agoniatitida Agoniatitida, also known as the Anarcestida, is the ancestral order within the cephalopod subclass Ammonoidea Ammonoids are a group of extinct Extinction is the termination of a kind of organism In biology, an organism (from Ancie ...
, which in later epochs evolved to new ammonoid orders, for example Goniatitida and
Clymeniida Clymeniida is an order of ammonoid cephalopods from the Upper Devonian characterized by having an unusual dorsal siphuncle. They measured about in diameter and are restricted to Europe, North Africa, and possibly Australia. Morphologic charact ...
. This class of
cephalopod A cephalopod is any member of the mollusca Mollusca is the second-largest phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the gram ...
molluscs would dominate the marine fauna until the beginning of the
Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles and the Age of Conifers, is the second-to-last era An era is a span of time defined for the purposes of chronology or historiography, as in the regnal eras in the history of a given monarchy ...
Era. ;Middle Devonian The Middle Devonian comprised two subdivisions: first the
Eifelian The Eifelian is one of two faunal stage In chronostratigraphy, a stage is a succession of rock strata laid down in a single age on the geologic timescale The geologic time scale (GTS) is a system of chronological dating that classifies Geolo ...
, which then gave way to the
Givetian The Givetian is one of two faunal stage In chronostratigraphy, a stage is a succession of rock strata laid down in a single age on the geologic timescale The geologic time scale (GTS) is a system of chronological dating that classifies Geol ...
. During this time the jawless
agnathan Agnatha (, Ancient Greek 'without jaws') is a superclass (biology), superclass of jawless fish in the phylum Chordata, subphylum Vertebrata, consisting of both present (Cyclostomata, cyclostomes) and extinct (conodonts and ostracoderms) species. ...
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
jawed fishes
. 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. ;Late Devonian Finally, the Late Devonian started with the
Frasnian The Frasnian is one of two faunal stages in the Late Devonian period. It lasted from million years ago to million years ago. It was preceded by the Givetian stage and followed by the Famennian stage. Major reef-building was under way during the ...
, , during which the first forests took shape on land. The first tetrapods appeared in the fossil record in the ensuing
Famennian The Famennian is the latter of two faunal stage In chronostratigraphy, a stage is a succession of rock strata laid down in a single age on the geologic timescale The geologic time scale (GTS) is a system of chronological dating that classif ...
subdivision, the beginning and end of which are marked with extinction events. This lasted until the end of the Devonian, .


Climate

The Devonian was a relatively warm period, and probably lacked any
glacier A glacier (; ) is a persistent body of dense ice Ice is into a state. Depending on the presence of such as particles of soil or bubbles of air, it can appear transparent or a more or less bluish-white color. In the , ice is abunda ...

glacier
s. The temperature gradient from the equator to the poles was not as large as it is today. The weather was also very arid, mostly along the equator where it was the driest. Reconstruction of tropical sea surface temperature from
conodont Conodonts (Greek language, Greek ''kōnos'', "cone", + ''odont'', "tooth") are an extinct group of agnathan (jawless) vertebrates resembling eels, classified in the Class (biology), class Conodonta. For many years, they were known only from their ...
apatite Apatite is a group of phosphate minerals, usually referring to hydroxyapatite Hydroxyapatite, also called hydroxylapatite (HA), is a naturally occurring mineral In geology and mineralogy, a mineral or mineral species is, broadly speaki ...

apatite
implies an average value of in the Early Devonian. levels dropped steeply throughout the Devonian Period. The newly evolved forests drew carbon out of the atmosphere, which were then buried into sediments. This may be reflected by a Mid-Devonian cooling of around . The Late Devonian warmed to levels equivalent to the Early Devonian; while there is no corresponding increase in concentrations, continental weathering increases (as predicted by warmer temperatures); further, a range of evidence, such as plant distribution, points to a Late Devonian warming. The climate would have affected the dominant organisms in
reef A reef is a ridge or shoal A tidal sandbar connecting the islands of Waya and Wayasewa of the Yasawa Islands, Fiji ">Fiji.html" ;"title="Yasawa Islands, Fiji">Yasawa Islands, Fiji In oceanography, geomorphology, and earth sciences, a s ...

reef
s;
microbes A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical process ...
would have been the main reef-forming organisms in warm periods, with corals and stromatoporoid sponges taking the dominant role in cooler times. The warming at the end of the Devonian may even have contributed to the extinction of the stromatoporoids.


Paleogeography

The Devonian Period was a time of great
tectonic Tectonics (; ) are the processes that control the structure and properties of the Earth's crust and its evolution through time. These include the processes of mountain building A mountain is an elevated portion of the Earth's crust, gen ...
activity, as
Euramerica Laurasia (), a portmanteau for Laurentia and Asia, was the more northern of two large landmasses (the other being Gondwana) that formed part of the Pangaea supercontinent from around (Mya (unit), Mya). It separated from Gondwana (beginning in t ...
and
Gondwana Gondwana () or Gondwanaland was a supercontinent In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (ge ...

Gondwana
drew closer together. The continent
Euramerica Laurasia (), a portmanteau for Laurentia and Asia, was the more northern of two large landmasses (the other being Gondwana) that formed part of the Pangaea supercontinent from around (Mya (unit), Mya). It separated from Gondwana (beginning in t ...
(or Laurussia) was created in the early Devonian by the collision of
Laurentia Image:North america craton nps.gif, upright=1.4, Laurentia, also called the North American craton Laurentia or the North American Craton is a large continental craton that forms the Geology of North America, ancient geological core of North Ameri ...
and
Baltica Baltica is a paleocontinent A paleocontinent or palaeocontinent is a distinct area of continental crust 350px, The thickness of Crust (geology)#Earth's crust, Earth's crust (km) Continental crust is the layer of Igneous rock, igneous, Sedim ...
, which rotated into the natural dry zone along the
Tropic of Capricorn The Tropic of Capricorn (or the Southern Tropic) is the circle of latitude A circle of latitude or line of latitude on is an abstract – connecting all locations around Earth (ignoring ) at a given . Circles of latitude are often ...
, which is formed as much in Paleozoic times as nowadays by the convergence of two great air-masses, the
Hadley cell#REDIRECT Hadley cell The Hadley cell, named after George Hadley, is a global scale tropical atmospheric circulation Atmospheric circulation is the large-scale movement of Atmosphere of Earth, air and together with ocean circulation is the mean ...
and the
Ferrel cell Atmospheric circulation is the large-scale movement of air File:Atmosphere gas proportions.svg, Composition of Earth's atmosphere by volume, excluding water vapor. Lower pie represents trace gases that together compose about 0.043391% of th ...
. In these near-deserts, the
Old Red Sandstone The Old Red Sandstone is an assemblage of rocks in the North Atlantic region largely of Devonian The Devonian ( ) is a period (geology), geologic period and system of the Paleozoic, spanning 60.3 million years from the end of the Silurian, mil ...
sedimentary beds formed, made red by the oxidised iron (
hematite Hematite (), also spelled as haematite, is a common iron oxide Iron oxides are chemical compounds composed of iron and oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member o ...

hematite
) characteristic of drought conditions. Near the
equator The Equator is a circle of latitude, about in circumference, that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the N ...

equator
, the plate of Euramerica and Gondwana were starting to meet, beginning the early stages of the assembling of
Pangaea Pangaea or Pangea () was a supercontinent In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology) ...

Pangaea
. This activity further raised the northern
Appalachian Mountains The Appalachian Mountains, often called the Appalachians, are a system of mountains in eastern North America North America is a continent A continent is any of several large landmasses. Generally identified by convention (nor ...

Appalachian Mountains
and formed the Caledonian Mountains in
Great Britain Great Britain is an island An island (or isle) is an isolated piece of habitat that is surrounded by a dramatically different habitat, such as water. Very small islands such as emergent land features on atoll An atoll (), ...

Great Britain
and
Scandinavia Scandinavia; Sami Places * Sápmi, a cultural region in Northern Europe * Sami, Burkina Faso, a district of the Banwa Province * Sami District, Gambia * Sami, Cephalonia, a municipality in Greece * Sami (ancient city), in Elis, Greece * Sa ...

Scandinavia
. 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 Idaho () is a state State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a monthly magazine published by the U.S. Department of State * The State (newspaper), ''The State'' (newspaper), a daily newspaper in ...

Idaho
and
Nevada Nevada (, ) is a state State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a monthly magazine published by the U.S. Department of State * The State (newspaper), ''The State'' (newspaper), a daily newspaper i ...

Nevada
; an approaching volcanic
island arc Island arcs are long chains of active volcanoes with intense seismic activity found along convergent tectonic plate boundaries (such as the Ring of Fire). Most island arcs originate on oceanic crust and have resulted from the descent of the litho ...

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. Sea levels were high worldwide, and much of the land lay under shallow seas, where tropical
reef A reef is a ridge or shoal A tidal sandbar connecting the islands of Waya and Wayasewa of the Yasawa Islands, Fiji ">Fiji.html" ;"title="Yasawa Islands, Fiji">Yasawa Islands, Fiji In oceanography, geomorphology, and earth sciences, a s ...

reef
organisms lived. The deep, enormous
Panthalassa Panthalassa, also known as the Panthalassic Ocean or Panthalassan Ocean (from Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located i ...
(the "universal ocean") covered the rest of the
planet A planet is an astronomical body orbiting a star or Stellar evolution#Stellar remnants, stellar remnant that is massive enough to be Hydrostatic equilibrium, rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and ...

planet
. Other minor oceans were the
Paleo-Tethys Ocean The Paleo-Tethys or Palaeo-Tethys Ocean was an ocean The ocean (also the or the world ocean) is the body of that covers approximately 70.8% of the surface of and contains 97% of . Another definition is "any of the large bodies of water ...
, Proto-Tethys Ocean,
Rheic Ocean The Rheic Ocean was an ocean The ocean (also the sea or the world ocean) is the body of salt water which covers approximately 71% of the surface of the Earth.world map, originally prepared by Joan Blaeu for his ''Atlas Maior'', published ...
, and
Ural Ocean The Ural Ocean (also called the Uralic Ocean) was a small, ancient ocean that was situated between Siberia Siberia (; rus, Сибирь, r=Sibir', p=sʲɪˈbʲirʲ, a=Ru-Сибирь.ogg) is an extensive geographical region spanning much of N ...
(which was closed during the collision with
Siberia Siberia (; rus, Сибирь, r=Sibir', p=sʲɪˈbʲirʲ, a=Ru-Сибирь.ogg) is an extensive geographical region, constituting all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has been a part of R ...
and Baltica). During the Devonian, Chaitenia, an
island arc Island arcs are long chains of active volcanoes with intense seismic activity found along convergent tectonic plate boundaries (such as the Ring of Fire). Most island arcs originate on oceanic crust and have resulted from the descent of the litho ...

island arc
, accreted to
Patagonia Patagonia () refers to a geographical region that encompasses the southern end of South America South America is a continent A continent is one of several large landmasses. Generally identified by convention (norm), convent ...
.


Life


Marine biota

Sea levels in the Devonian were generally high. Marine faunas continued to be dominated by
bryozoa Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) are a phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the ...

bryozoa
, diverse and abundant
brachiopod Brachiopods (), phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the grammatical number, grammatical category of number. The plural of a ...
s, the enigmatic hederellids, microconchids and
coral Corals are marine invertebrates Marine invertebrates are the invertebrates that live in marine habitats. Invertebrate is a blanket term that includes all animals apart from the vertebrate members of the chordate phylum. Invertebrates lack a ver ...

coral
s. Lily-like
crinoid Crinoids are marine animals that make up the class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class ...

crinoid
s (animals, their resemblance to flowers notwithstanding) were abundant, and
trilobite Trilobites (; meaning "three lobes") are a group of marine s that form the Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the of the ( ...

trilobite
s were still fairly common. Among vertebrates, jawless armored fish (
ostracoderm Ostracoderms () are the armored jawless fish Agnatha (, Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often r ...

ostracoderm
s) declined in diversity, while the jawed fish (gnathostomes) simultaneously increased in both the sea and
fresh water Fresh water or freshwater is any naturally occurring liquid or frozen water Water (chemical formula H2O) is an , transparent, tasteless, odorless, and , which is the main constituent of 's and the s of all known living organisms (in ...

fresh water
. 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. Early cartilaginous (
Chondrichthyes Chondrichthyes (; ) is a class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an an ...

Chondrichthyes
) and bony fishes (
Osteichthyes Osteichthyes (), popularly referred to as the bony fish, is a diverse taxonomic Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may al ...

Osteichthyes
) also become diverse and played a large role within the Devonian seas. The first abundant genus of shark, '''', appeared in the oceans during the Devonian Period. 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. The first ammonites also appeared during or slightly before the early Devonian Period around 400 Mya.


Reefs

A now-dry barrier reef, located in present-day Kimberley Basin of northwest
Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

Australia
, once extended , fringing a Devonian continent. Reefs in general are built by various
carbonate In chemistry, a carbonate is a salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), salts; salt in its natural form as a crystallinity, crystalline mi ...

carbonate
-secreting organisms that have the ability to erect wave-resistant structures close to sea level. Although modern reefs are constructed mainly by corals and calcareous
algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic Photosynthesis is a process used by plants and other organisms to convert Conversion or convert may refer to: Arts, entertainment, and media * Co ...

algae
, Devonian reefs were either microbial reefs built up mostly by
autotrophic An autotroph or primary producer is an organism that produces complex organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bo ...
cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the grammatical number, grammatical ...

cyanobacteria
, or coral-stromatoporoid reefs built up by coral-like stromatoporoids and tabulate and rugose corals. Microbial reefs dominated under the warmer conditions of the early and late Devonian, while coral-stromatoporoid reefs dominated during the cooler middle Devonian.


Terrestrial biota

By the Devonian Period, life was well underway in its colonisation of the land. The
moss Mosses are small, non-vascular flower A flower, sometimes known as a bloom or blossom Cherry blossoms in Paris in full bloom. In botany, blossoms are the flowers of stone fruit fruit tree, trees (genus ''Prunus'') and of some other plant ...

moss
forests and
bacteria Bacteria (; common noun bacteria, singular bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typ ...

bacteria
l and algal mats of the Silurian were joined early in the period by primitive rooted plants that created the first stable
soil Soil is a mixture In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, comp ...

soil
s and harbored arthropods like
mite Mites are small arachnid Arachnida () is a class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Cl ...
s,
scorpion Scorpions are predatory Predation is a biological interaction In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including hum ...

scorpion
s, trigonotarbids and
myriapods Myriapoda (Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycen ...

myriapods
(although arthropods appeared on land much earlier than in the Early Devonian and the existence of fossils such as ''
Protichnites ''Protichnites'' is an ichnogenus An ichnotaxon (plural ichnotaxa) is "a taxon In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processe ...

Protichnites
'' suggest that amphibious arthropods may have appeared as early as the
Cambrian The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place. These peri ...
). By far the largest land organism at the beginning of this period was the enigmatic ''
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 height, made up of ...
'', which was possibly the fruiting body of an enormous fungus, rolled liverwort mat, or another organism of uncertain affinities that stood more than tall, and towered over the low, carpet-like vegetation during the early part of the Devonian. Also the first possible fossils of insects appeared around 416 Mya, in the Early Devonian. Evidence for the earliest
tetrapod Tetrapods (; ) are four-limbed animals constituting the superclass Tetrapoda (). It includes extant Extant is the opposite of the word extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a sp ...
s 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.


The greening of land

Many List of Early Devonian land plants, Early Devonian plants did not have true roots or leaves like extant plants although vascular tissue is observed in many of those plants. Some of the early land plants such as ''Drepanophycus'' likely spread by vegetative growth and spores. The earliest land plants such as ''Cooksonia'' consisted of leafless, Dichotomous branching, dichotomous axes and terminal sporangia and were generally very short-statured, and grew hardly more than a few centimetres tall. Fossils of ''Armoricaphyton, Armoricaphyton chateaupannense'', about 400 million years old, represent the oldest known plants with woody tissue. By the Middle Devonian, shrub-like forests of primitive plants existed: Lycopodiophyta, lycophytes, Equisetales, horsetails, ferns, and progymnosperms had evolved. Most of these plants had true roots and leaves, and many were quite tall. The earliest-known trees appeared in the Middle Devonian. These included a lineage of lycopods and another arborescent, woody vascular plant, the Cladoxylopsida, cladoxylopsids. These tracheophytes were able to grow to large size on dry land because they had evolved the ability to biosynthesize lignin, which gave them physical rigidity and improved the effectiveness of their vascular system while giving them resistance to pathogens and herbivores. These are the oldest-known trees of the world's first forests. By the end of the Devonian, the first seed-forming plants had appeared. This rapid appearance of so many plant groups and growth forms has been called the "Devonian Explosion". The 'greening' of the continents acted as a carbon sink, and Atmosphere of Earth, atmospheric concentrations of carbon dioxide may have dropped. This may have cooled the climate and led to a massive extinction event. (''See''
Late Devonian extinction The Late Devonian extinction was one of five major extinction event An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a shar ...
).


Animals and the first soils

Primitive arthropods co-evolved with this diversified terrestrial vegetation structure. The evolving co-dependence of insects and seed-plants that characterised a recognisably modern world had its genesis in the Late Devonian Epoch. The development of soils and plant root systems probably led to changes in the speed and pattern of erosion and sediment deposition. The rapid evolution of a terrestrial ecosystem that contained copious animals opened the way for the first vertebrates to seek out a terrestrial living. By the end of the Devonian, arthropods were solidly established on the land.


Gallery

Image:D_Terrelli.png, ''Dunkleosteus'', one of the largest armoured fish ever to roam the planet, lived during the Late Devonian Image:Eastmanosteus pustulosus.jpg, Lower jaw of ''Eastmanosteus pustulosus'' from the Middle Devonian of Wisconsin Image:Onychodus.jpg, Tooth of the lobe-finned fish ''Onychodus'' from the Middle Devonian of Wisconsin Image:Devonianfishes ntm 1905 smit 1929.gif, Early shark '''', several Sarcopterygii, lobe-finned fishes, including ''Eusthenopteron'' that was an early marine tetrapod, and the placoderm ''Bothriolepis'' in a painting from 1905 Image:Melocrinites nodosus spinosus.jpg, ''Melocrinites nodosus spinosus'', a spiny, stalked
crinoid Crinoids are marine animals that make up the class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class ...

crinoid
from the Middle Devonian of Wisconsin Image:PhacopidDevonian.jpg, Enrolled phacopid
trilobite Trilobites (; meaning "three lobes") are a group of marine s that form the Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the of the ( ...

trilobite
from the Devonian of Ohio Image:AuloporaDevonianSilicaShale.jpg, The common tabulate coral ''Aulopora'' from the Middle Devonian of Ohio – view of colony encrusting a
brachiopod Brachiopods (), phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the grammatical number, grammatical category of number. The plural of a ...
valve Image:Tropidoleptus carinatus.jpg, ''Tropidoleptus carinatus'', an orthid brachiopod from the Middle Devonian of New York Image:Pleurodictyum americanum Kashong.jpg, ''Pleurodictyum, Pleurodictyum americanum'', Kashong Shale, Middle Devonian of New York Image:HederelloidSEM.jpg, SEM image of a hederelloid from the Devonian of Michigan (largest tube diameter is 0.75 mm) Image:HederellaOH3.jpg, Devonian spiriferid brachiopod from Ohio which served as a host substrate for a colony of hederelloids


Late Devonian extinction

The
Late Devonian extinction The Late Devonian extinction was one of five major extinction event An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a shar ...
is not a single event, but rather is a series of pulsed extinctions at the Givetian-Frasnian boundary, the Frasnian-Famennian boundary, and the Devonian-Carboniferous boundary. Together, these are considered one of the "Big Five" mass extinctions in Earth's history. The Devonian extinction crisis primarily affected the marine community, and selectively affected shallow warm-water organisms rather than cool-water organisms. The most important group to be affected by this extinction event were the reef-builders of the great Devonian reef systems. Amongst the severely affected marine groups were the brachiopods, trilobites, ammonites, and acritarchs, and the world saw the disappearance of an estimated 96% of vertebrates like
conodont Conodonts (Greek language, Greek ''kōnos'', "cone", + ''odont'', "tooth") are an extinct group of agnathan (jawless) vertebrates resembling eels, classified in the Class (biology), class Conodonta. For many years, they were known only from their ...
s and Osteichthyes, bony fishes, and all of the ostracoderms and placoderms. Land plants as well as freshwater species, such as our tetrapod ancestors, were relatively unaffected by the Late Devonian extinction event (there is a counterargument that the Devonian extinctions nearly wiped out the tetrapods). The reasons for the Late Devonian extinctions are still unknown, and all explanations remain speculative. Canadian paleontologist Digby McLaren suggested in 1969 that the Devonian extinction events were caused by an asteroid impact. However, while there were Late Devonian collision events (see the Alamo bolide impact), little evidence supports the existence of a large enough Devonian crater.


See also

* Celsius Bjerg Formation - in Greenland, with fossils dating back to the Devonian Period. * , Indiana, United States. One of the largest exposed Devonian fossil beds in the world. * * * ''(with link directory)'' * , a Devonian trilobite ;Categories: *


Notes


References


External links

* * – site introduces the Devonian * * * * * {{Authority control Devonian, Geological periods Geology of Devon, .