2026-04-10 11:33:25
A sea creature once hailed as the world’s oldest octopus has officially lost its title, after new research revealed the 300‑million‑year‑old fossil wasn’t an octopus in the first place.
Scientists now say the specimen — long listed by Guinness World Records as the earliest known octopus — actually belonged to a shelled cephalopod more closely related to a nautilus.
The fossil, Pohlsepia mazonensis, has been debated for decades, but a new study led by University of Reading zoologist Dr Thomas Clements has finally settled the mystery.
He explained: “It’s a very difficult fossil to interpret.
“If you’re a cephalopod researcher, it does superficially look a lot like a deep‑water octopus.”
The hand‑sized fossil was discovered in Illinois’ Mazon Creek region — a treasure trove of prehistoric life dating back long before dinosaurs roamed the planet.
When researchers identified it as an octopus in 2000, it dramatically pushed back the evolutionary timeline of the eight‑armed creatures.
The next‑oldest confirmed octopus fossil is just 90 million years old, leaving a staggering gap that many scientists found difficult to reconcile.
To re‑examine the fossil, Clements’ team used a synchrotron — a machine that fires electrons at extreme speeds to produce ultra‑bright beams of light.
Inside the rock, they discovered a radula: a ribbon‑like structure lined with rows of tiny teeth.
Crucially, each row had 11 teeth. Modern octopuses have seven or nine, while ancient nautiloids had more — instantly overturning the original classification.
Clements added: “This has too many teeth, so it can’t be an octopus.”
The pattern matched another fossil from the same area, Paleocadmus pohli, a known nautiloid species.
Researchers believe the creature’s shell likely decomposed before fossilisation, making the misidentification more likely.
Following the study’s publication in Proceedings of the Royal Society B, Guinness World Records confirmed it will retire the “oldest octopus fossil” title.
Managing editor Adam Millward called the findings “a fascinating discovery” and said the organisation will review the new evidence.
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