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The Illinois state fossil, the Tully monster, has long had a significant problem: It couldn’t be assigned to a known group. New evidence discovered by scientists from the Field Museum of Natural History, Argonne National Laboratory and Yale University, has helped identify the Tully monster as a vertebrate and descendant of the lamprey.
Tully monster basics
Though called a “monster” it is 3 to 15 inches long.
- Official name: Tullimonstrum gregarium
- Discovered: Francis Tully in 1955
- Age of fossil: 309-307 million years old
- Location of discovery: Mazon Creek deposits in Will and Grundy counties in an area that was once an ocean
- State symbol: Designated in 1989
Link to lampreys
Through examination and comparison of more than 1,200 specimens, scientists were able to relate a combination of features of the fossils to a lineage of lampreys (jawless fish with a toothed, funnel-like sucking mouth), as well as defining it as a vertebrate. What they discovered:
- Tail fins: Elongated body with a fin used to swim
- Notochord: A backbonelike rod made of cartilage.
- Gill pouches: Up to five are evident.
- Eyes: Stick out laterally on a rigid bar, similar to a hammerhead shark, assumed to protect the optic nerve.
- Brain: Three lobes are similar in placement and size to a typical lamprey.
- Proboscis: The creature had an elongated, flexible proboscis, basically a long nose with teeth. It probably grabbed food with it and scraped pieces off with its tongue. This variety of proboscis is similar to lamprey-related fossils from the same area.
- Teeth: Multiple rows of insect-like stylets or piercing teeth next to the mouth, similar to lampreys.
Sources: Department of Geology and Geophysics, Yale University, American Museum of Natural History, Field Museum of Natural History, Argonne National Laboratory and Yale Peabody Museum of Natural History
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