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This Week In Illinois History: The Tully Monster (August 31, 1989)

An artist’s rendition of Tullimonstrum gregarium, aka, the Tully Monster
Nobu Tamura (nobu.tamura@yahoo.com)
An artist’s rendition of Tullimonstrum gregarium, aka, the Tully Monster

Illinois' state bird is the northern cardinal. The state vegetable is corn, of course. We even have an obvious state snack: popcorn. But did you know that Illinois has a state fossil? And it’s a weird one.

On August 31, 1989, Governor James Thompson signed legislation making the Tullimonstrum gregarium, or the Tully Monster, the official state fossil.

The Tully Monster is named after the amateur fossil collector who discovered it in 1955, Francis Tully. He found the bizarre fossil in the Mazon Creek fossil beds of northern Illinois. These fossil-rich beds contain a mixture of sea life from the carboniferous period, 300 million years ago.

The fossil looked like a long tube with two fins on its tail and a thin, claw-like proboscis with sharp teeth protruding from its head. At the base of this proboscis is a bar-like organ tipped by two eyes.

Additional fossil records show that Tully Monsters grew between 3 and 15 inches. But the Mazon Creek area could have been a breeding ground. The creatures may have grown larger elsewhere.

Tully took his find to Chicago’s Field Museum. Not only had they never seen this creature, they couldn’t agree how to classify it. Was it a mollusk? An arthropod? Paleontologists couldn’t even decide if it was a worm or a fish.

Its classification remained a mystery until 2016 when scientists determined that the Tully Monster was a vertebrate, and possibly an early ancestor of the lamprey.

Today, thousands of Tully Monster fossils have been found but only in Illinois.

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