The largest predators in Earth’s oceans are typically vertebrates, so when palaeontologists recently announced they’d found fossils from a 19m-long octopus that lived during the Late Cretaceous, it’s no surprise a lot of people were left scratching their heads.
What is Nanaimoteuthis haggarti?
This colossal cephalopod is perhaps the closest palaeontologists have ever got to finding a real-life kraken.
How big was Nanaimoteuthis haggarti?
At approximately 19m in length, it’s not only the largest octopus that ever lived, but perhaps the largest underwater predator from the Late Cretaceous; larger even than Mosasaurus hoffmani, a 17m-long marine reptile that was long considered the apex predator of the period.
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Such large estimates also make N.haggarti the largest non-colonial invertebrate ever discovered. The largest known prior to N.haggarti’s discovery were the 3m-long millipede ancestor Arthropleura and the 2.5m-long predatory sea scorpion Jaeklopterus.
Today, the title of ‘largest non-colonial invertebrate’ is held by the enigmatic colossal squid (Mesonychoteuthis hamiltoni), a distant relative of N.haggarti that can reportedly grow up to 14m in length - though the largest ever, officially recorded complete specimen only measured 4.2m.
What group does this giant octopus belong to?
N.haggarti belongs to a genus of extinct octopuses that was first described in 2008 following the discovery of a smaller (but still relatively large) species known as Nanaimoteuthis jeletzkyi. This close relative was originally estimated to have reached sizes of 1.1m, but according to a recent study that re-estimated the size of N.haggarti, it may have grown to lengths of 7.7m.
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Both N.haggarti and N.heletzkyi are what’s known as cirrate octopuses. This group is distinguished from other octopuses by having small, internal shells and two fins on their heads, which they use to swim. They’re also exclusively deep-sea creatures, living at depths in excess of 300m and sometimes as deep as several thousand metres!
Nanaimoteuthis is the oldest known member of this group and therefore a long-lost ancestor of several living, ridiculously cute species such as the dumbo octopus, the flapjack octopus, and the big-finned jellyhead octopus - seriously, check out photos of these deepsea critters, they’re amongst the cutest animals on Earth.
How was this giant octopus discovered?
While N.haggarti has made the headlines in recent weeks, the species was actually discovered in 2008 and at the same time as N.jeletzkyi.
It was originally named Paleocirroteuthis haggarti based on the discovery of two partial lower jaws from rocks belonging to the 84-million-year-old Haslam Formation on Vancouver Island, Canada. At the time they were discovered, both N.jeletzkyi and P.haggarti were considered vampire squid based on the size and shape of their jaws.
After recently re-examining more than a dozen fossil jaws previously found on Vancouver Island, as well as in Hokkaido, Japan, researchers identified a giant, exceptionally well-preserved specimen. This specimen allowed them to revise Paleocirroteuthis haggarti, re-assign it to Nanaimoteuthis, and identify the genus as a type of octopus, rather than a vampire squid.
As well as revising the taxonomy of this giant octopus, researchers were able to use this newly identified, well-preserved specimen to re-estimate its size. They did this by studying the relationships between jaw size, head size, and body size in living octopuses, which led them to their new, jaw-dropping estimates of 7-19m.
Even the lowest estimates place N.haggarti in a similar size bracket to the colossal squid and make it nearly twice the size of the Giant Pacific Octopus (Enteroctopus dofleini) - the largest species of octopus alive today, measuring 5m across when stretching its arms.
Where did this giant octopus live?
Based on where specimens of N.haggarti and N.jeletzkyi have been found - Vancouver Island, Canada, and Hokkaido, Japan - researchers believe these giant octopuses inhabited the North Pacific Ocean.
The smaller of the two species of Nanaimoteuthis, N.jeletzkyi, lived from 100 to 72 million years ago, while the larger, N.haggarti, lived for a much shorter period roughly 84 million years ago.
As cirrate octopuses, it’s believed both N.haggarti and N.jeletzkyi inhabited deep waters, though perhaps not quite as deep as many of their living relatives. The cutest of Nanaimoteuthis’ relatives, the dumbo octopus, has been sighted at depths exceeding 7,000m!
It’s unknown exactly how deep these giant octopuses would have ventured; researchers think they stuck primarily to the shelf seas of the circum-North Pacific, which was the largest ocean during the Late Cretaceous. The mean depth of the Pacific Ocean today is 4,000m.
What did this giant octopus eat?
Most living octopuses are carnivorous, consuming a variety of soft and hard prey. Their diets consist mainly of crustaceans, shelled molluscs, and bony fishes, though they are also known to eat cephalopods, including squid, cuttlefish, and even other octopuses!
The act of feeding on hard prey creates identifiable patterns of wear on the mouthparts of octopuses. From studying these patterns on extant octopuses and comparing them to patterns seen on specimens of N.haggarti and N.jeletzkyi, researchers have been able to work out that these giant, extinct octopuses ate more hard-shelled animals than their living relatives.
Hard, coil-shelled cephalopods known as ammonites were some of the most abundant animals in Late Cretaceous oceans. These iconic invertebrates were preyed on by mosasaurs, pliosaurs, plesiosaurs, ichthyosaurs, and - if the latest research is anything to go off - giant octopuses as well.
During their research, the authors of the latest study on N.haggarti also spotted long scratches distributed on wide areas of the jaw, which they believe reflects “the dynamic use of the entire jaw for dismantling prey.” This kind of behaviour in cephalopods has been linked to highly developed brains and increased levels of cognition, suggesting this boneless behemoth was not only giant, but devilishly smart too.
Did anything prey on this giant octopus?
It’s likely only the largest predators of the period could have taken on a fully-grown N.haggarti - and even then they might have gotten more than they bargained for, soon finding themselves as dinner for the ‘Kraken of the Cretaceous’.
N.jeletzkyi, on the other hand, may have been targeted by lots of different predators, due to its smaller size. Based on the preserved stomach contents of mosasaurs and other marine reptiles, we know they had a particular taste for cephalopods; though it’s uncertain whether they dined on N.jeletzkyi specifically.
While N.haggarti may have been depicted warring with, and even consuming, mosasaurs, it seems unlikely the two predators would have ever met. N.haggarti was most likely a deep-dwelling octopus, while mosasaurs were primarily shallow-water marine reptiles that needed to stay near the surface where they could breathe atmospheric air.
That said, sperm whales (air-breathing marine mammals) are capable of holding their breath for more than two hours as they dive to depths of more than 3,000m to hunt giant and colossal squid - it’s not beyond the realms of imagination to think some mosasaurs might have been able to do the same.
Was this giant octopus really that big?
Not everyone has accepted the jaw-dropping estimated lengths proposed by this latest study on N.haggarti, published April 23rd, 2026, in the journal Science.
Craig R. McClain, an animal body size expert at Duke University in Durham, USA, suggested in a recent post on Blueskythat lengths of 7-19m may be overestimated.
“I know everyone wants there to be a Giant Cretaceous Octopus but after looking at methods and tables, I really don’t think this is a reality,” wrote McClain shortly after the release of the latest study.
Other researchers have pointed out that determining body size in cephalopods from their jaws alone is very species dependent, suggesting that deriving size estimates of extinct species from extant species is fraught with problems.
When did octopuses evolve?
The evolutionary history of octopuses has puzzled palaeontologists for centuries. Just recently, a 300-million-year-old fossil thought to be the world’s oldest octopus was re-identified as a long-lost relative of modern nautiluses.
Using the latest synchrotron imaging techniques, the University of Reading’s Thomas Clements examined the controversial fossil and found evidence of a ribbon-like feeding structure (known as a radula) that had 11 tooth-like elements per row. Since octopuses only have seven or nine, this ruled them out of his prehistoric lineup.
Instead, the tooth-like elements matched those of a fossil nautiloid known as Paleocadmus pohli, which was already known from the same site where the supposed ‘oldest octopus fossil’ was found.
Like octopuses, nautiluses are cephalopods - themselves a group of derived molluscs. These exclusively marine animals are characterised by a prominent head and a set of arms (or tentacles) modified from the primitive foot of their molluscan ancestors. Based on fossil evidence, they emerged in the Cambrian roughly 530 million years ago.
However, it wasn’t until nearly 400 million years later, in the Middle Jurassic (approximately 155 million years ago), that octopuses finally appeared. This makes N.jeletzyki and N.haggarti some of the earliest octopuses, as well as some of the largest.
It’s thought octopuses evolved from hard-shelled, squid-like ancestors that ultimately lost their shells. As other cephalopods, such as ammonites, evolved larger (and harder) shells in response to the emergence of more diverse predators during the Mesozoic Marine Revolution, octopuses decided to do the opposite, losing their shells in order to become more agile.
The loss of their protective shells is believed to be a key factor in the evolution of higher intelligence in octopuses. That’s not to say that other, hard-shelled cephalopods aren’t smart though; cuttlefish have solved many of the same human-set puzzles octopuses have and are known to communicate using skin colour/pattern changes, as well as their own form of sign language!
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Top image: A sketch of the giant octopus. (Image: Yohei Utsuki, Department of Earth and Planetary Sciences, Hokkaido University)
