From site: The plants and animals found in concretions recovered from the Francis Creek Shale are some of the most exciting and important fossils that have been found in the state of Illinois. These fossils are known as the Mazon Creek fossils because they were originally found along Mazon Creek in northeastern Illinois.
The quality and diversity of fossils recovered in Mazon Creek nodules makes these localities important worldwide. In most fossil deposits only the hard parts of organisms (shells, bones, teeth, etc.) are preserved. This means that in most fossil deposits only animals that have hard parts are preserved.
Because of the unique conditions of fossilization, Mazon Creek fossils frequently have both hard and softer parts preserved. In addition, many soft-bodied organisms that do not usually fossilize are preserved.
These factors mean that the fossils from Mazon Creek provide scientists with an extraordinary view of biodiversity 300 million years ago.
Mazon Creek Fossils
