Giant Octopuses May Have Ruled the Oceans 100 Million Years Ago

New research suggests that ancient octopuses were not the shy, soft-bodied creatures often imagined, but massive apex predators that ruled the oceans during the age of dinosaurs. Scientists from Hokkaido University in Japan have uncovered exquisitely preserved fossil jaws dating back to the Late Cretaceous period, between 100 and 72 million years ago, revealing that early octopuses may have grown up to 20 meters in length and possessed powerful bites capable of crushing hard shells and skeletons.

The study, published in Science on April 23, 2026, overcomes a long-standing challenge in paleontology: the rarity of octopus fossils due to their soft bodies, which rarely fossilize. By focusing on fossilized jaws—more likely to survive over millions of years—and using high-resolution grinding tomography combined with an artificial intelligence model, researchers identified these remains embedded in rock samples. This innovative approach allowed them to reconstruct the size and predatory capabilities of these ancient cephalopods.

Analysis of the fossil jaws indicates uneven wear patterns from left to right, suggesting the animals may have favored one side when feeding—a trait linked in living animals to advanced brain function. This finding supports the hypothesis that these prehistoric octopuses were not only large but also behaviorally complex, potentially exhibiting lateralized feeding behaviors similar to those seen in modern vertebrates and some invertebrates.

While today’s octopuses are known for their intelligence, flexibility, and ability to hide in reefs or drift through deep waters, their ancient ancestors appear to have occupied a very different ecological niche. Rather than being elusive drifters, they were likely active hunters at the top of the marine food chain, preying on large fish and marine reptiles. The study estimates a body length of 1.5 to 4.5 meters, which, when combined with long arms, results in a total length of roughly 7 to 19 meters—making them potentially the largest invertebrates ever known to science.

This research reshapes the understanding of cephalopod evolution, challenging the long-held assumption that invertebrates like octopuses and squid played only supporting roles in ancient oceans. Instead, it positions early octopuses as formidable predators that coexisted with dinosaurs and may have competed with vertebrate apex predators such as mosasaurs and plesiosaurs. The findings open new avenues for exploring how intelligence and predatory behavior evolved in soft-bodied marine animals over geological time.