The Paleozoic Era (Silurian and Devonian Periods)

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Evolutionary Biology

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The Paleozoic Era (Silurian and Devonian Periods)

The Paleozoic Era (The Silurian and Devonian Periods)

Introduction:The Paleozoic era began about 542 million years ago and lasted until 251 million years ago.It was characterized by the breaking of the supercontinent of Pannotia and the formation of the supercontinent of Pangea.The Paleozoic era was divided into 6 periods: Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian.

The Silurian Period

The Devonian Period

Introduction:The Silurian period began 443 million years ago and ended 416 million yeras ago.Its name was given to it by Sir Frederick Murchison, a Scottish aristocrat, who named it after a Celtic Welsh tribe called the Silures.

Ecosystem:Due to the low height of landmasses during the Silurian period, sea levels rose and allowed the formation of shallow marine ecosystems where sunlight was able to penetrate and help create the first coral reefs.Reefs in this period were built from tabulate and horn corals.This new flourishing ecosystem led to the diversification of fish such as Agnatha, a class of jawless fish which was the most common in the period.Another species known as a Placoderm - a primitve armored fish with a cartilage skeleton - was one of the first fish to develop jaws.The dominant predator during the period were the Eurypterids who were arthropods, related to the modern horseshoe crab.The stable climate also allowed for another siginificant evolution, the first land plants. Lichens were the first photosynthetic plants to develop above the water and cling to rocky coasts.Another evolution in plants was the formation of Cooksonia, a plant that had vascular tissue for water transport.Finally there was the development of the first air-breathing animals such as millipedes, centipedes, and arachnids.

Climate:The Silurian period began with a very cold climate that affected the entire planet. This was the result of Gondwana's position near the southern pole which caused glaciers of ice to form on land and in shallow seas. However, as the Silurian period progressed the temperature of the planet began to warm up and become stable. This new warmer temperature caused many of the ice sheets to melt and, as a result, cause sea levels to rise.

Introduction:The Devonian Period began 416 million years ago and ended 358 million years ago.The name of the period comes from the town of Devon, England where the red sandstone from the period was first studied.

Climate:As the temperature rose in the Silurian, during the Early and Mid Devonian the temperature was arid and warmer than it was in the preceeding period. It wasn't until the Late Devonian when the lowering of CO2 in the atmosphere caused global temperatures to lower and cause glaciation in many areas of the planet.

Ecosystem:This period was characterized by a time of extensive and diverse reef development, which contained brachipods, trilobites, tabulate, and horn corals.Placoderms underwent great changes and diversification and also became the top predators of the period. Placoderms were known for their simple jaws, mouths with bony structures, and their 33 feet lenght.Another group of fishes that started developing during this period was the cartilaginous fish, such as sharks and rays.Fish were also divided into two types: ray-finned fish and lobe-finned fish.Ray-finned fish had paired pelvic and pectoral fins supported by many thin bones powered by muscles within the trunk. Lobe-finned fish had fleshy pectoral and pelvic fins connected to the shoulder or pelvis by a single bone, which was powered by muscles within the fin.Another important development was the formation of the first land forests composed of lycophytes, horsetails, and ferns.By the end of the Devonian, progymnosperms like Arcaheopteris became the first successful trees.They would grow to 98 feet with a trunk diameter of 3 feet. It had softwood trunks similar to modern conifers. It had fern-like structures which were joined to the branches directly.This abundance of plants now filled the air with oxygen and depleted the air of Carbon Dioxide and led to a cooling planet.The first insects, like Rhyniella praecusor, also emerged. This insect was a flightless hexapod with antennae and a segmented body.Another organism that evolved during this period were the tetrapods. Tiktaalik roseae was considered to be the link between the lobe-finned fish and early amphibians. This organism that was able to "walk" on the shallow banks of estuaries. It also had a crocodile-like head and nostrils for breathing air.

Mass Extinction:The Late Devonian Period was characterized by a mass extinction event. There has been speculation that the abundace of oxygen and lowering of CO2 in the atmosphere caused the climate to cool and lower the global sea level. Also during the Late Devonian there was an abundance of algae in the oceans which drained up the oxygen in the water and caused over 70% of marine invertebrates to die. Aside from this, most terrestrial organisms were left unharmed.

References:The Devonian Period. (n.d.). Retrieved from Period: Climate, Animals ' Plants. (n.d.). Retrieved from Paleozoic Era. (n.d.). Retrieved from Era: Facts ' Information. (n.d.). Retrieved from Period Facts: Climate, Animals ' Plants. (n.d.). Retrieved from Silurian Period. (n.d.). Retrieved from


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