Oldest octopus fossil found to not be an octopus

A groundbreaking revelation has emerged regarding the fossil known as Pohlsepia mazonensis, once believed to be the oldest octopus, dating back to between 311 and 306 million years ago during the late Carboniferous period. This unassuming fossil, found in Illinois, has significantly altered our understanding of cephalopod evolution. Initially described in 2000, Pohlsepia was an anomaly, as existing fossil evidence indicated that the group of crown coleoids—which includes octopuses, squid, and cuttlefish—diverged much later in the Jurassic period. To clarify this evolutionary conundrum, paleontologist Thomas Clements from the University of Leicester and his team employed advanced imaging techniques to analyze the fossil. The results were surprising: Pohlsepia was not an octopus as previously thought, but rather a decomposed and flattened nautiloid. This misidentification had persisted for nearly 25 years, primarily due to the unique fossilization process that occurred in the Mazon Creek Lagerstätte. Approximately 300 million years ago, this region was a brackish marine basin that frequently received deposits of iron-rich river sediment. When organisms perished and were buried under this sediment, the high iron levels led to the formation of the mineral siderite around their remains, encasing them in hard nodules. While this preservation method can retain soft tissues, it does not create three-dimensional structures. Instead, the soft parts of the organisms often appear as flat stains against the dark rock, challenging early paleontologists to decipher their anatomy, much like interpreting abstract art. This discovery not only corrects a long-standing misconception but also sheds light on the complexities of cephalopod evolution, inviting further exploration into the ancient marine life that once inhabited our planet.