This is Mazon Monday post #317.  What’s your favorite Mazon Creek fossil?  Tell us at  email:esconi.info@gmail.com.

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A new paper “Synchrotron data reveal nautiloid characters in Pohlsepia mazonensis, refuting a Palaeozoic origin for octobrachians” in the journal Proceedings of the Royal Society B Biological Sciences refutes the classification of Pohlsepia mazonensis as an octopus and reclassifies it as a soft-bodied nautiloid as Paleocadmus pohli.

The authors used a suite of advanced imaging methods, including synchrotron elemental mapping, micro-CT scanning, and multispectral imaging, to reexamine the original specimen along with similar fossils from Mazon Creek. These techniques revealed something that had never been seen before… a radula (toothed feeding structure) and beak hidden within the fossil.

The radula turned out to be the key. Its structure—specifically the number and arrangement of teeth—does not match octopuses. Instead, it closely matches that of nautiloids, particularly the Mazon Creek genus Paleocadmus. With this evidence, the researchers concluded that Pohlsepia is not an octopus at all, but rather a soft-bodied nautiloid, likely synonymous with Paleocadmus pohli.

This research rewrites cephalopod evolution as Pohlsepia mazonensis was the oldest known octopus. Earlier interpretations had pointed to arms, fins, an ink sac, and eyes. However, those features appear to be either poorly preserved remain or the result of decay and taphonomic distortion.

This reinterpretation has big implications:

• Pohlsepia can no longer be used as evidence for a Carboniferous origin of octopuses
• The origin of modern octopuses (octobrachians) is once again placed in the Mesozoic, consistent with other fossil and molecular data
• The fossil instead represents the oldest known soft-bodied nautiloid in the fossil record

This study is also a reminder of just how tricky Mazon Creek fossils can be. Soft tissues are often preserved as faint stains, and decay prior to burial can significantly alter an organism’s appearance.

With modern tools, Mazon Creek continues to surprise us and even well-known fossils can yield completely new interpretations.

Synchrotron data reveal nautiloid characters in Pohlsepia mazonensis, refuting a Palaeozoic origin for octobrachians

Abstract

Pohlsepia mazonensis, from the late Carboniferous Mazon Creek Lagerstätte (311–306 Ma), has been suggested to be the oldest fossil octopus. This single specimen provides a key calibration point for molecular clock studies, which estimated a Palaeozoic origin for octobrachians, pushing the fossil record of crown octopuses back 150 million years. Despite being a textbook ‘phylogenetic fuse’ example, the systematic position of Pohlsepia is controversial and, consequently, our understanding of cephalopod evolution remains in flux. We present the first comprehensive reassessment of this enigmatic fossil, alongside multiple new specimens, using a suite of advanced analytical techniques. Synchrotron micro-X-ray fluorescence elemental mapping reveals a radula obscured by the matrix, definitively confirming a molluscan affinity. Crucially, radular tooth count and morphology indicate that Pohlsepia is not an early octobrachian but rather a decomposed nautiloid. This reinterpretation refutes a Palaeozoic origin for octobrachians and provides the only unequivocal evidence of nautiloid soft tissue in the Palaeozoic fossil record. Our findings demonstrate how advanced analytical methods can be used to resolve the interpretive challenges posed by the exceptional but often ambiguous soft tissue preservation in the Mazon Creek Lagerstätte, offering great potential for the re-evaluation of other fossil specimens from this iconic site.