Two Archimedes Screw Bryozoan Fossils - Illinois

Here is a nice example of two Archimedes sp. fossils from the Warsaw Formation of Illinois. This unusual cork-screw shaped bryozoan commonly referred to as an "Archimedes Screw" is unique to the Mississippian aged rocks of North America.

Bryozoans are microscopic aquatic invertebrates that live in colonies, forming skeletal structures similar to corals. Each skeletal structure has a form unique to each particular species. The individual byrozoans forming these colonies are fileter feeders called zooids, straining nutrients from the surrounding water.