Scientists just discovered a 60-foot-long, kraken-like octopus

It's the stuff of science fiction.

A kraken-like octopus that could grow to 60 feet long, prowl the oceans as a fierce predator, seize prey with long, agile arms and crush its catches with massive jaws.

But it turns out that such fantastical creatures actually did roam the depths of the ancient world, according to research published Thursday in the journal Science.

Scientists have long focused on sharks and large aquatic reptiles as the top ocean predators during the Cretaceous period, which spanned roughly 145 million to 66 million years ago. But the novel discovery details how colossal octopuses also hunted the Late Cretaceous seas, competing with - and perhaps even preying upon - apex predators such as mosasaurs.

The findings begin to lift the veil on that largely overlooked aspect of how ancient marine ecosystems functioned.

"Some of the earliest octopuses were much larger than we had imagined," Yasuhiro Iba, a professor at Hokkaido University and co-author of the study, said in an email to The Washington Post. "Invertebrates - especially soft-bodied animals like octopuses - have remained largely invisible in the fossil record, and their ecological roles have been poorly understood."

Because soft-bodied animals rarely fossilize, paleontology has historically focused on organisms with hard skeletons or shells. But new technologies have allowed researchers new insights into key animals that left fewer traces behind.

"In that sense," Iba said, "we are just beginning to see parts of ancient ecosystems that were previously almost invisible."

To determine the size and prowess of these Cretaceous invertebrates, a group of researchers from Japan and Germany analyzed patterns of wear on the fossilized jaws of ancient octopus relatives - the result of biting into hard, skeletal prey. In addition to examining 15 large fossil jaws of octopus relatives, the group used advanced digital fossil-mining techniques to uncover a dozen additional jaws of finned octopuses from Late Cretaceous sediments.

In analyzing the jaws and using their measurement to estimate overall body size, they identified two species - Nanaimoteuthis jeletzkyi and N. haggarti - the latter of which grew to about 7 to 19 meters, or about 23 to 62 feet, rivaling giant marine reptiles of the time.

But their size alone was only one piece of discovery.

"The novelty of our study is not simply that 'large octopuses existed,'" Iba said. Rather, by analyzing the intense wear preserved on their jaws, the research team was able to demonstrate that "these octopuses were capable of processing hard prey such as shells and bones, and may have reached a similar ecological level to large vertebrate apex predators in the Cretaceous ocean."

Neil Landman, curator emeritus in the division of paleontology at the American Museum of Natural History in New York, called the latest research meticulous and "very exciting stuff" that offers a new perspective.

"The community is very intrigued by their work," said Landman, who was not involved in the study.

He said a key challenge in trying to learn more about non-vertebrates that lived millions of years ago is that they had soft bodies.

"You don't get a really great fossil record," Landman said. "The brilliance of this team was they said, 'Well, let's look at the jaws.'"

The study also helps to illuminate and reshape how scientists think about the food web of the Cretaceous period, he said, when sea levels generally were far higher than they are today and global temperatures were much warmer. Landman said the researchers' approach could also expand scientists' view into the marine systems of the older Jurassic era and beyond.

"There is a lot of potential here to begin to illuminate ancient worlds," he said.

What eventually happened to the immense octopuses that stalked the Cretaceous oceans?

The precise answer remains a mystery, Iba said. While there are records of the giant finned octopuses they studied from the Late Cretaceous, similar creatures "have not yet been found after that." But that could reflect limitations of fossil recovery methods, he said. And researchers cannot rule out the possibility that similar forms existed more recently.

Octopuses themselves did not disappear, of course. They remain widespread today. But forms like the wondrous Nanaimoteuthis are no longer present - the result of what Iba calls a "major ecological shift in octopus evolution" as part of a broader restructuring of marine ecosystems over millions of years.