300-Million-Year-Old Fossil Gets New Identity After 24 Years

For nearly a quarter century, a 300-million-year-old fossil held the title of world's oldest octopus. Scientists just discovered they got it wrong, and the real story is even more fascinating.

The fossil Pohlsepia mazonensis, discovered in Illinois's Mazon Creek fossil beds, was identified as an ancient octopus back in 2000. But new research published in Proceedings of the Royal Society B reveals the creature was actually a relative of the nautilus, a shell-covered cephalopod with tentacles that still exists today.

University of Reading zoologist Thomas Clements led the team that solved the mystery. Looking at the fossil, he admits it's challenging to interpret. "It kind of just looks like a white mush," he told reporters.

The breakthrough came when researchers used a synchrotron, a powerful imaging tool, to peek inside the fossil and examine its teeth. They found 11 teeth per row, more than the seven or nine typically seen in octopuses. The teeth matched perfectly with Paleocadmus pohli, an ancient nautiloid from the same region.

The misidentification makes sense when you understand what happened to the creature. Researchers believe it decomposed and lost its shell before fossilization, making it look remarkably similar to a modern deep-water octopus at first glance.

The Bright Side

This discovery doesn't just correct a scientific record. It gives us the oldest soft-tissue nautilus fossil ever found, offering a rare window into how these remarkable creatures evolved over hundreds of millions of years.

The correction also resolves a puzzle that had bothered scientists for decades. The next oldest known octopus fossil is only 90 million years old, creating a mysterious 210-million-year gap that never quite added up. "That big gap got researchers questioning whether this thing was actually an octopus," Clements explained.

Paul Mayer, who manages fossil invertebrate collections at Chicago's Field Museum where the specimen lives, welcomed the news. Scientists have questioned the original classification since day one, and the debate has only strengthened our understanding of ancient marine life.

The reclassification shows how science gets better over time, with new technology revealing truths that were hidden in plain sight for decades. Every question answered opens the door to new discoveries waiting to be made.