Massive, soft-bodied cephalopods up to 19 m (62 feet) long rivaled — and perhaps hunted — the ocean’s fiercest reptiles in the Cretaceous period, according to new research led by Hokkaido University paleontologists.
An artist’s impression of an ancient giant octopus. Image credit: Yohei Utsuki, Hokkaido University.
For hundreds of millions of years, marine ecosystems were thought to be dominated by large vertebrate apex predators. Invertebrates served as smaller prey.
However, unlike shelled invertebrates, octopuses followed a unique evolutionary trajectory.
Instead of protective shells, these creatures evolved soft-bodies, which gave them unprecedented mobility, vision, and intelligence.
Some of these species grew to enormous sizes, too, and have functioned as top-tier predators, yet their precise ecological role has remained uncertain due to limited fossil evidence.
“Our findings suggest that the earliest octopuses were gigantic predators that occupied the top of the marine food chain in the Cretaceous,” said Professor Yasuhiro Iba, a paleontologist at Hokkaido University.
“Based on exceptionally well-preserved fossil jaws, we show that these animals reached total lengths of up to nearly 19 m, 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.”
Produced when biting into hard prey, wear on the jaw leaves characteristic damage similar to the damage seen in modern shell-crushing cephalopods. Measurements of an octopus jaw can also be used to estimate their overall body size.
In their study, Professor Iba and colleagues identified clear signs of wear on 15 large fossil jaws of ancient octopus relatives previously reported from Cretaceous sediments of Japan and Vancouver Island.
Additionally, they discovered 12 jaws of finned octopuses from Cretaceous rocks of Japan through the digital fossil-mining method.
In analyzing these new specimens, they identified two main species: Nanaimoteuthis jeletzkyi and Nanaimoteuthis haggarti.
These finned octopuses, Nanaimoteuthis haggarti in particular, grew to exceptional sizes, ranging from 7 to 19 m (23-62 feet), rivaling the size of contemporaneous giant marine reptiles and potentially representing the largest invertebrates currently described.
Moreover, in the largest individuals, the jaws showed extensive wear, with once-sharp features in small juveniles becoming blunted and rounded over time.
The wear patterns suggest that these creatures were active carnivores that routinely crushed hard shells and bones with powerful bites.
They used their long, flexible arms to seize prey while dismantling it with their strong beaks, a behavior that has been linked to advanced intelligence.
“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,” Professor Iba said.
“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.”
The findings were published online April 23, 2026 in the journal Science.
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Shin Ikegami et al. 2026. Earliest octopuses were giant top predators in Cretaceous oceans. Science 392 (6796): 406-410; doi: 10.1126/science.aea6285
