In 1958 in an Illinois creek bed, an amateur fossil collector named Francis Tully discovered the fossilized remains of a bizarre creature that resembled a mollusk, insect, and worm yet was none of those things. Since then, thousands of 300 million-year-old fossilized "Tully Monsters" have turned up and the creature was officially named as the Illinois state fossil.
Yet its scientific classification was unknown until last year when researchers made news when they published scientific papers claiming that the Tully Monster is in fact a vertebrae, specifically a lamprey. Now though, University of Pennsylvania paleobiologist Lauren Sallan and her colleagues have published a paper claiming that the previous papers are flawed and the Tully Monster is still a mystery. From Penn News:
"This animal doesn't fit easy classification because it's so weird," said Sallan, an assistant professor in the Department of Earth and Environmental Science of Penn's School of Arts & Sciences. "It has these eyes that are on stalks and it has this pincer at the end of a long proboscis and there's even disagreement about which way is up. But the last thing that the Tully monster could be is a fish…"
The researchers said that an improper classification of such an unusual species has ripple effects on the larger field of evolution.
"Having this kind of misassignment really affects our understanding of vertebrate evolution and vertebrate diversity at this given time," Sallan said. "It makes it harder to get at how things are changing in response to an ecosystem if you have this outlier. And though of course there are outliers in the fossil record—there are plenty of weird things and that's great—if you're going to make extraordinary claims, you need extraordinary evidence."