Devonian (420-354 mya)
Generally a two-stage collision and accretion of Baltica
then Avalonia to Laurentia forming a new continent called Euramerica.
This represents the second stage of mountain building in the Appalachian
The PaleoMap Project (www.scotese.com)
Life in the
Devonian (Age of Fishes):
the period is characterized warmer climates, rising sea level. Reefs
still dominated by tabulate & rugose corals and stomatatoperoid
sponges grow larger than earlier forms.
first appear in Devonian age rocks as a transition from the
straight-shelled nautiloid to the curve-shell organism.
(bony-jawless fish) is abundant but, it’s in the Devonian that
predatory jawed fish become the dominant form of fish in the Devonian
Fish: Age of Fishes
Gondwanaland begins to move northward toward Euramerica.
Placoderms for example
are jawed predatory fish One example called Dunkleosteus
is known to be 23 ft long and has been found in the Cleveland Shale in
Coelacanths are a group
of lobe-finned fish that were believed to be extinct but are now found
living off SE Africa and near Indonesia
Plants & Climate
forests were composed of plants called archaeopteris (a
from of club moss). The first seeded plants – form of club moss also
form between fish and modern amphibians are found in Devonian age rocks.
By the end of
the Devonian, there is evidence in that a new ice age began which may be
related to a decrease in atmospheric CO2. This decrease may
be tied rise of land plants which take in CO2 during
A marine mass
extinction eliminated the tabulate-strom reef that had
dominated the oceans
is marked by a
continued sea level rise, development of the warm equatorial sea with
deposition of thick limestone bed and cold polar areas.
But, for the
first, organisms precipitate aragonite in the oceans instead of calcite.
The end of the
Mississippian is marked by rocks representing a regression by inland sea
and extinction of crinoids, ammonoids, and the armored placoderm fish.
suggests sea level dropped due to glaciation on Gondwanaland.
deposits were formed in swamps found along the foothills of young
These coal beds
and alternating shallow marine sediments formed a sequence of rocks
called cyclothems. Much of the coal mined in the Midwest
comes from these cyclothem deposits.
bearing plants like Lepidodendron and Sigillaria
and seed fern Glossopteris (in Gondwanaland).
These plants were the abundant forms of vegetation
found in Carboniferous swamps. The first gynosperms are found.
Pangea comes together
This is referred to as the Alleghenian Orogeny: the
last phase of formation for the Appalachian Mountains (continues into
terrestrial animals were represented by new winged-insects, like
giant dragonflies and a number of modern size insects.
first in Pennsylvanian with evolution of the amniote egg (shelled
two-sac egg: one with nutrition and embryo and the other to collect
advanced jaws and developed blade-like teeth.
Last of the
This collision of Euramerica and Gondwanaland
continued during the Permian forming southern Appalachian Mountains.
Blue Ridge Mountains consist of uplifted Proterozoic
metamorphic rocks, the Valley and Ridge province is deformed
sedimentary sandstones and shales formed during Taconic and Acadian.
This orogeny along with Ural Mountains orogenesis
completed the assemblage of Pangea by the end of Paleozoic.
and carnivores (Dimetrodon supported by long vertebral spines)
pelycosaurs (fin backed reptiles) that later evolved into mammal like
therapsids. Pelycosaurs were ectothermic (cold-blooded). Therapsids were
endothermic (warm-blooded), could maintain activity and were covered
End of the
Late Permian the largest extinction event in the
Earth history. It is believed to be a 2-stage extinction event
The first extinction (Guadalupian) killed the
remaining rugose and tabulate corals (reef-builders), trilobites and
The terminal extinction saw the loss of 20 families of
Theripods, 70% of marine species were lost.
This extinction was sudden and might be caused by
severe decrease in oxygenated seawater, sea regression, glaciation, and
volcanic gas emission that triggered ice age.