The Silurian Period was a time of uplift and erosion. There are no rocks of this age in Wyoming. As such, there are no Silurian fossils. In neighboring western states, however, a restricted distribution of poorly preserved coral fossils has been documented.

Seas transgressed and flooded the western part of Wyoming in the Devonian Period. Marine plants (crinoids) and animals (amphibians, cephalopods, and primitive fish) are common fossils of Devonian age, as are fossil land plants.

During the Mississippian Period, Wyoming was submerged in a shallow sea and marine fossils such as trilobites, brachiopods, fish, and crinoids, are common in rocks of this age. In the Pennsylvanian, the sea began to regress, but marine fossils are still common for this period.

In the Permian, the shallow sea continued to regress. Fossils include marine flora and fauna such as pelecypods, corals, belemnites, and conodonts, as well as gastropods. Reptiles and coniferous trees originated during the Permian. A mass extinction marked the end of the Permian. Most of Earth's marine species and more than half of the terrestrial reptiles, amphibians, insects, and plant life were lost.

Contact:

Colby Schwaderer, colby.schwaderer@wyo.gov