Field Museum Scientists Reveal Tully Monster’s True Nature

Nearly 60 years ago, an amateur fossil collector named Francis Tully stumbled upon an incredibly peculiar fossil. The odd jumble of physical attributes – a tube-shaped body, eyes on stalks, and a long, skinny snout with a claw or jaw at the end – looked like they would be more at home in a Dr. Seuss book than in the swamps of Illinois.

Paleontologists were flummoxed. Was it a mollusk? An arthropod? A worm? Or none of the above? Thanks to a yearlong Field Museum collaboration with Yale University scientists and other institutions, the Tully monster's true nature has finally been revealed—and it’s a vertebrate! 

[Illinois ‘Monster’ Mystery Solved in Part by Field Museum Scientists]

“People don’t know how to classify it taxonomically,” Field Museum Fossil Invertebrates Collections Manager Paul Mayer said. “What group of animals did it belong to?  Was it a gastropod that didn’t have a shell? Was it some kind of worm like a leech? Or was kind of chordate, or a jawless fish? People have gone back and forth on these type of ideas. Now finally with the publication, we’ve determined it is a vertebrate.”

But how could such a bizarre creature live in Illinois? Roughly 307 million years ago, Illinois was a very different place.

“It was a very different and much more pleasant place to live,” Field Museum Curator of Invertebrate Paleontology Scott Lidgard said. “It was a tropical environment and that is because it was only a few degrees north or south of the equator for this entire interval of time.”

Mayer said that the Tully Monster’s classification was a puzzle for decades.

“It solves a mystery that the Tully monster has been kind of the poster child for problematic fossils – a mystery for 50 years – that people have been wondering, ‘What is this animal?’” Mayer said. “It starts filling in some blanks on the tree of life.”

The Field Museum created the video below, "Tully: Monster versus Method," to show more about the technology and methodology behind the Tully monster breakthrough. 

Tully: Monster vs Method from The Field Museum on Vimeo.


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