Ancient Octopuses Were Much Larger Than Previously Thought

The fossil record for cephalopods, which include octopuses and squids, is inconsistent, unlike the well-preserved remains of their spiral-shelled relatives like nautiloids and ammonites.

Soft-bodied organisms pose a challenge for fossilization because their tissues usually decompose rapidly before the long process of mineralization can begin. The most commonly preserved parts are chitinous jaw-like beaks and internal gladii structures.

Prior estimates suggested that ancient octopuses were similar in size to modern giant squids, but a 2026 study employing advanced imaging technology found this to be incorrect.

Researchers analyzed 15 large fossilized jaws from Hokkaido, Japan, and Vancouver Island, Canada, discovering that these ancient cephalopods were significantly larger, potentially the biggest in Earth's history.

Researchers utilized a meticulous layered photography technique on rock samples extracted from Hokkaido, carefully documenting each newly exposed layer.

An artificial intelligence model was then developed to integrate these two-dimensional photographs, constructing accurate three-dimensional images of the delicate fossils hidden within the rock matrix.

Nanaimoteuthis, previously identified as a relative of the vampire squid, was re-evaluated in the new study based on distinct features of its jaws.

These new anatomical insights link Nanaimoteuthis to the Cirrata group, also known as finned octopuses, indicating that these ancient octopuses had longer bodies compared to their modern descendants.

The smaller of the two species, Nanaimoteuthis jeletzkyi, had jaws suggesting a mantle length exceeding half a meter, possibly approaching two meters, and a total body length of up to 7.5 meters including its arms.

For comparison, North Pacific giant octopuses have a maximum arm span of 6 meters. The jaws of Nanaimoteuthis haggarti were up to 50% larger than those of modern giant squids, with an estimated total body length ranging from 6.6 to an astounding 18.6 meters.

Researchers face significant challenges in observing deep-sea giants, as modern giant squids—the longest living invertebrates—and colossal squids—the heaviest, reaching nearly 500 kilograms—were not captured on live film until 2005.

Modern giant cephalopods, like giant squid, consume a varied diet including fish, crustaceans, and other squid, indicating their position at the top of their food webs.

Studies on nitrogen isotopes in their tissues confirm this high trophic level, although large sharks and sperm whales are known to occasionally prey on them.

Feeding wear accounts for as much as 10% of the jaw length in Nanaimoteuthis, while massive arm structures and powerful muscles point to a predator capable of consuming mosasaurs and plesiosaurs.

Evidence of up to 10% jaw length loss due to feeding wear indicates a powerful bite, and the massive arm structure combined with strong jaw muscles imply they were capable of preying on large marine reptiles like mosasaurs and plesiosaurs.

Nanaimoteuthis jeletzkyi, dating back 100 million years, is now confirmed as the oldest known octopus fossil, which significantly revises the previous understanding of octopus evolution.

A 2026 X-ray study re-identified Pohlsepia mazonensis, previously believed to be a 300-million-year-old octopus, as a nautiloid, specifically Paleocadmus, resolving a long-standing point of confusion.

Signs of decomposition in the fossilized tissues of Nanaimoteuthis jeletzkyi suggest the carcass had undergone significant breakdown before being preserved, likely contributing to initial challenges in identification and dating.

Asymmetrical wear patterns found on the jaws of Nanaimoteuthis indicate lateralization, suggesting these ancient krakens favored one side of their jaw while feeding.

Lateralization is a trait frequently associated with higher cognitive functions in animals, implying that Cretaceous octopuses were not only intelligent and versatile but also dangerous apex predators in their marine environment.