The Tully monster: Illinois’ scary official fossil


In life, it was only about a foot long, but it might trigger nightmares if you saw it swim past. It would wriggle like a worm or an eel through the water. At the end of an elephant-like snout, a toothy mouth would reach out and tear into onto your flesh to suck out nutrients as it waved its eyes at you…

Since 1989, the Tully monster has been the official state fossil of Illinois.

It lived about 300 million years ago. At that time, Illinois lay near the equator. Dense swamps were pierced by meandering, muddy rivers full of animals like the early relatives of jellyfish and shrimp. The mud rapidly buried creatures that died and preserved them even if they had soft bodies.

The nodules containing these fossils were discovered around Mazon Creek in the 1850s and attracted fossil collectors. In the 1950s, Francis Tully found something new and took it to the Field Museum of Natural History, where the paleontologists named it Tullimonstrum gregarium or “Tully’s common monster,” because Mr. Tully had found it, it was highly unusual (a monster), and there turned out to be quite a few of that kind of fossil at Mazon Creek. And only at Mazon Creek. They may have been common worldwide, but only special circumstances could preserve an animal like that.

It had a long, soft, segmented body with no shell or backbone. At one end were fins. At the other writhed a trunk-like snout with jaws and teeth. In the middle were two eyes on stalks.

Is it a worm? A mollusc? A very early vertebrate? Hard to know. Beyond all doubt, creepy.

We don’t know what creatures, if any, we’ll find on other planets, but Earth’s past is a warning. We might not like it.

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