•Duration: about 30 millions years.
• Maximunm thickness: 70,000 feet.
• The Silurian Period (from the name of an ancient British tribe, the
Silures) lies between approximately 439 mya and 409 mya.
• The name was given by Marchison 1885 for agroup of formations in Wales in an area inhabited
by the Silurian tribe.
•During this time, a great deal of volcanic activity was taking place, generating lava flows and ash.
•No new major groups of organisms appeared at this time, with old groups flourishing or declining
Silurian : Facies
Different facies can be found:
1-Black clayey Graptoloitic - shals radiolaria shale (deep water facies)
2- Sandy shales , sandston, Conglomerate(shallow water facies)
3- Volcanic facies.
4-Shelly facies: sandy and calcareous(coastal facies of littoral platform rich in fossils as
Life on Land
It was during the Silurian that the first life came out of the water
and colonized the land.
Increased ozone from photosynthetic water plants provided
protection from ultraviolet rays, make the terrestrial environment
hospitable to those organisms that could prevent desiccation.
First Vascular Plants
The first plants with internal vascular channels appeared in the
Silurian. Plants were now able to transport food and gases to other
parts of their structure, allowing for a significant increase in size.
The insects arose in the Silurian, probably becoming the first animal
forms to venture out of the water.
First Jawed Vertebrates
The first fish with jaws appeared during the Silurian, providing a
much better predator capability and ultimately giving rise to the
vertebrates known today.
Some Typical Siluria Organisms
443 to 417 Million Years Ago
• The Silurian (443 to 417 million years ago) was a time when the
Earth underwent considerable changes that had important
repercussions for the environment and life within it.
• The Silurian witnessed a relative stabilization of the earth's general
climate, ending the previous pattern of erratic climatic fluctuations.
One result of these changes was the melting of large glacial
formations. This contributed to a substantial rise in the levels of the
major seas .
• Coral reefs made their first appearance during this time, and the
Silurian was also a remarkable time in the evolution of fishes.
• Not only does this time period mark the wide and rapid spread of
jawless fish, but also the highly significant appearances of both the
first known freshwater fish as well as the first fish with jaws.
• It is also at this time that our first good evidence of life on land is
preserved, including relatives of spiders and centipedes, and also
the earliest fossils of vascular plants.
• Subdivisions of the Silurian:
• The chart at left shows the major
subdivisions of the Silurian Period. This
chart is mapped, to allow you to travel
back to the Ordovician or forward to
• The Silurian Period is part of the
Paleozoic Era. Upper Silurian=
The lower Silurian had a great variation in the nature of these sediments. The fauna are
well distinct. Shelly deposits are characterized by the abundance of Brachiopods.The Graptolitic
facies on the other hand are defined by Monograptus, Diplograptus, Dictynema,
In the middle Silurian ; the previously mentioned facies are interstratified and much
limestone was formed. This latter is due to the greater spread of waters which took place during
the middle of the period.
In the late Silurian ; along and nearly complete emergence took place giveng rise to
sandy beds with no graptolites.
• The Silurian lasted from about 443 to 417 million years ago. Its
stratigraphy is subdivided into four epochs (from oldest to
youngest): the Llandovery, the Wenlock, the Ludlow, and the Pridoli.
• Each epoch is distinguished from the others by the appearance of
new species of graptolites.
• Graptolites are a group of extinct colonial, aquatic animals that
put in their first appearance in the Cambrian period (543 -490 million
years ago) and persisted into the Early Carboniferous (354-290
million years ago).
• The beginning of the Silurian (and the Llandovery) is marked by the
appearance of Parakidograptus acuminatus, a species of graptolite.
• The Llandovery (443-428 million years ago) preserves its fossils in
shale, sandstone, and gray mudstone sediment. Its base (beginning)
is marked by the appearance of the graptolites Parakidograptus
acuminatus and Akidograptus ascensus.
• The Llandoverian epoch is subdivided into the Rhuddanian,
Aeronian, and Telychian stages.
Life of the Silurian
The most distinective of the Silurian-----------------------Tabulate Tetracorsls
1-Reef building Coelenterates:
a-Tetracorals : flourished to the end of the Paleozoic represented by Cyathophyllum,
Goniophyllum and Zaphrentis
b- Heliolitides , Stromatoporoides.
c-Tabulata: confined to the Paleozoic) very aboundant e.g. Honey Corals Favosites and chain Corals
HalysitesDictyonema, Diplograptus, Phyllograptus and Monograptus
4-Brachiopods: Spirifer, Orthis, Atrypa
5-Crinoides: flourished in clear water and they were important reef builders
6-Trilobites: Calymene, Phacops,Dalma, Asaphus
7-Mollusca: Cephalopods are abundant Nautiloids e.g. Orthoceras , Cyrtoceras and Trochoceras reach
their maximum in the Silurian
8-Eurypterids: ( earliest sea scorpions)this group reached the peak of its development in the Silurian
and declined abruptly in the Devonian.
9-Fishes: In the upper Silurian beds , of Sweden and Norway, well preserved fossils of very primitive
Jaw –less fishes have been found.
10-Land plants: in 1953, a single type of plant fossil from the late Silurian of Australia was described
as a land plant.There is still no evidence of Silurian land plant at the end of the period and this could be
considered the start of terrestial life
Silurian Critters : On the left, Dalmanites
limuluris, a trilobite from the Silurian of New
To the right, Grammysia cingulata, a
brachiopod from the Upper Ludlow of England.
Early Plants : Cooksonia, on the left, has usually been considered the oldest
known land plant. Fossils assigned to several species are known from North America, Europe,
Asia, and Africa, and from both the Late Silurian and Early Devonian.
The lycophyte Baragwanathia, on the right, is structurally more complex than
Cooksonia, but Silurian fossils of this plant have been found in Australia, significantly earlier
than in the Northern Hemisphere.
Silurian: Tectonics and Paleoclimate
• During the Silurian , the Earth witnessed many changes in the way
in which landmasses were distributed around the globe. Although
there were no major volcanic events, a deglaciation and rise in sea
levels occurring at that time produced varying periods of continent
coverage and exposure.
• The variation of ocean levels occurred along side the process of
continental fragmentation and grouping that occurred from the
Cambrian to the present .
• At that time, the continents were distributed very differently than
they are today. The Silurian world consisted of a vast north polar
ocean and a south polar supercontinent (Gondwana) with a ring of
approximately six continents.
• By the Silurian period, a large portion of the Rodinian landmass had
become fragmented, and those fragments migrated toward the
equatorial region. Most of these fragments were eventually
assembled by a series of plate collisions into the super-continents
of Laurussia and Laurasia. The modern Philippine islands were most
likely inside the Arctic Circle, while Australia and Scandinavia
resided in the tropics; South America and Africa were probably over
the South Pole.
• There was no major volcanic activity during the Silurian; however,
• The period is marked by major orogenic (mountain-building) events
in eastern North America and in northwestern Europe, resulting in
the formation of the mountain chains
• there. This was called the Caledonian Orogeny.
• In other areas, large igneous rock formations of the Middle Silurian
arose, such as those in Central Europe, as well as light
sedimentation throughout the Baltic region. While not characterized
by dramatic tectonic activity, the Silurian world experienced gradual
continental changes that would be the basis for greater global
consequences in the future, such as those that created terrestrial
• The Silurian oceans are also of particular interest for activity
between the regions known as Laurentia Baltica and Avalonia. The
ocean basins between these areas substantially closed together,
continuing a geologic trend that had begun much earlier. The new
marine habitats produced by these profound changes in the Silurian
seas provided the framework for significant biological events in the
evolution of life Coral reefs, for example, made their first
appearances in the fossil record during this time
• During the middle and late Paleozoic, about a third of the Rodinian mass was torn apart and
moved to equatorial regions.
• Most of these blocks were assembled by a series of plate collisions into the super continents of
Laurussia [the Old Red continent] by the Devonian and Laurasia by the Pennsylvanian.
• Meanwhile the remains of Rodinia, Gondwana, rotated clockwise and moved northward to
collide with Laurasia -- the result was the super continent Pangaea [all land]. Pangaea was
shaped like a huge "pack man", mouth agape and facing eastward across the equator. The
large,open mouth was the Tethys Ocean. Baltica and the attached micro continent Avalonia
begin colliding with North America in scissors fashion [north to south] to form the Caledonian-
1- In Europe the silurian facies border the following areas:
• The Baltic shield zone
• The Northern European Geosyncline
• The Middle European zones (Armerican, Bohemia)
• The Mediterranean zones, including the following:
B- Carnic Alps
2- In Egypt: Silurian deposits occur :
• Um Bogma-Abu Durba---Central Sinai
• Western Desert (Southern part)golf kebeir plateau
• Eastern Desert( Qena Valley-El-Dakhala)
• Generally warm, mild especially in the middle of the period. Both lithology and biology
offer evidences, since L.S. are widely spread and corals are well
developed. Arid climate prevailed locally.
• At the end of the Periods, the rising of the Caledonian mountains took
place. This chain north-eastward across the British Isles and Scandinavia . Very little
igneous activity in the British area.
• The distribution of Oceans and continents is not much more different from that
during the Ordovician except that some parts of the land are floaded by sea water such as
North Russia, West China and Brazil.
•Duration: 50 millions years .
•Maximum thickness : 62,000 feet.
•The Devonian Period (after Devon, England) began about 417 million
years ago and ended about 354 million years ago.
• During this time, Europe and North America were still drifting together, and the northern
Appalachians were being formed. North America was mostly tropical or subtropical, and
numerous shallow, saltwater seas surrounded the coasts.
•During this period, much of Europe was submerged by the transgressive sea from the
beginning still near its end . By the close of the periods, emergence was gradual and finally
Two distinct facies could be distinguished :-
• Marine (Typical Devonian) Facies: These are
formed of continuous sheets of great extension covering large parts of earth crust. They
are composed of the normal succession of marine deposits of a transgressing sea. They
contain Trilobites, Molluscs, Brachiopods and Corals
• Lacustrine ( Old Red Sandsone) Facies: These
are formed of vast thickness of fossilifeous sands and muds, that accumulated from the
rugged mountains being aggraded by streams. They are mostly cofined to the British Isles,
North and Western Europe and North America. They were laid down in basins were
denudation was extremely active.
• These sediments are characterized by their bright colour althought red is the dominant
• Oxidation products of Fe and Mg ions stained also the sandstones, siltstones and shales .
• This Oxidation is due to good aeration of the soil during dry seasons. The dominant fossils
of the old red are fresh – water fished and Eurypterids. Plant fossils are locally abundant.
Sharks and Bony Fish
The first sharks and bony fishes appeared in the Devonian, which is frequently called
the "Age of Fishes."
Rise of Amphibians
It was during the Devonian that the first colonization of the land by vertebrates
occurred. Amphibians like Ichthyostega, while predominantly aquatic, had the physical
capabilities necessary for life on land.
The first land plants appeared in the Silurian, but it was in the Devonian that many
new forms first appeared. The lycopods, bryophytes, sphenophytes, and pteridophytes
all appeared in the Devonian. Among these were the first seed plants, those that could
reproduce in the absence of water.
• The Rhynie Chert in Scotland is a Devonian age deposit containing
fossils of both Zosterophyllophytes and Trimerophytes, the two
major lines of vascular plants. This indicates that prior to the start
of the Devonian, the first major radiations of the plants had already
happened. The oldest known vascular plants in the Northern
Hemisphere are Devonian
• The vegetation of the early Devonian consisted primarily of small
plants, the tallest being only a meter tall. By the end of the
Devonian, ferns, horsetails and seed plants had also appeared,
producing the first trees and the first forests. Archaeopteris, shown
below left, is one of these first trees.
• Also during the Devonian, two major animal groups colonized the
land. The first tetrapods, or land-living vertebrates, appeared during
the Devonian, as did the first terrestrial arthropods, including
wingless insects and the earliest arachnids. In the oceans,
brachiopods flourished, like the beautifully pyritized brachiopod
Paraspirifer bownockeri from Ohio, pictured above and to the right.
Crinoids and other echinoderms, tabulate and rugose corals, and
ammonites were also common. Many new kinds of fish appeared.
• During the Devonian, there were three major continental masses:
North America and Europe sat together near the equator, much of
their current land underneath seas. To the north lay a portion of
modern Siberia. A composite continent of South America, Africa,
Antarctica, India, and Australia dominated the southern hemisphere.
Subdivisions of the
The chart at left shows the
major subdivisions of the
Devonian Period. This
image is mapped to take
you back to the Silurian,
or forward in time to the
The Devonian Period is
part of the Paleozoic Era.
Subdivisions of the Devonian:
•Upper Devonian: red slates overlying massive L.S. with Rhynchonella
•Middle Devonian: mostly slates , rare grits, important volcanic tuffs,
calcareous bands with abundant Calceola
•Lower Devonian: mostly slates and grits, volcanic rocks not of great
extent. Spirifer abundant
Life of the Devonian
The most distinective of the Devoian-----------------------Tetracorsls and Fishes
Flora: Vascular land plants include the Psilophytales and the Lycopod-like form Baragwanathia
Sigillaria, Calamites, Lepidodendron, flowering plants
Coelentrates: Corals play an important role as reef buildes, all are tetracorals e.g.
Calceola sandalina, Stromatoporoids are abundant
Graptolites are rare in the lower part become Extinct before the end of the
Devonian Period . only dendroid forms e.g. Dictyonema still present.
Echinoderms: Echinoides, cystoids and blastoids play only minor role. Crinoids are very
abundant and their remain build up the crinoidal L.s.
Brachiopods: Productus, Spirifer, Atrypa, Orthis , Stringocephalus, and Rhynchonella are
Mollusca: Pelecypods and Gastropods are of no interes Nautiloids more highly developed
represented by: Cyrtoceras, Phramoceras and Gyroceras.
Cephalopods: Calymena sedgwickii
Crustaceans: represented by Phacops and Dalmanites Eurypterids were also flourishing
during the Devonian.
Fish: Represented by selacians , ganoids and placodems.
Ganoid fishes: Osteolepis
Armoured fishes: Cephalaspis, Pterichtys
Amphibians: small amphibians were recorded from upper Devonian rocks.
Insects: May fly.
N.B. 1-Graptolites were entirely absent. 2- in the Lacustrine deposites , remains
of Eurypterids were recorded.
Life of the Devonian
1-Change in the Devonian Seas
• The Devonian seas were dominated by brachiopods, such as the
spiriferids, and by tabulate and rugose corals, which built large bioherms, or
reefs, in shallow waters. Encrusting red algae also contributed to reef
building. In the Lower Devonian, ammonoids appeared, leaving us large
limestone deposits from their shells. Bivalves, crinoid and blastoid
echinoderms, graptolites, and trilobites were all present, though most
groups of trilobites disappeared by the close of the Devonian.
• The Devonian is also notable for the rapid diversification in fish.
• Benthic armored fish are common by the Early Devonian. These early fish
are collectively called ostracoderms", and include a number of different
• By the Mid-Devonian placoderms, the first jawed fish, appear. Many of these
grew to large sizes and were fearsome predators.
• Of the greatest interest to us is the rise of the first sarcopterygiians, or the
lobe-finned fish, which eventually produced the first tetrapods just before the
end of the Devonian.
2-Change in the Devonian Landscape
• By the Devonian Period, life was well underway in its colonization of the
land. Before this time, there is no organic accumulation in the soils, causing
these soil deposits to be a reddish color. This is indicative of the
underdeveloped landscape, probably colonized only by bacterial and algal
• By the start of the Devonian, however, early terrestrial vegetation had begun to
spread. These plants did not have roots or leaves like the plants most common today, and
many had no vascular tissue at all.
• They probably spread largely by vegetative growth, and did not grow much more than a
few centimeters tall.
• These plants included the now extinct zosterophylls and trimerophytes. The early fauna
living among these plants were primarily arthropods: mites, trigonotarbids, wingless
insects, and myriapods, though these early faunas are not well known.
• By the Late Devonian, lycophytes, sphenophytes, ferns, and progymnosperms had
• Most of these plants have true roots and leaves, and many are rather tall plants.
• The progymnosperm Archaeopteris, whose leaves are shown at right, was a large tree with
true wood. In fact it is the oldest such tree known, and produced some of the world's first
• By the end of the Devonian, the first seed plants had appeared. This rapid
appearance of so many plant groups and growth forms has been called the "Devonian
Explosion". Along with this diversification in terrestrial vegetation structure, came a
diversification of the arthropods.
Devonian: Localities•Devonian localities on
this server: (see map above)
Hunsrück Shale, Germany
Rhynie Chert - This Early
Devonian fossil bed in Scotland
includes some of the most
famous fossil plants ever found,
as well as fossil fungi and
arthropods. It is the oldest
terrestrial ecosystem found so
•Distribution of the Devonian
1-Region of the Old Red Sandstone: this is
found in the Scandnivia and in the Baltic
countries in the form of continental and
2- Region of the Ardennes : it is characterized
by the presence of shaly- sandy facies.
3-The Mediterranean Region: this is
characterized by the presence of deep water
4- Eastern Europe: There is a passage from
continental facies in the Russian plarform to
geosynclinal type in the Ural Mountains.
In Egypt: Devonian deposits occur :
• Um Bogma-Abu Durba---Central Sinai
• Western Desert (Southern part) golf kebeir plateau
• Eastern Desert( Qena Valley-El-Dakhala)
• Culmination of folding and evolution in Scotland, Lake District and
Wales. Then local sinking in fresh water basins with periods of
renewed uplift in Scotland.
• About the Middle Devnian, the Acadian revolution
• Started , uplift of sediments accompanied by igneous activity which
continued still the end of the period. Volcancity was prominent
through the whole period.
• Could possibly be hot, coloration was due to high
Temperature. Seasnal aridity was recorded in differents of the world
Paleogeography of the Devonian
•The rising up of the Caledonian chain took place after the
silurian and its effect is restricted to Scotland, Ireland and
Norway. At the same time, a great tract of land appeared in N.
Western Europe that played an important part during the
subsequent Paleozoic history.
Devonian: Tectonics and Paleoclimate
• Significant changes in the world's geography took place during the Devonian. During this
period, the world's land was collected into two supercontinents, Gondwana and
Euramerica. These vast landmasses lay relatively near each other in a single hemisphere,
while a vast ocean covered the rest of the globe.
• These supercontinents were surrounded on all sides by subduction zones. With the
development of the subduction zone between Gondwana and Euramerica, a major
collision was set in motion that would bring the two together to form the single world-
continent Pangea in the Permian.
• In addition to global patterns of change, many important regional activities also
occurred. The continents of North America and Europe collided, resulting in massive
granite intrusions and the raising of the Appalachian Mountains of eastern North America.
Vigorous erosion of these newly uplifted mountains yielded great volumes of sediment,
which were deposited in vast lowlands and shallow seas nearby.
• Extensive reef building, producing some of the world's largest reef complexes, proceeded
as stromatoporoids and corals appeared in increasing numbers. These were built in the
equatorial seas between the continents. Large areas of shallow sea in North America,
central Asia, and Australia became basins in which great quantities of rock salt, gypsum,
and other minerals precipitated.
• Near the end of the Devonian, a mass extinction event occurred.
• Glaciation and the lowering of the global sea level may have triggered this crisis, since the
evidence suggests warm water marine species were most affected.
• Meteorite impacts have also been blamed for the mass extinction, or changes in
atmospheric carbon dioxide. It is even conceivable that it was the evolution and spread of
forests and the first plants with complex root systems that may have altered the global
climate. Whatever the cause, it was about this time that the first vertebrates moved onto
The Devonian Mass Extinction
• Species Affected
• The Devonian mass extinction occurred during the latter part of the Devonian at the
Frasnian - Famennian boundary.
• The crisis primarily affected the marine community, having little impact on the terrestrial
flora. This same extinction pattern has been recognized in most mass extinctions throughout
• The most important group to be affected by this extinction event were the major reef-
builders including the stromatoporoids, and the rugose and tabulate corals
• This late Devonian crisis affected these organisms so severely that reef-building was
relatively uncommon until the evolution of the scleractinian (modern corals in the
Mesozoic era. Among other marine invertebrates, seventy percent of the taxa did not
survive into the Carboniferous.
• Fast Facts
•Devonian period ranged from 417-354 million years ago.
•A major intra-Devonian extinction occurred at the Frasnian-Famennian boundary
•Following the Ordovician mass extinction rediversification of surviving groups occurred
throughout the Silurian and Devonian. In addition, the Devonian saw the first appearance of
sharks, bony fish, and ammonoids During the Devonian the world's oceans were dominated by
reef-builders such as the stromatoporoids, and corals and some of the world's largest reef
complexes were built. Terrestrial newcomers in the Devonian included amphibians, insects, and
the first true land plants, giving rise to the first forests.
•Amongst the severely affected groups were the brachiopods trilobites conodonts
and acritarchs as well as all jawless fish, and placoderms
Speculated Causes of the Devonian
• Evidence supporting the Devonian mass extinction suggests that warm water marine species were the most
severely affected in this extinction event.
• This evidence has lead many paleontologists to attribute the Devonian extinction to an episode of global
cooling, similar to the event which is thought to have cause the late Ordovician mass extinction.
• According to this theory,the extinction of the Devonian was triggered by another glaciation event on
Gondwana, as evidenced by glacial deposits of this age in northern Brazil. Similarly to the late Ordovician
crisis, agents such as global cooling and widespread lowering of sea-level may have triggered the late
• Meteorite impacts at the Frasnian-Famennian boundary have
also been suggested as possible agents for the Devonian mass
extinction. Currently, the data surrounding a possible
extra-terrestrial impact remains inconclusive, and the
mechanisms which produced the Devonian mass extinction
are still under debate