Scientists Reclassify 300-Million-Year-Old Fossil as Nautiloid, Not Oldest Octopus

A 300-million-year-old fossil, long considered the oldest known octopus, has been reidentified as belonging to a nautiloid, a relative of modern nautiluses. The specimen, named Pohlsepia mazonensis, was discovered at the Mazon Creek site south of Chicago, Illinois. The reclassification appears in a study published on Wednesday in the journal Proceedings of the Royal Society B.

Paleontologists initially classified the fossil as an octopus in 2000, based on its appearance. The fossil predates the next oldest confirmed octopus by about 210 million years, as the latter dates to approximately 90 million years ago. Its octopus-like features resulted from weeks of decomposition before burial, according to the study's lead author, Thomas Clements, a lecturer in invertebrate zoology at the University of Reading, England.

his team applied multiple analytical methods unavailable in 2000 to reexamine the fossil.

These included scanning electron microscopy and geochemistry analysis. Initial efforts did not yield clear results, prompting the use of synchrotron imaging, which employs X-rays more powerful than those from the sun to reveal subsurface structures. The synchrotron scan uncovered a radula, a feeding structure with rows of teeth, in the fossil.

The radula featured at least 11 teeth per row, differing from the seven or nine teeth per row in octopuses. This anatomical detail confirmed the fossil's identity as a decomposed nautiloid with tentacles and an external shell.

“We basically used a wide selection of new analytical techniques to discover hidden anatomical characteristics within the rock.”

The study demonstrates how emerging technologies, such as synchrotron imaging, enable detection of hidden features in fossils. These tools are becoming more accessible and affordable, facilitating discoveries like ancient proteins and biomolecule analysis.

Clements noted that such methods, including those adapted from engineering to assess dinosaur bite strength, are transforming the field. The reclassification resolves prior debates over the fossil's features, such as arm length and shape, which did not align with expected octopus traits.

It provides a more accurate timeline for octopus evolution, placing their origins closer to 90 million years ago. Future research may apply similar techniques to other ambiguous fossils at sites like Mazon Creek.