Pohlsepia mazonensis PE51727a (part) and PE51727b (counterpart).
The excitement creationists may feel on hearing that science has got it wrong yet again because a fossil once classified as the oldest known octopus has now been reidentified, will no doubt be tempered by the awkward fact that the animal it really belonged to lived 300 million years before, according to their beliefs, there was even a universe, let alone life on Earth. As so often, the truth poses no problem for science; it is creationism that stumbles over it.
Far from showing that science is unreliable compared with the supposed ‘eternal truth’ of religion, this revision is a vindication of the scientific method and a demonstration of its self-correcting nature. Unlike religions, which cling to ‘sacred truths’ that, when tested against reality, turn out to be little more than the best guesses and campfire tales of our ignorant and fearful ancestors, science is a method for moving ever closer to the truth. It remains the best tool we have for discovering reality precisely because nothing is sacred except truth itself, and because scientific understanding is always provisional — open to revision whenever new evidence demands it, unlike religions which are doxastically and doctrinally closed to new information.
On this occasion, the fossil re-examined and found not to be what it was once thought to be was the famous Pohlsepia mazonensis, identified as an octopus 25 years ago and even entered in the Guinness Book of Records as the oldest known fossil octopus. Using modern synchrotron imaging to peer inside the fossil and reveal details the original investigators could not see, researchers discovered tiny teeth and other internal features showing that it was not an octopus at all, but a nautiloid — a cephalopod with an external shell. The team recently published their findings in the journal Proceedings of The Royal Society B.
Nautiloid or octopus~ How scientists told the difference. A crucial question raised by the re-examination of Pohlsepia mazonensis is how scientists could tell that it was not, after all, an octopus. The answer lies in anatomy. When the fossil was first described in 2000, its rounded body, fin-like structures and apparent arms made it look rather like a cirrate, or “dumbo”, octopus. Because cirrate octopuses differ in some respects from the more familiar octopuses, the absence of certain expected features did not seem fatal to that interpretation. [1]
Modern imaging techniques allowed researchers to look beneath the rock surface and examine details that the original investigators could not see. What they found undermined the octopus interpretation. The fossil lacks a siphon and does not preserve clearly distinct arms or tentacles. More importantly, it contains a radula — a toothed feeding structure — with at least 11 tooth-like elements in each row. That is inconsistent with an octopus, which typically has seven or nine, but it fits much better with a nautiloid affinity. [1]
The radula is especially significant because it closely resembles that of Paleocadmus pohli, a fossil nautiloid already known from Mazon Creek. The most likely explanation is that Pohlsepia was a nautiloid whose body had partly decayed before burial, losing the more obvious clues to its shelled identity and leaving behind a misleading outline. So the fossil was not evidence that octopuses existed in the Carboniferous after all, but it remains important as the oldest known preservation of nautiloid soft tissue. [1]
The publication is accompanied by a news item from the University of Reading:
‘Oldest octopus’ fossil is no octopus at all, scans reveal
A famous 300-million-year-old fossil that was thought to be the world's oldest octopus – even featuring in the Guinness Book of Records – has turned out to be something else altogether.
In what amounts to a case of mistaken identity, the fossil hid its true nature through decay 300 million years ago, before being fossilised.
Using the latest synchrotron imaging to search inside the fossil rock, researchers discovered tiny teeth preserved inside the rock that prove that Pohlsepia mazonensis is not an octopus at all, but an animal related to a modern Nautilus – a multi-tentacled animal with an external shell. Pohlsepia mazonensis
This revelation, shared today (Wednesday, 8 April 2026) in the journal Proceedings of the Royal Society B, solves a long-running puzzle in the understanding of octopus evolution that has confused scientists for decades. It also provides evidence of the oldest nautiloid soft tissue preservation known in the fossil record and means that the record-holding 'oldest octopus’ should be quietly written out of the Guinness Book of Records.
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. 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. Sometimes, reexamining controversial fossils with new techniques reveals tiny clues that lead to really exciting discoveries.
Dr Thomas Clements, lead author.
Lecturer in Invertebrate Zoology
Department of Ecology and Evolutionary Biology
School of Biological Sciences
University of Reading
Reading, UK.
Cold case X-ray
Pohlsepia mazonensis being scanned.
Found in Illinois, USA, the first analysis of the fossil was published in 2000 and was later used in studies of how octopuses and their relatives evolved. Scientists thought the fossil showed eight arms, fins, and other features typical of an octopus, pushing back the known history of octopuses by around 150 million years.
Doubts had been raised about the identification for years, but without a clear way to test them until recently. The scientists in the new study used synchrotron imaging – a technique that uses beams of light brighter than the sun – to scan for structures invisible to the eye beneath the surface, revealing hidden details inside the rock. The scientists likened the process to giving a 300-million-year-old suspect a modern forensic examination.
What they found was a radula, a ribbon-like feeding structure with rows of teeth only found in molluscs. With at least 11 tooth-like elements per row, the shape and number ruled out an octopus entirely. Octopuses have seven or nine, while nautiloids have 13.
The teeth matched those of a fossil nautiloid called Paleocadmus pohli, already known from the same site where it was found, and the researchers concluded the animal had partially rotted before fossilisation, causing it to look very different from its true self.
Octopus origins pushed back.
The Nautilus is a shelled sea creature still alive today, with its ancient origins leading some to describe it as a “living fossil”. The Paleocadmus fossils found at the Mazon Creek site in Illinois now represent the oldest known nautiloid soft tissue in the fossil record – beating the previous record by around 220 million years.
These findings change the picture of when octopuses first evolved. The data now supports octopuses appearing much later, during the Jurassic period. Scientists now believe the split between octopuses and their ten-armed relatives such as squids happened in the Mesozoic era, not hundreds of millions of years earlier as previously thought.
It's amazing to think a row of tiny hidden teeth, hidden in the rock for 300 million years, have fundamentally changed what we know about when and how octopuses evolved.
.Dr Thomas Clements.
Publication:
So, far from being an embarrassment to science, the reclassification of Pohlsepia mazonensis is a perfect example of why science works. Scientists did not cling dogmatically to an old claim because it was familiar, flattering or ideologically useful; they revisited the evidence with better tools, found that the earlier interpretation was wrong, and corrected it. That is not failure. It is intellectual honesty in action.
For creationists, however, the story is far more awkward. Their standard tactic is to pounce on any scientific revision as though it somehow discredits the entire enterprise, while continuing to defend beliefs that are immune to evidence and unchanged by facts. But this fossil, whether misidentified or correctly identified, still comes from a world hundreds of millions of years older than their mythology allows. The details may change as knowledge improves; the fatal problem for creationism does not.
In reality, this discovery strengthens science in two ways. It sharpens our understanding of cephalopod evolution, and it demonstrates yet again that science is self-correcting because it values evidence above ego, tradition and wishful thinking. Religion preserves ancient certainties by shielding them from scrutiny; science advances by exposing its ideas to it. That is why science keeps getting closer to the truth, while creationism remains trapped defending the errors of a prescientific age.
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