The ‘World’s Oldest Octopus’ Held That Title for 25 Years. It’s Not Really an Octopus.
For a quarter century, a hand-sized fossil pulled from the rocks of northern Illinois held one of the coolest titles in paleontology: the world’s oldest octopus. Guinness World Records listed it. Scientists cited it. The story was tidy and thrilling — a 300-million-year-old eight-armed creature that predated dinosaurs.
There was just one problem. It was never an octopus at all.
New research has revealed that Pohlsepia mazonensis — the fossil that rewrote the evolutionary timeline when paleontologists identified it as an octopus in 2000 — is actually a relative of the nautilus, a shelled cephalopod that looks nothing like the boneless, big-brained creatures most people picture when they hear “octopus.”
The Fossil That Fooled Everyone
The discovery came from University of Reading zoologist Thomas Clements, the lead researcher behind the new findings.
“It’s a very difficult fossil to interpret,” he said, per The Associated Press. “To look at it, it kind of just looks like a white mush.”
“If you look at it and you are a cephalopod researcher and you’re interested in everything octopus, it does superficially look a lot like a deep-water octopus,” he added.
So how did scientists get it wrong for so long? Clements suggested that the animal’s shell likely broke down before fossilization, removing the one key feature that would have made it easier to recognize. Without a shell, it looked soft-bodied — and soft-bodied plus tentacles equals octopus, at least to the researchers who first examined it.
The 11-Tooth Smoking Gun
Clements’ team cracked the case by examining the fossil using a synchrotron, a machine that produces extremely powerful beams of light by accelerating electrons to very high speeds. The technology allowed them to see inside the rock without breaking it open.
What they found changed everything. Inside the fossil, they discovered a tooth-bearing ribbon called a radula, a feature shared by all mollusks such as nautiluses and octopuses. But the arrangement of the teeth stood out: each row contained 11 teeth, while modern octopuses typically have either seven or nine per row.
“This has too many teeth, so it can’t be an octopus,” Clements said. “And that’s how we realize that the world’s oldest octopus is actually a fossil nautilus, not an octopus.”
The teeth were consistent with those of a fossil nautiloid named Paleocadmus pohli, which had been discovered in the same region.
A Gap That Never Made Sense
Here’s the detail that should have raised red flags much earlier. If Pohlsepia mazonensis really were an octopus, it would have been 300 million years old. The next oldest known octopus fossil is roughly 90 million years old.
“It’s a huge gap,” Clements said. “And so that big gap got researchers sort of questioning, ‘Is this thing actually an octopus?’”
That 210-million-year void in the fossil record was always awkward. It meant either that octopuses evolved far earlier than anyone believed and then left virtually no trace for hundreds of millions of years, or that the original identification was simply wrong.
The new findings, published this month in the Proceedings of the Royal Society B, point firmly toward the latter.
Following the research, Guinness World Records announced that it would remove Pohlsepia mazonensis from its listing as the earliest known octopus. Managing Editor Adam Millward described the researchers’ work as an “intriguing discovery.” He added that the organization would temporarily retire the title of “oldest octopus fossil” while it reviews the new findings.
That means, for now, there is no official record holder for the world’s oldest octopus.
Where the Fossil Lives — and How It Got Its Name
The creature was found in the Mazon Creek area of Illinois, about 50 miles southwest of Chicago, a region rich in fossils from a period before dinosaurs walked the Earth. It is the size of a human hand.
Pohlsepia mazonensis was named after its discoverer, James Pohl, and is housed in the Field Museum in Chicago. Paul Mayer, who oversees the museum’s fossil invertebrate collection, said he was somewhat surprised by the reclassification as a nautiloid. However, he also noted that the fossil’s identity as an octopus had been questioned repeatedly since the original study was published in 2000.
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