About 100 million years ago, during the late Cretaceous, the seas were ruled not only by mosasaurs and giant sharks but by octopuses far larger than any alive today. A new paper in Science describes fossilized remains of two extinct octopus species preserved inside large seafloor concretions from what is now northern Japan. Using digital fossil‑mining, 3D reconstruction and an AI model to reassemble thin slices of rock, researchers uncovered chitinous beaks — the durable jaws of octopuses — that point to truly enormous animals.
Lead author Yasuhiro Iba (Hokkaido University) and coauthor Jörg Mutterlose digitally rebuilt the fossil-bearing layers and identified unusually large upper and lower jaws, the biggest reported for any octopus. By comparing jaw dimensions to modern relatives, the team estimated arm spans on the order of 60 feet for some individuals, dwarfing the modern giant Pacific octopus, which typically reaches arm spans around 13 feet.
The preserved beaks also carry telltale wear: chips and scratches consistent with crushing hard-shelled prey such as shrimp, lobsters, bivalves and nautilus‑like animals. That pattern suggests these Cretaceous octopuses used long, powerful arms to seize and dismember prey, then used their beaks to bite pieces off. Many specimens showed heavier damage on the right side, implying one-sided use of the beak — a form of lateralized behavior that may reflect a more complex nervous system and problem-solving ability than previously assumed for ancient cephalopods.
The finds push our picture of cephalopod evolution and Mesozoic marine ecosystems. Fernando Ángel Fernández‑Álvarez, a zoologist not involved in the study, said the size estimates were surprising. The authors argue that traits such as intelligence, flexible bodies and specialized predatory habits have deep evolutionary roots stretching back into the Cretaceous. While it remains speculative whether these octopuses attacked other large predators, the fossils add to a vivid image of a seafloor crowded with diverse, hungry megafauna.
Beyond the dramatic size estimates, the study highlights how modern imaging and reconstruction techniques can reveal rare soft‑bodied organisms trapped in ancient rock. A handful of well-preserved specimens can therefore reshape our understanding of ancient life: these extinct octopuses appear to have been powerful, specialized predators that played significant ecological roles in Cretaceous oceans.