World’s Oldest Octopus Fossil From Guinness World Records Was Misidentified — Here’s What It Really Is
A 300-million-year-old fossil once considered the world’s oldest octopus has turned out to be something else entirely.
Pohlsepia mazonensis was thought to push the origins of octopuses back by millions of years, even earning a place in the Guinness Book of Records. But a new study published in Proceedings of the Royal Society B shows the fossil was misidentified. Instead of an early octopus, it belongs to a group of shelled marine animals related to the modern nautilus.
The answer came from a closer look inside the fossil using synchrotron imaging, a technique that can reveal microscopic structures hidden within rock. The scans uncovered a row of tiny teeth that change how researchers interpret the fossil and, in turn, the timeline of octopus evolution.
“It turns out the world’s most famous octopus fossil was never an octopus at all,” said Thomas Clements, lead author, in a press release. “Decomposition is what made it look so convincingly octopus-like.”
Reidentifying the Oldest Octopus Fossil
A diagram showing the anatomy of Pohlsepia mazonensis
(Image Credit: Dr Thomas Clements, University of Reading)
The breakthrough came when researchers identified a radula, a ribbon-like feeding structure lined with rows of teeth (found in many mollusks).
Octopuses typically have seven or nine tooth elements per row. This fossil had at least 11 — too many to belong to an octopus, but consistent with nautiloid relatives, which have more.
The teeth closely matched those of a known fossil species, Paleocadmus pohli, previously found at the same site in Illinois. That match helped confirm what the fossil really was.
What had once been interpreted as arms and fins now appears to be the result of decay. The animal likely decomposed for weeks before being buried, distorting its soft tissues in ways that mimicked octopus features.
Read More: Octopuses Don’t Need Eyes to Mate — Their Arms Do the Work
A Fossil Cold Case Reopened With New Technology
The fossil was first described in 2000 and quickly became a cornerstone in studies of cephalopod evolution. At the time, scientists relied on surface features visible in the rock, which seemed to show classic octopus traits.
Some researchers had questioned the identification, but there was no way to test those doubts. New imaging techniques finally made that possible.
Using synchrotron imaging, researchers were able to scan beneath the fossil’s surface without damaging it. The technique uses extremely bright beams of light to reveal internal structures in fine detail.
The result was something like a forensic re-investigation of a 300-million-year-old case, one that finally uncovered the evidence hidden all along.
Rethinking When Octopuses First Appeared
The finding does more than correct the fossil’s identity; it shifts the timeline of octopus evolution in the process.
Without Pohlsepia as evidence, octopuses likely appeared much later than previously thought, during the Jurassic period rather than hundreds of millions of years earlier. The split between octopuses and their closest relatives, such as squids, now appears to have occurred in the Mesozoic era.
At the same time, the fossil sets a new record of its own. It preserves the oldest known soft tissue from a nautiloid, extending that record by roughly 220 million years. Nautiloids are still alive today, with species like the chambered nautilus often described as “living fossils.”
For researchers, the study shows how new tools can lead to new interpretations of familiar fossils.
“Scientists identified Pohlsepia as an octopus 25 years ago, but using modern techniques showed us what was beneath the surface to the rock, which finally cracked the case. 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 shared in the press release.
Read More: Octopuses Pick Up On Invisible Microbial Cues to Avoid Rotting Food
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