In addition to being the Age of Dinosaurs, the Cretaceous Period is famous for  enormous ocean-dwelling beasts – giant sea turtles, massive predatory fish, and mosasaurs that could grow  more than 13 meters long.

But it wasn’t just animals with  backbones growing huge back then. Deep within those same oceans,  there lurked real-life krakens – octopuses that dwarfed any  of their living relatives, big enough to tangle with even the most  immense of their aquatic neighbors.

The biggest octopuses, and maybe the  biggest invertebrates, of all time. The discovery of these sea monsters  is not only just plain awesome – it also changes what we know  about ancient marine food webs, and rewrites the timeline of  squid and octopus evolution. [intro] The fossil record is pretty hot and  cold when it comes to cephalopods – that’s the group that includes octopus and squid. Species with shells are very  well-represented in the fossil record.

This includes the spiral-shelled  nautiloids and ammonites, and the cone-shelled belemnites. Those hard shells make for great fossils. But octopus and squid have mostly done away  with that shell through their evolution, and their squishy bodies tend to rot  away before they can become fossilized.

But these softies do have some hard parts – their beak-like jaws are stiffened with  chitin like the exoskeleton of insects, and some species have small bits  of internal shells called gladii. Often, these resilient structures are  all that survives into the fossil record. It’s not much, but even these scant  remains can reveal unexpected things about ancient ocean life.

During the Late Cretaceous Period, the North Pacific Ocean was home to a  whole bunch of soft-bodied cephalopods. Jaws and gladii from a variety  of ancient squids and octopuses have been discovered in fossil deposits in  Hokkaido, Japan and Vancouver Island, Canada. And some of them were big … like, really big.

Scientists have estimated that the largest ones might have been the size  of modern-day giant squid. But a 2026 study showed that this was wrong. They were actually bigger.

Much bigger. The biggest cephalopods in Earth’s history. That study started by re-examining 15 of   these large fossilized jaws from  Hokkaido and Vancouver Island, ranging from around 100 million  to 72 million years ago.

These included two different species of  an ancient genus called Nanaimoteuthis. The researchers also found a dozen new sets  of jaws using a clever imaging strategy. They carved into some rocks from Hokkaido, photographing each uncovered layer as they went, and then developed an  artificial intelligence model to stitch the photographs together into  three-dimensional images of the fragile fossils that had been hiding within the rock.

The new jaws they uncovered  included one absolute monster – a set of jaws about one-and-a-half  times the size of a giant squid’s jaws. This is our first glimpse at the  enormous kraken of the Cretaceous seas! With only the jaws to go on, figuring out the actual size of this  kraken is tough, but not impossible.

In modern cephalopods, the size of the jaws correlates pretty  well with the size of the mantle – that’s the main part of the  body where all the guts are – and with the total length of the body and arms. But this ratio can vary a bit between  different cephalopod lineages, so first, we need to know just what  sort of cephalopod we’re dealing with. Nanaimoteuthis was originally identified as belonging to a family called Vampyroteuthidae, which includes modern-day vampire squid.

These are small, deep-sea critters with a  cloak of webbing between their eight arms. But the new study identified  features of these jaws that separate them from the vampires, and instead link them to a group called Cirrata, also known as finned octopuses. Broadly speaking, octopuses come in two varieties.

Some are finless, like your classic  blue-ringed and giant Pacific species, and others have fin-like extensions  coming off of their mantles, like the adorable deep-sea Dumbo octopus. Some finned octopus species have elongated bodies, kind of like a squid, while others  have shorter, rounded bodies. Fortunately, body shape also  correlates with the shape of the jaws.

So, just from their jaw anatomy, the researchers could identify Nanaimoteuthis as ancient, long-bodied, finned octopuses. And by examining jaw-to-body ratios  of their closest living relatives, they could estimate the full  size of these Cretaceous krakens. The smaller of the two species  is Nanaimoteuthis jeletzkyi.

Its jaws indicate a mantle more  than half a meter in length and possibly up to almost two meters, and a full body – arms and all – as much as seven-and-a-half meters long. That beats our biggest living octopuses, North Pacific giant octopuses, which can have a total arm span of six meters. However, it’s not nearly on par with giant squid, our largest living cephalopods, whose arms and body can stretch  an impressive 12 meters long.

But the second of these fossil species, Nanaimoteuthis haggarti, is truly enormous, with jaws up to 50% larger than giant squid jaws. The researchers estimate its mantle  size ranging between 1.5 and 4.5 meters, with a total body length  between 6.6 and 18.6 meters. That upper size estimate is not  only much longer than giant squid, it also rivals the largest of  the Cretaceous marine reptiles.

Of course, with only the jaws preserved,  its exact size is hard to say for sure. But even the midpoint of that size  estimate makes Nanaimoteuthis haggarti at least the size of a giant squid. This means that while dinosaurs were  stomping around on land and pterosaurs were flying through the skies, the ocean was home to perhaps the  largest octopus that has ever lived.

Inferring the lifestyle of these krakens is tough. We have a hard enough time  understanding the giant cephalopods of our present-day oceans! Giant squid are the largest  living invertebrates by length, and colossal squid are the  largest in terms of weight, reaching up to almost 500 kilograms.

Both species live in cold, deep ocean waters, and both have hardly ever been seen by humans. The first video of a live giant squid  in the wild wasn’t captured until 2005! Needless to say, we have almost zero idea of  what these animals are doing in their day-to-day lives.

But we do know a bit about their diets. Some lucky scientists have had the chance to plunder the stomachs of giant squid and have found the remains  of fish, crustaceans, clams, and even other squid. Others have performed studies  on the nitrogen composition of colossal squid tissues – which can reflect the diet of the animal – and have found that they match the  chemical profile of a top predator.

So both of our modern-day giant cephalopods sit at the top of their respective food webs. Of course, they’re not alone up there – the beaks of giant squids have been found in the bellies of large sharks and sperm whales. We don’t have any stomach  contents for Nanaimoteuthis, but their jaws give us some clues  as to what they were eating.

As an octopus eats, its food  causes wear and tear on its jaws. The jaws of Nanaimoteuthis are  covered in chips and scratches which indicate a diet of hard  foods like shells and bones. In the largest specimens, as much as 10% of the jaw length had been lost due to wear from feeding!

The size of the jaws would seem  to suggest a powerful bite, and this idea is supported by  some proportionately large areas for jaw muscles to attach. With powerful jaws and a bunch of massive arms, the Cretaceous krakens would have been  able to catch and eat fish of all sizes, spiral-shelled ammonites, maybe even other large predators  like mosasaurs and plesiosaurs. And just like today’s giant cephalopods, these krakens might have been on the menu for other big, powerful carnivores in the seas.

Someday, if we’re really lucky, we might find a well-preserved kraken  with food still in its stomach. Until then, we can only make the  scientifically-informed hypothesis that they ate probably whatever they wanted. So, if you were planning on taking a trip  through time to sail the Cretaceous seas … well, maybe don’t.

But there’s more! These aren’t just among the largest octopuses, they’re also among the earliest. Fossils of the smaller species, Nanaimoteuthis jeletzkyi, go  back to 100 million years old, making it the oldest known  octopus in the fossil record.

But we only know that because of a different study that was published literally two  weeks before the kraken paper. See, for a long time, there was a lot of confusion over  the timeline of octopus evolution. That’s because nearly all known octopus fossils were from the Late Cretaceous  or younger … except for one.

Pohlsepia mazonensis was scientifically  described in the year 2000. It comes from the Mazon Creek  fossil beds of Illinois – that’s the same fossil locality as  some other famous ancient invertebrates like the Tully Monster. The fossils at this site are a  little over 300 million years old.

Like other Mazon Creek critters, Pohlsepia was discovered  within a chunk of ironstone, which had preserved its soft body, allowing researchers to get a close look at its mantle, fins, and arms, spotting several features that identified it as an octopus. This was an exciting discovery, but it also presented a conundrum: all other fossil octopuses were  under 100 million years old, but this one is more than three times that age! This implied a long “evolutionary fuse” – basically, that octopuses evolved way early on, but remained a relatively minor  component of aquatic ecosystems until a burst of diversity occurred  during the Cretaceous Period.

It wouldn’t be the first such  case in the fossil record, but there were still debates around some  of Pohlsepia’s supposed octopus features. So, hoping to resolve the issue, a 2026 study did a detailed  X-ray scan of the fossil. Deep within the sediment, hidden  from paleontologists previously, the study found a radula - a tongue-like structure found in  mollusks like snails and octopuses.

But the anatomy of the radula doesn’t match what we see in octopus, or squid … instead, Pohlsepia is a nautiloid. Nautiloids are a very ancient  group of shelled cephalopods. Today, their only living representatives  are the rare and mysterious nautiluses, but they were much more common in the past. 300 million years old is a very  reasonable time period to find nautiloids.

In fact, those hidden internal features revealed that Pohlsepia is the same as an  already-known Mazon Creek nautiloid named Paleocadmus! The original misidentification of Pohlsepia can be blamed in part on  the condition of the fossil. The 2026 study identified signs of  decomposition in the fossilized tissues, suggesting that the carcass  had broken down a bunch before becoming sealed away in iron.

That process of decomposition had  separated the body from its shell and had obscured some of the  characteristic nautiloid soft tissues. So, with Pohlsepia reclassified, it’s likely that octopuses didn’t evolve  until close to the Cretaceous Period, and it leaves Nanaimoteuthis  as the current record-holder for oldest known fossil octopus. It seems octopuses wasted little time  evolving into gigantic apex predators.

Oh, and they were probably smart, too. Modern octopuses are famously intelligent, great at solving puzzles and  escaping their enclosures – just ask anyone who’s ever  worked with one at an aquarium. Now, estimating the intelligence of an  extinct species is just about impossible, but the jaws of Nanaimoteuthis do  hold one more little surprise – the feeding damage is asymmetrical.

That means these krakens favored one side of  their jaw more than the other while eating. They were left- or right-handed … or, in this case, jawed. This is called lateralization, and it’s often associated with  higher cognitive function – that is, smarter animals.

So, given their asymmetric jaws and  their notoriously clever living cousins, it’s a good bet that these  ancient giants were pretty smart. And that would have made them even  more versatile and dangerous predators. So if you’re gonna ignore our advice  and go sailing on the Cretaceous sea … you might need a bigger boat. [ outro ]