Ancient Ocean Mystery Deepens: World’s Oldest ‘Octopus’ Fossil Reclassified as Nautilus Relative After Decades of Misidentification

A fossil long celebrated as the world’s oldest known octopus — dating back approximately 300 million years to the Carboniferous period — has been reclassified by researchers as a relative of the nautilus, fundamentally reshaping scientific understanding of when octopuses first appeared in Earth’s oceans. The stunning reassessment, published in a peer-reviewed study, corrects a misidentification that persisted for decades and reopens profound questions about the evolutionary timeline of one of the ocean’s most intelligent creatures.

The fossil at the center of this scientific reversal was originally collected from the Bear Gulch Limestone formation in Montana, a site renowned among paleontologists for its exceptionally preserved Carboniferous-era marine life. The specimen sat in museum collections for years before being formally described in 2022. At that time, researchers identified what they believed were ten arms and two rows of suckers — hallmark features of vampyropod cephalopods, the group that includes modern octopuses and vampire squid. The announcement generated worldwide attention, as it pushed the evolutionary origins of octopuses back by more than 80 million years beyond previous estimates. The creature was named Syllipsimopodi bideni, after President Joe Biden, in what the original authors described as a nod to their hopes for science-friendly policy. The naming itself drew both praise and criticism, underscoring the intersection of science and politics even in paleontology.

The new study, however, paints a dramatically different picture. Researchers conducting a detailed re-examination of the fossil identified features that are inconsistent with octopus or vampyropod anatomy and instead align with nautiloids — the group of shelled cephalopods represented today by the chambered nautilus. Critical to the reassessment was analysis of what appears to be a siphuncle, a tube-like structure running through the chambers of a shell that nautiloids use to regulate buoyancy. The presence of this structure, combined with reinterpretation of the alleged arm impressions, convinced the team that the original classification was erroneous. This kind of taxonomic correction, while not uncommon in paleontology, is particularly consequential because it removes the key piece of evidence that octopuses existed during the Paleozoic era. Without it, the oldest verified octopus fossils come from Jurassic-era deposits, roughly 164 million years old, found in locations such as Lebanon. This gap of more than 130 million years is not trivial — it fundamentally alters models of cephalopod diversification and the tempo of octopus evolution.

The implications of this reclassification extend well beyond a single fossil. Molecular clock studies — which estimate divergence times based on rates of genetic mutation — have long suggested that octopuses originated somewhere in the Mesozoic era, potentially the late Jurassic or early Cretaceous. The 2022 identification of Syllipsimopodi as an octopus relative had created a significant tension between the fossil record and molecular evidence, as it placed vampyropods more than 100 million years earlier than genetic models predicted. The new reclassification actually resolves that discrepancy, bringing fossil evidence back into closer alignment with molecular data. Scientists note, however, that the absence of Paleozoic octopus fossils does not definitively prove octopuses did not exist during that period — it simply means there is currently no physical evidence to support such a claim. The search for the true oldest octopus continues, and researchers emphasize that new discoveries in exceptional preservation sites could once again rewrite the timeline.

Looking ahead, this episode serves as a powerful reminder of the self-correcting nature of science. The original 2022 team and the current researchers both operated within the framework of peer review and evidence-based analysis. Paleontologists have noted that such corrections, while sometimes perceived as embarrassing, are in fact evidence of the scientific process working as intended. The reclassification is expected to prompt renewed scrutiny of other ambiguous cephalopod fossils and may spur additional fieldwork at Carboniferous-era sites. For the broader public, the story underscores just how much remains unknown about the deep evolutionary history of life on Earth — and how a single fossil, reinterpreted under new analytical techniques, can reshape entire fields of study.