Scientists have just discovered that the world’s oldest octopus is something else entirely
For 25 years, a single, crushed, 300-million-year-old fossil sat comfortably atop the squid hall of fame. Pohlsepia mazonensis had a Guinness World Record. It had a reputation. Scientists cited it as the oldest known squid on Earth. And all the time it was something completely different.
New research published in Proceedings of the Royal Society B confirms it Absorption was never an octopus. It was a nautiloid—a shelled squid more closely related to the nautiluses still plying the seas today than to anything with eight arms and posture.
When the fossil was first discovered in 2000 in the Mazon Creek Lagerstätte in Illinois, it was already in rough shape. The creature had been in disintegration for several weeks before mud swallowed it and locked it away for geological eternity. Paleontologists saw what looked like eight limbs, two eyes and an ink sac and called it an octopus. Fair enough, given the tools they had at the time. The problem is that rot does strange things to a body.
What finally settled the case? Teeth. Small, old, hidden teeth.
How Scientists Used Teeth to Prove the Octopus Wasn’t an Octopus
Using synchrotron imaging – a technique that fires X-rays produced by particle accelerators through dense objects, producing light billions to trillions of times brighter than a hospital X-ray – Thomas Clements and his team at the University of Reading found 11 tiny tooth-like structures lined up inside the fossil. It is a radula, a band-like feeding structure covered in denticles found exclusively in molluscs.
Squids typically have seven or nine elements per row. Nautiloids have 13. Absorption landed on 11, and the shape of these structures looked far more nautiloid than squid. The lack of ink sac didn’t help matters either – no melanosomes, no pigment, no ink sac.
“The world’s most famous squid fossil was never a squid at all,” Clements said ScienceAlert. “It was a nautilus relative that had been decomposing for several weeks before being buried and later preserved in the rock, and that decomposition is what made it look so convincingly squid-like.”
When researchers compared their findings to other fossils from the same site, the radula matched Paleocadmus moveda nautiloid already identified at Mazon Creek—meaning Absorption was never even a distinct species. Just a badly degraded specimen of something the scientists had already named correctly.
The implications rewrite the timeline at both ends. Nautiloid soft tissue preservation now extends back another 220 million years. The earliest confirmed evidence of actual cephalopods moves forward by about 150 million years.
That science gets it wrong and then corrects itself isn’t a scandal, that’s the whole point. The researchers in 2000 worked with what they had. In 2025, the researchers had a particle accelerator.
The oldest, most famous answer in space still deserves a second look. Even if it has a Guinness World Record.
