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What you’ll find - Bertie Formation fossils - possibly Bois Blanc fossils
The Bertie Formation is dated to the last of the Silurian Period, Přídolí Epoch (which is dated to 423
±1.5to 419.2 ±2.8 Ma).
Proposed in 2010
Source: Revised correlation of Silurian Provincial Series of North America with global and regional
chronostratigraphic units and δ13Ccarb chemostratigraphy; M A Kleffner, D K Loydell, A Munnecke,
C Corradini; Lethaia; 2010
“Upper Silurian - Bass Islands (Bertie) Formation - The Bass Islands (Bertie) Formation forms the
bedrock in a narrow band extending from Fort Erie through Hagersville, New Hamburg, Harriston, and
Walkerton to Southampton on Lake Huron. The Formation consists of medium bedded to massivebedded aphanitic brown dolomite with minor thin-bedded shaly dolomite. Along the outcrop area
between Fort Erie and Hagersville the thickness varies from 35 to 60 feet. It thickens to 495 feet in
the subsurface.
Sanford (GSA, 1969) used the term Bertie Formation from Fort Erie to the vicinity of Hagersville and
the term Bass Islands Formation north and west of Hagersville. The Formation is correlated with the
Bass Islands Formation of Michigan. The Bertie Dolomite is quarried for crushed stone at Fort Erie,
Port Colborne, Dunnville, Cayuga, and Hagersville. It is the uppermost Formation of the Silurian
System in Ontario.”
Source: Paleozoic Geology of Southern Ontario; D F Hewitt; Ontario Division of Mines, Geological
Branch, Ontario Natural Resources; 1972
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Oldest Near-Complete Acanthodian: The First Vertebrate from the Silurian Bertie Formation
Konservat-Lagerstätte, Ontario; C J Burrow, D Rudkin; PLOSONE; 2014
spiny sharks
Abstract
Background:
The relationships between early jawed vertebrates have been much debated, with cladistic analyses
yielding little consensus on the position (or positions) of acanthodians with respect to other groups.
Whereas one recent analysis showed various acanthodians (classically known as ‘spiny sharks’) as
stem osteichthyans (bony fishes) and others as stem chondrichthyans, another shows the
acanthodians as a paraphyletic group of stem chondrichthyans, and the latest analysis shows
acanthodians as the monophyletic sister group of the Chondrichthyes.
Methodology/Principal Findings:
A small specimen of the ischnacanthiform acanthodian Nerepisacanthus denisoni is the first
vertebrate fossil collected from the Late Silurian Bertie Formation Konservat- Lagerstätte of southern
Ontario, Canada, a deposit well-known for its spectacular eurypterid fossils. The fish is the only near
complete acanthodian from pre-Devonian strata worldwide, and confirms that Nerepisacanthus has
dentigerous jaw bones, body scales with superposed crown growth zones formed of ondontocytic
mesodentine, and a patch of chondrichthyan-like scales posterior to the jaw joint.
Conclusions/Significance:
The combination of features found in Nerepisacanthus supports the hypothesis that acanthodians
could be a group, or even a clade, on the chondrichthyan stem. Cladistic analyses of early jawed
vertebrates incorporating Nerepisacanthus, and updated data on other acanthodians based on
publications in press, should help clarify their relationships.
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http://fossiling.com/12.html - 2007-2013- excerpt from:
We ventured over the border into Ontario to comb the floor of Ridgemount Quarries for eurypterids.
Popularly known as sea scorpions, eurypterids were the largest arthropods ever. Some species
topped 9 feet and were surely the apex predators of the Silurian. Others were likely as placid as their
distant cousin the horseshoe crab. At Ridgemount they seemed to hide in plain site even though
bulldozers had scoured the shale down to their level. We found that what was wanted - along with
crack hammers and extra flat chisels - was a good stiff kitchen broom to clear away the dust and
debris. Our quarry revealed themselves mostly as scattered abdominal segments, dark straps on the
pale stone. Eventually, Gordon became adept at finding articulated telsons - tails - several over the
course of the day. After a few hot, frustrating hours my own luck finally manifested at the other end of
the animal: I scored a couple of nice heads.
eurypterids (sea scorpions)
Ridgemount Quarries; a eurypterid tail as well as a head, 2 inches across - text + pictures copyright
Alan Zdinak.
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Great Canadian Lagerstätten - The Silurian
eurypterid Eurypterus remipes, from the Bertie
Formation near Ridgemount, Ontario (ROM
56889) (photo © David Rudkin, Royal Ontario
Museum); GeoCanada 2010 conference
eurypterids (sea scorpions)
Eurypterids and More – The Eramosa and Bertie
Lagerstätten (Silurian), Southern Ontario D
Rudkin; Department of Natural History
(Palaeobiology), ROM; 2010
The renowned eurypterid-bearing ... Bertie
Lagerstätten of southern Ontario provides
exceptional taphonomic windows on a narrow
range of shallow marginal marine environments
in Silurian subtropical Laurentia. ... Bertie
occurrences ... are hosted in finely crystalline
dolostone-dominated facies with intervals of
microbial laminae ... and large and conspicuous
non-biomineralized faunal components
chelicerate and mandibulate arthropods. ...
Sediments of the mid- Přídolí Bertie Formation
were deposited on the paleo-southern side of the
subsiding Algonquin Arch, flanking the northern
rim of the Appalachian Foreland Basin. ... the
Fiddlers Green and Williamsville members of the
Bertie Formation in the Ridgemount area of
Ontario represent the northwestern edge of a
much broader outcrop belt of long-famous
“waterlime” deposits that extends into eastcentral New York State. These massive cementlike to argillaceous dolostones originated in
subtidal to intertidal lagoonal settings, under alternating hypersaline and brackish estuarine
conditions.
Eurypterids, including species of Eurypterus, Dolichopterus and Acutiramus, are the best known and
most spectacular non-biomineralized faunal elements of the Bertie Lagerstätte, and although most
specimens appear to represent moults, they are often exquisitely preserved as thin organic films.
Other arthropods include Bunaia (a “synziphosurine”), the phyllocarid Ceratiocaris acuminata, and an
exceptionally rare naraoiid.
Both fertile (Cooksonia sp.) and sterile (Hostinella sp.) axes of early land plants are occasionally
found, along with presumed non-calcified algae (Inocaulis sp.). Lingulide brachiopods, nautiloids, and
ostracods comprise the most common shelly components of the biota.
A new late Silurian Přídolían naraoiid euarthropoda Nektaspida from the Bertie Formation of Southern
Ontario delayed fallout from the Cambrian Explosion; J-B Caron, D M Rudkin, S Milliken; SEPM
Society for Sedimentary Geology; 2004
The discovery of a new naraoiid nektaspid in the Upper Silurian (Přídolían) of southeastern Ontario
significantly extends the range of this unusual group. Nektaspids are non-mineralized arthropods (sea
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scorpions) typical of Early and Middle Cambrian soft-bottom communities, but were thought to have
become extinct in the Late Ordovician. The unique holotype specimen of Naraoia bertiensis n. sp.
comes from a Konservat-Lagerstätte deposit renowned for its eurypterid fauna (the Williamsville
Member of the Bertie Formation). Naraoia bertiensis lacks thoracic segments and is morphologically
similar to Naraoia compacta from the Middle Cambrian Burgess Shale, save for the presence of a
long ventral cephalic doublure and a subtly pointed posterior shield. To examine the phylogenetic
relationships of the new naraoiid, we coded characters of the holotype specimen and of nine
previously described nektaspids. The results confirm a sister taxon relationship between Naraoia
compacta and Naraoia bertiensis and the monophyly of nektaspid forms lacking thoracic segments
(family Naraoiidae). This latter group may have arisen from an ancestral segment-bearing form
through heterochronic loss of thoracic segments early in the Cambrian. The disjunct occurrence of a
naraoiid nektaspid in the Late Silurian resembles the reappearance of other "Lazarus taxa" that were
thought to have been eliminated during mass extinction events. The naraoiid lineage survived the
Late Ordovician biotic crisis, but in this case the "Lazarus effect" seems likely to be taphonomic in
origin.
https://archive.org/details/royalontariomuseum?and[]=fossils%20of%20ontario (Digital Library, ROM)
Fossils of Ontario Part 1: The Trilobites; R Ludvigsen; 1985 - pp 61-67 for Silurian Trilobites
Fossils of Ontario Part 3: The Eurypterids and Phyllocarids (crustaceans); M J Copeland, T E Bolton;
1985
corals, brachiopods, crinoids, naraoiids, nautiloids, ostracods, trilobites
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Cooksonia & Hostinella - early land plants
Source: Palaeos & The National Library of Wales
THE REST IS ABOUT THE SILURIAN, in general
Resources and © Wikipedia, UCMP Berkeley, National Geographic, LiveScience, Palaeos,
Smithsonian Institute
https://en.wikipedia.org/wiki/Silurian
Silurian
The Silurian is a geologic period and system
that extends from the end of the Ordovician
Period, about 443.8 ± 1.5 million years ago
(Ma), to the beginning of the Devonian
Period.[5] As with other geologic periods, the
rock beds that define the period's start and
end are well identified, but the exact dates
are uncertain by several million years. The
base of the Silurian is set at a major
extinction event when 60% of marine species
were wiped out. See Ordovician-Silurian
extinction events.
A significant evolutionary milestone during
the Silurian was the diversification of jawed
and bony fish. Life also began to appear on
land in the form of small, moss-like, vascular
plants that grew beside lakes, streams, and
Silurian Period
443.4–419.2million years ago
Mean atmospheric O2
content over period
duration
Mean atmospheric CO2
content over period
duration
Mean surface
temperature over period
duration
ca. 14 vol%[1]
(70% of modern level)
ca. 4500 ppm[2]
(16 times pre-industrial
level)
ca. 17°C[3]
(3°C above modern level)
Around 180m, with shortSea level (above present
term negative
day)
excursions[4]
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coastlines, and also in the form of small terrestrial arthropods. However, terrestrial life would not
greatly diversify and affect the landscape until the Devonian.
Subdivisions
Llandovery
See also: Llandovery Group
The Llandovery Epoch lasted from 443.4 ±1.5to 433.4 ±2.8 Ma, and is subdivided into three stages:
the Rhuddanian,[8] lasting until 440.8 million years ago, the Aeronian, lasting to 438.5 million years
ago, and the Telychian. The epoch is named for the town of Llandovery in Carmarthenshire, Wales.
Wenlock
See also: Wenlock (Silurian)
The Wenlock, which lasted from 433.4 ±1.5to 427.4 ±2.8 Ma, is subdivided into the Sheinwoodian (to
430.5 million years ago) and Homerian ages. It is named after Wenlock Edge in Shropshire, England.
During the Wenlock, the oldest known tracheophytes of the genus Cooksonia, appear. The
complexity of slightly younger Gondwana plants like Baragwanathia indicates a much longer history
for vascular plants, perhaps extending into the early Silurian or even Ordovician. See Evolutionary
history of plants. The first terrestrial animals also appear in the Wenlock, represented by air-breathing
millipedes from Scotland.[9]
Ludlow
See also: Ludlow Group
The Ludlow, lasting from 427.4 ±1.5to 423 ±2.8 Ma, comprises the Gorstian stage, lasting until 425.6
million years ago, and the Ludfordian stage. It is named for the town of Ludlow (and neighbouring
Ludford) in Shropshire, England.
Přídolí
The Pridoli, lasting from 423 ±1.5to 419.2 ±2.8 Ma, is the final and shortest epoch of the Silurian. It is
named after one locality at the Homolka a Přídolí nature reserve near the Prague suburb Slivenec in
the Czech Republic. Přídolí is the old name of a cadastral field area.[10]
Regional stages
In North America a different suite of regional stages is sometimes used:
Cayugan (Late Silurian - Ludlow)
Lockportian (middle Silurian: late Wenlock)
Tonawandan (middle Silurian: early Wenlock)
Ontarian (Early Silurian: late Llandovery)
Alexandrian (earliest Silurian: early Llandovery)
Geography
With the supercontinent Gondwana covering the equator and much of the southern hemisphere, a
large ocean occupied most of the northern half of the globe.[11] The high sea levels of the Silurian and
the relatively flat land (with few significant mountain belts) resulted in a number of island chains, and
thus a rich diversity of environmental settings.[11]
During the Silurian, Gondwana continued a slow southward drift to high southern latitudes, but there
is evidence that the Silurian icecaps were less extensive than those of the late Ordovician glaciation.
The southern continents remained united during this period. The melting of icecaps and glaciers
contributed to a rise in sea level, recognizable from the fact that Silurian sediments overlie eroded
Ordovician sediments, forming an unconformity. The continents of Avalonia, Baltica, and Laurentia
drifted together near the equator, starting the formation of a second supercontinent known as
Euramerica.
When the proto-Europe collided with North America, the collision folded coastal sediments that had
been accumulating since the Cambrian off the east coast of North America and the west coast of
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Europe. This event is the Caledonian orogeny, a spate of mountain building that stretched from New
York State through conjoined Europe and Greenland to Norway. At the end of the Silurian, sea levels
dropped again, leaving telltale basins of evaporites in a basin extending from Michigan to West
Virginia, and the new mountain ranges were rapidly eroded. The Teays River, flowing into the shallow
mid-continental sea, eroded Ordovician strata, leaving traces in the Silurian strata of northern Ohio
and Indiana.
The vast ocean of Panthalassa covered most of the northern hemisphere. Other minor oceans
include two phases of the Tethys— the Proto-Tethys and Paleo-Tethys— the Rheic Ocean, a seaway
of the Iapetus Ocean (now in between Avalonia and Laurentia), and the newly formed Ural Ocean.
Climate and sea level
Marine extinction intensity during the Phanerozoic
The blue graph shows the apparent
percentage (not the absolute number) of
marine animal genera becoming extinct
during any given time interval. It does not
represent all marine species, just those
that are readily fossilized. The labels of the
"Big Five" extinction events are clickable
hyperlinks; see Extinction event for more
details. (source and image info)
The Silurian period enjoyed relatively
stable and warm temperatures, in contrast
with the extreme glaciations of the
Ordovician before it, and the extreme heat
of the ensuing Devonian.[11] Sea levels
rose from their Hirnantian low throughout
the first half of the Silurian; they subsequently fell throughout the rest of the period, although smaller
scale patterns are superimposed on this general trend; fifteen high-stands can be identified, and the
highest Silurian sea level was probably around 140m higher than the lowest level reached. [11]
During this period, the Earth entered a long, warm greenhouse phase, and warm shallow seas
covered much of the equatorial land masses. Early in the Silurian, glaciers retreated back into the
South Pole until they almost disappeared in the middle of Silurian. The period witnessed a relative
stabilization of the Earth's general climate, ending the previous pattern of erratic climatic fluctuations.
Layers of broken shells (called coquina) provide strong evidence of a climate dominated by violent
storms generated then as now by warm sea surfaces. Later in the Silurian, the climate cooled slightly,
but in the Silurian-Devonian boundary, the climate became warmer.
Perturbations
The climate and carbon cycle appears to be rather unsettled during the Silurian, which has a higher
concentration of isotopic excursions than any other period.[11] The Ireviken event, Mulde event and
Lau event each represent isotopic excursions following a minor mass extinction [12] and associated
with rapid sea-level change, in addition to the larger extinction at the end of the Silurian.[11] Each one
leaves a similar signature in the geological record, both geochemically and biologically; pelagic (freeswimming) organisms were particularly hard hit, as were brachiopods, corals and trilobites, and
extinctions rarely occur in a rapid series of fast bursts.[11]
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Flora and fauna
1) Silurian sea bed fossils collected
from Wren's Nest Nature Reserve,
Dudley UK; 2) Crinoid fragments in
a
Silurian (Pridoli) limestone
(Saaremaa, Estonia); 3) Silurian sea
bed fossils collected from Wren's
Nest Nature Reserve, Dudley UK; 4)
Artist's impression of Silurian; 5)
Cooksonia, the earliest vascular
plant, middle Silurian
The Silurian was the first period to see
macrofossils of extensive terrestrial biota, in the form of moss forests along lakes and streams.
However, the land fauna did not have a major impact on the Earth until it diversified in the
Devonian.[11]
The first fossil records of vascular plants, that is, land plants with tissues that carry food, appeared in
the second half of the Silurian period.[13] The earliest known representatives of this group are
Cooksonia (mostly from the northern hemisphere) and Baragwanathia (from Australia). Most of the
sediments containing Cooksonia are marine in nature. Preferred habitats were likely along rivers and
streams. Baragwanathia, appears to be almost as old dating to the Early Ludlow (420 million years)
and has branching stems and needle-like leaves of 10–20cm. The plant shows a high degree of
development in relation to its age. As mentioned, fossils of this plant are only found in Australia. [14]
The much-branched Psilophyton was a primitive Silurian land plant with xylem and phloem but no
differentiation in root, stem or leaf. It reproduced by spores, had stomata on every surface, and
probably photosynthesized in every tissue exposed to light. Rhyniophyta and primitive lycopods were
other land plants that first appear during this period. Neither mosses nor the earliest vascular plants
had deep roots. Silurian rocks often have a brownish tint, possibly a result of extensive erosion of the
early soils.[citation needed]
Eurypterus, a common Upper Silurian eurypterid
The first bony fish, the Osteichthyes, appeared, represented by
the Acanthodians covered with bony scales; fish reached
considerable diversity and developed movable jaws, adapted
from the supports of the front two or three gill arches. A diverse
fauna of Eurypterids (sea scorpions)—some of them several
meters in length—prowled the shallow Silurian seas of North
America; many of their fossils have been found in New York
state. Leeches also made their appearance during the Silurian
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Period. Brachiopods, bryozoa, molluscs, hederelloids, tentaculitoids, crinoids and trilobites were
abundant and diverse.[citation needed] Endobiotic symbionts were common in the corals and
stromatoporoids.[15][16]
Reef abundance was patchy; sometimes fossils are frequent but at other points are virtually absent
from the rock record.[11]
The earliest known terrestrial animals appear during the Mid Silurian, including the millipede
Pneumodesmus.[9] Some evidence also suggests the presence of predatory trigonotarbid arachnoids
and myriapods in Late Silurian facies.[17] Predatory invertebrates would indicate that simple food webs
were in place that included non-predatory prey animals. Extrapolating back from Early Devonian
biota, Andrew Jeram et al. in 1990[18] suggested a food web based on as yet undiscovered
detritivores and grazers on micro-organisms.[19]
http://www.ucmp.berkeley.edu/silurian/silurian.php
The Silurian Period
The Silurian (443.7 to 416.0 million years ago)* was a time when the Earth underwent considerable
changes that had important repercussions for the environment and life within it. 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. The Silurian witnessed a relative stabilization of the Earth's general climate, ending
the previous pattern of erratic climatic fluctuations.
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, such
as relatives of spiders and centipedes, and also the earliest fossils of vascular plants.
Life
The Silurian is a time when many biologically significant events occurred. In the oceans, there was a
widespread radiation of crinoids, a continued proliferation and expansion of the brachiopods, and the
oldest known fossils of coral reefs. As mentioned earlier, this time period also marks the wide and
rapid spread of jawless fish, along with the important appearances of both the first known freshwater
fish and the appearance of jawed fish. Other marine fossils commonly found throughout the Silurian
record include trilobites, graptolites, conodonts, corals, stromatoporoids, and mollusks.
On the left, Dalmanites limuluris, a trilobite from the Silurian of New York. To the
right, Grammysia cingulata, a brachiopod from the Upper Ludlow of England.
It is also in the Silurian that we find the first clear evidence of life on land. While it is possible that
plants and animals first moved onto the land in the Ordovician, fossils of terrestrial life from that
period are fragmentary and difficult to interpret. Silurian strata have provided likely ascomycete fossils
(a group of fungi), as well as remains of the first arachnids and centipedes.
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Perhaps most striking of all biological events in the Silurian was the evolution of vascular plants,
which have been the basis of terrestrial ecology since their appearance. Most Silurian plant fossils
have been assigned to the genus Cooksonia, a collection of branching-stemmed plants which
produced sporangia at their tips. None of these plants had leaves, and some appear to have lacked
vascular tissue. Also from the Silurian of Australia comes a controversial fossil of Baragwanathia, a
lycophyte. If such a complex plant with leaves and a fully-developed vascular system was present by
this time, then surely plants must have been around already by the Ordovician. In any event, the
Silurian was a time for important events in the history of evolution, including many "firsts," that would
prove highly consequential for the future of life on Earth.
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.
Stratigraphy
The Silurian's stratigraphy is subdivided into four epochs (from oldest to youngest): the Llandovery,
Wenlock, Ludlow, and 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 and persisted into the early Carboniferous. The beginning of the
Silurian (and the Llandovery) is marked by the appearance of Parakidograptus acuminatus, a species
of graptolite.
The Llandovery (443.7-428.2 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.
At the close of the Telychian stage, the appearance of Cyrtograptus centrifugus marks the start of the
Wenlockian epoch (428.2 to 422.9 million years ago).* The fossils are found in siltstone and
mudstone under limestone. Missing from the fossil record of the Wenlock was the conodont
Pterospathodus amorphognathoides, present in earlier strata. This is an epoch with excellent
preservations of brachiopod, coral, trilobite, clam, bryozoan, and crinoid fossils. The Wenlock is
subdivided into the Sheinwoodian and Homerian stages.
The Ludlow (422.9 to 418.7 million years ago)* consists of siltstone and limestone strata, marked by
the appearance of Neodiversograptus nilssoni. There is an abundance of shelly animal fossils. The
Gorstian and Ludfordian stages make up the Ludlow epoch.
Platy limestone strata rich in cephalopods and bivalves characterize the Pridolian (418.7 to 416.0
million years ago),* the final epoch of the Silurian. It is marked by the appearance of the index fossil
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Monograptus parultimus, and also by two new species of chitinozoans (marine plankton), Urnochitina
urna and Fungochitina kosovensis, which appear at the base or just above the base of the Pridoli.
Tectonics and paleoclimate
Although there were no major periods of volcanism during the Silurian, the period is marked by major
orogenic events in eastern North America and in northwestern Europe (the Caledonian Orogeny),
resulting in the formation of the mountain chains there. The ocean basins between the regions known
as Laurentia (North America and Greenland), Baltica (central and northern Europe and Scandinavia)
and Avalonia (western Europe) closed substantially, continuing a geologic trend that had begun much
earlier. The modern Philippine Islands were near the Arctic Circle, while Australia and Scandinavia
resided in the tropics; South America and Africa were over the South Pole. 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
ecosystems. A deglaciation and rise in sea levels created many new marine habitats, providing the
framework for significant biological events in the evolution of life. Coral reefs, for example, made their
first appearance in the fossil record during this time.
The Silurian Period's condition of low continental elevations with a high global stand in sea level can
be strongly distinguished from the present-day environment. This is a result of the flood of 65% of the
shallow seas in North America during the Llandovery and Wenlock times. The shallow seas ranged
from tropical to subtropical in climate. Coral mound reefs with associated carbonate sediments were
common in the shallow seas. Due to reduced circulation during the Ludlow and Pridoli times, the
process of deposition of evaporites (salts) was set in motion. Some of these deposits are found in
northern Europe, Siberia, South China and Australia.
http://science.nationalgeographic.com/science/prehistoric-world/silurian/
Silurian Period
The Paleozoic era's Silurian period saw animals and plants finally emerge on land. But first there was
a period of biological regrouping following the disastrous climax to the Ordovician.
The recovery soon got under way in the oceans as climbing temperatures and rising sea levels
reproduced the shallow, marine environments of earlier times. Huge reef systems flourished in the
clear, tropical seas—evident today in the many limestone rock formations that date to this period.
Previous reef-builders such as bryozoans were joined by corals and prehistoric sponges known as
stromatoporoids, which formed a hard outer skeleton. They survived solely by eating microscopic
animals trapped by their stinging tentacles.
The growth of corals and other marine organisms was stoked by oceans teeming with tiny planktonic
creatures. Waiting at the other end of the food chain were the fearsome eurypterids, or sea scorpions.
Some species grew to more than six feet (two meters) in length and are considered the largest
arthropods ever to have lived. Bearing a resemblance to their scorpion descendents, eurypterids had
a pair of huge, compound eyes for searching out primitive fish, which they grabbed with their
powerful, clawlike pincers.
Fish were now diversifying and extending their feeding options beyond simply vacuuming meals off
the seabed. A group called acanthodians, or spiny sharks, evolved more menacing mouths with jaws.
While these fish, the first true jawed fish, reached no great size during the Silurian, they were on their
way to becoming one of the planet's top predators.
Creepy-crawlies also began to appear on land. Starting off small, they measured no more than a few
centimeters long. These terrestrial pioneers were arthropods, such as primitive centipedes and
arachnids, the ancestors of spiders.
First True Plants
The first true plants began to take root on land some 430 million years ago. They evolved rigid stems,
enabling them to stand upright, and the tubular tissues common to all vascular plants that allowed the
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transport of water and nutrients. These first colonizers lacked leaves, but mosses and other plants
followed, providing a thin layer of waterside vegetation that encouraged more aquatic animals to
make the transition to land.
The climate remained warm and stable throughout most of the Silurian. The supercontinent of
Gondwana was still positioned over the South Pole but the vast icecaps of the late Ordovician period
melted almost to nothing. Sediments formed from massive quantities of broken shells suggest violent
storms were triggered by the warmth of tropical oceans.
The Silurian drew to a close with a series of extinction events linked to climate change; however,
these were relatively minor compared with those of other geologic periods.
http://www.livescience.com/43514-silurianperiod.html
Underwater life thrived during the Silurian
Period, 443 million years ago to 416 million
years ago.
Credit: Alena Hovorkova
Silurian Period Facts: Climate, Animals &
Plants
The Silurian Period occurred from 443 million to
416 million years ago. It was the third period in
the Paleozoic Era. It followed the Ordovician
Period and preceded the Devonian Period.
During this time, continental landmasses were
low and sea levels were rising. This meant rich shallow sea ecosystems with new ecological niches.
Silurian fossils show evidence of extensive reef building and the first signs that life beginning to
colonize the new estuary, fresh water and terrestrial ecosystems.
Plate tectonics and mountain building
The supercontinent Gondwana had drifted southward and covered most of the southern latitudes.
Much of the northern half of the planet was ocean with two smaller continents, Laurentia and Baltica,
near the equator. Another micro-continent, Avalonia, rifted from the northern edge of Gondwana and
drifted northward. Beginning in the late Ordovician and continuing throughout the Silurian and into the
Devonian, the three northern continents collided, forming the new supercontinent, Euramerica. This
collision resulted in a major mountain building event known as the Caledonian Orogeny. The hills and
mountains of Scotland, Ireland, Wales and the northern Appalachians are remnants of this event, as
are the mountains of Sweden and Norway.
Marine life
Much of the landmass that would become western North America was under a shallow ocean for
much of the Silurian Period. These shallow waters enabled sunlight to penetrate, and marine animals
underwent rapid differentiation. Silurian fossils show extensive coral reefs built from tabulate and horn
corals with calcium carbonate skeletons. In the early Silurian, a class of jawless fish, Agnatha, similar
to modern hagfish and lampreys, was most common. In the mid-Silurian, the first species of
Romundina, a Placoderm - a primitive armored fish with a cartilage skeleton - is earliest fish known to
have developed jaws.
Eurypterids were the apex predators of the Silurian oceans. Eurypterids were arthropods, probably
most closely related to modern horseshoe crabs. They had a semi-circular anterior carapace followed
jointed section and a long tapering tail. Most species had two pairs of jointed walking legs followed by
a pair of paddle-shaped swimming appendages. Some had a spike on the end of their tails, which
may have been used to inject venom into prey, giving rise to the common name “sea scorpion.” By
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the Devonian Period, these animals became the largest known arthropods to ever have lived on
Earth.
Movement onto land
During the Silurian Period, the climate was generally warm and stable, in contrast to the glaciers of
the late Ordovician and the extreme heat of the Devonian. A warm, stable climate provided for one of
the most significant developments to take place during the Silurian Period: the arrival of the first
plants to colonize the land. Lichens were probably the first photosynthetic organisms to cling to the
rocky coasts of the early continents. When organic matter from decaying lichens joined the action of
erosion to wear away rock, the first real soil began to build up in shallow, protected estuaries.
Bryophytes such moss, hornworts and liverworts first appeared in the late Ordovician. The first known
plant to have an upright stalk, and vascular tissue for water transport, was the Cooksonia of the midSilurian deltas. This little plant was a few centimeters high with a branched structure with small
bulbous tips. It lacked true leaves, suggesting that the stalk developed to disperse spores and was
not itself photosynthetic. The first known air-breathing animals were arthropods. Millipedes,
centipedes and the earliest arachnids first appear in the Silurian. Since arachnids are exclusively
predatory, this represents the first terrestrial food web.
http://palaeos.com/paleozoic/silurian/silurian.htm
The Silurian
The Silurian Period of the Paleozoic Era: 444 to 416 Ma
Geography
The early Paleozoic saw the continents clustered around the equator, with Gondwanaland continues
it's slow southern drift. Meanwhile Siberia, Laurentia and Baltica converge at the equator. By the end
of the Silurian, these colliding continents had began to raise mountains and forge a new
supercontinent,Laurussia.
Stratigraphy
Period/System Epoch/Series
Age/Stage
When began
Devonian
Early Devonian
Lochkovian
416.0 Ma
Pridoli
(not subdivided) 418.7
Ludfordian
421.3
Gorstian
422.9
Homerian
426.2
Sheinwoodian
428.2
Telychian
436.0
Aeronian
439.0
Rhuddanian
443.7
Ludlow
Silurian
Wenlock
Llandovery
Ordovician
Late Ordovician Hirnantian
445.6
See also the very useful biostratigraphic chart at Silurian Time Scale.
Climate
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The Earth entered a long warm greenhouse phase. However latitudinal variations in climate were
rather similar to today, with glaciers occurring in the higher latitudes (over 65 o). Regions of marked
aridity occurred within 40o of the Silurian equator. Warm shallow seas covered much of the equatorial
land masses.
Silurian Sites
The Much Wenlock Limestone Formation
The Much Wenlock Limestone Formation of Britain reveals one of the most diverse, and wellpreserved fossil assemblages known, with well over 600 species of invertebrates recorded.
The Much Wenlock Limestone Formation of Wales and the Welsh Borderland contains a diverse
fauna of well over 600 species (mainly crinoids, corals, brachiopods, trilobites, algae and bryozoans)
deposited during the early Silurian when this area was covered by a relatively warm, shallow shelf
sea.
The Bryozoan of Much Wenlock
However, the Wenlock bryozoans remain poorly studied and understood, even though they constitute
an important part of the fauna. Species concepts are often insufficient, and there is a need for revised
descriptions, incorporating thin-section work. Furthermore, phylogenetic, ecological and functional
morphological studies also need to be carried out, as these areas have not been investigated in
detail. Preliminary work on one particularly characteristic Wenlock bryozoan, Ptilodictya lanceolata
(Goldfuss, 1829), a cryptostome, has revealed new information on its functional morphology, together
with patterns of seasonal development based on zooid measurements. In addition, multivariate
statistical analyses are currently being used to review the fenestrate species. Past workers have
relied too heavily on the so-called ‘micrometric formula’ and, as a result, taxonomically important
characters have often been overlooked, and little thin-section work has been carried out. It is hoped
that this research, utilizing a wider range of characters, will provide a reliable taxonomic platform for
the study of Silurian bryozoan phylogeny and palaeoecology" (Snell 1999).
The Crinoids of Much Wenlock
The Crinoidea account for around 10% of this number with an estimated 35 genera and 56 species.
The high quality of preservation has revealed a range of small-scale morphological features among
the aboral surfaces of the arms and calyces of this group. Small, circular to sub-circular depressions
and parabolic traces are randomly situated in the calcite plates of a number of the crinoid taxa. A
small number of these features indicate in vivo formation through the presence of rims and gall-like
features surrounding the trace. These structures are interpreted as a response by the crinoid to the
presence of another organism through either a mechanical or a chemical stimulant. The lack of
penetration into the body cavity and the extent of the reaction structures suggest a symbiotic
relationship existed between host crinoid and trace maker. A high degree of host-selectivity is
observed with only 15% of crinoid species being affected. This number includes some of the most
abundant crinoid species in fossil collections as well as a number of much rarer species. Work is now
commencing on the taxonomic identity of the pit-producing organisms" (Widdison 1999).
Life - the Biosphere
Following the Ordovician extinction event there was a rapid recovery of invertebrate
faunas during the Silurian. The high sea levels and warm shallow continental seas
provided a hospitable environment for marine life of all kinds. The biota and ecological
dynamics were basically still similar to that of the Ordovician, but was more diverse
Brachiopods are the most common hard-shelled organisms, making up 80% of the total species.
Among these, pentamerids first appear and are abundant, rhynchonellids, and the spire-bearing
athyridids and atrypidids are also common, as are other groups that continue from the Ordovician.
Tropical reefs are common in the shallow seas of this period, formed by tabulate and rugose corals,
stromatoporoid organisms, bryozoa and calcareous algae. Trilobites, cephalopods, gastropods, and
echinoderms. The Trilobites, having reached their acme in the Cambrian and Ordovician, are now in
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decline. The trinucleids and asaphids are absent, whilst encrinites and illaenids do not survive the
end of the Silurian
Planktonic graptolites remain common and diverse. The single-spined Monograptus is the
predominant genus, and its species are useful as zone fossils.
Jawless fish invade brackish and fresh water, as do eurypterids, xiphosurids, scorpions, which may
have been semi-aquatic. rhyniophytes, primitive lycophytes, and myriapods became the first proper
land organisms. At the end of the period Jawed fish appeared for the first time, but they remain
insignificant.
Some Typical Silurian Organisms
Gastropod
Eurypterid
Echinoderm
Jawless fish
Platyceras
Silurian Ecosystems
Benthic
A Silurian sea floor, showing numerous tabulate corals of the
genus Favosites large Stromatoporoids, the "sunflower coral"
(possibly a green alga) Ischadites, and rugose corals of the
genera Entelophyllum, Kodonophyllum, Streptelasma and
Craterophyllum. Crawling among the coral and
stromatoporoids are various kinds of gastropods. In the
background are crinoids of the genus Laubeocrinus, and
orthocerid straight shelled nautiloids (Kionoceras).url - image
originally from Spinar, Life Before Man
Pelagic
Silurian pelagic organisms included planktonic graptolites, trilobites,
(although most were crawlers, some were swimmers), crustaceans,
"thelodont" jawless fish, and cephalopods
Of all of these, the cephalopods were the largest and most impressive animals of the marine biota.
While most were pelagic or benthopelagic, there were some that were bottom-dwellers. The following
sketch illustrates the diversity of Silurian forms
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Marginal Marine
A typical Silurian (Wenlock-Ludlow) vertebrate fauna from Saaremaa Island, Estonia. This
fauna is dominated by agnaths, including thelodonts (1, Phlebolepis), heterostracans (2,
Toypelepis), anaspids (3, Rhyncholepis), and osteostracans (4, Procephalaspis; 5, Witaaspis;
6, Thyestes; 7,
Dartmuthia; 8,
Tremataspis; 9,
Oeselaspis). Jawed
fishes are also
present, especially
acanthodians (10.
Nostolepis) and
possibly the earliest
known osteichthyans
(11. Andeolepis,
known only from
isolated scales and
teeth). All these
fishes lived in a
marine environment,
but osteostracans
were more confined
to lagoonal, shallowwater facies, whereas
acanthodians and thelodonts were probably epipelagic.
Reconstruction and most of caption from Janvier 1996, p, 4
Estuarine biota
Lingulids, ostracods, eurypterids, limulids, scorpions, myriapods, trilobites, bivalves,
agnathans, and possible also acanthodians were present or probably present in estuarine
environments during the Middle and -Late Silurian (ref
Devonian times - going upstream)
Eurypterids
Eurypterus remipes Fiddler's Green Formation,
Herkimer County, New York
from Dr Peter's Fossil Collection (former site)
"Eurypterids, an extinct group of aquatic chelicerates,
were undoubtedly affected by environmental
constraints imposed by their physiology and gross
morphology, as are modern aquatic organisms.
Kjellesvig-Waering (1961) proposed a series of
distinct ecological phases for eurypterids, defined by
the environment in which they lived, and based on the
Upper Silurian Welsh Borderland fauna. However,
evidence from the eurypterid fauna of the Upper
Silurian Bertie Waterlime Formation, New York,
suggests that two distinct transitional assemblages existed, perhaps caused by a difference in the
environmental preferences of juvenile and adult eurypterids (‘ontogenetic segregation’) (Manning
1993). The eurypterids from the Upper Silurian of the Welsh Borderland may represent a previously
undescribed, ontogenetically mixed, eurypterid assemblage, influenced by a series of facies changes;
this is supported by sedimentological evidence (Manning, 1993). The distinct ecological phase model
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(Kjellesvig-Waering 1961) is rejected in favor of ecological gradients overlapping non-distinct
eurypterid phases (inter-phase mixing). Inter-phase mixing might have been complicated further by
the influence of ontogenetic migration of species across both physiological and environmental
gradients. Combining this with new fossil evidence on the dual respiratory and osmoregulatory
systems of eurypterids (Manning 1993; Manning & Dunlop 1995) leads to a better understanding of
the palaeoecology of this enigmatic group" (Manning 1999).
Terrestrial
The most important evolutionary development of this period, was that of the first true terrestrial
ecosystem
The first fossil records of vascular plants, that is, land plants with tissue that carries food, appeared in
the Silurian period. They were simple plants that had not developed separate stems and leaves.
By the Middle Silurian, a very simple early terrestrial community with simple plant producers,
millipede herbivores, centipede and arachnid carnivores, worm detritivores, and fungal decomposers
had developed. The Mid-Late Silurian terrestrial biota included small plants along the water's edge,
and arthropods such as trigonotarbids and myriapods (ref Devonian Times - going upstream). Fungi,
nematodes, and perhaps earthworms were most likely present as well, although they did not leave a
fossil record (except for possible fungi).
http://paleobiology.si.edu/geotime/main/htmlversion/silurian1.html
OVERVIEW
Silurian 444 - 416 Ma
Defining Characteristics:
• distinct estuarine,
freshwater, and terrestrial
ecosystems develop—the
start of significant life on dry
land
• Map of the Silurian World
Secondary Characteristics:
• first vascular plant fossils
• wide and rapid spread of
jawless fishes
• first extensive coral reefs
The Silurian physical world was vastly different in many ways from the world of today. For example,
the equator passed through what is now North America, and a nearly continuous inland sea extended
from New York to Nevada. Life was also quite different. Following the end-Ordovician extinction
event, Silurian marine faunas rebounded in the warm, shallow continental seas. Large coral reefs
made their first appearance during this time. Although marine life was diverse and abundant, there
were only a few types of small plants and terrestrial arthropods on land in the Silurian. However,
these represent the first true terrestrial ecosystems on Earth and include the first fossil records of
vascular plants. These terrestrial ecosystems became more complex, especially during the Late
Silurian, as upright plants evolved and populated the wet parts of lowland landscapes.
Silurian Marine Life
Marine life thrived and diversified during the Silurian; many forms were similar to those of the earlier
Ordovician Period. Although the later Devonian Period is often called the “Age of Fishes,” the Silurian
also was an important time in the evolution of this group. In particular, it was marked by the wide and
rapid spread of jawless fishes (agnathans). Only two of their jawless descendants—lampreys and
hagfishes—survive today, but many different kinds populated the Silurian seas.
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Among the invertebrates, brachiopods were especially diverse and abundant. Many survived from the
Ordovician, but other new forms evolved as well, so that brachiopods represented nearly 80% of all
Silurian marine invertebrate species. Although the planktonic graptolites lost many species in the endOrdovician mass extinction, they also remained abundant. The common genus Monograptus included
many species that are useful today as biostratigraphic fossils. Tabulate and rugose corals, calcareous
algae, stromatoporoids, and bryozoans formed shallow-water tropical reefs. Cephalopods,
gastropods, and echinoderms were among the active predators of the time. Trilobites began to
decline in diversity after having reached their peak in the Cambrian and Ordovician.
The Invasion of Land
Early vascular plants, collectively known as rhyniophytes, first appeared in the late Early Silurian and
diversified considerably through the Late Silurian. These plants had evolved an internal system of
tubular cells through which water traveled up the body of the plant, allowing them to maintain cell
functions higher above the land surface than would otherwise have been possible. Simple, small
plants such as Cooksonia lacked leaves, roots, seeds and the capability to grow in diameter, but they
were the dominant early terrestrial plants.
By the Middle Silurian, very early terrestrial communities had developed around the tiny, vertically
growing plants that acted as primary producers. True herbivores were absent from these early land
ecosystems. Dead plants were recycled by fungi and bacteria. Early arthropods—possibly related to
millipedes—also fed on dead and decaying plant matter rather than on living plant tissues. These
arthropod detritivores may also have digested the bacteria and fungi that lived in the soil. Other
arthropods, possibly related to centipedes, preyed upon the detritivores. The Mid–Late Silurian
terrestrial biota was probably confined to relatively wet areas.
The brackish and freshwater habitats near land were invaded by a variety of animal species, including
eurypterids, xiphosurids, scorpions, and jawless fishes. This increase is probably linked to the
expansion of vascular plants into aquatic and terrestrial habitats, which would have increased the
amount of food available. Most aquatic animals were relatively small (less than 20 centimeters), but
some eurypterids exceeded a meter in length and are, in fact, the largest known arthropods. Feeding
dynamics in Late Silurian estuaries appear to have been relatively simple. Most animals probably fed
on benthic (bottom) detritus and/or algae. Eurypterids and aquatic scorpions were the dominant large
predators.
Geology and Climate
During the Silurian, Earth underwent considerable changes that had important repercussions for the
environment and life within it. Plate tectonic activity continued to shift the continents during the
Silurian. The great southern continent of Gondwana drifted farther across the South Pole, while
Siberia, Laurentia and Baltica clustered around the equator. Laurentia and Baltica collided at the end
of the Silurian, forming a new supercontinent, Euramerica, and raising new mountain ranges. Rising
sea level formed a nearly continuous sea from New York to Nevada, and other shallow seas still
covered parts of other continents.
The Early Silurian was also a time of global icehouse climate that included great ice sheets at high
latitudes. By the middle of the Silurian, however, global climate had become much warmer,
comparable to that of most of the Ordovician and Devonian Periods. A new greenhouse phase
began, leading to the melting of many large glacial ice sheets, which contributed to a substantial rise
in global sea level. The result was a world with distinct north-south climatic zones, much as today.
Glaciers remained at high latitudes, but lower latitudes were relatively warm and arid conditions led to
the formation of extensive evaporite (salt) deposits near the equator.