For years, a particular fossil known as Pohlsepia mazonensis held a prestigious title in the annals of paleontology: the oldest octopus ever discovered. However, modern evidence suggests that this ancient creature was not an octopus at all, but rather a member of a different lineage of cephalopods.
The reclassification comes after researchers utilized advanced imaging technology to peer through the stone and identify specific biological markers that had previously remained hidden. The discovery that the oldest octopus fossil found to not be an octopus is actually a nautiloid provides a rare glimpse into the soft-tissue anatomy of ancient marine life, shifting our understanding of how these creatures evolved during the Paleozoic era.
The transition from “octopus” to “nautiloid” is not merely a semantic change. While both are cephalopods, nautiloids are the ancient, shelled relatives of modern octopuses and squids. In the case of Pohlsepia, the lack of a visible shell in the fossil record had led previous researchers to believe it was a shell-less octopus. The new findings suggest the creature simply lost its protection through the natural process of decay before it was preserved in the earth.
The Smoking Gun: A Toothed Tongue
The breakthrough in identification came from the discovery of a radula—a specialized, chitinous, conveyor-belt-like tongue that mollusks use to scrape food. While the presence of a radula confirmed the specimen was a mollusk, the specific architecture of the teeth provided the definitive answer regarding its identity.
Using a synchrotron scan—a high-energy X-ray technique that allows for extreme precision—researchers were able to count individual tooth impressions across the radula’s transverse rows. The scan revealed a highly specific 11-element configuration per row, consisting of:
- A central rachidian tooth
- Pairs of lateral teeth
- Marginal teeth
- Smooth marginal plates
According to the study, this exact configuration is unique to nautiloids. The precision of the synchrotron imaging allowed the team to move past the “ambiguous stain” of the fossil and identify the biological blueprint of the animal.
“Pohlsepia mazonensis is a nautiloid that died, decomposed, lost its protective shell and was subsequently flattened into the mud and preserved as an ambiguous stain,” said researcher Clements.
From ‘Oldest Octopus’ to ‘Oldest Soft Tissue’
While Pohlsepia has lost its status as the world’s oldest octopus, it has gained a different set of superlatives. The specimen is now recognized as the oldest unequivocal evidence of nautiloid soft tissues ever found in the Paleozoic fossil record. Most other nautiloid fossils consist primarily of their hard shells. finding preserved soft tissue is an extraordinary rarity in paleontology.
Clements described the process of analyzing the specimen as a paradoxical experience, noting that it was “of course the most difficult fossil to work on” that he had ever encountered, while simultaneously being “the most fun fossil” of his career. The difficulty stemmed from the fossil’s degraded state, which required the highest levels of imaging technology to decode.
This discovery highlights the precarious nature of fossil identification. Because Pohlsepia was flattened into the mud and lacked its shell, it mimicked the appearance of a soft-bodied octopus. This serves as a reminder to the scientific community that “shell-less” fossils are not always evidence of a shell-less species, but can be the result of taphonomy—the process of how an organism decays and becomes fossilized.
The Future of the Mazon Creek Fossils
The Pohlsepia specimen was recovered from the Mazon Creek fossil beds, a site renowned for its exceptional preservation of soft-bodied organisms. The success of the synchrotron scans on this specimen has opened the door for a broader re-examination of other fossils from the same region.
Clements and his team now intend to apply these advanced imaging techniques to other “weird” fossils found at Mazon Creek that have remained unstudied or misunderstood for decades. By looking past the surface “stains” of the rock, researchers hope to uncover more soft-tissue evidence that could rewrite the evolutionary timeline of various marine invertebrates.
The implications of this work extend beyond a single species. By establishing a clear anatomical benchmark for nautiloid radulae, scientists can now more accurately identify other fragmentary fossils, reducing the likelihood of misidentification in the fossil record.
| Feature | Previous Identification | Current Identification |
|---|---|---|
| Taxonomy | Octopus (Cephalopod) | Nautiloid (Cephalopod) |
| Key Evidence | Lack of shell / General shape | 11-element radula configuration |
| Significance | Oldest known octopus | Oldest unequivocal nautiloid soft tissue |
| Preservation | Soft-bodied fossil | Decomposed shell-bearing fossil |
Despite the change in title, the story of Pohlsepia mazonensis is far from over. Now that it is recognized as the oldest known nautiloid with preserved soft tissue, it becomes a primary subject for further study to understand the early biology of these creatures.
The full details of the study are published in the journal Proceedings of the Royal Society B Biological Sciences.
The research team’s next step involves applying these synchrotron scanning techniques to a wider array of specimens from the Mazon Creek site to determine if other “octopuses” in the record are actually misidentified nautiloids.
Do you think advanced imaging will lead to a massive reclassification of Paleozoic fossils? Share your thoughts in the comments below.
