After baffling paleontologists for more than 55 years, a fossil enigma known as the Tully Monster has finally been definitively identified in a new report published in the journal Nature.

A relative of the modern-day lamprey, the Tully Monster is an oddly constructed sea creature with teeth at the end of a slender, trunk-like extension of its head and eyes that sit on both sides of a long, stiff bar.

In the study, paleontologists has established the 300-million-year-old animal, which grew just a foot long, was a vertebrate, with gills and a stiff notochord, which supported its body– characteristics that weren’t previously known.

“I was first intrigued by the mystery of the Tully Monster. With all of the exceptional fossils, we had a very clear picture of what it looked like, but no clear picture of what it was,” study author Victoria McCoy, a graduate researcher at Yale University, said in a press release.

Uncovering the mystery of the Tully Monster

Discovered in 1958 and described in 1966, the Tully Monster has never been identified down to the phylum level until this latest research effort.

The species is named after amateur fossil hunter Francis Tully, the man who discovered the first specimen. Tully found the fossil in the coal-mining pits of northeastern Illinois, and thousands of other specimens were later discovered in the same location.

Since its discovery, the Tully Monster has achieved cult celebrity status in Illinois and it became the official state fossil in 1989.

“Basically, nobody knew what it was,” said study author Derek Briggs, curator of invertebrate paleontology at the Yale Peabody Museum of Natural History. “The fossils are not easy to interpret, and they vary quite a bit. Some people thought it might be this bizarre, swimming mollusk. We decided to throw every possible analytical technique at it.”

To precisely describe the Tully Monster, the study team analyzed more than 2,000 specimens at the Field Museum in Chicago. Using synchrotron elemental mapping and other state-of-the-art tools, the researchers were able to identify gills and a notochord, neither of which had been identified in the previously.

“It’s so different from its modern relatives that we don’t know much about how it lived,” McCoy said. “It has big eyes and lots of teeth, so it was probably a predator.”

There are still a lot of unanswered questions about the Tully Monster, including when it first appeared and when it went extinct.

“We only have this little window,” Briggs said.

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Image credit: Yale University

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