Illinois State Museum

Tropical Forest, Rock Island County, Illinois, 320 million years ago

map of ecosystems

During the early Pennsylvanian Period, northwestern Illinois was at the western edge of the Illinois Basin. The basin was a spoon-shaped depression that covered nearly all of Illinois, southwestern Indiana, and western Kentucky. It was a region of swamps and shallow seas, dotted by a few upland areas 15 to 30 meters (about 50–100 ft.) above sea level.

This reconstruction is based on fossils and the preserved landforms from one of these uplands. They were uncovered in a quarry in Milan, Illinois.

Variation Across Space
Ecosystems change through time, but they also vary across space—from place to place. Today in Illinois, Changes Institute scientists study environmental variation from lake ecosystems to rivers, prairies, and forests. During the Pennsylvanian (320–290 million years ago) we find evidence of the same variation. We find fossils preserved from upland forests, river deltas, swamps, shallow oceans environments, and the deep sea.