Octopus Fossil Reclassified After New Scan Reveals a Different Sea Creature

octopus evolution has taken a sharp turn after scientists re-examined a 300-million-year-old fossil once hailed as the oldest known example of its kind. In a finding that cuts against years of assumption, the specimen now appears to be a different animal altogether, with the revised identification tied to new imaging and internal details that were not visible before. The research centers on a fossil found in Illinois and now points away from an octopus and toward a nautiloid relative.

What Scientists Found Inside the Fossil

The fossil, named Pohlsepia mazonensis, was originally described in 2000 and later entered the Guinness Book of Records as the oldest known octopus. At the time, scientists believed it showed eight arms, fins, and other features associated with octopuses, but later scanning told a different story. Using high-powered imaging, researchers at the University of Reading examined the fossil’s interior and found tiny teeth that matched those of a nautiloid rather than an octopus.

The key discovery was a radula, a ribbon-like tongue covered in microscopic teeth. Dr Thomas Clements of the University of Reading, the study’s lead author, said the internal scan revealed a 300-million-year-old radula seen by human eyes for the first time. He said the tooth count and shape were enough to show that Pohlsepia mazonensis is not an octopus, and that decomposition before burial made the animal look misleadingly octopus-like.

Why the Reclassification Matters

The shift is more than a label change. Experts say the new evidence supports the view that octopuses first appeared during the Jurassic period, much later than previously thought. That pushes the earliest evidence for octopuses forward and means the fossil that once shaped part of the octopus timeline no longer belongs in that story.

The specimen was found at Mazon Creek in the U. S. state of Illinois and is known from a single fossil. Scientists now say its features were difficult to interpret because the animal had partially decomposed on the seafloor before fossilisation. That decay, they say, blurred the soft tissues and made the fossil hard to decipher for years.

Immediate Reaction From Researchers

Dr Thomas Clements said: “It turns out the world’s most famous octopus fossil was never an octopus at all. ” He added that modern techniques allowed researchers to see beneath the rock surface and “finally cracked the case. ”

He also said the fossil was a nautilus relative that had been decomposing for weeks before burial and later preservation. In his view, that process created the octopus-like appearance that led to the original identification. The University of Reading team used advanced synchrotron imaging, which relies on X-rays produced by particle accelerators to see inside dense material without destroying it.

How the Picture Changed

The new analysis also matters because it shows how much fossil interpretation can change when better tools become available. The fossil had long been treated as evidence in octopus evolution, but the internal scan now aligns it more closely with an ancient nautiloid already known from the same site. In effect, octopus history has been pulled back into a narrower and later window.

For now, the fossil’s revised identity leaves one clear takeaway: the celebrated octopus fossil was not an octopus, and octopus origins remain tied to a later period than this specimen once suggested. As scientists continue re-checking older finds with newer methods, octopus evolution may still have more surprises ahead.