For years, ‘Pohlsepia mazonensis’ was believed to be the earliest known octopus, with what appeared to be eight tentacles, eyes, and possibly an ink sas
For over 20 years, a fossil named ‘Pohlsepia mazonensis’ was celebrated as the world’s oldest known octopus, dating back roughly 300 million years. It even made its way into the Guinness Book of World Records, shaping how scientists understood the evolution of these intelligent sea creatures. But new research now reveals that this ancient marine animal has been misidentified all along.
The fossil, was discovered at the Mazon Creek site in Illinois, USA. For years, it was believed to be the earliest known octopus, with what appeared to be eight tentacles, eyes, and possibly an ink sac, features that perfectly matched modern octopuses.
Using cutting-edge synchrotron imaging, scientists were able to peer deep inside the fossil like never before. What they found changed everything- rows of tiny teeth that simply do not match an octopus.
Lead researcher Thomas Clements from the University of Reading explained, “We basically used a wide selection of new analytical techniques to discover hidden anatomical characteristics within the rock. And we were able to determine that it is not an octopus, but is actually a very decomposed nautiloid.”
The fossil had decayed so much before it was preserved that it created a case of mistaken identity lasting over a decade.
Octopuses typically have fewer teeth per row, but this fossil had 11, a clear sign it belonged to a different group altogether. Instead, researchers now say the creature is more closely related to a nautilus, a shelled marine animal that still exists today.
So how did experts misread it for decades? The answer lies in decay.
Before fossilisation, the animal’s body had already started breaking down, masking key features like its shell. What remained looked soft and sack-like, eerily similar to an octopus.