Fossilization is a rare process. In fact, most of the plants, animals, and insects that existed on earth have not been retained in the fossil record because the conditions required must come together with such precision and timeliness that most just miss the boat. Occasionally, a fossil is produced – a leaf, a tooth, maybe a partial skeleton. From these, paleontologists try to piece together the earth’s history.
Most of the time, it is the hard parts of an animal that are fossilized because bone and teeth don’t succumb to the decay process as quickly as the soft parts of an animal, such as muscle tissue. Think about a banana left out on your kitchen counter too long – it will rot away, decomposed by bacteria. Every once in a while though, the conditions are just right to where the fossilization process includes those soft parts. This is rare, but can provide a more complete picture of an animal or an entire paleo-ecosystem. These are truly a remarkable resource, permitting us to look back in time.
Fossils from the Mazon Creek area in Illinois are associated with the Francis Creek Shale formation and date to approximately 307 million years ago, during the Pennsylvanian. This site is unique in that the fossil assemblage includes the preservation of soft tissue, even of animals such as worms and jellyfish! This paleontological site is called a “lagerstätten” or “mother lode” due to the diversity of the flora and fauna represented. Such sites are recognized worldwide as having importance for our national heritage and the process of understanding earth’s history.
Here are a few of the fossil specimens from the Mazon Creek area in the Academy’s museum collections:
Mazonomya mazonensis -- a clam
Euphoberia sp. -- a spiny millipede
Tullimonstrum gregarium - the "Tully Monster",
a carnivorous marine soft-bodied animal, and the Illinois state fossil
Lobatopteris sp. -- a fern
Annularia stellata -- a plant similar to a horsetail