Describe and discuss the marine communities of the Ordovician, Silurian, and Devonian. How

do they compare with present-day marine communities? What will be an ideal response?


The Middle Ordovician was noted for a major marine transgression causing wide-spread epeiric
seas over much of the North American craton. This shallow marine environment was home to a
variety of brachiopods, bryozoans, and corals. Acritarchs also were abundant. A major mass
extinction occurred at the end of the Ordovician and was followed by a rediversification of
marine organisms. Eurypterids and ammonoids made up a large part of the populations during
these periods. Another mass extinction occurred at the end of the Devonian.

Environmental & Atmospheric Sciences

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