A hundred million years ago during the late Cretaceous period, the oceans were filled with giant predators, prowling for their next meal. There was the mosasaur — a giant toothy marine reptile (and a surprise hero in Jurassic World). There were large sharks.
And now, in the journal Science, researchers present evidence for ancient colossal octopuses — what they believe are the largest invertebrates ever described. Using innovative fossil reconstruction techniques, the researchers revealed remnants of two extinct species locked inside large rocks. They appear to have been up to 60 feet long — longer than a school bus — rivaling other apex predators of the time, and calling to mind the Kraken of legend.
"I wasn't expecting any octopus of this magnitude at all," says Fernando Ángel Fernández-Álvarez, a zoologist at the Spanish Institute of Oceanography who wasn't involved in the study. "And we now have the proof that they were living in the past."
The findings also reveal that these squishy leviathans likely feasted on crunchy prey items (think shrimp and lobster) and favored one side of their jaw over the other.
"I already thought octopuses were extraordinary animals," says Yasuhiro Iba, a paleontologist at Hokkaido University and lead author on the new publication. "But this study made me feel even more strongly that their uniqueness has deep evolutionary roots."
Jaws encased in ancient rocks
The findings are all the more remarkable because octopuses don't tend to preserve well.
Fossils usually form from bones and other hard materials. So a creature like an octopus — which is made up of almost entirely soft tissue — has been harder to come by in the fossil record.
"There are very few, very rare records about the octopus and their evolution," says Jörg Mutterlose, a paleontologist at Ruhr University Bochum in Germany and one of the researchers. This has limited our understanding of the development of these creatures and their habitats across time.
But more than a decade ago, Iba approached Mutterlose with an idea. He wanted to examine the fossilized contents of big rocks called concretions that had formed on the seafloor some 100 million years ago in what's now northern Japan.
"We thought there was a real possibility that octopus remains might also be hidden inside them," says Iba, "even if nothing was visible from the outside."
So he approached Mutterlose and they worked together, using a new technique that they call digital fossil-mining. They cut the concretions into thin slices, took pictures of any preserved fossils, and then created 3D reconstructions, a process facilitated by an AI model.
And there, locked inside, were octopus jaws, "which is very similar to the beak of a bird," says Mutterlose. They consist of a lower jaw, "which is like a shovel" and an upper jaw. Octopus jaws are hard, so they can fossilize.
And the animals use them like we do — to chomp down on food. The jaws aren't big enough to swallow a large animal, says Mutterlose, so the ancient octopuses would have used their long, strong arms to catch prey and "tear it apart into pieces."
A majestic view
The lower jaws were the biggest ones ever found for an octopus, and they offered a window into the lives of these animals. Considering work done in other species, Mutterlose says, "archaeologists reconstruct quite a lot about evolutionary history simply based on the size and form of teeth."
To that end, he and his colleagues used the jaws to estimate the body size of the octopuses. And that's when their calculations revealed that these animals were probably gargantuan — well larger than the giant Pacific octopus, today's biggest member of the family whose arm span often exceeds 13 feet.
Closer inspection of the specimens revealed numerous chips and scratches. "Obviously, something happened to the jaws," observes Mutterlose.
That something was likely the consumption of prey with hard exoskeletons, including shrimp, bivalves, lobsters and nautilus-like animals that would have worn away the jaw as they were crushed and eaten, leaving the marks behind.
These were active carnivores — and the researchers say they may have even hunted other large predators, but this remains speculative.
In addition, the right side of the jaws tended to be more worn down than the left side. "Single-sided usage might indicate that the brain was already fairly well developed," suggests Mutterlose. This means that these early octopuses may have already been displaying the advanced intelligence that they are known for today.
"Modern octopuses are intelligent, flexible and very unusual predators," says Iba. "Our results suggest that some of those remarkable traits may already have been emerging in early octopuses during the Cretaceous."
One can discern quite a lot from a few key specimens, says Mutterlose. "Just [a] few fossil findings may shed very new light on the evolution of the biosphere," he says.
Fernández-Álvarez says the results paint a vivid picture of the ocean ecosystem of the late Cretaceous — one that would have been filled with myriad large and hungry predators.
It must have been, he says, "a very majestic view."
