300-Million-Year-Old Fossil Reclassified as Nautilus Relative
Advanced imaging reveals that a fossil once thought to be the world's oldest octopus is actually related to modern nautiluses.
A 300-million-year-old fossil, previously identified as the world's oldest octopus, has been reclassified as a relative of the modern nautilus. The fossil, known as Pohlsepia mazonensis, was discovered in Illinois and initially thought to be an octopus due to its eight arms and fin-like structures.
Recent studies using advanced synchrotron imaging have revealed the presence of a radula—a ribbon-like feeding structure with rows of teeth—within the fossil. The radula contained at least 11 tooth-like elements per row, a characteristic feature of nautiloids, whereas octopuses typically have seven or nine. This discovery led researchers to conclude that Pohlsepia is not an octopus but a nautiloid.
Dr. Thomas Clements, lead author and Lecturer in Invertebrate Zoology at the University of Reading, stated, :
"It turns out the world's most famous octopus fossil was never an octopus at all. 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."
The reclassification of Pohlsepia mazonensis has significant implications for the understanding of cephalopod evolution. It suggests that octopuses appeared much later than previously thought, likely during the Jurassic period, and provides the earliest known example of preserved soft tissue from a nautiloid. The findings were published on April 8, 2026, in the journal Proceedings of the Royal Society B.