300-million-year-old sea creature loses title as world’s oldest octopus

Ancient Sea Creature Loses Title as World’s Oldest Octopus After Scientific Reclassification

A 300-million-year-old fossilized sea creature long considered the world’s earliest known octopus has been reclassified following new scientific analysis, upending previous understandings of cephalopod evolution.

Research published this week in the Proceedings of the Royal Society B reveals that the fossil specimen known as Pohlsepia mazonensis—previously recognized by Guinness World Records as the oldest octopus—is actually a relative of the nautilus, a shelled cephalopod with tentacles.

The misidentified fossil was discovered in the Mazon Creek area of Illinois, approximately 50 miles southwest of Chicago. This region is renowned for its rich deposits of fossils dating to the Carboniferous period, well before dinosaurs roamed the Earth.

“It’s a very difficult fossil to interpret,” explained Dr. Thomas Clements, a zoologist at the University of Reading and lead researcher behind the findings. “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 look a lot like a deep-water octopus.”

The fossil, roughly the size of a human hand, created significant scientific excitement when paleontologists identified it as an octopus in 2000. The classification dramatically altered scientific understanding of cephalopod evolution, suggesting octopuses emerged far earlier than previously believed.

The reclassification resolves what had been a puzzling evolutionary gap. The next oldest confirmed octopus fossil dates to just 90 million years ago—creating a 210-million-year gap in the evolutionary record that had troubled researchers.

“It’s a huge gap,” Clements noted. “And so that big gap got researchers sort of questioning, ‘Is this thing actually an octopus?'”

To resolve the mystery, Clements’ team employed advanced technology rarely available when the fossil was first classified. They used a synchrotron—a particle accelerator that generates extremely bright light—to examine the fossil’s interior structure without damaging it.

The breakthrough came when researchers identified a radula, a ribbon-like structure containing rows of teeth common to mollusks. Critically, each row contained 11 teeth, which differs from the tooth pattern found in octopuses, which have either seven or nine teeth per row.

“This has too many teeth, so it can’t be an octopus,” Clements explained. “And that’s how we realize that the world’s oldest octopus is actually a fossil nautilus, not an octopus.”

Further analysis revealed the teeth matched those of a fossil nautiloid called Paleocadmus pohli previously discovered in the same area. Researchers believe the confusion likely occurred because the creature decomposed and lost its characteristic shell before fossilization, complicating its identification.

The misidentification highlights the challenges paleontologists face when examining ancient soft-bodied organisms, which typically leave less distinct fossil evidence than creatures with hard skeletons or shells.

In response to the findings, Guinness World Records confirmed it will no longer list Pohlsepia mazonensis as the earliest known octopus. Adam Millward, Managing Editor at Guinness World Records, called it “a fascinating discovery” and stated they would be “resting the original ‘oldest octopus fossil’ title” pending review of the new evidence.

Pohlsepia mazonensis, named after its discoverer James Pohl, remains in the collection of Chicago’s Field Museum. Paul Mayer, manager of the museum’s fossil invertebrate collection, expressed mild surprise at the reclassification but noted that scientists have questioned the specimen’s identification since its original classification.

“People have been questioning whether it was an octopus ever since the original paper was first published in 2000,” Mayer said. He welcomed the renewed interest in the Mazon Creek fossils, adding that new technologies for scientific investigation were “great for our collections and hopefully new discoveries will be made and new stories will be revealed.”

Dr. Clements suggested the Field Museum should view the reclassification positively. “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. “They now have the oldest soft tissue nautilus in the world.”

This discovery demonstrates how advancing scientific techniques continue to refine our understanding of Earth’s evolutionary history, sometimes dramatically revising long-held classifications of ancient species.