A prehistoric sea creature that held the distinction of being the planet’s most ancient octopus has been dethroned after researchers determined the fossil belongs to an entirely different species.
Recent scientific analysis has revealed that the 300-million-year-old specimen currently recognized by Guinness World Records as the earliest octopus discovery is actually the remains of a nautilus-related creature — a tentacled sea animal that also possessed a protective shell.
Thomas Clements, a zoologist from the University of Reading who spearheaded the investigation, explained that the fossil specimen known as Pohlsepia mazonensis has sparked controversy among scientists for years.
“It’s a very difficult fossil to interpret,” he said. “To look at it, it kind of just looks like a white mush.”
“If you look at it and you are a cephalopod researcher and you’re interested in everything octopus, it does superficially look a lot like a deep-water octopus,” Clements added.
The hand-sized blob was discovered in Illinois’s Mazon Creek region, located roughly 50 miles southwest of Chicago — an area known for its abundance of prehistoric fossils that predate the dinosaur era.
When paleontologists first classified the specimen as an octopus in 2000, it dramatically altered scientific understanding of how eight-armed cephalopods evolved, indicating they appeared far earlier in Earth’s history than experts had believed. The second-oldest confirmed octopus fossil dates back only 90 million years.
“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 puzzle of this “weird blob,” Clements and his research team employed a synchrotron — a device that accelerates electrons to generate light beams more intense than sunlight — to peer inside the fossilized rock. Their examination revealed a strip of feeding structures called a radula, containing rows of teeth found in all mollusks, including both nautiluses and octopuses. Each row contained 11 teeth, while octopuses possess either seven or nine.
“This has too many teeth, so it can’t be an octopus,” Clements said. “And that’s how we realize that the world’s oldest octopus is actually a fossil nautilus, not an octopus.”
The dental pattern corresponded with those of Paleocadmus pohli, a fossilized nautiloid species previously found in the same location. Clements suggested the misidentification likely occurred because the animal’s distinctive shell deteriorated before fossilization, making proper classification challenging.
Following the publication of these findings in this week’s edition of Proceedings of the Royal Society B, Guinness World Records announced it will remove Pohlsepia mazonensis from its listing as the earliest known octopus.
Managing Editor Adam Millward called the research “a fascinating discovery.”
“We will be resting the original ‘oldest octopus fossil’ title and look forward to reviewing this new evidence,” he said.
The specimen, named after its discoverer James Pohl, is housed at Chicago’s Field Museum.
Clements suggested the museum shouldn’t feel disappointed by the new findings, noting they now possess “the oldest soft tissue nautilus in the world.”
“The Field Museum have a small collection of these ancient nautiluses, which I think as a cephalopod worker is probably the best thing ever,” he said.
The museum has been contacted for their response to the discovery.
