The story
The Tully monster, Tullimonstrum gregarium, lived about 307 million years ago in a river delta near a shallow sea in what is now Illinois. Francis Tully, an amateur collector, found the first specimen in 1958 in the Mazon Creek beds, where iron-rich nodules that formed in mud preserve soft bodies. It was about 8 to 35 centimetres long, with a flexible body, a tail fin, two eyes on stalks and a long snout ending in a claw with tiny teeth. Illinois made it the state fossil in 1989.
No one knew what it was. In 2016 two teams studied the same fossils and drew opposite conclusions: Victoria McCoy and colleagues argued in Nature that it was a vertebrate related to lampreys, citing a gill pouch, a notochord and eye pigment-bearing structures, while Thomas Clements and colleagues argued the features were not those of a vertebrate. Later studies kept the argument going. The Tully monster shows how unusual body plans can survive among well-known groups, and how hard it is to place soft-bodied fossils. It is found only at Mazon Creek, which also preserves jellyfish, shrimp, worms and many plants.
Why it mattered
- It shows how many odd animal forms existed that left no descendants and how difficult classification of soft bodies can be.
- Its preservation in Mazon Creek nodules gives a rare picture of soft-bodied life in coal-age swamps.
- The dispute is a model for how new imaging and chemical methods reshape debates about old fossils.
Sources
- Research the Tully Monster Florida Museum
Contested history
Consensus: Tullimonstrum is a real soft-bodied animal from Mazon Creek; whether it was a vertebrate is unresolved.
- Research the Tully Monster Florida Museum
- Enigmatic Tully Monster Finds a Home on the Tree of Life Harvard Science in the News
- Is Tullimonstrum a vertebrate? Palaeocast
Community notes
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