A hundred million years ago in the late Cretaceous, oceans teemed with enormous predators: mosasaurs, large sharks and — researchers now report — colossal octopuses. In a paper published in Science, scientists describe remnants of two extinct octopus species preserved inside large seafloor rocks (concretions) from what is now northern Japan. Using digital fossil‑mining and 3D reconstruction aided by an AI model, they revealed hardened octopus jaws that indicate animals with arm spans up to about 60 feet — rivaling other apex predators of the era and evoking the Kraken of legend.
Octopuses are mostly soft tissue, so they rarely fossilize. But the beak‑like jaws are chitinous and can be preserved. Lead author Yasuhiro Iba of Hokkaido University and coauthor Jörg Mutterlose examined concretions by slicing them thinly, photographing fossil-bearing layers and digitally rebuilding the material. Inside, they found unusually large lower and upper jaws — the biggest ever recorded for an octopus. From jaw size and comparisons with living species, the team estimated truly gigantic body sizes, far exceeding the modern giant Pacific octopus, whose arm span often tops about 13 feet.
The jaws also carried numerous chips and scratches consistent with crushing hard‑shelled prey: shrimp, lobsters, bivalves and nautilus‑like animals. These wear patterns suggest the animals actively tore apart captured prey with their long, powerful arms and then used their beaks to bite pieces off. The damage was greater on the right side of many specimens, hinting at single‑sided usage. Mutterlose says this lateralized wear could indicate an already well‑developed brain and behavioral lateralization — early signs of the intelligence octopuses display today.
The discovery pushes back our knowledge of cephalopod evolution and ecology. “I wasn’t expecting any octopus of this magnitude at all,” says Fernando Ángel Fernández‑Álvarez, a zoologist not involved in the study. Iba adds that traits such as intelligence, flexibility and specialized predatory behavior may have deep evolutionary roots extending into the Cretaceous. While the idea that these octopuses might have preyed on other large predators remains speculative, the fossils do paint a vivid picture of a Cretaceous seascape crowded with diverse, hungry megafauna.
The study demonstrates how modern imaging and reconstruction techniques can reveal rare soft‑bodied organisms trapped in ancient rocks, and how a few key specimens can illuminate evolutionary history and past ecosystems. The authors say their findings suggest ancient octopuses were already remarkable predators with ecological roles and behaviors that helped shape marine communities 100 million years ago.