From Richard Leary, Illinois State Museum
The Tully Monster, a soft-bodied animal, is a marine fossil invertebrate from the Pennsylvanian Period or "Coal Age," approximately 300 million years ago. It had a flexible, segmented body that is thought to have been round or oval. Its tail carried triangular fins that propelled and guided the animal through the water. What appears to be a long flexible neck ends with a "jaw" with eight sharp teeth. What may have been eyes extended away from the body.
The Tully Monster has been designated as the official state fossil for Illinois. It was first found in 1958 by Mr. Francis Tully in the Mazon Creek region in Will and Grundy counties. The fossils are associated with clams, shrimp, fish, and other marine animals in ironstone deposits in central Illinois.
The scientific name is Tullimonstrum gregarium.
Courtesy Illinois State Geological Survey