Devonian 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.
It is named after Devon, England, where rocks from this period were
The first significant adaptive radiation of life on dry land occurred
during the Devonian. Free-sporing vascular plants began to spread
across dry land, forming extensive forests 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. Various terrestrial arthropods
also became well-established.
Fish reached substantial diversity during this time, leading the
Devonian to often be dubbed the "Age of Fish". The first ray-finned
and lobe-finned bony fish appeared, while the placoderms began
dominating almost every known aquatic environment. 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. In the oceans, primitive sharks became more numerous than in
Silurian and Late Ordovician.
The first ammonites, species of molluscs, appeared. Trilobites, the
mollusk-like brachiopods and the great coral reefs, were still common.
Late Devonian extinction
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.
The palaeogeography was dominated by the supercontinent of
the south, the continent of Siberia to the north, and the early
formation of the small continent of
Euramerica in between.
5.1 Marine biota
5.3 Terrestrial biota
5.3.1 The greening of land
5.3.2 Animals and the first soils
Late Devonian extinction
7 See also
9 External links
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The rocks of Lummaton Quarry in
Devon played an early role
in defining the
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
The Great Devonian Controversy was a long period of
vigorous argument and counter-argument between the main protagonists
Roderick Murchison with
Adam Sedgwick against Henry De la Beche
supported by George Bellas Greenough. Murchison and Sedgwick won the
debate and named the period they proposed as the Devonian
While the rock beds that define the start and end of the Devonian
period are well identified, the exact dates are uncertain. According
International Commission on Stratigraphy (Ogg, 2004), the
Devonian extends from the end of the
Silurian 419.2 Mya, to the
beginning of the
Carboniferous 358.9 Mya (in North America, 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
Old Red Sandstone 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 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.
Devonian has also erroneously been characterized 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
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. 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. In the Late Devonian, by contrast, arid
conditions were less prevalent across the world and temperate climates
were more common.
Devonian Period is formally broken into Early, Middle and Late
subdivisions. The rocks corresponding to those epochs are referred to
as belonging to the Lower, Middle and Upper parts of the Devonian
Early Devonian lasted from 419.2 ± 2.8 to 393.3
± 2.5 and began with the
Lochkovian stage, which lasted until
the Pragian. It spanned from 410.8 ± 2.8 to 407.6
± 2.5, and was followed by the Emsian, which lasted until the
Middle Devonian began, 393.3± 2.7 million years
Middle Devonian comprised two subdivisions: first the Eifelian,
which then gave way to the
Givetian 387.7± 2.7 million
years ago. 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. 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 started with the Frasnian, 382.7
± 2.8 to 372.2 ± 2.5, during which the first forests
took shape on land. The first tetrapods appeared in the fossil record
in the ensuing
Famennian subdivision, the beginning and end of which
are marked with extinction events. This lasted until the end of the
Devonian, 358.9± 2.5 million years ago.
Devonian was a relatively warm period, and probably lacked any
glaciers. 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 apatite implies an
average value of 30 °C (86 °F) in the Early Devonian.
CO2 levels dropped steeply throughout the
Devonian period as the
burial of the newly evolved forests drew carbon out of the atmosphere
into sediments; this may be reflected by a Mid-
Devonian cooling of
around 5 °C (9 °F). The
Late Devonian warmed to levels
equivalent to the Early Devonian; while there is no corresponding
increase in CO2 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 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. The warming at the end of the
Devonian may even have
contributed to the extinction of the stromatoporoids.
Paleo-Tethys Ocean opened during the Devonian
Devonian period was a time of great tectonic activity, as
Gondwana drew closer together.
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
Paleozoic times as nowadays by the convergence of two great
Hadley cell and the Ferrel cell. In these
Old Red Sandstone
Old Red Sandstone sedimentary beds formed, made red
by the oxidized iron (hematite) characteristic of drought
Near the equator, the plate of
Gondwana were starting
to meet, beginning the early stages of the assembling of Pangaea. This
activity further raised the northern
Appalachian Mountains and formed
the Caledonian Mountains in
Great Britain and Scandinavia.
The west coast of
Devonian North America, by contrast, was a passive
margin with deep silty embayments, river deltas and estuaries, found
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.
Sea levels were high worldwide, and much of the land lay under shallow
seas, where tropical reef organisms lived. The deep, enormous
Panthalassa (the "universal ocean") covered the rest of the planet.
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).
Spindle diagram for the evolution of fish and other vertebrate
classes. The diagram is based on Michael Benton, 2005.
See also: Evolution of fish § Devonian: Age of fishes
Sea levels in the
Devonian were generally high. Marine faunas
continued to be dominated by bryozoa, diverse and abundant
brachiopods, the enigmatic hederellids, microconchids and corals.
Lily-like crinoids (animals, their resemblance to flowers
notwithstanding) were abundant, and trilobites were still fairly
common. Among vertebrates, jaw-less armored fish (ostracoderms)
declined in diversity, while the jawed fish (gnathostomes)
simultaneously increased in both the sea and 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) and bony fishes (Osteichthyes) also
become diverse and played a large role within the
Devonian seas. The
first abundant genus of shark, Cladoselache, appeared in the oceans
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
The first ammonites also appeared during or slightly before the early
Devonian Period around 400 Mya.
A now dry barrier reef, located in present-day Kimberley Basin of
northwest Australia, once extended a thousand kilometers, fringing a
Reefs in general are built by various
carbonate-secreting organisms that have the ability to erect
wave-resistant frameworks close to sea level. The main contributors of
Devonian reefs were unlike modern reefs, which are constructed
mainly by corals and calcareous algae. They were composed of
calcareous algae and coral-like stromatoporoids, and tabulate and
rugose corals, in that order of importance.[clarification needed]
Dunkleosteus, one of the largest armoured fish ever to roam the
planet, lived during the late Devonian
Early shark Cladoselache, several lobe-finned fishes, including
Eusthenopteron that was an early marine tetrapod, and the placoderm
Bothriolepis in a painting from 1905
Enrolled phacopid trilobite from the
Devonian of Ohio
The common tabulate coral
Aulopora from the
Middle Devonian of Ohio
– view of colony encrusting a brachiopod valve
Tropidoleptus carinatus, an orthid brachiopod from the Middle Devonian
of New York.
Pleurodictyum americanum, Kashong Shale,
Middle Devonian of New York
SEM image of a hederelloid from the
Devonian of Michigan (largest tube
diameter is 0.75 mm)
Devonian spiriferid brachiopod from
Ohio which served as a host
substrate for a colony of hederelloids
Devonian Period, life was well underway in its colonization of
the land. 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 Climactichnites
suggest that land arthropods may have appeared as early as the
Cambrian). Also the first possible fossils of insects appeared around
416 Mya in the Early Devonian. 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.
The greening of land
Devonian period marks the beginning of extensive land colonization
by plants. With large land-dwelling herbivores not yet present, large
forests grew and shaped the landscape.
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
spread by vegetative growth and spores. 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 centimeters tall. By far the largest land organism
during 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
meters tall, and towered over the low, carpet-like vegetation. By the
Middle Devonian, shrub-like forests of primitive plants existed:
lycophytes, horsetails, ferns, and progymnosperms had evolved. Most of
these plants had true roots and leaves, and many were quite tall. The
earliest known trees, from the genus Wattieza, appeared in the Late
Devonian around 385 Mya. In the Late Devonian, the tree-like
Archaeopteris which had conifer-like true wood
and fern-like foliage and the cladoxylopsids grew. (See also:
lignin.) 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 "
The 'greening' of the continents acted as a carbon sink, and
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.
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 characterized a recognizably modern world had its
genesis in the
Late Devonian period. 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.
Late Devonian extinction
Late Devonian extinction
Late Devonian is characterised by three episodes of extinction
A major extinction occurred at the beginning of the last phase of the
Devonian period, the
Famennian faunal stage (the Frasnian-Famennian
boundary), about 372.2 Mya, when all the fossil agnathan fishes, save
for the psammosteid heterostraci, suddenly disappeared. A second
strong pulse closed the
Devonian period. The
Late Devonian extinction
was one of five major extinction events in the history of the Earth's
biota, and was more drastic than the familiar extinction event that
closed the Cretaceous.
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
Amongst the severely affected marine groups were the brachiopods,
trilobites, ammonites, conodonts, and acritarchs, as well as jawless
fish, and all placoderms. Land plants as well as freshwater species,
such as our tetrapod ancestors, were relatively unaffected by the Late
Devonian extinction event (but see  for 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
Falls of the
Ohio State Park USA, Indiana. One of the largest exposed
Devonian fossil beds in the world.
Geologic time scale
Early Devonian land plants
List of fossil sites
List of fossil sites (with link directory)
Phacops rana: a
Phanerozoic Carbon Dioxide.png
^ Image:All palaeotemps.png
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^ Rudwick M.S.J. 1985 The great
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Sedgwick and Murchison coined the term "
Devonian system" in: Adam
Sedgwick and Roderick Impey Murchison (1840) "On the physical
structure of Devonshire, and on the subdivisions and geological
relations of its older stratified deposits, etc.," Transactions of the
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for the future, to designate these groups collectively by the name
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Sedgwick and Murchison acknowledged William Lonsdale's role in
proposing, on the basis of fossil evidence, the existence of a
Devonian stratum between those of the
Silurian and Carboniferous
periods. From (Sedgwick and Murchison, 1840), p. 690: "Again, Mr.
Lonsdale, after an extensive examination of the fossils of South
Devon, had pronounced them, more than a year since, to form a group
intermediate between those of the
William Lonsdale stated that in December 1837 he had suggested the
existence of a stratum between the
See: William Lonsdale (1840) "Notes on the age of limestones from
south Devonshire," Transactions of the Geological Society of London,
2nd series, 5 (part II) : 721-738 ; see especially pp. 724
and 727. From p. 724: " … Mr. Austen's communication [was] read
December 1837, … . It was immediately after the reading of that
paper … that I formed the opinion relative to the limestones of
Devonshire being of the age of the old red sandstone; and which I
afterwards suggested first to Mr. Murchison and then to Prof.
Sedgwick, … ."
^ Gradstein, Felix M.; Ogg, James G.; Smith, Alan G. (2004). A
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^ Age of Fishes Museum
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^ Benton, M. J. (2005)
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"Periodicity of reproductive growth in lycopsids: An example from the
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^ Citation needed
Ogg, Jim; June, 2004, Overview of Global Boundary Stratotype Sections
and Points (GSSP's)
Accessed April 30, 2006.
Age of Fishes Museum
Wikisource has original works on the topic: Paleozoic#Devonian
Wikimedia Commons has media related to Devonian.
Devonian times - an excellent and frequently updated resource
focussing on the
UC Berkeley site introduces the Devonian.
International Commission on Stratigraphy (ICS)". Geologic Time Scale
2004. Retrieved September 19, 2005.
Geologic history of Earth
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Carboniferous (298.9–358.9 Mya)
Pennsylvanian (298.9–323.2 Mya)
Mississippian (323.2–358.9 Mya)
Devonian (358.9–419.2 Mya)
Late (358.9–382.7 Mya)
Middle (382.7–393.3 Mya)
Early (393.3–419.2 Mya)
Silurian (419.2–443.8 Mya)
Pridoli (419.2–423.0 Mya)
Ludlow (423.0–427.4 Mya)
Wenlock (427.4–433.4 Mya)
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Series 3 (497–509 Mya)
Series 2 (509–521 Mya)
Terreneuvian (521–541.0 Mya)
(541.0 Mya–2.5 Gya)
Neoproterozoic era (541.0 Mya–1 Gya)
Ediacaran (541.0-~635 Mya)
Cryogenian (~635-~720 Mya)
Tonian (~720 Mya-1 Gya)
Mesoproterozoic era (1–1.6 Gya)
Stenian (1-1.2 Gya)
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kya = thousands years ago. Mya = millions years ago.
Gya = billions
years ago.¹ =
Phanerozoic eon. ² =
Source: (2017/02). International Commission on Stratigraphy. Retrieved
13 July 2015. Divisions of Geologic Time—Major Chronostratigraphic
and Geochronologic Units USGS Retrieved 10 March 2013.