World's Oldest Octopus Fossil Reclassified as Nautilus Relative in Groundbreaking Study
In a stunning scientific reversal, a 300-million-year-old marine creature previously celebrated as the world's oldest octopus has lost its prestigious title after researchers determined it belongs to an entirely different cephalopod family. Newly published research reveals that the fossilized remains, officially listed by Guinness World Records as the earliest known octopus, actually represent a relative of the nautilus—a shell-bearing cephalopod with tentacles.
Decades of Scientific Debate Resolved Through Advanced Imaging
University of Reading zoologist Thomas Clements, lead researcher of the study, explained that the fossil known as Pohlsepia mazonensis has long perplexed scientists. "It's a very difficult fossil to interpret," Clements stated. "To look at it, it kind of just looks like a white mush. If you look at it and you are a cephalopod researcher interested in everything octopus, it does superficially resemble a deep-water octopus."
The creature, discovered in the fossil-rich Mazon Creek area of Illinois approximately 50 miles southwest of Chicago, measures about the size of a human hand and dates from a period predating dinosaurs. Its original identification as an octopus in 2000 dramatically challenged established theories about eight-tentacled cephalopod evolution, suggesting they emerged significantly earlier than previously believed.
Dental Evidence Provides Definitive Proof
To solve the mystery of what researchers called the "weird blob," Clements and his team employed sophisticated synchrotron technology—using fast-moving electrons to generate light beams brighter than the sun—to peer inside the fossil rock. Their investigation revealed a crucial detail: a ribbon of teeth known as a radula, common to all mollusks including both nautiluses and octopuses.
"Each row had 11 teeth," Clements explained. "Octopuses have either seven or nine teeth per row. This has too many teeth, so it can't be an octopus. That's how we realized the world's oldest octopus is actually a fossil nautilus, not an octopus."
The dental structure perfectly matched that of a fossil nautiloid called Paleocadmus pohli previously discovered in the same geological formation. Clements suggested the initial misidentification likely occurred because the creature decomposed and lost its characteristic shell before fossilization, complicating accurate classification.
Record Books Rewritten and Museum Collections Reinterpreted
Following publication of these findings in the prestigious journal Proceedings of the Royal Society B, Guinness World Records confirmed it will no longer list Pohlsepia mazonensis as the earliest known octopus. Managing Editor Adam Millward acknowledged the researchers' "fascinating discovery," stating, "We will be retiring the original 'oldest octopus fossil' title and look forward to reviewing this new evidence."
The fossil, named for discoverer James Pohl and housed in Chicago's Field Museum collection, now assumes a different historical significance. "The museum should not be disappointed," Clements emphasized. "This means they now have the oldest soft tissue nautilus in the world. The Field Museum has a small collection of these ancient nautiluses, which I think as a cephalopod researcher is probably the best thing ever."
This reclassification leaves a substantial gap in the octopus fossil record, with the next oldest confirmed octopus fossil dating to approximately 90 million years ago—a difference of 210 million years. "It's a huge gap," Clements noted, explaining why researchers had questioned the original identification. The Field Museum has been approached for comment regarding this significant reinterpretation of their collection.
