True nature of ‘Tully monster’ revealed

Ancient oddity is a lamprey ancestor

illustration of a tully monster

IDENTITY CRISIS  An ancient oddball animal that defied identification for decades may be an ancestor of lampreys. 

Paul Mayer/Field Museum of Natural History

If some of the most bizarre zoo animals merged into one cartoonish creature, it might look something like the “Tully monster.”

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 (not a slug, or a worm, or an arthropod). 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.

CREATURE FEATURES In this fossil specimen of Tullimonstrum gregarium, the tail fin (left) and long nose (right, narrow tube folded over the body) are visible. Paul Mayer/Field Museum of Natural History

Meghan Rosen is a staff writer who reports on the life sciences for Science News. She earned a Ph.D. in biochemistry and molecular biology with an emphasis in biotechnology from the University of California, Davis, and later graduated from the science communication program at UC Santa Cruz.

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