Illinois State Museum

Animals of the Swamp Forests

lizard in exhibit
Lizard in Penssylvanian Exhibit
Illinois State Museum

Hundreds of animal species have been described from fossils preserved in concretions from the Francis Creek Shale near Braidwood (the Mazon Creek region) of northeastern Illinois. Many are arthropods—insects (including cockroaches and giant dragonflies), large millipedes, spiders, and centipedes. Aquatic animals include fish, snails, clams, shrimp, and worms. The common horseshoe crab (Euproops danae), though usually an aquatic animal, may have also crawled on the forest floor.

Fossils of amphibians and reptiles are rare. Nine species of archaic amphibians are known, including the snake-like Ophiderpeton, salamanders, and larval stages. Changes Institute scientists have found one reptile, the lizard Cephalerpeton.