The Tully Monster, one of the weirdest creatures that ever lived, has finally been identified

For more than half a century, scientists have scratched their heads over the nature of an outlandishly bizarre creature dubbed the Tully Monster that flourished about 307 million years ago in a coastal estuary in what is now northeastern Illinois.

But researchers on Wednesday announced they have finally solved the mystery.

They analysed numerous fossils of the creature, named Tullimonstrum gregarium, and determined it was not a blobby segmented worm or a free-swimming slug, as once hypothesised, but rather a type of jawless fish called a lamprey.

“I would rank the Tully Monster just about at the top of the scale of weirdness,” said paleontologist Victoria McCoy of Britain’s University of Leicester, who conducted the study while at Yale University.

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 35cm 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.

“I’ve always loved detective work, and in paleontology it doesn’t get much better than this,” said paleontologist James Lamsdell of the American Museum of Natural History in New York. “Our re-study of the specimens has shown that it is a very strange lamprey, a group of eel-like vertebrates that live in rivers and seas today.”