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 During the Silurian and Devonian periods most of the Earth’s
continents were on a collision course to form supercontinents.
These plate movements had important consequences for ocean
circulation patterns, climate, and ultimately for the organisms
living in these changing habitats. Plants, arthropods, fungi,
and, by the close of the Devonian, tetrapods were in the process
of invading terrestrial environments during this time, and the
evolutionary rise of cartilaginous, ray-finned, and lobe-finned
fish in the oceans earned the Devonian the nickname “The Age of
Fishes.”
Learning Objectives
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How did the evolution of jaws and teeth affect other
evolutionary developments?
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What problems had to be overcome in order for animals
and plants to move from aquatic to terrestrial
environments?
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As plants moved into more and more terrestrial
environments, how were other organisms affected?
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What type of fish gave rise to tetrapods?
 Did you ever wonder where all that coal came from? Huge, swampy
forests of seedless vascular plants formed in coastal areas,
sequestering so much CO2 from the atmosphere that they may have
triggered a major glacial event. Many cycles of sea level
fluctuation caused by advancing and retreating glaciers
repeatedly inundated the swamps with water and sediment,
eventually forming the large coal reserves found in Europe and
North America.
During this time period plants and tetrapods became firmly
established on land, and many new ecosystems came into being.
Both seeds and the amniotic egg evolved, lessening the
dependence of plants and animals on water and allowing them to
occupy many previously unoccupied niches. The Permian period
ended with the largest extinction event in Earth’s history.
Learning Objectives
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Why do large landmasses tend to have dry interiors?
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How might the large amounts of vegetation in the coal
swamps have cooled the atmosphere?
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Understand the differences in the mechanisms of
fertilization between seedless vascular plants and
seed plants.
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What are some of the evolutionary innovations in the
amniotic egg?
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What factors may have contributed to the extinction
event at the end of the Permian period?
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