Illinois Fossil

Tully Monster

(Tullimonstrum gregarium)

Adopted in 1989.

Illinois State Geological Survey paleontologist Donald Mikulic lobbied the State Legislature for designation of the Tully Monster, Tullimonstrum gregarium, as the state fossil, and a bill to this effect was passed in 1989.

It is a soft bodied animal. It preserves as outlines and flattened forms in nodules of ironstone from several areas in Illinois. It lived in the ocean that covered much of Illinois during the Pennsylvanian Period (about 300 million years ago). It was probably an active, swimming carnivore.

The flexible body was probably round or oval in cross section. It may have been segmented, but some recent work suggests that it was not. The tail had horizontal fins and a dorsal fin; all three of these fins were triangular.

The Tully Monster had a long proboscis. At the end was a "jaw" that contained eight small, sharp teeth. There is no evidence that the throat went down the proboscis. It seems more likely that the proboscis was a muscular organ used to pass food to the mouth.

Near the middle of the body was a transverse bar the passed through the body. This bar had swellings on the end. These may have been the animal's sensory organ.

Scientists do not know to what other animals the Tully Monster is related. Some scientists have speculated that it is related to snails and other mollusks.