Ancient octopuses may have been up to 19m long, study finds

TOKYO – Giant octopuses that lived between 72 million and 100 million years ago may have reached a size of up to 19m, making them among the largest invertebrates known to science and likely apex ocean predators, according to new research led by a Japanese university.

The study published in the journal Science on April 23 suggests that while marine ecosystems have been dominated by vertebrate predators like sharks for hundreds of millions of years, these finned octopuses, whose size evokes the mythical kraken, may have been a rare exception.

“Our findings suggest that the earliest octopuses were gigantic predators that occupied the top of the marine food chain in the Cretaceous period,” said Dr Yasuhiro Iba, a paleontologist at Hokkaido University, which led the study.

In reaching their conclusions, the researchers studied “exceptionally well-preserved” fossil jaws found in Cretaceous sediments in Japan and Canada. Soft-bodied animals rarely fossilise, but octopuses’ chitinous jaws are more resistant to decay.

They used high-resolution grinding tomography, cutting the rock into thin layers, imaging each slice and using artificial intelligence to reconstruct the fossils in three dimensions.

Based on jaw size, they estimated the total body length of these octopuses at around 7m to 19m, with the longest rivaling contemporaneous marine reptiles such as mosasaurs and plesiosaurs, and exceeding modern giant squid.

Dr Iba said the “most surprising” finding was the extent of wear on the fossil jaws, including chipping, scratching and cracking caused by crushing hard skeletons.

“In well-grown specimens, up to 10 per cent of the jaw tip relative to the total jaw length had been worn away,” he said. “This indicates repeated, forceful interactions with their prey, revealing an unexpectedly aggressive feeding strategy.”

The researchers also detected uneven wear between the two sides of the jaws, suggesting a preference for using one side – a behaviour known as “lateralisation” and linked to a highly developed brain and cognition, as seen in modern octopuses.

As for why they are no longer around, Dr Iba said it remains a topic for future research, adding that “we don’t know whether it was due to competition or large-scale environmental changes, but they likely went extinct”. KYODO NEWS