The creature that swam into the Guinness Book of Records as the planet's earliest known octopus just got its title revoked. New high-powered scans of the 300-million-year-old fossil Pohlsepia mazonensis reveal it's not an octopus at all, but a relative of today's nautilus—with a set of tiny teeth being the giveaway. Dr. Thomas Clements, lead author of the study published in Proceedings of the Royal Society B, says the animal—a shelled mollusk with many tentacles—had decomposed for weeks before it was buried. That warped its shape in a way that led scientists to believe it was an octopus in an analysis published in 2000.
More than two decades later, scientists using synchrotron imaging—an approach that employs "beams of light brighter than the sun," per a press release—detected a radula, a teeth-covered ribbon-like structure specific to mollusks. The number and shape of those teeth don't match octopuses but align with a known fossil nautiloid, Paleocadmus pohli, that has been found at the same Mazon Creek site in Illinois where the fossil was discovered. As Nautilus explains, the imaging revealed 11 teeth per row, which better syncs with the 13 teeth nautiloids have versus the 7 to 9 in octopuses; the study authors suspect a couple of teeth were simply lost.
The find now stands as the oldest preserved soft tissue from a nautiloid and forces a rewrite of octopus history: Their origins likely sit in the later Jurassic period. Said Clements, "It's amazing to think a row of tiny hidden teeth ... have fundamentally changed what we know about when and how octopuses evolved."
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