More than five decades after fossils of the strange-looking Tully Monster were first discovered, scientists have finally confirmed that the creature was a vertebrate. It was named after Francis Tully, a fossil hunter who discovered it in 1958. Results of the study were published Wednesday in the journal Nature. The study offers the clearest picture yet of this 300-million-year old sea monster.

Confirmed: The 300-Million-Year Old Tully Monster Was A Vertebrate

Tully Monster fossils were difficult to interpret

The Tully Monster, Tullimonstrum gregarium, indeed looked like a monster. It was just a foot long, but its mouth was located at the end of a long trunk-like neck. At first glance, it looks more like a claw than mouth. The creature’s wide-set eyes were placed above the midsection on either side of the body at the end of a bar. Researchers have recovered more than a thousand fossils of Tully Monster from what is now a coal mine in Illinois.

For decades, scientists wondered where the sea creature belonged in terms of lineage. “I was first intrigued by the mystery of the Tully Monster,” said lead author Victoria McCoy of the University of Leicester. She started studying the fossil records while a grad student at Yale University. The fossils were not easy to interpret, so researchers threw every possible analytical technique at it including the synchrotron elemental mapping, which uses x-rays to light up various parts of a fossil’s anatomy.

Many unanswered questions

Research suggested that the creature’s notochord served as a rudimentary vertebra, and that it had gills. Scientists didn’t know about these two things until now. Given its big eyes and lots of teeth, Tully Monster was likely a predator.

Even though the study sheds light on its anatomy, several questions are yet to be answered. It’s still a mystery why the fossils have been found only at a single mining site in Illinois. The creature’s evolutionary history such as when it first appeared and when went extinct are not well understood yet.