This 300-Million-Year-Old ‘Octopus’ Fossil Was Actually Something Else All Along
For nearly 25 years, a hand-sized fossil pulled from the rocks of Illinois held a remarkable title: the oldest known octopus on Earth. Guinness World Records listed it. Researchers cited it. It reshaped what scientists thought they knew about when eight-armed cephalopods first appeared in ancient seas.
There was just one problem. It was never an octopus at all. University of Reading zoologist Thomas Clements, the lead researcher behind the new findings, finally cracked the code on the fossil known as Pohlsepia mazonensis. His team used a synchrotron — a machine that produces extremely powerful beams of light by accelerating electrons to very high speeds — to peer inside the rock without breaking it open.
How Were Teeth Involved in This Discovery?
What they found changed everything. Buried within the stone was a tooth-bearing ribbon called a radula, a feature shared by all mollusks such as nautiluses and octopuses. But the arrangement of those teeth was wrong for an octopus. 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 told The Associated Press. “And that’s how we realize that the world’s oldest octopus is actually a fossil nautilus, not an octopus.”
The creature, Clements and his team determined, is actually a relative of the nautilus — a cephalopod with both tentacles and a shell. The teeth were consistent with those of a fossil nautiloid named Paleocadmus pohli, which had been discovered in the same region.
What’s the White Mush on the Fossil?
To understand how the misidentification happened in 2000, it helps to know what researchers were working with.
“It’s a very difficult fossil to interpret,” Clements said. “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.
Clements suggested that the original misidentification likely occurred because the animal’s shell broke down before fossilization, removing a key feature that would have made it easier to recognize. Without that shell, the soft remains looked convincingly octopus-like.
When paleontologists identified it as an octopus in 2000, it challenged earlier views about how eight-armed cephalopods evolved, indicating they appeared far earlier than scientists had believed. The next oldest known octopus fossil is roughly 90 million years old — creating a gap of more than 200 million years that nagged at researchers for decades.
“It’s a huge gap,” Clements said. “And so that big gap got researchers sort of questioning, ‘Is this thing actually an octopus?’”
Following Clements’ results, which were published this month in the Proceedings of the Royal Society B, Guinness World Records announced that it would remove Pohlsepia mazonensis from its listing as the oldest 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 the question of when octopuses first appeared in Earth’s oceans is now wide open again.
A Fossil From Before the Age of Dinosaurs
The creature, about the size of a human hand, 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. Dinosaurs lived during the Mesozoic Era, which lasted from about 252 million years ago to 66 million years ago. This fossil predates that entire era by tens of millions of years.
What This Means for the Octopus Family Tree
The reclassification doesn’t just strip a record. It reopens a fundamental question about one of the ocean’s most intelligent creatures. With the 300-million-year-old contender now out of the running, the earliest confirmed octopus fossils sit at roughly 90 million years old — still ancient, but a far cry from the timeline researchers had accepted for a quarter century.
The next time someone asks when octopuses first appeared, science has an honest answer: we’re still figuring that out. And sometimes, it takes a synchrotron and 11 tiny teeth to prove that a 25-year-old discovery was hiding a completely different animal inside.
This article was created by content specialists using various tools, including AI.
