About 100 million years ago, during the late Cretaceous, the seas were home to more than mosasaurs and huge sharks. A new study in Science describes fossil evidence that suggests colossal octopuses swam those ancient waters — animals that may rank among the largest invertebrates ever known and that help explain some of the kraken legends.
Octopus bodies are almost entirely soft tissue and rarely fossilize, but their hard, beak-like jaws can survive. Paleontologist Yasuhiro Iba and colleagues examined large seafloor concretions from what is now northern Japan. By slicing the concretions into thin sections, photographing preserved material, and building 3D reconstructions using an AI-assisted digital fossil-mining workflow, the team revealed unusually large octopus jaws embedded in the rock.
The lower jaws they recovered are the largest known for any octopus. By comparing jaw shape and size with living relatives, the researchers estimated arm spans that could have approached roughly 60 feet, far exceeding modern giants like the giant Pacific octopus, whose arms typically reach about 13 feet. If the estimates hold, these animals would have been top invertebrate predators in Cretaceous seas.
Microscopic examination of the jaws showed chips and scratches consistent with crushing and eating hard-shelled prey: shrimp and lobsters, bivalves, and nautilus-like cephalopods. The wear patterns suggest active carnivory, with long arms used to seize prey and the powerful beak to slice and crush it into pieces.
Interestingly, the right side of the jaws showed more wear than the left, implying a feeding bias toward one side. That lateralized use mirrors handedness or side preferences seen in some living octopuses and hints at complex neural and behavioral specializations deep in cephalopod evolution.
These finds change how we picture Cretaceous marine ecosystems by adding giant, behaviorally sophisticated invertebrate predators to a seascape already dominated by large reptiles and fishes. They also demonstrate how a few well-preserved hard parts, revealed with modern imaging and reconstruction methods, can illuminate the lives of otherwise ephemeral soft-bodied animals.