Oldest Octopus Fossil Reclassified After New Study
▼ Summary
– The fossil *Pohlsepia mazonensis*, described in 2000, was originally identified as the oldest known octopus from the late Carboniferous period.
– This classification was an anomaly because all other evidence suggested octopuses and related species evolved much later, during the Jurassic.
– Advanced imaging revealed the fossil is not an octopus but a decomposed and flattened nautiloid.
– The fossil formed in the Mazon Creek area, where iron-rich mud encased organisms in siderite nodules, preserving them as two-dimensional stains.
– The fossil’s vague, stain-like appearance led to its long-term misidentification, similar to interpreting an inkblot test.
The fossil known as Pohlsepia mazonensis, discovered in Illinois, was once celebrated as a landmark find that reshaped the timeline of cephalopod evolution. Described in 2000, it was identified as the oldest known octopus fossil, dating to the late Carboniferous period approximately 311 to 306 million years ago. This classification created a significant scientific puzzle, as all other fossil evidence strongly indicated that modern coleoids, the group including octopuses, squid, and cuttlefish, did not appear until the Jurassic period, much later in Earth’s history.
A new study led by paleontologist Thomas Clements of the University of Leicester has now resolved this mystery. Using advanced imaging techniques, his team re-examined the specimen and determined it is not an octopus. The fossil is actually the compressed and decomposed remains of a nautiloid, a different type of cephalopod with an external shell. This reclassification removes the problematic outlier from the evolutionary timeline, bringing the fossil record back into better alignment with genetic and anatomical models of cephalopod diversification.
The initial misidentification stemmed from the unique and challenging preservation conditions at the Mazon Creek fossil site. Roughly 300 million years ago, this area was a brackish tidal basin that experienced periodic inundations of iron-rich mud. When organisms died and were buried, the high iron content triggered the formation of siderite nodules around their decaying bodies, encasing them in stone. While this process can preserve soft tissues, it does not create detailed three-dimensional fossils. Instead, the remains are typically flattened into faint, two-dimensional stains on dark rock.
Interpreting these indistinct impressions requires a significant degree of inference. The original researchers were essentially analyzing a vague smear, attempting to reconstruct an entire animal’s anatomy from minimal contrast. This scenario is akin to interpreting an abstract inkblot test, where perception can be heavily influenced by expectation. For nearly 25 years, the scientific community accepted the interpretation that this ambiguous stain represented a soft-bodied octopus, a conclusion now overturned by more precise analytical technology. This case underscores the importance of revisiting historic specimens with new tools, as it can correct long-held assumptions and refine our understanding of deep evolutionary history.
(Source: Ars Technica)