Fossils of Tullimonstrum gregarium, a soft-bodied animal that lived roughly 300 million years ago in what is now Illinois, feature wide-set eyes like a hammerhead shark, a nose like an elephant, and a mouth that could pass for a crab claw with teeth. It’s one of the “weird wonders” of its time, and for more than 50 years, it has stymied scientists debating its identity.
Now, an analysis of more than 1,200 museum specimens, reported March 16 in Nature, says the Tully monster was a vertebrate. A long, thin tube running down the creature’s back, for example, was not part of the gut, as some scientists had suggested, but a notochord, a structural hallmark of vertebrates.
The creature was probably an ancestor of lampreys, jawless fish that can latch onto prey like a vacuum cleaner hose with teeth, study coauthor Victoria McCoy of Yale University and colleagues suggest.
Even among lampreys, the Tully monster stands out. With its stubby body and potentially tail-propelled swimming style, the creature’s place in the lamprey family tree might be best likened to yet another zoo animal: black sheep.