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The Silurian period did not have a spectacular ending, however, the boundary was set and now we will discuss the Devonian period. Sometimes called ‘the Age of Fishes’ it was a time of many changes also in Earth’s land life. The name comes from the English county Devon, where explorers found the first evidence from that period.
Devonian Coral Reefs
The name ‘Age of Fishes’ didn’t come from anywhere. During the Devonian fish became a very diverse group. The jawed fishes started dominating over jawless species, due to their unique adaptations. Other kinds of fishes, including most advanced bony fishes, also started developing and many new species appeared. Among them was even the first shark- Cladoselache. Soon, fish occupied not only the sea but also freshwaters, like rivers and lakes. Moreover, static invertebrates like corals started rapidly developing, creating a hospitable environment for other species. That led to creating a complex ecosystem, we know today as coral reefs. However, Devonian reefs were built mostly of now-extinct species of corals, and sponges. Moreover, marine life was still very different from today’s, so the first reefs were very different than those we can observe today.
Development of land life
Not only marine life developed rapidly during the Devonian period many major changes appeared also within terrestrial life. First of all, plants started greening the land. Many kinds of horsetails and horsetails grew high and created the first forest-like environments. By the end of the period first, seed-forming trees also appeared, creating first forests. Due to their appearance combined with fungi and microorganisms the first soil began to form. That led to the development of many arthropods, including land scorpions. It’s also possible that insects also evolved in that period. The first four-legged animals evolved probably from fish, starting with extinct early amphibians- Batrachomorpha. However, it was still a long way for animals to take over the world. You may be a little surprised if I tell you, that the biggest land-living forms of the Devonian period were fungi. That’s right, Prototaxites could grow up to 8 m high!
Geology and climate during the Devonian period
The sea levels kept on rising during the Ordovician period. Warm climate, with an average temperature of about 30 degrees Celsius, and lots of oxygen due to land plants created a very hospitable environment for life. Later on, Earth cooled a little, and that’s when corals and sponges took over the seas. However, at the end of the period, the warming started again and maybe contributed to the extinction of some reef builders. When it comes to continents, during the Devonian plate tectonics moved a lot, firstly causing the formation of Laurasia. Gondwana was the second main continent, and at some point started getting closer to Laurasia. That caused the formation of the supercontinent later on, and the creation of the Appalachian mountains.
The end of the period
After the extinction-lacking end of Silurian, we are back to the mass extinction event way to close the periods. The late Devonian extinction marks the boundary between the Devonian and the Carboniferous. Its cause may be the land greening. The plant explosion led to a huge drop in CO2 levels in the atmosphere. As a result, temperatures dropped, which led to the extinction of many species. Another theory suggests the trigger was an effect of an asteroid or even magmatism. 50% of all species were wiped out, moreover, it took vertebrates 10 million years to come back. Reefs collapsed and corals did not return until Mesozoic, trilobites, and brachiopods went almost extinct. The early amphibians did not survive the event and the same forms never appeared again. Scientists still argue whether extinction happened as one big event or a couple of smaller ones.
Devonian period evidence
It comes as no surprise, that most of the Devonian evidence includes fossils of plants. It shows how fast they developed and conquered a new, terrestrial environment. Many fossils of fish, corals, and of course still developing trilobites, also provide a lot of useful information. Tiktaalik is an important genre of fish because it’s the form closest to modern tetrapods. Near Kimberley Basin in Australia, scientists found remains of the huge barrier reef, unfortunately now completely dry. Another evidence shows that identical rocks appear in modern America and Europe, which suggests there were once one continent (Laurasia). Similar evidence suggests also the existence of both Gondwana and the supercontinent Pangea.
Previous in series: The Silurian Period (The Life Rebound)
I hope reading this article helped you understand how life moved to the land, as well as other changes in the Devonian period. If you enjoyed it, please share with your family and friends. In the next article, we will discuss the next Paleozoic period- the Carboniferous. If you have any questions, feel free to contact me, you can find the email address in the ‘Our team’ section of the page.