LECTURE NOTES: THE MID-LATE PALEOZOIC WORLD:
Devonian,
Carboniferous: Mississippian and Pennsylvanian & the Permian.

The 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 Mountains

The PaleoMap Project  (www.scotese.com)

Life in the Devonian (Age of Fishes):

Generally, the period is characterized warmer climates, rising sea level. Reefs still dominated by tabulate & rugose corals and stomatatoperoid sponges grow larger than earlier forms.

Ammonites first appear in Devonian age rocks as a transition from the straight-shelled nautiloid to the curve-shell organism.

The Ostracoderm (bony-jawless fish) is abundant but, it’s in the Devonian that predatory jawed fish become the dominant form of fish in the Devonian

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 NE Ohio.

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

Devonian Plants & Climate

The first forests were composed of plants called archaeopteris (a from of club moss). The first seeded plants – form of club moss also evolve.

Intermediate 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 respiration.

A marine mass extinction eliminated the tabulate-strom reef that had dominated the oceans

Paleogeography of Mississippian

The PaleoMap Project  (www.scotese.com)

Early Carboniferous—Mississippian

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.

Research suggests sea level dropped due to glaciation on Gondwanaland.

Pennsylvanian

Extensive coal deposits were formed in swamps found along the foothills of young Appalachian Mountains.

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.

Plants from Pennsylvanian Swamps

Lycopods -spore 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.

Pennsylvanian: Pangea comes together

This is referred to as the Alleghenian Orogeny: the last phase of formation for the Appalachian Mountains (continues into the Permian)

The PaleoMap Project  (www.scotese.com)

Pennsylvanian Animals

Freshwater and terrestrial animals were represented by new winged-insects, like giant dragonflies and a number of modern size insects.

Reptiles appear first in Pennsylvanian with evolution of the amniote egg (shelled two-sac egg: one with nutrition and embryo and the other to collect waste).

Reptiles advanced jaws and developed blade-like teeth.

Last of the Paleozoic: Pangea

The PaleoMap Project  (www.scotese.com)

Alleghenian Orogeny

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.

Permian reptiles

Herbivores (Edaphosaurus) 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 with hairs.

End of the Paleozoic

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 fusulinid forams.

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.

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