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!
“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.
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