Vertebrates became the top predators in almost all marine ecosystems shortly after the evolution of jaws, about 370 million years ago. This has allowed them to shape the structure of these ecosystems, as they have repeatedly evolved large body sizes, combined with increased strength, mobility, and cognitive abilities. In the Mesozoic Era marine predators such as Fish and Sharks were joined by Marine Reptiles such as Ichthyosaurs, Plesiosaurs, Mosasaurs, and Turtles, which secondarily returned to the seas from the land. In the Tertiary Mammalian predators such as Whales and Seals also followed this route. The evolution of the ability to crush shells and other hard parts (durophagy) among various Vertebrate groups caused a major reshaping of marine ecosystems during the Mesozoic (sometimes known as the 'Mesozoic Marine Revolution') in which many marine Invertebrates became smaller, more heavily shelled, and more cryptic in their habits, in response to this increased predation.
The only Invertebrate group which has apparently been occasionally able to challenge the vertebrates for this top-predator status are the Cephalopods (Octopuses, Cuttlefish, Squid, Nautiluses, and the extinct Ammonoids), free-swimming Molluscs which independently evolved jaws at about the same time as Vertebrates. Modern Octopuses are highly intelligent mid-level predators which have either lost their shells or retain them only as vestigial structures. This loss of a mineralised shell has enabled the Octopuses to become more mobile, develop better eyesight, and much greater intelligence.
The Mesozoic fossil record has produced a number of large Cephalopod jaws which have been interpreted as those of Octobranchians (Octopuses or Vampire Squid) likely to have exceeded 2 m in total length. The owners of these jaws have been assumed to have been 'high-level' predators, but little has actually been determined about them, as there are no cases of soft tissue preservation nor stomach contents from which this could be determined. Furthermore, it is very hard to determine the diet of a Cephalopod from its jaw structure, as, while there is considerable variation in such structure across the group, it does not appear to be related to diet.
In a paper published in the journal Science on 23 April 2026, Shin Ikegami of the Department of Earth and Planetary Sciences at Hokkaido University, Jörg Mutterlose of the Department of Geosciences at Ruhr University Bochum, Kanta Sugiura, also of the Department of Earth and Planetary Sciences at Hokkaido University, Yusuke Takeda of the Spectroscopy and Imaging Division at the Japan Synchrotron Radiation Research Institute, Mehmet Oguz Derin of Morgenrot Inc., Aya Kubota of the Department of Geosciences at Osaka Metropolitan University, Kazuki Tainaka of the Brain Research Institute at Niigata University, Takahiro Harada, also of Morgenrot Inc., Harufumi Nishida of the Department of Biological Sciences at Chuo University, and Yasuhiro Iba, once again of the Department of Earth and Planetary Sciences at Hokkaido University, re-examine the status of large Cephalopod jaws from the Mesozoic.
Ikegami et al. examined wear on the jaws of fossil Cephalopods. All such jaws are made from stiffened chitin in life, and therefore are more prone to cracking and wear in more durophagous species, i.e. those which are using their beaks to crack the skeletons of their prey.
Octopus jaws. (A) The entire body of a finned octopus and the position of their upper and lower jaw. (B) Anatomy of feeding organs. (C) The upper jaw. (D) The lower jaw. Ikegami et al. (2026).
Ikegami et al. examined 15 sets of large Octobranchian jaws which had previously been described from Japan and Vancouver Island. They also discovered a series of 12 further such jaws by using a method which they describe as 'digital fossil mining', in which high resolution tomography combined with an artificial intelligence system was used to search for specimens within Cretaceous rocks from Japan. All 27 specimens came from outer-shelf environments lacking wave or current influence, so that transportation-related abrasion to the jaws is unlikely.
Precise, automatic segmentation of an Octopus jaw fossil and its fine structures using zero-shot learning AI. Ikegami et al. (2026).
All of the preserved specimens are interpreted as having come from members of the Order Cirrata (Finned Octopuses). The excellent preservation of the specimens and the lack of any potential to have been caused during preparation in specimens which had not been freed from the matrix allowed identification of wear patterns caused by the feeding habits of the living Octopuses with some confidence. Pigmentation patterns within the jaws enabled the reconstruction of growth patterns, and the large dataset being used enabled a reassessment of the taxonomy of Cretaceous Cirratans.
Descriptive terms of the Coleoid lower jaw. (A) Inner and outer lamellae. (B) Terms for the individual parts of the lower jaw. (C) Terms for the specific morphological characteristics of the lower jaw. (D) Morphological terms for the area near the jaw edges. (E) Measurements of lengths. Ikegami et al. (2026).
Previous studies have led to the description of five species of Octobranchians from the Cretaceous, all on the basis of fossil jaws. Upon re-examination of this material, Ikegami et al. conclude that only two of these species are valid, Nanaimoteuthis jeletzkyi and Nanaimoteuthis haggarti. Both are assigned to the genus Nanaimoteuthis, which was formerly thought to be a Vampire Squid, i.e. a member of the Order Vampyromorpha, but which Ikegami et al. reassign to the Winged Octopuses, Suborder Cirrata. Modern Winged Octopuses come in two forms, long-bodied forms, which have broad jaw wings, and short-bodied forms, which have narrow wings on their jaws. Because both species of Nanaimoteuthis have broad wings on their jaws, they are interpreted as long-bodied Winged Octopuses. Taking all the specimens, including the newly discovered ones, into account, Nanaimoteuthis jeletzkyi first appeared in the earliest Cenomanian (about 100 million years ago) and disappeared in the late Campanian (about 72 million years ago), while Nanaimoteuthis haggarti first appeared during the Santonian (about 86 million years ago, and also disappeared in the late Campanian (about 72 million years ago).
Huge lower jaws of fossil Octopuses and of an extant Giant Squid. (A) and (B) The largest lower jaws of the Late Cretaceous Finned Octopus species Nanaimoteuthis jeletzkyi, (A) NMNS DS00042 3LmvTpM, and Nanaimoteuthis haggarti, (B) KMNH IvP 902001. Both specimens show extensive loss of jaw material caused by wear. (C) A lower jaw of the extant Giant Squid Architeuthis dux (NSMT-Mo 85956), a species having the largest jaw among modern Cephalopods. (A) is a digital fossil jaw visualized as a 3D model; (B) is an exceptionally well-preserved non-digital fossil jaw; and (C) is a modern jaw dissected from a carcass of about 10 m total body length. Solid lines indicate the extension of striation on the outer surface of the hood and broken lines show the estimated outline of the rostrum without wear. The hood and lateral walls lost by weathering, shown as shadowed areas, are reconstructed based on the holotype and specimen NMNS DS00182 Ru8pBBo. (A) and (C) are exhibited in a mirrored position. Scale bar is 20 mm. Ikegami et al. (2026).
In Cephalopods, there is a direct relationship between the growth of the jaws and that of the soft body, allowing reliable body-size calculations to be made from the jaws alone. Based upon this, the largest specimens of Nanaimoteuthis jeletzkyi are estimated to have had a mantle length of between 67 cm and 184 cm, with a total body-length (including tentacles) of 2.8-7.7 m, while the largest specimens of Nanaimoteuthis haggarti are estimated to have had a mantle length of between 158 cm and 443 cm, with a total body length of 6.6-18.6 m, making it potentially one of the largest predators in the seas of the Late Cretaceous.
Body size estimation of Late Cretaceous Octopuses. The graph shows an allometric relationship between the length of the jaw and mantle in long-bodied species of extant Finned Octopus. The name of the corresponding species is shown along each growth curve. The sizes of Nanaimoteuthis jeletzkyi and Nanaimoteuthis haggarti are based on their largest specimens and are indicated by black vertical lines. Reconstruction of these two species, the extant Giant Squid, and gigantic Vertebrate predators in the Late Cretaceous are shown with their maximum total length. Ikegami et al. (2026).
The largest specimens of both species have beaks blunted and worn by continuous wear, while in juveniles the beaks tend to be sharp. However, it was possible to reconstruct the unworn beak length from the striations and ornamentation of the jaw surface. Thus the largest specimen of Nanaimoteuthis jeletzkyi has lost about 5.7 mm from the tip of its rostrum, while the largest specimen of Nanaimoteuthis haggarti has lost about 10.6 mm. In both cases this represents about 10% of the total jaw length. In both species the right edge of the jaw is more worn than the left edge. Wear takes the form of chips, scratches, and polishing, with the largest chips exceeding 1 mm in both species. The outer surface of the rostrum is polished, removing the original striations, but show numerous scratches, with these reaching up to 5 mm in length, extending vertically or obliquely from the jaw edge. In Nanaimoteuthis jeletzkyi the inner surface of the oral cavity is more heavily worn than the outer surface, which is indicative of the chewing of food. In Nanaimoteuthis haggarti there are many transverse cracks on the rostrum, these again reaching up to 5 mm in length.
Wear on the lower jaw of a modern Giant Pacific Octopus, Enteroctopus dofleini, (NSMT-Mo 85957). (A) Dorsal view of the entire mouth. (B) to (D) Close-ups of the wear, the positions of which are indicated by boxes in (A). (B) Lateral view of the right jaw edge. (C) Anterior view around the rostrum. (D) Dorsal view of the rostrum. Enteroctopus dofleini is the largest modern octopus species. Scale bars are 10 mm for (A) and 1 mm for (B) to (D). Ikegami et al. (2026).
There are two living suborders of Octopuses, the Finned Octopuses, or Cirrata, which are generally found in deep ocean environments, and the Finless Octopuses, of Incirrata, which are found in coastal environments. The discovery of specimens of the Finned Octopus Nanaimoteuthis jeletzkyi in deposits from the earliest Cenomanian (about 100 million years ago) pushes back the fossil record of the Ciratta by about 15 million years, and of crown-group Octopuses by about 5 million years. The presence of these fossils in Japan and on Vancouver Island indicates that large Finned Octopuses were found in outer shelf environments on either side of the Pacific during the Late Cretaceous (at which time the Pacific was already the world's largest ocean).
Wear on the largest lower jaw of Nanaimoteuthis jeletzkyi. (A) and (B) The entire specimen in (A) dorsal view and (B) anterior view. The broken line in (A) shows the boundary where striations become lost. (C) to (H) Close-ups of wear, of which the positions are indicated by boxes in (A) and (B). (C) Lateral view of the right jaw edge with chips (arrows). (D) Dorsal view of the rounded rostral part with scratches (arrows). (E) Oblique view of the rostral part with chips (arrows). (F) Area showing striations, which extends vertically in this figure (arrows). (G) Polished area where striation is lost, with scratches (arrows). (H) Asymmetric loss of the jaw edges (arrows), indicated by a mirrored image in 50% transparency overlaid beneath the original image. All panels show the specimen NMNS DS00042 3LmvTpM. Scale bars are 10 mm for (A), (B), and (H), and 1 mm for (C) to (G). Ikegami et al. (2026).
The living Cirrata can be split into two morphological groups, long-bodied forms (families Cirroctopodidae, Cirroteuthidae, Grimpoteuthidae, and Stauroteuthidae), and short-bodied forms (Family Opisthoteuthidae). Ikegami et al.'s analysis strongly suggests that both species of Nanaimoteuthis are long-bodied forms, something which is in line with both evidence from previously reported fossils, with more than 50 genera of Mesozoic Octobranchians discovered, all of which are long-bodied forms, and molecular phylogenies, which suggest that the Incerrata arose from within the Cerrata, implying that long-bodied forms arose first and that short-bodied forms evolved from these.
Wear on the largest lower jaw of Nanaimoteuthis haggarti. (A) and (B) The entire specimen in (A) dorsal view and (B) anterior view. (C) to (K) Close-ups of the wear, of which the accurate positions are indicated by boxes in (A), (B), and (G). (C) and (G) Lateral view of the right jaw edge with chips, scratches, and cracks. (E) Dorsal view of the rounded rostral part with scratches and cracks. Schematic drawings of (C), (E), and (G) are shown in (D), (F), and (H), respectively. (I) Area showing striation, which extends vertically in this figure. (J) Polished area where striation is lost. (K) Asymmetric loss of the jaw edges (arrows), indicated by a mirrored image in 50% transparency overlaid beneath the original image. All panels show the specimen KMNH IvP 902001. The broken line in (A), (G), and (H) shows the boundary where striation becomes lost. Scale bars are 10 mm for (A), (B), (E) to (H), and (K), and 1 mm for (C), (D), (I), and (J). Ikegami et al. (2026).
Nanaimoteuthis haggarti is significantly larger than Nanaimoteuthis jeletzkyi and examination of pigment patterns in the jaws of specimens of both species suggests that it grew significantly faster. Since the first known fossils of Nanaimoteuthis haggarti appeared about 86 million years ago, while the first specimens of Nanaimoteuthis jeletzkyi appeared about 100 million years ago, this suggests that these ancient Cirratans went through an evolutionary change enabling the emergence of gigantic forms about 10 million years after they first appeared.
The growth rate of Nanaimoteuthis haggarti and Nanaimoteuthis jeletzkyi based on pigmentation patterns. (A) Schematic drawings for the ontogenetic changes from juvenile to adult jaws, based on modern Octopuses. Unpigmented regions decrease with growth. (B) Nanaimoteuthis haggarti (NMNS_DS00182_Ru8pBBo.stl), corresponding to the left stage of (A). (C) Nanaimoteuthis jeletzkyi (NMNS_DS00173_P74Doy1.stl), corresponding to the middle stage of (A). The broken lines in (B) and (C) indicate the original outline including unpigmented parts, reconstructed based on the adults of the same species. The posterior and ventral margins of (B) and (C) taper without fractures, indicating that they retain the original pigmentation patterns. The specimen of Nanaimoteuthis haggarti has a weakly pigmented inner lamella compared to that of Nanaimoteuthis jeletzkyi with a smaller size. This pattern indicates that Nanaimoteuthis haggarti is in an earlier growth stage compared to Nanaimoteuthis jeletzkyi. Therefore, Nanaimoteuthis haggarti grew faster than Nanaimoteuthis jeletzkyi. Scale bars are 1 mm. Ikegami et al. (2026).
The extremely large size of Nanaimoteuthis haggarti makes it larger than the Giant Squid, Architeuthis dux, which has a maximum jaw length of about 80 mm, by about 50%. The Giant Squid can have a mantle length of about 2.5 m and a total length of about 12 m, something which has made it the largest known living or fossil invertebrate until now. It also rivals or exceeds the dimensions of the largest Vertebrates in the Cretaceous Seas, including the Ray-finned Fish, Xiphactinus audax, which reached about 5 m in length, the Lamniform Shark, Ptychodus mortoni, which reached about 10 m, Plesiosaurs of the genus Styxosaurus, which reached about 12 m, and the giant Mosasaur, Mosasaurus hoffmannii, the longest specimens of which may have reached about 17 m. Thus Nanaimoteuthis haggarti appears to have been one of the largest organisms in the Cretaceous oceans.
Most living Cephalopods are generalist carnivores, preying on Crustaceans, shelled Molluscs, other Cephalopods, and Bony Fish. Wear to the tip and edges of the beak is typically present in durophagous forms such as Octopuses and Cuttlefish, but absent in non-durophagous forms such as Squid. Thus the presence of such wear can be used to make judgements about the diet of fossil Cephalopods, such as Nanaimoteuthis jeletzkyi and Nanaimoteuthis haggarti. In these Cretaceous Cirratans it is estimated that about 10% of the jaws of large adult specimens had been worn away, but such wear is absent in juvenile specimens, as it is in contemporaneous Squid. The extent of wear seen is greater than is found in any living Cephalopod, suggesting that these were active carnivores, frequently using their beaks to crush hard shells and bone. The distribution of the wear on the jaws is asymmetric, which suggests lateralized behaviour (i.e. these Octopuses had a preferred side when manipulating prey, similar to handedness in Humans), something which is associated with cognative ability in Cepahlopods, suggesting that these Cretaceous Octopuses were already highly intelligent.
The jaws of Nanaimoteuthis jeletzkyi and Nanaimoteuthis haggarti are much shorter than the jaws of most Late Cretaceous predatory marine Vertebrates. However, the long lateral walls of these jaws suggest they had powerful jaw muscles, and the cracks and chips on the beaks suggests that they were exerting forces which exceeded the resistance of the strongest parts of the jaw. In the larger Nanaimoteuthis haggarti transverse cracking is also present, probably representing larger shear failures caused by greater forces being applied. Thus these jaws appear to have been used to break up food items of considerable size and resilience. The difference in overall size is likely to have derived from the way in which Octopuses hunt, using their elongated arms to capture and overwhelm prey, rather than their jaws as in most marine Vertebrates.
Vertebrates have been the top predators in the oceans for most of the past 370 million years. The appearance of durophagous predation in a variety of lineages in the Mesozoic enabled a greater diversity of such predators, and drove marine ecosystems towards the structure we have today. Mesozoic Invertebrates have chiefly been viewed as prey during this process, adapting to increased predation pressures by becoming smaller, more heavily armoured, and more cryptic in their habits (better at hiding). Ikegami et al.'s study suggests that some Octopuses did not follow this path, instead becoming giant predators which rose to the top of the food web.
Convergent evolution among marine top predators in the Palaeozoic–Mesozoic. This model shows the acquisition of jaws and the reduction of superficial skeletons in the evolutionary history of marine Vertebrates (top) and Cephalopods (bottom) to become top predators. The grey horizontal bars show the chronological range of some selected groups of Vertebrates and Cephalopods. For Cephalopods, stepwise reductions of skeletons are indicated by the blue background. Ikegami et al. (2026).
Both Vertebrates and Cephalopods first evolved jaws in the Late Silurian or Early Devonian, between 423 and 407 million years ago, something which greatly improved their hunting efficiency. Vertebrates subsequently lost their external bony plates, and in larger species greatly reduced their scaly coverings to achieve smooth skin, while at the same time Cephalopods first internalised and then gradually lost their shells. In both cases, this was associated with increased swimming speeds, size, and intelligence. Vertebrates became top predators in the oceans long before Cephalopods completed this process, but during the Cretaceous some Octopuses were able to evolve a bodyplan which enabled them to compete with the very largest Vertebrates.
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