About the Symbol
The Tully Monster (Tullimonstrum gregarium)
was 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
horizonal 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
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 molluscs.
The Tully Monster was first found by Mr. Francis Tully in 1958. He took the
specimen to the Field Museum of Natural History in Chicago. The specimen defied identification and became
known as the "Tully Monster." The name stuck. When Dr. Eugene Richardson
formally described the new animal, he gave it the name Tullimonstrum
The species name gregarium means common. This refers to the fact
that Tully Monsters are fairly common fossils in the Mazon Creek deposits. More
recently they have also been found in open-pit coal mines in central Illinois.
The Mazon Creek deposits are located in Will and Grundy Counties. They are
some of the most important fossil deposits in North America because the soft
parts of many organisms are preserved. The deposits contain the remains of both
plants and animals. Some of the organisms lived in the ocean; others were washed
in from the nearby shore. The material is preserved in concretions of ironstone.