The Devonian Period of geological spans from approximately 410 mya to 367 mya. During this period as in the preceeding era's, Oklahoma was covered by shallow seas. Devonian sea life was very abundant, and by some respects may be considered to be the most abundant period of sea population during the Paleozoic era.
Positions of Landmasses during the Devonian period
From the PaleoMap Project
Among the marine invertebrates of the time there was little change from the Silurian. Reefs were predominantly built by the corals and stromatoporoids. Trilobites were still on the decline, however, the largest trilobites were living at this time, some reaching lengths of up to 28 inches. The brachiopods were reaching their maximums both in abundance and diversity. The most dominant creature of the Devonian is believed to be the fishes. The first jawed fishes, which appeared at the end of the Silurian, were now reaching abundance in the Devonian. Some of the fishes of the Devonian were very large, reaching lengths of over 30 feet.
During the Silurian, new freshwater environments were becoming colonized, primarily by the bi-valves. Interestingly, the fossil record begins to show gastropods moving onto the landmasses. During the late Silurian, arthropods (possibly millipedes and scorpions) began to develop trachea and were adapting to terrestrial conditions. Because plant life was the first suspected land grabber, it reasons that the first terrestrial organisms were plant eaters, but predators were surely not too far behind, such as the primitive spiders of the late Devonian found in Germany. Amphibians have also been found in Devonian rocks located in Greenland.
Plants were beginning to switch from depending on water for reproduction to relying on seeds and pollenization to reproduce. Seed ferns are very abundant in the fossil records of exposed landmasses during the Devonian.
The Devonian ended with a mass extinction event similar to that of the Ordovician. Approximately 25% of all families became extinct, particularily affected were the ammonoids, fishes, and amphibians. Some speculate that the Devonian mass extinction was promulgated by a change in sea levels combined with an extra-terrestrial event (asteroid impact.)
Devonian sedimentary rocks can be found in the Ouchita, Wichita, and Ozark uplifts in Oklahoma.
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