Scientific reclassification of the 300-million-year-old Pohlsepia mazonensis fossil

A 300-million-year-old fossil, Pohlsepia mazonensis, discovered in the Mazon Creek area of Illinois, has been reclassified after being considered the oldest known octopus for 25 years. Research led by zoologist Thomas Clements of the University of Reading utilized synchrotron technology to examine the internal structure of the specimen. The analysis revealed a radula, a feeding organ with 11 teeth per row, whereas octopuses typically possess seven or nine teeth. Consequently, scientists concluded that the organism is a relative of the nautilus rather than an octopus. This reclassification affects the evolutionary timeline, moving the oldest known evidence of soft tissue in nautiloids back by approximately 220 million years. Conversely, the first appearance of octopuses in the fossil record is now shifted forward by about 150 million years. The misidentification, which was previously recognized by the Guinness World Records, was attributed to the specimen's state of decomposition, which created an appearance mimicking an octopus.