Synchrotron Scans Reveal 300-Million-Year-Old 'Oldest Octopus' Fossil Is Actually a Nautiloid Relative

New research proves the 300-million-year-old Pohlsepia fossil is a nautilus relative, not an octopus, shifting the timeline of cephalopod evolution.

By: AXL Media

Published: Apr 8, 2026, 11:08 AM EDT

Source: Information for this report was sourced from EurekAlert

Forensic Re-examination of a Paleontological Icon

A landmark study published in the journal Proceedings of the Royal Society B has officially stripped the fossil known as Pohlsepia mazonensis of its title as the world's oldest octopus. For over two decades, this 300-million-year-old specimen held a place in the Guinness Book of Records and served as a cornerstone for theories regarding the ancient origins of cephalopods. However, new analysis led by Dr. Thomas Clements of the University of Reading suggests that the fossil was a victim of historical mistaken identity, caused by the natural process of decay that occurred long before the animal was encased in stone.

High-Intensity Light Pierces Ancient Stone

The breakthrough was made possible through the application of synchrotron imaging, a high-tech scanning method that utilizes beams of light significantly brighter than the sun. This technique allowed scientists to look beneath the surface of the Illinois-sourced rock without damaging the specimen. According to Dr. Clements, the process acted as a modern forensic examination for a 300-million-year-old suspect. The scans revealed microscopic structures that were completely invisible to the naked eye, providing the empirical evidence needed to settle a debate that has simmered in the scientific community for twenty-five years.

Dental Evidence Settles the Evolutionary Case

The definitive proof came in the form of a radula, a specialized feeding ribbon found in mollusks that contains rows of tiny teeth. Upon counting the elements, researchers found at least 11 teeth per row, a number that directly contradicts octopus biology, which typically features seven or nine. Conversely, nautiloids are characterized by 13 teeth, a much closer match to the revealed structures. The tooth morphology specifically aligned with Paleocadmus pohli, a known nautiloid from the same Illinois site. This confirms that the specimen’s eight-armed appearance was merely a byproduct of tissue decomposition rather than its actual biological form.