The jaw tips were worn down by as much as 10% of their length. That detail, more than any size estimate, is what convinced a Hokkaido University team that the earliest octopuses were not timid creatures hiding in reefs.
Their paper appeared in Science on April 23, 2026. It describes fossil jaws from the Late Cretaceous, between 100 and 72 million years ago, found in rock from Japan and Vancouver Island. Calm seafloor conditions at those sites kept fine detail intact. The animals belonged to Cirrata, an extinct group of finned octopuses.
Finding a soft animal in stone
Octopuses are a paleontologist’s headache. Without bones or shells, they almost never fossilize, so the team went after the one hard part they have: the jaws. The researchers used high-resolution grinding tomography, paired with an artificial intelligence model, to pick jaws out of rock samples. Size, shape and surface wear then told them how the animals lived.
The verdict was blunt. These were active hunters that cracked hard prey with strong bites. Professor Yasuhiro Iba of Hokkaido University said the animals “reached total lengths of up to nearly 20 meters, which may have surpassed the size of large marine reptiles of the same age.”
What the wear says
The jaws showed chipping, scratching, cracking and polishing. Iba called the amount of damage the most surprising result. “In well-grown specimens, up to 10% of the jaw tip relative to the total jaw length had been worn away, which is larger than that seen in modern cephalopods that feed on hard-shelled prey,” he said, adding that this “indicates repeated, forceful interactions with their prey, revealing an unexpectedly aggressive feeding strategy.”
There was a second clue. In both species studied, one side of the biting surface was more worn than the other, which suggests the animals favoured one side of the jaw. Biologists call that lateralization, and in living animals it goes with advanced brain function. The team treats it as a hint that these octopuses may have behaved intelligently, though a worn jaw is hardly a brain scan.
A longer family tree
The fossils push the earliest known finned octopuses back by about 15 million years. The wider octopus record moves back by around 5 million years, to roughly 100 million years ago.
They also cut against a long-held picture of ancient seas, in which vertebrate predators ran the show and invertebrates played small parts. Giant octopuses, the evidence suggests, climbed to the top of the food web and competed head to head with large vertebrates.
Iba put it more strongly: “This study provides the first direct evidence that invertebrates could evolve into giant, intelligent apex predators in ecosystems that have been dominated by vertebrates for about 400 million years.” In his view, powerful jaws and the loss of superficial skeletons were what made it possible to grow that large.
The method may travel further than the octopuses. Scanning rock digitally and letting a model flag fossils could turn up many more hidden specimens, and the team says it could allow far more detailed reconstructions of ancient ecosystems.
