The top ocean predators during the Cretaceous were primarily giant marine reptiles and sharks, or so researchers have thought. Now, a new study suggests colossal “kraken-like” octopuses once hunted Late Cretaceous seas, growing as large as 19 meters in length and competing with – and perhaps even preying upon – large ocean apex predators like mosasaurs. For hundreds of millions of years, marine ecosystems were thought to be dominated by large vertebrate apex predators. Invertebrates served as smaller prey. However, unlike shelled invertebrates, octopuses followed a unique evolutionary trajectory. Instead of protective shells, these creatures evolved soft-bodies, which gave them unprecedented mobility, vision, and intelligence. Some of these species grew to enormous sizes, too, and have functioned as top-tier predators, yet their precise ecological role has remained uncertain due to limited fossil evidence.

To aim to fill this gap, Shin Ikegami and colleagues evaluated the patterns of wear on fossilized jaws of ancient octopus relatives. Wear on the jaw – produced when biting into hard, skeletal prey – leaves characteristic damage similar to the damage seen in modern shell-crushing cephalopods. Measurements of an octopus jaw can also be used to estimate their overall body size. Ikegami et al. reexamined 15 large fossil jaws from ancient octopus relatives and identified clear signs of wear on particularly well-preserved specimens. Using advanced digital fossil-mining techniques, they uncovered 12 additional jaws of finned octopuses from Late Cretaceous sediments (~100 to 72 million years ago). In analyzing them, they identified two main species – Nanaimoteuthis jeletzkyi and N. haggarti. These finned octopuses, N. haggarti in particular, grew to exceptional sizes, say the authors, ranging from ~7 to 19 meters, rivaling the size of contemporaneous giant marine reptiles and potentially representing the largest invertebrates currently described. Moreover, in the largest individuals, the jaws showed extensive wear, with once-sharp features in small juveniles becoming blunted and rounded over time. The wear patterns suggest that these creatures were active carnivores that routinely crushed hard shells and bones with powerful bites, and used their long, flexible arms to seize sizable prey while dismantling it with their strong beaks, a behavior that has been linked to advanced intelligence. According to Ikegami et al., the findings indicate that N. jeletzkyi and N. haggarti were not merely prey but highly active participants in shaping marine ecosystems while occupying roles previously attributed only to large vertebrates.