Famous 'Oldest Octopus' Fossil Was Actually a Nautilus

For over a decade, the Guinness World Record for earliest known octopus belonged to a fossil that wasn't an octopus at all.

Scientists at the University of Reading just solved a 25-year mystery by examining the 300-million-year-old Illinois fossil called Pohlsepia mazonensis with cutting-edge synchrotron imaging. This super-bright X-ray technique let them peek beneath the surface and find something revealing: a tongue-like structure called a radula, covered in rows of teeth.

Here's where it gets interesting. All mollusks have radulas, but octopuses only have seven or nine teeth per row. This fossil had at least 11 teeth in each row, plus the wrong tooth shape entirely.

The discovery means Pohlsepia wasn't an octopus but likely a relative of the modern nautilus, those shelled cephalopods often called "living fossils" because they've barely changed over millions of years. Nautiloids have 13 teeth per row on their radulas, making them a much better match.

The original misidentification wasn't anyone's fault. The creature had been decomposing for weeks before it fossilized, which made it look convincingly octopus-like to researchers who first studied it 25 years ago. That decay process fooled paleontologists into thinking they'd found eight arms and fins typical of octopuses.

"It's been a real trouble for paleontologists to try to understand how Pohlsepia fits into our understanding of octopus evolution," says lead author Thomas Clements.

Why This Inspires

This correction isn't just about fixing a mistake. It's about how science gets better over time through curiosity and better tools.

The team didn't just take away a record. They replaced it with something equally exciting: Pohlsepia is now the oldest soft tissue evidence of a nautiloid ever found. That's a brand new world record in itself.

The revision also gives us a clearer picture of life's timeline. Octopuses likely appeared during the Jurassic period, between 145 and 201 million years ago, rather than 150 million years earlier. That's a major shift in understanding how these intelligent, three-hearted creatures evolved.

Guinness World Records has already retired the original title and congratulated the researchers on their discovery. Alexander Pohle, a paleontologist who wasn't involved in the study, called it "great to see this debate settled with such detailed work."

Sometimes the best discoveries come from questioning what we think we already know.