Bus-sized cephalopods reminiscent of the legendary kraken may have sat at the top of the food chain, using their smarts to hunt down prey in the oceans of the Late Cretaceous.
Large vertebrates such as mosasaurs, plesiosaurs, sharks, and large fish are thought to have dominated the list of apex predators in the ocean for over 370 million years, while invertebrates like squid and ammonoids were typically viewed as prey.
But researchers now suggest that some giant octopuses may also have been part of that upper predatory tier. They described two species of finned octopus, Nanaimoteuthis haggarti and N. jeletzkyi, from the Late Cretaceous period around 100 million to 75 million years ago, reaching up to 60 feet (around 19 meters) long. These octopuses may represent some of the largest invertebrates to have ever lived.
“Cretaceous ocean may have included not only large marine reptiles and sharks, but also giant octopuses as important predators,” a paleontologist, Yasuhiro Iba at Hokkaido University, tells Refractor. These giant predatory invertebrates had previously been overlooked, “making ancient food webs more complex than we imagined.”
Around 200 million years ago, in the late Mesozoic era, the explosion of shell-crushing predators initiated a phase of predator-driven evolution that also shaped the modern-type marine ecosystem. During this time, the invertebrates served as small prey. In response to this pressure, these soft-bodied animals evolved hard, mineralized shells for protection.
Some octopuses, however, followed a different evolutionary pathway, demineralizing their outer, protective shells. This resulted in the evolution of the octopuses into soft-bodied creatures with enhanced swimming ability, improved eyesight, and intelligence.
Several fossils of these, belonging to the non-tentacled superorder Octobrachia, have already been documented. But their position in the food chain remained unknown due to the lack of direct evidence, such as stomach contents. Clues from fossils, such as jaw morphology, don't tend to be reliable for evaluating eating behaviour, at least on their own.
To investigate the ecological role of the earliest known finned octopuses, Iba and his colleagues used a method different from traditional fossil analysis. They examined the physical wear and tear on the fossilized jaws to reconstruct their carnivorous feeding habits.
A total of 27 large fossilized jaws were analyzed. The researchers looked for specific damage – such as chips, deep scratches, and polished surfaces – that occur when modern cephalopods (animals like squid, octopus, or nautilus) crack open hard-shelled prey.
The team found some intense wear, with up to 10% of the original jaw length missing due to severe abrasion. This indicates that these octopuses possessed a powerful bite force used to crush the hard shells and bones of large prey.
“The wear on Nanaimoteuthis jaws indicates that they processed prey with hard structures, such as ammonites, large bivalves, crustaceans, and fish bones,” says Iba.
Based on the largest fossilized jaw, N. jeletzkyi might have reached a length of 2.8 to 7.7 meters; meanwhile, N. haggarti was an estimated total length of 6.6 to 18.6 meters. “The most surprising part was the size of the jaws and the body size estimated from them,” he adds.
The paleontologists also found asymmetric wear on the jaws, indicating lateralized behavior, meaning that the animals may have used one side more frequently during feeding. In the animal kingdom, this behavioral trait is correlated with complex brain development and advanced intelligence.
“But we cannot directly measure intelligence from fossils. What we can say is that these octopuses may already have had some of the complex behavioral abilities seen in modern octopuses,” Iba told us.
Based on the fossil deposits from the period, the researchers suggest that Cretaceous finned octopuses used ecological settings different from those of their modern relatives. Modern finned octopuses prefer deep-sea environments.
Iba says that this lineage may later have shifted toward the mainly deep-sea, smaller-bodied lifestyles we see today.
“Marine ecosystems changed greatly from the end of the Cretaceous into the Cenozoic. Changes in predators, prey, and competition may have made it difficult for giant octopuses to maintain the same ecological role,” says Iba. “Future Cenozoic fossil records will be needed to test this idea.”
The study has been published in the journal Science
Fact-checked by Mike McRae
