This Fossil Held the World Record for the Earliest Known Octopus. Turns Out, It’s Not an Octopus After All

New research suggests the 300-million-year-old specimen is actually a relative of the nautilus

April 8, 2026

marine environment with dead animal — An artistic rendering shows the mysterious animal, which researchers now say was a nautilus relative, in its prehistoric environment. University of Reading

For more than a decade, an imposter may have been hiding among the many strange achievements highlighted by the Guinness World Records. According to new research, the so-called earliest known octopus wasn’t an octopus after all.

The specimen in question is a 300-million-year-old fossil discovered in Illinois and called Pohlsepia mazonensis. Around 25 years ago, scientists concluded that it was an octopus, meaning the cephalopods had evolved about 150 million years earlier than previously thought. They wrote that the fossil featured elements typical of an octopus, such as eight arms and some fins.

In those researchers’ defense, the animal had been decomposing before it fossilized, according to the new study, published April 8 in Proceedings of the Royal Society B: Biological Sciences. This decay made the fossil harder to interpret.

“It’s been a real trouble for paleontologists to try to understand how Pohlsepia fits into our understanding of octopus evolution,” lead author Thomas Clements, a paleontologist at the University of Reading’s Cole Museum of Zoology in England, tells Science News’ Jake Buehler.

Fun fact: The oddness of octopuses

Octopuses have three hearts—two that send blood past the gills, where it can gain oxygen, and one that brings the oxygenated blood to the organs and muscles.

To examine the fossil, Clements and his colleagues used synchrotron imaging, an X-ray technique that employs superbright light beams, allowing them to investigate what was going on beneath the fossil’s exterior. Their imagery found something revealing: a tongue-like body part covered in rows of teeth, called a radula.

Only mollusks have radulas. Octopuses are mollusks, but their radulas have either seven or nine teeth per row—and the team identified at least 11 toothlike features in each row of the radula fossil. That, plus the shape of those teeth, indicated to the researchers that the specimen wasn’t an octopus.

the imposter fossil — The only known fossil of *Pohlsepia mazonensis* University of Reading

“This is a fascinating discovery, and congratulations to the University of Reading on their research,” says Guinness World Records’ senior managing editor, Adam Millward, as reported by the London Times’ Kaya Burgess. “We will be resting the original title and look forward to seeing the new evidence.”

Instead, the team suggests, the mysterious creature might be a relative of the modern nautilus. Nautiloids have 13 teeth per row on their radulas. The only extant cephalopods with an external shell, nautiloids are dubbed “living fossils” because of how little they have evolved over time.

“It turns out the world’s most famous octopus fossil was never an octopus at all,” Clements says in a statement. “It was a nautilus relative that had been decomposing for weeks before it became buried and later preserved in rock, and that decomposition is what made it look so convincingly octopus-like.”

Luckily, the earliest octopus title was replaced by a new record.

“We now have the oldest soft tissue evidence of a nautiloid ever found and a much clearer picture of when octopuses actually first appeared on Earth,” Clements adds in the statement. With Pohlsepia out of the way, it seems like octopuses entered the world’s stage in the more recent Jurassic period (145 million to 201.3 million years ago).

“There had been serious doubts about the alleged octopod identity of Pohlsepia for some time,” Alexander Pohle, a paleontologist from Germany’s Ruhr University Bochum who did not participate in the study, tells Science News. “It’s great to see this debate settled with such detailed work!”

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