Researchers have identified fossil evidence suggesting that giant octopus-like creatures reached lengths of up to 19 metres during the Cretaceous period, challenging long-held assumptions about invertebrate roles in ancient marine ecosystems.
The findings stem from a study published in the journal Science, which analyzed 27 fossilized beaks — 15 previously known specimens and 12 newly uncovered using a technique called digital fossil mining — from sites in Japan and Canada’s Vancouver Island. These beaks, dating between 72 and 100 million years ago, belonged to a group of ancient octopus relatives known as Nanaimoteuthis.
By comparing the size and structure of these fossil beaks to those of modern octopuses, scientists estimated that the largest species, Nanaimoteuthis haggarti, could have grown between 7 and 19 metres in total length. This range surpasses the size of the modern giant squid, which reaches about 12 metres and had previously been considered the largest known invertebrate.
Wear patterns on the beaks provide direct evidence of their feeding behavior. The largest specimens showed significant abrasion, including scratches, chips, and rounded edges — signs that the animals regularly crushed hard prey such as shells and bones. As Yasuhiro Iba, lead author and paleontologist at Hokkaido University, explained, the creatures likely used their long arms to seize prey and their powerful beaks to dismantle it, a strategy mirrored in modern octopuses.
This evidence shifts the understanding of Cretaceous ocean food webs. For decades, the top predators of that era were thought to be exclusively large vertebrates like mosasaurs, plesiosaurs, and sharks. The new research suggests that invertebrates — specifically these giant octopus relatives — occupied apex predator roles alongside them.
For more on this story, see New Patagonian Dinosaur Fossil Reveals Unexpected Brachiosaurid Lineage in South America.
“Our study shows that these were not simply large versions of modern octopuses,” Iba said. “They were giant predators at the very top of the Cretaceous marine food web. This changes the view that Cretaceous seas were dominated only by large vertebrate predators.”
The scarcity of octopus fossils has long hindered research, as their soft bodies rarely preserve. The study overcame this limitation by focusing on the beak, the only hard, chitin-based structure in an octopus’s body. Neil Landman, a paleontologist at the American Museum of Natural History not involved in the research, noted that expanding the search for such fossils elsewhere could clarify how these creatures fit into broader marine ecosystems over time.
Thomas Clements, a palaeobiologist at the University of Reading who also did not participate in the study, remarked on the sheer scale of the uncover: “To see a beak this size is quite amazing, to be honest. It was a massive animal. I certainly wouldn’t have wanted to go swimming in the ancient oceans if these things were swimming around.”
How did scientists estimate the size of these ancient octopuses without full body fossils?
Researchers used the established ratio between beak size and body length in modern finned octopuses to extrapolate the total length of ancient specimens based on their fossilized beaks.
Why weren’t giant octopuses previously considered top predators in Cretaceous oceans?
Their soft bodies fossilize poorly, leading to a lack of evidence, and there was a longstanding assumption that invertebrates lacked the physical capacity to compete with vertebrate apex predators like mosasaurs and sharks.
