Jaw fossils suggest a 60-foot octopus was the ‘kraken’ of the Cretaceous

Mesozoic seas were full of marine monsters. There were snaggle-toothed fish, shell-crushing sharks, and, of course, enormous mosasaurs.

Now, researchers have revealed another dangerous denizen of the ancient deep, one that wielded eight arms, grew to mythic proportions, and likely bit prey with a bone-breaking beak.  

Enter the "Cretaceous kraken": Nanaimoteuthis haggarti.

Paleontologists recently examined a trove of fossilized beaks from octopuses that lived between 100 and 72 million years ago. Using the jaws, they estimated the size of the creatures. They found that N. haggarti stretched to about 60 feet long, longer than a city bus and surpassing the largest known giant squid by nearly 20 feet. That makes these ancient octopuses among the largest invertebrates to have ever lived.

The study, which was published Thursday in Science, also suggests that prehistoric vertebrate predators — such as sharks, plesiosaurs, and mosasaurs — may have met their match in these spineless cephalopods.

“It challenges the common view of an ‘age of vertebrates’ in marine ecosystems,” says Yasuhiro Iba, a paleontologist at Hokkaido University in Japan and an author of the new paper. He thinks these octopuses used their massive size, flexible arms, and powerful bites to achieve apex predator status in the ancient ocean.

A bevy of beaks 

The new findings provide evolutionary insights into a group of animals that left few fossils behind. These soft-bodied critters lost their protective shells hundreds of millions of years ago and largely lack any other hard parts that easily fossilize.

However, ancient octopuses did leave one telltale trace in the fossil record: their parrot-like beaks. These structures are composed primarily of chitin, the same material that forms the exoskeletons of insects and crustaceans. In living species, the size of an octopus’s beak is often indicative of the rest of the animal’s dimensions, allowing paleontologists to reconstruct the size of an ancient cephalopod based only on the beak it left behind.

Iba and his team analyzed 15 well-preserved beak fossils discovered in Late Cretaceous deposits in Japan and on Vancouver Island. To bolster the dataset, the team also used artificial intelligence-assisted software to uncover fossilized octopus beaks buried in Japanese sediment samples. The process, which the researchers refer to as digital fossil mining, allowed them to sift through the interiors of rocks. The AI tool then processed the wealth of interior images to detect hidden fossils.

“Using this approach, we were able to discover fossil jaws that would have been nearly impossible to find using conventional techniques, and to reconstruct them as detailed 3D digital fossils,” Iba says.

The effort yielded 12 additional fossilized octopus jaws, including several beaks from giants.

Re-estimate the kraken

Based on the shapes of the fossilized beaks, the scientists were able to connect the larger specimens to a pair of previously known species in the genus Nanaimoteuthis. These large octopuses were once thought to be closely related to vampire squids but are now viewed as ancient relatives of finned octopuses, called Cirrata, a group of distinctive deep-sea cephalopods that sport ear-like fins on the top of their heads and webbing between their arms. 

The newly discovered jaws show that finned octopuses reached titanic sizes during the Late Cretaceous. N. haggarti, which inhabited oceans between 86 and 72 million years ago, had the largest jaws, measuring 1.5 times longer than the beak of a giant squid.

The team also concluded that a closely related species, Nanaimoteuthis jeletzkyi, likely reached a length of about 26 feet. They also noted that the N. jeletzkyi fossils they found push back the record of octopuses by 5 million years and finned octopuses by 15 million years.

Not all scientists are convinced by these jaw-dropping dimensions.

Christian Klug, a paleontologist at the Natural History Museum at the University of Zürich who researches ancient cephalopod body size, says the top measurements for N. haggarti that place it at 60 feet long are “quite extreme.”

But Klug, who was not involved in the paper, acknowledges that the true dimensions are difficult to discern. “Of course, we have only the jaws, so there is some uncertainty,” he says.

An eight-armed apex predator

The revised size estimates of the two Nanaimoteuthis species suggest these octopuses were among the largest predators of their time. Klug places them at the top of the Cretaceous seafood chain.

“Their size would identify them as apex predators,” he says. He thinks the octopuses likely killed large prey before using their beaks to break their food into bite-sized chunks.

The fossilized beaks examined in the new paper show evidence of crushing bites. The scientists noticed signs of wear, such as chipping and scratching, and the sharp edges of many of the beaks have been worn down into rounded tips. Some jaws have even lost up to 10 percent of their total length. According to Iba, this wear indicates that these octopuses routinely bit through tough shells and potentially even the bones of mosasaurs and other large vertebrates.

However, more evidence, such as fossilized octopus gut contents or clear bite marks on bones, is needed to confirm what was on the menu for these massive octopuses, says Adiel Klompmaker, a paleontologist at the University of Alabama Museums who was not involved in the new work.

“Did they go after the largest ammonites or were they hunting bony fish, sharks, or small marine reptiles?” he says.

Another question is whether there were even bigger sea monsters out there. Klompmaker notes that the new fossilized beaks were found in relatively shallow water deposits.

“I wonder what was living in the deeper parts of the oceans during the Cretaceous,” he says. “What's lurking out there that we have not discovered yet?”