It's been more than half a century since Francis Tully found the monster that has since defied classification. Now, scientists say they know where the prehistoric oddball that lived some 308 million years ago fits on the Tree of Life: "The Tully monster is a vertebrate," according to research published Wednesday in Nature. That's a big step for the creature Tully discovered when he was hunting for fossils in the Mazon Creek geological deposits southeast of Chicago in 1955. Previously the Tully monster, with its torpedo body, hammerhead-like eyes, and long proboscis filled with sharp teeth, had been categorized as "problematica"—"creatures that defied ready classification," the Chicago Tribune reports. Some have speculated that Tullimonstrum gregarium—which, despite its name, is only about a foot long—was related to snails, worms, or insects and crabs, reports the New York Times.
"If you put in a box a worm, a mollusk, an arthropod, and a fish, and you shake," one paleontologist tells the Tribune, "then what you have at the end is a Tully monster," Some have even floated the idea that the Tully monster was a tiny version of the Loch Ness Monster, per Smithsonian. However, the researchers found that Tully is related to the lamprey, an "underwater bloodsucker," as the Times puts it. Using a synchrotron X-ray machine, researchers were able to determine that what was previously thought to be the creature's gut was actually a notochord, "the primitive backbone," study lead Victoria McCoy tells the Times. "The coolest thing is finding out that as weird as it looks it is part of a familiar group of animals." Check out a graphic of the Tully monster. (A 90 million-year-old fossil indicates T. rex got smart before it got big.)