The ‘oldest fossil octopus’ is probably another animal

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The separated shell is visible in the background. Other animals are visible, such as the marine worm Esconites zelus (foreground) and Bandringa rayi, a relative of sharks (back left). Dr. Thomas Clements, University of Reading By Jake Buehler April 7, 2026 at 7:01 pm Share this:Share Share via email (Opens in new window) Email Share on Facebook (Opens in new window) Facebook Share on Reddit (Opens in new window) Reddit Share on X (Opens in new window) X Print (Opens in new window) Print Listen to this article This is a human-written story voiced by AI. Got feedback? Take our survey . (See our AI policy here .) The oldest fossil octopus isn’t an octopus at all. That’s the conclusion from new research on a perplexing fossil previously thought to be the most ancient record of an octopus. The findings — published April 8 in Proceedings of the Royal Society B — suggest the roughly 310-million-year-old fossilized sea creature was actually a partly decomposed nautilus. Such a reclassification has implications for scientists’ understanding of the evolution of octopuses, nautiluses and cephalopods as a whole. Sign up for our newsletter We summarize the week's scientific breakthroughs every Thursday. In 2000, researchers described an odd fossil found not far from Chicago. It had a round body, finlike structures on one end and a tangle of arms. The fossil was classified as an octopus and named Pohlsepia mazonensis. But that classification produced a conspicuous time gap, given its age of over 300 million years, says paleontologist Thomas Clements at the University of Reading in England. Fossil octopuses were well-known, but not until far later in the geologic record — at least 150 million years.  “It’s been a real trouble for paleontologists to try to understand how Pohlsepia fits into our understanding of octopus evolution,” he says. When revisiting the mystery mollusk, Clements and his colleagues used high-powered X-rays on the fossil that illuminated different chemicals within the preserved minerals that formed around the soft tissues prior to their decay, giving the researchers a clearer view of Pohlsepia. This technique also revealed a clue about the animal: a preserved radula, the rasping tongue found in many mollusks, including snails, chitons and cephalopods.  “That was the big breakthrough,” says Clements. “Because it’s the only unequivocal character this fossil has.” The radula is made up of many rows of teeth. Octopuses have seven or nine teeth per row, but Pohlsepia showed at least 11. This is more consistent with a nautilus, an ancient shelled cephalopod that survives as a “living fossil” in oceans today. Pohlsepia’s teeth resembled those on fossilized nautilus radulae belonging to an extinct species, found at the same fossil site, called Paleocadmus pohli. Clements and his team think this is the true identity of the paleontological puzzle.  The octopus fossil Pohlsepia (shown) may be a nautilus fossil instead, suggests new research. The findings may rewrite our previous understanding of octopus evolution.Dr. Thomas Clements/University of Reading “There had been serious doubts about the alleged octopod identity of Pohlsepia for some time,” says Alexander Pohle, a paleontologist at Ruhr University Bochum in Germany not involved with the study. “It’s great to see this debate settled with such detailed work!” The fo