Image © and courtesy of the Illinois State Geological Survey,
Institute of Natural Resource Sustainability, University of Illinois, Champaign.
Tully’s common monster (Tullimonstrum gregarium), also known as the Tully monster, was selected as Illinois’ State Fossil in 1989. The first Tully monster fossil was discovered in 1958 by Francis Tully. Fossils of the Tully monster have been found only in Illinois.
The Tully monster was a soft-bodied animal. Its fossils are found in ironstone concretions, which are red-brown, rounded stones commonly found in rock removed from coal mines. This strange creature lived about 300 million years ago during the Pennsylvanian Period. It swam in the tropical ocean that covered Illinois at that time. Its sleek, tapered body and large tail fins imply that it was an active swimmer, perhaps a carnivore (meat-eater). Its segmented body was flexible and round or oval in shape. The body was about one foot in length.
The Tully monster had two eyelike projections on stalks. At the front of the body was an “arm” that ended in a mouthlike structure with eight to 14 sharp projections. The “arm” and projections may have been used for catching prey and bringing it to the mouth.
This animal is a mystery. Scientists don’t really know exactly what kind of animal it was. It may be related to snails, slugs and other mollusks, or it may have been a simple vertebrate. Researchers are continuing to search for the answer.
This drawing of a Tully monster shows it swimming through the ancient tropical Illinois ocean, searching for food. Beneath it, looking like small, bare trees, are two colonies built by tiny animals called bryozoans and a gastropod (snail) shell. In the background swims a cephalopod (Metacoceras sp.), a relative of the squid and octopus.