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

A recreation of the "Tully monster" (© Sean McMahon)A recreation of the "Tully monster" (© Sean McMahon)

Just over 307 million years ago, Illinois was home to a bizarre creature dubbed the Tully monster.

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The aquatic animal had a tube-shaped body, skinny snouts ending in a toothy jaw or claw, and Shrek-like eyes at the end of little stalks.

First discovered by amateur fossil collector Francis Tully in 1958, the creature's scientific origins were long disputed. Scientists ultimately categorized them as soft-bodied invertebrates – something more akin to a worm or snail. 

But not so, says a paper published Wednesday in the international science journal Nature: The creature is a vertebrate, a jawless fish similar to the lamprey.   

Detailed view of a sea lamprey's oral disc. (United States Environmental Protection Agency)Detailed view of a sea lamprey's oral disc. (United States Environmental Protection Agency)

“It’s a beautiful example of how science works to solve mysteries of nature, and how museums fit in,” said Scott Lidgard, the Field's curator of Invertebrate Paleontology who was also one of the paper's authors. 

The paper's research relied heavily on the Field's Tully monster collection, which, at over 2,000 specimens, is one of the world's best. Having the specimens allowed scientists to compare and analyze the animals' features. Digitization of those specimens, combined with X-ray analysis at the Argonne National Laboratory, helped paleontologists take an even closer look at the fossils.

The creature's specimens have only been found in the Mazon Creek region, one of the world’s richest fossil sites, about 50 miles southwest of Chicago. At the time the Tully monsters roamed (or swam), the area would have been a swampy shoreline bordering a tropical sea. 

Those interested in checking out a Tully monster fossil themselves can head to the Field Museum's "Evolving Planet," a permanent exhibition.  

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