An international team including scientists from the IPANEMA Institute and the PUMA beamline has revealed that a 300-million-year-old fossil, previously thought to be the oldest known octopus, is in fact a very different animal: a nautiloid.
This study, published in the Proceedings of the Royal Society B, resolves a major evolutionary paradox by confirming a much more recent origin for modern octopuses, while providing unique insights into the poorly-known soft tissues of nautiloids.
While the fossil record and molecular clocks* place the origin of modern octopuses in the Jurassic period, about 150 million years ago, a 300-million-year-old fossil named Pohlsepia mazonensis, discovered in the famous Mazon Creek concretions (Illinois), suggests an origin twice as old. This 150-million-year gap, with no intermediate fossils to bridge it, remained one of the greatest mysteries of cephalopod evolution.
Since its description in 2000, however, the identity of Pohlsepia has remained highly debated, as the soft tissues preserved in the Mazon Creek fossils are often limited to colored spots, which experts consider misleading when examined visually. Taking advantage of new imaging methods that have emerged since the 2010s, which allow for an unprecedented description of fossil anatomy, including internal structures and invisible details, scientists were able to reexamine this fossil in the manner of a true forensic investigation. While the 3D X-ray scanner proved largely uninformative because the fossil is almost entirely flat, another approach using X-rays at the PUMA beamline revealed Pohlsepia’s true identity.
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Image: Mounting of the two parts of the fossil on the PUMA beamline just before analysis, on June 22, 2022.