Giant octopuses may have ruled the oceans 100 million years ago

Tracing the origins of octopuses has long been difficult because their soft bodies rarely fossilize. Unlike animals with bones or shells, they leave behind very little physical evidence. To overcome this, researchers focused on fossilized jaws, a part of the body more likely to survive over millions of years, to uncover clues about their early evolution.

Using high-resolution grinding tomography along with an artificial intelligence model, the team discovered fossil jaws embedded within rock samples dating from the Late Cretaceous period, between 100 and 72 million years ago. These fossils were recovered from sites in Japan and Vancouver Island, where calm seafloor conditions helped preserve delicate details. Fine wear marks on the jaws provided valuable insight into how these ancient animals fed.

Evidence of Powerful Predatory Behavior

The fossils belonged to an extinct group of finned octopuses known as Cirrata. By studying the size, shape, and surface wear of the jaws, researchers determined that these animals were active hunters capable of crushing hard prey with strong bites.

"Our findings suggest that the earliest octopuses were gigantic predators that occupied the top of the marine food chain in the Cretaceous," says Professor Yasuhiro Iba of Hokkaido University. "Based on exceptionally well-preserved fossil jaws, we show that these animals reached total lengths of up to nearly 20 meters, which may have surpassed the size of large marine reptiles of the same age."

"The most surprising finding perhaps was the extent of wear on the jaws," says Iba. The fossil jaws showed extensive chipping, scratching, cracking, and polishing, all signs of a strong biting force. "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. This indicates repeated, forceful interactions with their prey, revealing an unexpectedly aggressive feeding strategy." These observations point to highly active predators that regularly consumed tough, abundant prey.

Pushing Back the Origins of Octopuses

This discovery significantly reshapes what scientists thought about early octopus evolution. The fossils extend the earliest known record of finned octopuses by about 15 million years and push back the broader octopus timeline by around 5 million years. This places their origins at roughly 100 million years ago.

Another striking detail came from uneven wear patterns on the jaws. In the two species studied, one side of the biting surface showed more wear than the other. This suggests the animals may have favored one side of their jaws, a behavior known as lateralization. In modern animals, lateralization is linked to advanced brain function. The findings raise the possibility that even these early octopuses exhibited complex, intelligence-related behavior.

Rethinking Ancient Ocean Food Chains

For many years, scientists have viewed ancient marine ecosystems as being dominated by vertebrate predators, with invertebrates playing smaller roles. This research challenges that assumption. The evidence suggests that giant octopuses were an exception, rising to the top levels of the food web and competing directly with large vertebrates.

"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. Our findings show that powerful jaws and the loss of superficial skeletons, common characteristics of octopuses and marine vertebrates, were essential to becoming huge, intelligent marine predators," says Iba.

Unlocking Ancient Ecosystems With AI

The study also highlights the potential of combining digital fossil-mining techniques with artificial intelligence. This approach could help scientists uncover many more hidden fossils and reconstruct ancient ecosystems in far greater detail than before.