A 300-million-year-old fossil, Pohlsepia mazonensis, initially identified as the world's oldest octopus, has been reclassified as an ancient relative of the nautilus. New research, utilizing advanced imaging techniques, revealed internal structures inconsistent with octopuses but aligned with nautiloids. This reclassification, detailed in the journal Proceedings of the Royal Society B, revises the understanding of cephalopod evolutionary timelines and establishes a new record for nautiloid soft tissue preservation.
The 300-million-year-old fossil Pohlsepia mazonensis, once hailed as the oldest octopus, has been reclassified as an ancient nautilus relative, reshaping our understanding of cephalopod evolution.
Reclassification Announced
The reclassification of Pohlsepia mazonensis was based on findings published recently in Proceedings of the Royal Society B. The fossil, discovered in Illinois, USA, in the Mazon Creek area, had been classified as an octopus since 2000.
This initial classification suggested octopuses evolved approximately 150 million years earlier than generally accepted, prompting significant scientific debate.
Dr. Thomas Clements, a Lecturer in Invertebrate Zoology at the University of Reading and lead author of the new study, stated that the fossil's octopus-like appearance likely resulted from decomposition over millions of years before fossilization. Paul Mayer, manager of fossil invertebrate collections at the Field Museum in Chicago, where the fossil is housed, noted that questions regarding its original identification as an octopus had persisted since the initial paper was published.
New Research Methodology
To definitively re-examine the fossil, researchers employed synchrotron imaging. This advanced technique uses bright X-ray beams from particle accelerators to scan the fossil rock, allowing for high-resolution internal viewing without damaging the specimen.
The fossil, roughly the size of a human hand, was transported from the Field Museum to a micro-X-ray synchrotron facility in Paris for detailed internal scans.
Key Findings
The synchrotron imaging revealed a well-preserved radula, a ribbon-like feeding structure containing rows of teeth, which is characteristic of mollusks.
The radula of Pohlsepia mazonensis was found to contain 11 tooth-like elements per row. This count differs from octopuses, which typically possess seven or nine teeth per row. In contrast, nautiloids possess 13 elements, and the shape and count of the observed denticles in Pohlsepia were found to be more consistent with nautiloids.
Advanced imaging revealed a radula with 11 tooth-like elements per row, a count inconsistent with octopuses but aligned with nautiloids.
The discovered teeth structure also matched that of Paleocadmus pohli, a fossil nautiloid already known from the same Mazon Creek locality. Researchers noted the absence of melanosome pigment, which would typically be present in an ink sac, further contradicting the previous identification of an ink sac structure.
The findings suggest that the animal had partially decayed and potentially lost its shell before fossilization, altering its original appearance and contributing to the initial misidentification.
Implications for Cephalopod Evolution
This reclassification significantly alters the understanding of octopus evolution. The findings indicate that octopuses likely appeared much later, during the Jurassic period, which aligns with evidence from other high-quality octopus fossils. Scientists now propose that the divergence between octopuses and their ten-armed relatives, such as squids, occurred in the Mesozoic era.
Furthermore, the study establishes the Paleocadmus fossils from the Mazon Creek site as the oldest known nautiloid soft tissue in the fossil record, surpassing the previous record by approximately 220 million years. This highlights how new technologies can provide improved insights into previously studied fossils.
The Paleocadmus fossils are now established as the oldest known nautiloid soft tissue, surpassing the previous record by approximately 220 million years.
Institutional Response and Records
Following the publication of these findings, Guinness World Records announced it would no longer list Pohlsepia mazonensis as the earliest known octopus. Adam Millward, Managing Editor for Guinness World Records, confirmed the organization's review of the new evidence.
The fossil remains part of the collection at the Field Museum in Chicago. While no longer recognized as the oldest octopus, its reclassification means the museum now houses the world's oldest known soft tissue nautiloid.