300-Million-Year-Old Fossil Reclassified as Nautilus Relative
Advanced imaging reveals that Pohlsepia mazonensis, once thought to be the world's oldest octopus, is actually a nautiloid.
A 300-million-year-old fossil, Pohlsepia mazonensis, previously identified as the world's oldest octopus, has been reclassified as a relative of the modern nautilus. Researchers from the University of Reading utilized advanced synchrotron imaging to examine the fossil's internal structures, revealing a radula—a ribbon of teeth—with 11 teeth per row, a characteristic feature of nautiloids. In contrast, octopuses typically possess seven or nine teeth per row. This discovery indicates that Pohlsepia mazonensis is not an octopus but a nautiloid, a group of cephalopods with external shells. The fossil was originally discovered in the Mazon Creek area of Illinois, a site renowned for its well-preserved fossils from the Carboniferous period. The misidentification is believed to have occurred because the creature's shell decomposed before fossilization, leading to its octopus-like appearance. As a result of these findings, Guinness World Records has removed Pohlsepia mazonensis from its listing as the earliest known octopus. The fossil remains part of the Field Museum's collection in Chicago.