| The Mazon Creek fossils are conservation lagerstätten found near Chicago, Illinois. The fossils are found in ironstone concretions formed approximately 300 mya in the mid-Pennsylvanian epoch of the Carboniferous. These concretions frequently preserve both hard and soft tissues of animal and plant materials, as well as many soft-bodied organisms that do not normally fossilize. The quality, quantity, and diversity of fossils, known since the mid-nineteenth century, make the Mazon Creek lagerstätte important to paleontologists in attempting to reconstruct the paleoecology of the sites. Reference |  |