Ancient fossil stripped of world's oldest octopus title in shock discovery

A 300-million-year-old fossil, once celebrated as the world’s oldest octopus, has been stripped of its title after new scientific research revealed it is, in fact, a relative of the nautilus. The creature, Pohlsepia mazonensis, previously listed by Guinness World Records as the earliest known octopus, has been reclassified following a detailed examination of its ancient remains.

The new findings, published in the journal Proceedings of the Royal Society B, conclude that the fossilised specimen belongs to a cephalopod with both tentacles and a shell, rather than an eight-armed octopus.

Thomas Clements, a zoologist at the University of Reading and lead researcher behind the discovery, noted that the fossil has long been a subject of scientific debate. "It’s a very difficult fossil to interpret," he explained. "To look at it, it kind of just looks like a white mush." He added that to a cephalopod researcher, "it does superficially look a lot like a deep-water octopus."

Discovered in the fossil-rich Mazon Creek area of Illinois, approximately 50 miles southwest of Chicago, the hand-sized blob dates back to a period predating the dinosaurs. Its initial identification as an octopus in 2000 significantly altered understanding of the cephalopod’s evolution, suggesting an emergence far earlier than previously believed. The next oldest known octopus fossil is a mere 90 million years old. "It’s a huge gap," Clements said. "And so that big gap got researchers sort of questioning, ‘Is this thing actually an octopus?"

To unravel the mystery of the "weird blob," Clements and his team employed a synchrotron, which uses fast-moving electrons to generate beams of light brighter than the sun, to peer inside the fossil rock. Their investigation uncovered a radula – a ribbon of teeth common to all molluscs, including nautiluses and octopuses. Crucially, each row of teeth contained 11, whereas octopuses possess either seven or nine.

"This has too many teeth, so it can’t be an octopus," Clements stated. "And that’s how we realize that the world’s oldest octopus is actually a fossil nautilus, not an octopus." The teeth structure closely matched that of Paleocadmus pohli, a fossil nautiloid found in the same region. Clements suggested the initial misidentification likely occurred because the creature decomposed and lost its distinctive shell before fossilisation, complicating its classification.

In light of these findings, Guinness World Records has confirmed it will no longer recognise Pohlsepia mazonensis as the earliest known octopus. Managing Editor Adam Millward described the scientists’ work as "a fascinating discovery." He added: "We will be resting the original ‘oldest octopus fossil’ title and look forward to reviewing this new evidence."

Pohlsepia mazonensis, named after its discoverer James Pohl, is part of the collection at the Field Museum in Chicago. Paul Mayer, manager of the museum's fossil invertebrates collection, admitted he was "a little surprised" by the new classification but acknowledged that "people have been questioning whether it was an octopus ever since the original paper was first published in 2000." He highlighted how new technologies are revitalising interest in Mazon Creek fossils.

Clements, however, believes the museum should not be disheartened, as it now possesses "the oldest soft tissue nautilus in the world." He concluded: "The Field Museum have a small collection of these ancient nautiluses, which I think as a cephalopod worker is probably the best thing ever."