Largest ever octopus was top predator in dinosaur-era oceans

Move over mosasaurs – the biggest predator in Cretaceous seas could have been an enormous octopus.

Measuring up to 19 metres long, Nanaimoteuthis haggarti would have been around the length of a bowling lane as it swam beneath the waves. Fish and molluscs would have been no match for this predator as it snared them in its arms and brought them towards its powerful beak.

Today, these beaks are one of the few signs that this mighty predator ever existed. New research carried out on fossils found in Canada and Japan is revealing more about these ancient animals.

Zoe Hughes, our Senior Curator of fossil cephalopods – the group containing octopuses, squids and their relatives – says that the study’s findings “show the true power of invertebrates”.

“Most Cretaceous octopuses that I’m aware of are about the size of my hand, but this is so much bigger!” she exclaims. “While we only have the hard parts of this animal to make a comparison, the ratios they’ve used to estimate this octopus’s size are based on reasonable and recent examples.”

“So, unless this species had a very different body shape to other octopuses, I think these are fair estimates for its size. It’s very cool to know that such a big invertebrate once lived on Earth.”

Giant Cretaceous invertebrates

The Late Cretaceous, which lasted from around 101 to 66 million years ago, was a time of ocean giants. One of the biggest was the 18-metre-long marine reptile Mosasaurus hoffmannii, which fed on fish, squid and other marine animals, while long-necked plesiosaurs such as Elasmosaurus could be over 10 metres in length.

Vertebrates like these weren’t the only big creatures lurking in the seas. The ammonite Parapuzosia seppenradensis reached up to two metres in diameter, while cephalopods such as Enchoteuthis melenae might have reached about 12 metres long, which is similar to modern giant and colossal squid.

Nanaimoteuthis has now joined the ranks of these enormous invertebrates. The team analysed 15 previously discovered fossil jaws, as well as identifying 12 more from rocks in Japan. Based on their shape and size, the researchers grouped the animals into two species, N. jeletzkyi and N. haggarti.

While both species were previously thought to be vampire squid, the team have now identified them as octopuses. This allowed the scientists to use the relationships between jaw size, head size and body size in living octopuses to work out just how big these long-extinct animals were.

They estimate that the older N. jeletzkyi, which lived between 100 and 72 million years ago, was probably between three and eight metres long. This makes it around the same size as the largest living octopus, the giant Pacific octopus.

As the Cretaceous continued, cephalopods got bigger and bigger. They reached their peak around 86 million years ago, when N. haggarti first appears in the fossil record. While its size is estimated at between seven and 19 metres long, even the lowest estimates secure it a place as one of the biggest ever octopuses.

What was the lifestyle of giant octopuses like?

Working out the lifestyle of extinct animals is always difficult, and that’s especially true when only the jaws survive. However, by examining the wear on the jaws, the researchers have been able to infer what these giant octopuses could have been eating.

The jaws of younger octopuses are less worn than those of fully grown adults, which are chipped and cracked. This suggests that they were eating hard prey, which probably included hard-shelled ammonites and bony fish. Bigger animals could also have been on the menu.

“Octopuses eat a wide variety of prey, and there’s an element of opportunism about their diet,” Zoe explains. “Their size means that they could probably attempt to eat bigger prey if they wanted, but we don’t know whether they did.”

The octopuses’ large size also would have made them a tempting target for other ocean predators. While N. jeletzkyi would have been more vulnerable due to its smaller size, N. haggarti could have only been taken on by the biggest predators.

“We know that mosasaurs and other marine reptiles ate cephalopods from preserved stomach contents, but we don’t know if they ate these octopuses specifically,” explains Zoe.

“If they did, however, these octopuses are capable of putting up a fight. We know that giant squid are capable of holding their own in fights against sperm whales, and it’s likely to have been the same for their ancient relatives.”

Around 72 million years ago, Nanaimoteuthis disappears from the fossil record. It’s unclear exactly what happened, as the octopus fossil record is pretty poor.

“There’s still a lot that we’re yet to understand about octopus evolution because of a lack of evidence,” Zoe adds. “It means that we can’t be certain if this is when Nanaimoteuthis died out, or if it continued to live on in one form or another without leaving any fossils behind.”

“It shows why it’s important to keep looking for more octopus fossils. Finding them will help to confirm what happened to these creatures, and solve ongoing puzzles about how the group evolved.”