For nearly 25 years, paleontologists hailed Pohlsepia mazonensis as the oldest known octopus fossil, dating back 306 million years. The specimen from Illinois' Mazon Creek formation appeared to have all the hallmarks of a deep-water octopus: a fused head and mantle, symmetrical fins, and eyespots. But high-tech imaging has revealed this was a case of mistaken identity.

Researchers used synchrotron X-rays and other advanced techniques to examine the fossil's chemical composition. They found no evidence of octopus features like suckers, arm cirri, or internal shells. The supposed eyespots contained no ocular pigments, and the ink sac was just mineral deposits. Even the mysterious stains near the body turned out to be non-biological.

Instead, the imaging revealed a radula - the toothed feeding structure of mollusks - with an 11-element configuration unique to nautiloids. The fossil is now recognized as the oldest soft-tissue evidence of nautiloids in the Paleozoic era. While it lost its title as the oldest octopus, the specimen earned new superlatives as the most challenging and fascinating fossil Clements' team has ever studied.