A 300-million-year-old fossil, considered for decades to be the oldest known octopus, has turned out to be a completely different marine organism, overturning one of the most important assumptions in paleontology. Researchers from the University of Reading used modern imaging techniques to analyze the internal structure of the fossil and discovered the presence of small teeth – a feature that does not belong to octopuses. Instead, the fossil belongs to a relative of the nautilus.

The fossil, known as Pohlsepia mazonensis, was even included in the Guinness Book of Records as the oldest octopus ever discovered. However, the new study shows that the initial identification was incorrect. The lead author of the study, Thomas Clements, explained that the misinterpretation had to do with the state of the organism before fossilization. According to him, the body had been decomposing for weeks, deforming the tissues and creating an appearance that resembled an octopus with eight tentacles.

The first study, published in 2000, was based solely on external morphological features. The new research used synchrotron imaging – a technology that uses beams of light much more powerful than the sun – to analyze the interior of rocks.

This method has revealed previously unseen structures, including teeth identical to those in nautiloid fossils found in Mazon Creek. The revision has important implications for understanding the evolution of cephalopods. According to the new data, octopuses appeared much later than previously thought, most likely during the Jurassic Period. Scientists also now believe that the split between octopuses and their ten-tentacled relatives occurred in the Mesozoic Era, rather than hundreds of millions of years ago as previously thought. The discovery highlights the importance of reexamining old discoveries with modern technology, showing that even the most established scientific theories can change in the face of new evidence.