Modern octopuses are known for their intelligence and flexibility, allowing them to squeeze through tight spaces, hide behind rocky reefs, and drift through deep water. But new research suggests that their distant ancestors lived very differently. Scientists now believe that early octopuses were not quiet, elusive creatures, but gigantic predators that hunted at the top of the marine food chain alongside larger vertebrates. The study, led by researchers at Hokkaido University, science April 23, 2026.
Tracing the origins of octopuses has long been difficult because their soft bodies rarely fossilize. Unlike animals with bones and shells, they leave little physical evidence behind. To overcome this, researchers focused on the fossilized jaw, a part of the body likely to survive millions of years, and uncovered clues about its early evolution.
Using a combination of high-resolution grinding tomography and artificial intelligence models, the researchers discovered the jaw fossil embedded in a rock sample from the Late Cretaceous Period, 100 million to 72 million years old. These fossils were recovered from locations in Japan and Vancouver Island, where mild ocean floor conditions helped preserve delicate details. Fine wear marks on the jaws provided valuable insight into how these ancient animals fed.
Strong evidence of looting
The fossil belonged to an extinct group of flattened octopuses known as Shirata. By studying the size, shape, and surface wear of their jaws, researchers determined that these animals were active hunters capable of crushing hard prey with a powerful bite.
“Our findings suggest that the earliest octopuses were giant predators that occupied the top of the marine food chain during the Cretaceous period,” said Professor Yasuhiro Iba of Hokkaido University. “Based on very well-preserved jaw fossils, we now know that these animals may have reached up to nearly 20 meters in total length, exceeding the size of contemporary large marine reptiles.”
“The most surprising finding was probably the degree of wear on the jaws,” Iva said. The fossil’s jaw showed extensive chipping, scratches, cracks, and polishing, all evidence of strong bite forces. “In well-grown specimens, up to 10% of the jaw tips were worn down relative to the total jaw length, which was greater than that seen in modern cephalopods that feed on hard-shelled prey. This indicates repeated and strong interactions with prey and reveals an unexpectedly aggressive feeding strategy.” These observations point to a highly active predator that regularly preys on tough and abundant prey.
Tracing the origin of the octopus
This discovery significantly changed scientists’ thinking about the evolution of early octopuses. The fossil extends the earliest known record of the long-finned octopus by about 15 million years and pushes back the age of the broader octopus by about 5 million years. This puts their origin at about 100 million years ago.
Another striking detail is the uneven wear pattern on the jaws. In the two species studied, one side of the occlusal surface wore more than the other. This suggests that the animals may have engaged in a behavior known as lateralization, in which they preferred one side of the jaw. In modern animals, lateralization is associated with advanced brain function. This finding raises the possibility that even these early octopuses exhibited behaviors associated with complex intelligence.
Rethinking the ancient marine food chain
Scientists have long observed that ancient marine ecosystems were dominated by vertebrate predators, with invertebrates playing a smaller role. This study challenges that assumption. 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 can evolve into large, intelligent apex predators in an ecosystem that has been dominated by vertebrates for about 400 million years. Our findings show that strong jaws and the loss of the superficial skeleton, common characteristics of octopuses and marine vertebrates, were essential for becoming large, intelligent marine predators,” Professor Iba said.
Unraveling ancient ecosystems with AI
The study also highlights the potential of combining digital fossil mining technology with artificial intelligence. This approach could help scientists discover even more hidden fossils and reconstruct ancient ecosystems in far more detail than before.
