Ancient ocean giant: scientists reveal a 19-metre predator octopus that once ruled the seas

A newly published study has uncovered evidence suggesting that giant octopuses, some reaching up to 19 metres in length, may have dominated Earth’s oceans around 100 million years ago during the age of dinosaurs. The findings challenge long-held assumptions that the largest marine predators of the time were only vertebrates such as fish and reptiles.

As per BBC, the research, conducted by scientists at Hokkaido University, is based on the analysis of exceptionally well-preserved fossil jaws. These remains suggest that ancient octopuses were far more formidable than previously believed, equipped with powerful beak-like structures capable of crushing shells and bones.

Fearsome hunters of the Cretaceous seas

According to the study, these ancient cephalopods likely possessed strong arms used to seize prey, combined with sharp jaws adapted for breaking through the hard exoskeletons of marine animals. Researchers estimate that their bodies ranged from 1.5 to 4.5 metres, but when fully extended arms are included, their total length could have reached between 7 and 19 metres.

Even at the lower end of this estimate, the creatures would have dwarfed modern octopuses. Today’s largest known species, the Giant Pacific Octopus, can reach arm spans of over 5.5 metres and is already considered an apex invertebrate predator.

Scientists believe these prehistoric octopuses likely preyed on a variety of marine life, including ammonites and possibly even small marine reptiles. Their role as active hunters marks a significant departure from earlier assumptions that ancient octopuses were relatively minor players in marine ecosystems.

Clues hidden in fossil jaws

One of the most intriguing discoveries from the fossil record is uneven wear on the preserved jaws, suggesting that these animals may have favoured one side while feeding. Researchers say this could indicate a form of lateralisation, a trait associated with more complex brain functions in modern animals.

Today’s octopuses are already known for their intelligence, problem-solving abilities, and remarkable camouflage skills. In fact, modern species are capable of sophisticated hunting strategies, and there are documented cases of large octopuses confronting and overpowering sharks.

Palaeontologist Christian Klug noted that the combination of strength and dexterity in octopuses makes them highly efficient predators, even by modern standards.

A lingering prehistoric mystery

Despite these revelations, many aspects of the ancient giants remain unknown. Scientists still do not know their exact body shape, swimming speed, or whether they possessed fins. No fossil evidence has yet revealed direct stomach contents, leaving their precise diet open to interpretation.

Nick Longrich suggests they may have primarily hunted ammonites but likely behaved as opportunistic predators, feeding on whatever prey they could overpower.

Researchers stress that much about these creatures remains speculative. As Longrich noted, “It’s going to take a while before we figure this thing out. It’s a bit of a mystery.”

Published in the journal Science, the study provides a rare glimpse into a lost world where enormous, intelligent invertebrates may have once competed with some of the most powerful predators in Earth’s history.