During the Cretaceous period, giant sharks and marine dinosaurs dominated the oceans. But apparently they also had competition from invertebrates at the top of the food chain: gigantic octopuses that caught their prey with long arms and effortlessly crushed bones and shells with their huge jaws. This is suggested by analyzes of fossil jaws of cephalopods that lived around 100 to 72 million years ago. The largest specimens could have reached a length of over 18 meters and were therefore among the largest sea predators of their time.
For hundreds of millions of years, the ocean’s top predators have been vertebrates, from giant marine dinosaurs to sharks and whales, which remain at the top of marine food webs today. “In contrast, Cretaceous invertebrates have previously been viewed primarily as prey that underwent protective adaptations,” explains a team led by Shin Ikegami from Hokkaido University in Japan. Many invertebrates developed hard shells and shells to protect themselves from predators, while their predators countered with increasingly powerful jaws.
But a group of invertebrates took a different evolutionary path: Instead of increasingly hard armor, octopuses relied on a soft, flexible body that gave them unprecedented mobility and also provided good conditions for excellent eyesight and high intelligence. In addition, some species grew to enormous sizes. However, what role they played in the ecological structure was previously unclear due to limited fossil evidence.
Invertebrate giants
Now Ikegami and his colleagues have analyzed 27 fossil octopus jaws, twelve of which were newly discovered. All finds came from sediments from the Late Cretaceous period, around 100 to 72 million years ago, and could be assigned to two species: Nanaimoteuthis jeletzkyi and Nanaimoteuthis haggarti. From the size of the jaws, the researchers concluded that both species reached enormous dimensions: “N. jeletzkyi probably had a total length of 2.80 to 7.70 meters and N. haggarti was probably even 6.60 to 18.60 meters tall,” reports the team. This means that the largest specimens of N. haggarti even surpassed iconic marine dinosaurs such as the approximately 17 meter long Mosasaurus and the approximately twelve meter long Plesiosaurus.
To find out more about the diet of the ancient giant octopuses, Ikegami and his colleagues examined the wear marks on the fossil jaws. They found that the adult individuals’ biting tools, which were made of hardened chitin, had numerous scratches and were partially chipped. Edges that were still sharp in young animals were ground down in older animals. “These wear patterns suggest that the giant octopuses of the Late Cretaceous were active carnivores, often crushing hard shells and bones,” the researchers explain.
Intelligent robbers
The researchers also found that in both species the right side of the jaw was more worn than the left. This suggests that the animals preferred one side – a trait that is associated with highly developed brains in modern cephalopods. “This suggests that the earliest octopuses already had advanced intelligence,” the team writes. The invertebrate giants probably cleverly used their flexible arms to capture prey and transport it into their maws, where they crushed the hard shells and bones. “Our study shows that the earliest gigantic octopuses were extraordinary invertebrates that occupied a position at the top level of Cretaceous food webs,” the research team concludes.
Source: Shin Ikegami (Hokkaido University, Sapporo, Japan) et al., Science, doi: 10.1126/science.aea6285