Million-year old mystery of Tully Monster solved finally

Tully Monster flourished about 307 million years ago in a coastal estuary in what is now north eastern Illinois, and people often wondered if it could have been a segmented worm or a free-swimming slug. After analysing numerous fossils of the creature named Tullimonstrum gregarium, scientists on Wednesday said it was a type of jaw-less fish called a lamprey. 

It boasted a torpedo-shaped body, a jointed, trunk-like snout ending in a claw-like structure studded with two rows of conical teeth, and its eyes were set on the ends of a long rigid bar extending sideways from the head. Up to about 14 inches long, it had a vertical tail fin and a long, narrow dorsal fin. 

A sophisticated reassessment of the fossils determined it was a vertebrate, with gills and a stiffened rod, or notochord, that functioned as a rudimentary spinal cord and supported its body. The notochord previously had been identified as the gut. 

Tullimonstrum shared its shallow marine environment with fish including sharks as well as jellyfish, shrimp and amphibians.