A hundred million years ago, during the late Cretaceous, oceans teemed with giant predators: mosasaurs, large sharks — and, researchers now report, colossal octopuses. A study in Science presents evidence for extinct octopuses that may be the largest invertebrates ever described. Remnants recovered from large seafloor concretions in what is now northern Japan suggest animals with arm spans that could have reached roughly 60 feet, rivaling other apex predators of the time and evoking legends of the Kraken.
Octopus bodies are almost entirely soft tissue, so they rarely fossilize. But their jaws — hard, beak-like structures composed of an upper and a shovel-shaped lower jaw — can preserve. More than a decade ago, paleontologist Yasuhiro Iba and colleagues targeted concretions formed about 100 million years ago, slicing them into thin sections, photographing preserved material, and producing 3D reconstructions using an AI-assisted digital fossil-mining workflow. Inside, they found unusually large octopus jaws.
These lower jaws are the largest ever recovered for an octopus, and by comparing jaw form and size to modern relatives, the team estimated body dimensions far exceeding living species such as the giant Pacific octopus (whose arm span often exceeds roughly 13 feet). Close study of the jaws revealed numerous chips and scratches consistent with crushing and consuming hard-shelled prey — shrimp, lobsters, bivalves and nautilus-like animals. The wear patterns indicate active carnivory, with the animals using long arms to capture prey and the beak to tear it into pieces.
Notably, the right side of the jaws showed more wear than the left, suggesting a single-sided preference in feeding. Such lateralized use may imply a relatively advanced brain organization, hinting that cognitive and behavioral specializations seen in modern octopuses have deep evolutionary roots.
Researchers say these findings reshape views of Cretaceous marine ecosystems, adding giant, intelligent invertebrate predators to a seascape already dominated by large reptiles and fishes. The study underscores how a few well-preserved hard parts, revealed through modern imaging and reconstruction methods, can illuminate the lives and ecological roles of otherwise fleeting soft-bodied organisms.