Giant octopus-like creatures that lived during the Cretaceous period were among the top predators in ancient oceans, according to a new study. Fossil evidence indicates that some species of these ancient cephalopods reached lengths of up to 19 metres (62 feet), potentially placing them on par with well-known marine reptiles such as mosasaurs and plesiosaurs in terms of predatory dominance.

The research, led by Dr. Yasuhiro Iba of Hokkaido University, focused on fossilised beaks—the only hard, preservable part of octopuses—which revealed distinct wear patterns. These patterns suggest these animals routinely crushed hard prey items, including bones and shells, using powerful jaws. The study challenges the traditional view that the Cretaceous seas were dominated solely by large vertebrates, positioning these giant cephalopods as significant, behaviorally sophisticated predators within the marine food web.

Until now, limited knowledge existed about ancient octopuses due to the rarity of soft-tissue preservation in the fossil record. The team re-evaluated 15 large fossil beaks that had previously been misidentified as belonging to vampire squids, concluding instead that they represented a group of extinct octopus relatives known as Nanaimoteuthis. Advanced digital imaging techniques also uncovered 12 additional beaks hidden within Cretaceous rock formations, dating from approximately 72 to 100 million years ago.

One species in particular, Nanaimoteuthis haggarti, possessed a beak larger than that of today’s giant squid, which can grow up to 12 metres long and was previously considered the largest known invertebrate. By applying a model relating jaw size to body length from living finned octopuses, the researchers estimated that N. haggarti could have measured between 7 and 19 metres in length, potentially making it the largest invertebrate species on record.

The fossil beaks showed signs of considerable wear, with features that were sharp in juvenile specimens appearing blunted and chipped in larger adults. This suggests the animals used their powerful jaws extensively to process hard prey such as bony fish, shelled animals, and possibly large marine reptiles comparable in size to themselves. The uneven wear on either side of the beaks also hints at lateralized behavior—analogous to handedness in modern octopuses—implying a degree of behavioral complexity in hunting and feeding strategies.

Dr. Thomas Clements, a palaeobiologist at the University of Reading who was not involved in the study, expressed surprise at the size of these creatures and lauded the findings as a significant insight into ancient marine ecosystems. He noted that the discovery shifts the perspective on predator-prey dynamics by showing this ancient octopus group may have hunted large vertebrates, unlike the usual portrayal of vertebrates preying on cephalopods.

Published in the journal Science, the study underscores how these ancient octopuses, with their formidable size and crushing beaks, occupied a distinctive ecological niche as apex predators in the Cretaceous seas, revealing a previously underappreciated aspect of prehistoric marine life.