Illinois’s Perplexing, Quirky, Venerable Tully Monster

Tully Monster reconstructed as a lamprey-like invertebrate by Paleo Equii via Wikimedia Commons





Long, narrow, and plumpish, with eyes on stalks and a mouthish, tiny-toothed claw at the end of its flexible, one-nostrilled nose, the Tully Monster is devoid of prettiness. Yet its ugliness is the sort that Picasso insisted could be beautiful. Francis Tully, an amateur fossil-hunter, unearthed this fourteen-inch puzzle sixty-five years ago in an Illinois coal pit in the Mazon Creek area of northern Illinois. More and more of the fossils were uncovered, and the General Assembly voted Tully the state fossil of Illinois.

Found nowhere else on earth, the fossil preserves a long-vanished creature that was named Tullimonstrum gregarium by the Field Museum scientist whom Tully consulted. “While this obscure but plentiful animal is being studied,” the scientist said, “I prefer not to assign it to a phylum.” Nor did he feel able to assign a phylum after three years of close study, which he called a “a serious and embarrassing matter.” No scientist has yet managed a definitive ID.

I rather love that Illinois has a state fossil. Missouri has one too, the lovely “sea lily” (Eperisocrinus missouriensis). But Illinois has the uncategorizable, inimitable Tully Monster. It looks, as Ed Yong put it, “like the rejected doodle of a drunk fantasy artist.” Gasps and shivers of delighted horror are invoked by the name, but its monstrousness is not the stuff of horror. Tully is monstrous by virtue of being outlandish, bizarre, and utterly unique, comparable to nothing. Scientists are still battling over what category it fits—is it a vertebrate, a mollusk, an arthropod, a conodont, a worm? It has a strip that might foreshadow a spinal cord and pouches that could be interpreted as gills. Its long, tubular body has been compared to a cigar and a torpedo and a chubby worm. One theory even links little Tully to the Loch Ness Monster.

Finally, in 2016, two studies, released simultaneously, blew a trumpet of taxonomic victory: Tully was no free-swimming slug. It was a vertebrate. One study said it was a basal vertebrate (low on the trunk of the family tree) and bore the greatest similarity to modern lampreys. The other study said it was a stem vertebrate because the eyes, set at the end of a rigid bar that extends on either side of its head, not only angle forward and backward but work like a camera, with layers of melanin pigment.

Melanin is not automatic for all vertebrates, snapped a dissenting team of scientists. Look at hagfish—they have none! As for the alleged spinal cord precursor, it extends in front of the level of the eyes, something that happens in no other vertebrate. And Tully’s supposed brain, though tri-lobed, is not connected to its eyes and has no associated nervous tissue. Oh, and that proboscis? It is thin and jointed, not designed at all for the ram or suction feeding used by open-water vertebrates.

Back to square one, with the humbling admission that not only do Tully’s structures confound us, but we are still not even sure which way is up. A 2023 three-D scan offered even more discrepancies between Tully and vertebrates and suggested it might be a non-vertebrate chordate, a rare category that verges on oxymoron. Only two known organisms are non-vertebrate chordates—tunicates and lancelets—and neither looks anything like Tully.

Science wants categories in order to draw neat maps of evolution. Outliers skew studies, too, making it harder to understand how different species respond to changes in the environment. “It has to be like something,” frustrated paleontologists have been muttering for decades. But what if it is not? What if this is a creature that defies categorization? I yearn for that status myself; political labels grow less appealing by the day, as do organized religions, and I have lost my long fascination with personality tests and types. We contain multitudes, all of us do. And when our species dies out, and little is left of us, what a puzzle we will be to those who can see us only in indentations and shadows, static and simple. Too often that is the only way we see one another now.

Forget its category for a minute—how did Tully live? Alongside jellyfish and sea cucumbers, we know, and perhaps in terror of ancient sharks. A few of the specimens “terminate abruptly,” scientists have noted, with part of their trunk torn away just as it would be by sharp shark’s teeth. But Tully, likely an active and efficient swimmer, could have been a predator, too, grabbing hold of smaller swimmers with its pincers and piercing their bodies with its eight tiny but sharp “teeth” and sucking their juices.

Three hundred million years ago, long before the dinosaurs roamed, Illinois was a few degrees north of the equator, tropical, and covered with swampy forests and shallow seas. Soft-bodied marine animals seldom get preserved as fossils; they decay too fast. But when a Tully died, it sank into the sea-bottom mud so fast, it saved itself from scavengers and decay. The salty seawater and the organic residue of dead animals and plants set off chemical reactions in the mud, causing reddish brown ironstone to harden around all the Tully corpses. That hardened mud preserved fine details from their soft bodies. Later, strip mining dumped mounds of discarded soil alongside the coal beds, and in the 1950s, fossil hunters realized there was treasure in those spoil heaps.

One collector, Tom Testa, was more interested in Tully’s body than its category. “I want to go down in history as the man who discovered Tully’s anus,” he told a reporter for the Chicago Reader. “To understand the creature you’d have to know what the situation with the gut is.” Testa is pretty sure he has found the anus, located right above the tail fin. “It’s continuous with what’s considered the gut, and it has a pucker,” he says. “The rectum was probably inflated by decay gases, making the anus visible.”

This small prehistoric creature puckered just as we do. It hoped, hunted, mated, suffered, died. And it left a wonderfully baffling legacy.

“I would rank the Tully Monster just about at the top of the scale of weirdness,” said paleontologist Victoria McCoy, who conducted the study that highlighted similarities to the lamprey. Similarity is the stuff of science, but weirdness is pure fun. Illinois plastered Tully on U-Haul trucks for its Venture Across America campaign. There are plush Tully Monsters, glow-in-the-dark Tully pins, pewter Tully necklaces, Tully stickers, and tees. They are delightful reminders that we cannot fathom and neatly categorize every creature on Earth. And to narcissists and anthropocentrists, they prove that the world was interesting long before we appeared.


Read more by Jeannette Cooperman here.