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Researchers have identified extremely rare fossils of a giant cephalopod that lived in the Cretaceous period and could reach 19 meters, changing theories about the evolution, intelligence, and size of modern octopuses’ ancestors.
According to ScienceDaily, a study led by researchers from Hokkaido University in Japan, published in Science magazine on April 23, 2026, identified jaw fossils of giant octopuses from the Cretaceous Period — between 100 and 72 million years ago — revealing animals with an estimated total length of between 7 and 19 meters. The main species described, Nanaimoteuthis haggarti, was dubbed the “Cretaceous Kraken” by National Geographic — and the nickname is technically justified. At 19 meters long, the animal would be almost as long as a school bus placed three times in a row.
Their jaws show intense wear with scratches, chips, and rounded edges indicating that these animals repeatedly crushed hard prey such as shells and bones. The asymmetry in jaw wear — with the front tip of both species worn down on a single side by up to 10% of the total size — is a sign of lateralized behavior, associated with more sophisticated intelligence.
“These were not just giant octopuses, but giant and intelligent octopuses,” said Yasuhiro Iba, co-author of the study and a paleontologist at Hokkaido University, to Live Science. “Our findings revise the view of the Cretaceous ocean as a world dominated only by large vertebrate predators. They show that giant invertebrates — octopuses — also occupied the top of the food chain.”
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The problem that kept octopuses out of history for decades
The fossil record of octopuses is notoriously scarce for a simple physical reason: their bodies are almost entirely soft. Unlike animals with skeletons, shells, or exoskeletons, a dead octopus leaves very little physical evidence over millions of years.
Octopuses have only one body structure rigid enough to survive the fossilization process: the jaw, made of hardened chitin — the same material that makes up the exoskeletons of insects and crustaceans. It is a small piece relative to the animal’s body, dark in color, easily mistaken for common rock in a superficial analysis.
To identify octopus jaws in rock samples, Hokkaido researchers developed a technique called “digital fossil mining”: high-resolution grinding tomography combined with an artificial intelligence model trained to recognize the specific profile of cephalopod jaws.
With this approach, the team analyzed 15 previously discovered jaws and identified 12 more in rock samples from Japan and Vancouver Island, Canada. The calm ocean floor conditions in these regions during the Cretaceous preserved details that would normally be lost. The result was the discovery of not one, but two species of Nanaimoteuthis — N. jeletzkyi and N. haggarti — with jaws of distinct sizes and morphologies.
Nineteen meters and bone-crushing jaws
To estimate the total length of the animals from only the preserved jaws, researchers used established proportions between jaw and body length of modern finned octopuses — such as the deep-sea Dumbo octopus.
The calculations produced a broad range: from 7 to 19 meters in total length. The Natural History Museum of London, commenting on the study, highlighted that even the lower end of this range would represent a gigantic animal — and that the upper end would place Nanaimoteuthis haggarti as potentially the largest invertebrate ever described in paleontological history. The museum’s senior curator of fossil cephalopods, Zoe Hughes, summarized the surprise of the discovery: “Most Cretaceous octopuses I know are the size of my hand, but this one is much bigger!”
The jaws show extensive wear that tells the story of what these animals ate. Scratches, chips, and progressively rounded edges from intense use indicate that Nanaimoteuthis regularly crushed prey with hard shells and bones — not as occasional opportunism, but as a systematic feeding strategy.
The study suggests that fish, mollusks, and potentially other shelled invertebrates were on the menu. And the evidence of lateralized behavior — consistently using a specific side of the jaw — is the same characteristic that in modern octopuses is associated with problem-solving and long-term memory.
The Cretaceous ocean that paleontology didn’t see
For decades, the paleontological narrative of the Cretaceous ocean was dominated by vertebrates: mosasaurs with serrated teeth like the 18-meter Mosasaurus hoffmannii, long-necked plesiosaurs like the over 10-meter Elasmosaurus, thick-enameled sharks, and giant fish. Invertebrates were classified as prey, not predators.
The discovery of Nanaimoteuthis directly challenges this narrative. With a potential length of 19 meters — comparable to Mosasaurus hoffmannii —, jaws with active predator wear, and evidence of behavioral intelligence, the animal repositions cephalopods at the top of the Cretaceous food chain alongside vertebrates, not below them. “This indicates that Cretaceous marine ecosystems were more complex and included a wider range of apex predators than previously thought,” Iba told CNN.
Science magazine itself, upon publishing the study, included an editorial perspective that articulates the conceptual shift: “For the past 370 million years, large vertebrates have dominated the apex of the marine food web, while invertebrates served as smaller prey.” The discovery of Nanaimoteuthis reverses this premise for at least one specific period of the Mesozoic.
Why the Kraken legend has a 19-meter real basis
The Kraken is a creature from Scandinavian folklore — a sea monster capable of sinking ships with its tentacles, described in 13th-century Norwegian texts and immortalized by poets and explorers throughout the centuries. Scientists always assumed the legend was an exaggeration based on sightings of giant or colossal squids, which reach a maximum of 13 meters.
National Geographic was direct in calling Nanaimoteuthis haggarti the “Cretaceous Kraken” — and the connection is not just metaphorical. The animal existed long before human emergence, so it could not be the direct source of medieval Scandinavian legends. But the confirmed existence of 19-meter octopuses as apex predators in prehistoric oceans retrospectively transforms the Kraken from pure fantasy into a documented evolutionary possibility.
If it existed once, the biological mechanism that allows a cephalopod to reach such proportions exists. The question paleontologists are now asking is whether more recent versions existed — in Paleogene or Neogene oceans — that the scarcity of the cephalopod fossil record simply did not preserve.
Evolutionary convergence: how octopuses and vertebrates arrived at the same result
One of the most technically fascinating aspects of the study published in Science is the conclusion about evolutionary convergence — the process by which completely different lineages arrive at similar solutions to the same ecological challenges.
The authors documented that powerful jaws and loss of external skeleton convergently transformed cephalopods and marine vertebrates into enormous and intelligent predators. In other words: octopuses and large marine reptiles reached the top of the food chain through completely distinct evolutionary paths, but using similar functional strategies — large body, ability to process hard prey, intelligent hunting behavior.
The loss of the external skeleton — which octopus ancestors had, and which was lost over evolution — is paradoxically what allowed the body of Nanaimoteuthis to grow without the restriction that a shell would impose. Without the weight and rigidity of an exoskeleton, the soft body could expand to proportions that a shelled mollusk would never achieve. It was the same evolutionary liberation that allowed whales to reach 30 meters and marine reptiles to reach 18 meters — and which apparently also worked for Cretaceous cephalopods.
What still needs to be understood
The Hokkaido study established that Nanaimoteuthis existed, was enormous, and was intelligent. What is still unclear is how these animals competed or shared the ocean with the large marine reptiles that surrounded them.
The preserved jaws show wear consistent with shell and bone prey, but without access to stomach contents — impossible to fossilize — it’s not possible to confirm if Nanaimoteuthis hunted mosasaurs and plesiosaurs, or if it shared the ocean by eating smaller prey and avoiding confrontation with the giant vertebrates.
Live Science was cautious in reproducing the opinion of experts external to the study: “There is no doubt that Nanaimoteuthis was a huge and efficient predator, but focusing only on the maximum size makes one forget that it is conceivable that they did not reach ten meters” — the lower limit of the calculated range.
What the study definitively establishes is that the Cretaceous ocean was more complex than paleontology recognized. And that the next discovery of cephalopod jaws in rock samples from other geological periods — using the same digital tomography and AI techniques from Hokkaido — may reveal that animals from the Nanaimoteuthis lineage survived the asteroid that extinguished the dinosaurs and continued to swim in seas that humans never got to know.
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