300-Million-Year-Old Fossil Reclassified as Ancient Nautilus, Not Octopus

A 300-million-year-old fossil once thought to be the oldest known octopus has been identified as an ancient nautilus, shedding new light on cephalopod evolution.

Apr. 10, 2026 at 2:27pm

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A bold, abstract painting featuring sweeping geometric arcs, concentric circles, and precise spirals in earthy tones of green, brown, and blue, representing the complex evolutionary history of ancient marine life.A conceptual illustration of the evolutionary journey of ancient cephalopods, as revealed by the reclassification of a 300-million-year-old fossil once thought to be the oldest known octopus.Chicago Today

A 300-million-year-old fossil, Pohlsepia mazonensis, previously identified as the oldest known octopus, has now been reclassified as an ancient nautilus after a team of researchers used advanced technology to examine the fossil's radula, or ribbon of teeth. The discovery has significant implications for our understanding of cephalopod evolution, as it suggests octopuses emerged later than previously thought.

Why it matters

This reclassification highlights the importance of rigorous scientific analysis and the ongoing evolution of our understanding of ancient marine life. It also underscores the challenges paleontologists face in interpreting fossils, especially when key features like shells have decomposed before fossilization.

The details

The fossil, found in the same area as a matching radula from a fossil nautiloid called Paleocadmus pohli, had initially been identified as an octopus due to its tentacled appearance and the era in which it was found. However, the radula in Pohlsepia mazonensis had 11 teeth per row, whereas octopuses typically have either seven or nine, leading the research team to reclassify the fossil.

  • The fossil in question, Pohlsepia mazonensis, was initially identified as the oldest known octopus.
  • In 2026, a team of researchers led by Thomas Clements, a zoologist at the University of Reading, used advanced technology to re-examine the fossil and reclassify it as an ancient nautilus.

The players

Thomas Clements

A zoologist at the University of Reading who led the study that reclassified the Pohlsepia mazonensis fossil as an ancient nautilus, not an octopus.

The Field Museum

A museum in Chicago that houses the Pohlsepia mazonensis fossil, as well as a small collection of other ancient nautiluses, which the researchers find particularly exciting.

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What they’re saying

“It's a very difficult fossil to interpret. To look at it, it kind of just looks like a white mush.”

— Thomas Clements, Zoologist, University of Reading

What’s next

The reclassification of the Pohlsepia mazonensis fossil has significant implications for our understanding of cephalopod evolution, suggesting that octopuses emerged later than previously thought. Further research and analysis of this and other ancient nautilus fossils could provide additional insights into the evolutionary history of these marine creatures.

The takeaway

This discovery highlights the importance of rigorous scientific analysis and the ongoing refinement of our understanding of the fossil record. It serves as a reminder that scientific knowledge is constantly evolving, and that even long-held beliefs about ancient life can be challenged and revised through meticulous research and the application of new technologies.