The 'Oldest Octopus'
Was Never an Octopus
Scientists just rewrote 300 million years of evolutionary history — and the truth is even stranger than the myth
Imagine holding a piece of rock in your hand, knowing that inside it rests a creature that lived when Earth looked nothing like it does today — when coal forests blanketed the continents, when sharks ruled the shallow seas, and when the very first reptiles were just beginning to crawl onto land. That is exactly what scientists thought they had with Pohlsepia mazonensis — a fossil long celebrated as the world's oldest known octopus. But in a stunning reversal, researchers have just confirmed: it is no octopus at all.
Published in the prestigious journal Proceedings of the Royal Society B, a new study from the University of Reading has reclassified this 300-million-year-old fossil, stripping it of its record-breaking title and placing it firmly in the family of nautiloids — ancient relatives of the modern nautilus. The implications ripple far beyond one misidentified fossil. They touch the very heart of how we understand the origins of some of the ocean's most intelligent and mysterious animals.
The Fossil That Fooled the World
The story begins in the badlands just south of Chicago, Illinois, at a place called Mazon Creek — one of the world's most celebrated fossil sites. Preserved in ironstone nodules formed roughly 307 million years ago during the Carboniferous period, thousands of extraordinary creatures have emerged from this site over the decades. Soft-bodied animals that almost never fossilize — jellyfish, worms, sea spiders — all found here in breathtaking detail.
Among them was Pohlsepia mazonensis, first formally described in the year 2000. Researchers at the time looked at its flattened, ink-black silhouette and saw the hallmarks of an early cephalopod — possibly an octopus. Eight arm-like projections. A soft, bag-shaped body. No obvious shell. The scientific world accepted the classification, and for more than two decades, Pohlsepia held the crown as the oldest octopus ever found — sitting an astonishing 210 million years before the next oldest known specimen.
But the crown always sat a little uneasily. The arms were the wrong length. The proportions were odd. Some features simply didn't add up, and a small but persistent group of paleontologists suspected that something was wrong.
The Scientist Who Looked Again
Lead study author Thomas Clements, a lecturer in invertebrate zoology at the University of Reading, decided it was time to look again — this time with tools that simply didn't exist in 2000. "We basically used a wide selection of new analytical techniques to discover hidden anatomical characteristics within the rock," Clements told CNN. "And we were able to determine that it is not an octopus, but is actually a very decomposed nautiloid, which is a relative of modern nautiluses."
We were able to determine that it is not an octopus, but is actually a very decomposed nautiloid — a relative of modern nautiluses.
— Thomas Clements, University of ReadingThe techniques Clements and his team employed belong to a new generation of palaeontological investigation. Modern imaging methods — including high-resolution photography under different wavelengths of light — can reveal structural details invisible to the naked eye. Chemical analysis of the rock matrix can distinguish between different types of preserved biological tissue. Comparative anatomy databases, now vastly larger and more detailed than they were 25 years ago, allow scientists to match features against thousands of known species with unprecedented precision.
What they found was not the sleek, arm-rich outline of an early octopus, but the remnants of something that had been rotting for weeks before it was buried in sediment. Decomposition, it turns out, is a master of disguise.
The Disguise of Decomposition
This is perhaps the most fascinating — and humbling — part of the story. When a nautiloid dies, its soft body begins to break down rapidly. The tentacles, normally bunched tightly inside the shell opening, spread outward and splay into what can look eerily like a ring of arms. The shell itself, if it breaks away or becomes detached during the fossilization process, disappears from the picture. What remains, pressed flat in rock, can look convincingly like a primitive octopus.
"The animal had been decomposing for weeks before it was buried," Clements explained, "giving its fossil an octopus-like appearance that led many scientists to conclude that octopuses had lived far earlier than previously thought." In other words, nature played an extraordinary trick — and fooled the scientific community for over two decades.
So… When Did Octopuses Actually Appear?
With Pohlsepia dethroned, the oldest known true octopus fossil dates back to about 90 million years ago — from the Cretaceous period. That gap — from 300 million years to 90 million years — is enormous in evolutionary terms. It represents more than 200 million years of history that we currently have almost no direct fossil evidence for in the octopus lineage.
Does this mean octopuses didn't exist before 90 million years ago? Almost certainly not. Soft-bodied animals simply don't fossilize well. Octopuses have no shell, no bones, no hard parts — just flesh that decays almost instantly after death. The 90-million-year record is almost certainly a gap in our knowledge, not the true origin of the group.
⚡ Quick Science Facts
- Octopuses are cephalopod molluscs, closely related to squid, cuttlefish, and nautiluses.
- Modern octopuses have three hearts, blue blood, and are among the most intelligent invertebrates on Earth.
- Nautiluses are sometimes called "living fossils" — their body plan has changed relatively little in hundreds of millions of years.
- Mazon Creek has yielded over 400 species of fossil organisms, including some found nowhere else on Earth.
- The Carboniferous period (359–299 million years ago) is also known as the "Age of Coal."
- Soft-bodied fossils require extraordinary conditions — typically rapid burial in oxygen-poor sediment.
A Timeline of Ancient Cephalopods
The first cephalopods appear in the fossil record — shelled animals related to today's nautiluses, swimming the Cambrian seas.
Pohlsepia mazonensis lives and dies in the warm Carboniferous seas near what is now Illinois — now reclassified as a nautiloid, not an octopus.
The current oldest known true octopus fossil — a Cretaceous specimen that retains the unmistakable anatomy of the modern group.
Around 300 known octopus species roam the world's oceans, from tropical coral reefs to the cold deep sea.
Why This Discovery Matters Beyond the Headlines
It would be easy to read this story as merely a correction — a scientific mistake found and fixed. But that would dramatically undersell what's happening here. This reclassification is a testament to science doing exactly what it's supposed to do: questioning its own conclusions, embracing new evidence, and following the truth wherever it leads — even when that means dismantling a celebrated record.
It also highlights how rapidly the tools available to paleontologists are evolving. The fossil examined by Clements' team has been sitting in a museum collection for decades. It hasn't changed. What changed is our ability to see it. The same rock, studied with 21st-century eyes, revealed a completely different story. And that raises an extraordinary question: how many other fossils in museum drawers around the world are waiting to be reinterpreted?
The same rock, studied with 21st-century eyes, revealed a completely different story — raising the question: how many other fossils are waiting to be reinterpreted?
— Science CommentaryThe Nautilus — Survivor Across the Ages
The nautilus itself is an animal worth celebrating. With its mesmerizing spiral shell divided into gas-filled chambers, it rises and sinks through the ocean by adjusting its buoyancy — a biological submarine that has been sailing the seas for hundreds of millions of years. It is often called a "living fossil," though that term undersells its remarkable adaptability. When mass extinctions wiped out the ammonites and countless other shelled cephalopods, the nautilus survived. When the dinosaurs vanished, the nautilus endured. Today, half a dozen species still glide through the warm waters of the Indo-Pacific, largely unchanged in form from their ancient ancestors.
To know that Pohlsepia mazonensis belongs to this extraordinary lineage is, in some ways, more satisfying than the octopus story ever was. The nautiloids are survivors. And this particular nautiloid, misidentified for so long, has finally come home.
The Lesson for All of Us
There is something deeply human about this story. We looked at a strange shape in a piece of rock and we saw what we wanted to see — or perhaps what we expected to see. We told a compelling narrative, built a record-breaking headline around it, and moved on. And for 25 years, that story held.
Science, unlike myth, has a mechanism for self-correction. It is messy, slow, and occasionally embarrassing. But it works. The oldest octopus turned out not to be an octopus. The record is gone. The story is better. And somewhere in a museum near Chicago, a small, flat, 300-million-year-old piece of stone is finally telling the truth about who it really was.
The ancient seas of the Carboniferous were full of wonders we are only beginning to properly understand. Every time we look again — with better tools, fresher eyes, and the humility to question what we think we know — the past reveals a little more of itself. And that, perhaps, is the most exciting thing of all.