During the Devonian period, 365 million years ago, Iowa was an ocean. Most of the fossils found currently at the Fossil & Prairie Park Preserve are from a shallow sea environment and are marine invertebrates.

Commonly found fossils include:

• Brachiopods
• Gastropods
• Horn Corals
• Colony Corals
• Crinoids
• Bryzoans
• Cephalopods