Cephalopod Shells Research Articles

Accumulations of Fossil Cephalopod Shells and Attached Epizoans from Some Late Ordovician Localities (Barrandian Area, Czech Republic)

Abstract As yet undescribed accumulations of shells of orthoconic cephalopods, which are in some aspects comparable to cephalopod limestones known from the Silurian and Lower Devonian of the Barrandian area and other regions of the world, occur in the Letná and Zahořany formations (middle Sandbian and lower Katian stages, Upper Ordovician, central Bohemia). These accumulated shells are often colonized by sessile organisms. Only a small proportion of these organisms could be attached to shells of alive cephalopods; the majority of them used empty shells as solid substrates. The most abundant epizoan is the cystosporate bryozoan of the genus Ceramopora that often overgrows the cephalopod shells extensively. Holdfasts of the genus Sphenothallus and problematic fossils assigned to the genus Conchicolites are common. Rarer epibionts include the bryozoan Spatiopora, the cystoid echinoderm Codiacystis and the brachiopod Ptychopeltis. Varying sizes of bryozoan colonies occurring on the same cephalopod shell point to several recurring attachment events, probably reflecting reproduction cycles.

Noteworthy Taphonomic Attributes of a Nautiloid Cephalopod from the Middle Silurian (Wenlock) Massie Formation of Southern Indiana

A specimen of the nautiloid cephalopod Dawsonoceras annulatum from the middle Silurian (Wenlock) Massie Formation of southeastern Indiana, USA, is herein described because of its suite of uncommon taphonomic characteristics. Three noteworthy features are observable. First, an articulated calymenid trilobite is preserved in the sediment infill of the cephalopod, having been either swept into the open shell post-mortem or rapidly buried alive while sheltering inside the hollow cavity. Second, a series of small (pinhole-sized) borings, potentially produced by ctenostomate bryozoans, are present on the upward-facing and lateral surfaces of the cephalopod shell, a feature that is otherwise unreported in this fauna. There appears to be a preference for boring into raised portions of the shell. Third, a number of tightly coiled microconchids are encrusting the exterior of the shell, an association not previously documented in this unit. Some of these phenomena represent first reports from a fossil fauna in a region strongly affected by dolomitization and are worthy of description on that basis alone. However, their co-occurrence on a single specimen highlights the fact that relatively common taxa such as cephalopods are still capable of yielding rare and/or significant taphonomic and paleoecological data.

Fractal-like geometry as an evolutionary response to predation?

Fractal-like, intricate morphologies are known to exhibit beneficial mechanical behavior in various engineering and technological domains. The evolution of fractal-like, internal walls of ammonoid cephalopod shells represent one of the most clear evolutionary trends toward complexity in biology, but the driver behind their iterative evolution has remained unanswered since the first hypotheses introduced in the early 1800s. We show a clear correlation between the fractal-like morphology and structural stability. Using linear and nonlinear computational mechanical simulations, we demonstrate that the increase in the complexity of septal geometry leads to a substantial increase in the mechanical stability of the entire shell. We hypothesize that the observed tendency is a driving force toward the evolution of the higher complexity of ammonoid septa, providing the animals with superior structural support and protection against predation. Resolving the adaptational value of this unique trait is vital to fully comprehend the intricate evolutionary trends between morphology, ecological shifts, and mass extinctions through Earth's history.

Cryptic moulting behaviour of some Carboniferous Ostracoda

AbstractMonospecific accumulations of ostracods, represented by spine‐bearing Janischewskya? sp. and a smooth‐shelled Cavellina? sp., were detected inside the body chamber, siphuncle and camerae of three cephalopod specimens (a nautiloid and two goniatites) from the Carboniferous (Mississippian) Cracoean reefs of North Yorkshire, UK. The ostracods occur as isolated valves packed together and are well‐preserved, with delicate spines of Janischewskya? sp. still intact on numerous specimens. Such a mode of ostracod preservation inside the cephalopod conchs and their paucity in the surrounding matrix outside the shells indicate that the valves were not concentrated due to sedimentary processes. Rather, the ostracods deliberately entered the empty cephalopod shells in order to seek sheltered habitats for moulting. In the case of the smooth‐shelled Cavellina? sp., the ostracod valves preserved inside a camera of the nautiloid have similar size, indicating that a synchronized mass moulting took place in this species. Additionally, the presence of putative eggs closely associated with the spine‐bearing Janischewskya? sp. valves inside a siphuncle of the nautiloid shows that the empty conchs could have also served as safe places for egg deposition. The present finds are thus the first examples of cryptic moulting behaviour in ostracods. They also imply that such behaviour in this group of arthropods has a long evolutionary history, at least since the Carboniferous, and potentially may persist in present day ostracods.

Sheltered preservation of cyrtocrinid crinoids from the Lower Cretaceous of Madagascar and their palaeogeographic significance

Sheltered preservation, in which organisms are trapped within shells of cephalopods, is a well-known phenomenon. This preservational style constitutes an important source of paleontological data. Here, we report the first crinoid preserved inside the early Albian ammonite Cleoniceras besairiei Collignon from Madagascar. This crinoid is assigned to the aspidocrinid phyllocrinid (Apsidocrinus, Phyllocrinidae), and constitutes the first phyllocrinid from the African continent, the second from the southern margin of the Tethys (after New Zealand), and also from the southern hemisphere. This specimen represents the youngest occurrence of a phyllocrinid in the world as well, and constitutes one of the youngest occurrences of cyrtocrinids from shallow sea environments, before predation-induced migration of the stalked crinoids to the deep sea refugia due to the so-called Mesozoic Marine Revolution. This finding highlights that ammonite shells may also be a convenient material for studying echinoderms.

DIVERSITY OF FOSSILS IN THE SECTIONS OF СHORTKIV SUITE (LOCHKOVIAN) IN PODILLIA

The paper deals with a collection of fossils collected by the authors from two outcrops of the Chortkiv Formation of the Lokhkivian stage of the Devonian: on the Dniester River south of Zalishchyky and near the village of Bilche-Zolote on the Seret River (Ternopil region, Ukraine). Although the collection is small, it is represented by a wide variety of fossils from the rock mass of greenishgrey siltstone with interbedded limestone. The section has a thickness of almost 140 m and is rhythmic in nature, with argillites dominating. The systematic composition of the finds testifies to its marine genesis. Cephalopod phragmocones predominate. Their modern representatives live in sea basins with normal salinity. We have no reason to doubt that cephalopods existed in Devonian seas under similar conditions. The remains of pelecypods are second in abundance. The remains of brachiopods, which were also exclusively marine, have been found, but their numbers and diversity have decreased compared to the previous stage. Tentaculites are represented by two species. It is interesting to note that their elongated conical shells are mainly oriented in one direction, in accordance with the hydrodynamics of the environment. The collection contains a number of different ostracods that have not yet been identified. An increase in their number could indicate an abnormal salinity. Finally, the bryozoans are represented by the remains of one species, mostly inlaid with cephalopod shells. All the fossils in our collection are of marine origin, since the modern representatives of the species live in seas with normal salinity. It is planned to use the collection to improve the museum’s Devonian exhibition.

Calcium isotope values of modern and fossil cephalopod shells – Trophic level or proxy for seawater geochemistry?

Carbonate hardparts of marine organisms are frequently explored archives of their ambient seawater composition. Among the various materials used, the hardparts of molluscs are particularly relevant because their accretionary growth allows for the compilation of time-resolved proxy data sets. Here, we explore to which extent the calcium isotope values of aragonitic cephalopod hardparts represent proxies for seawater composition or record a trophic level signal. In a first step, we collect Ca isotope data from a diverse set of modern cephalopods, including Nautilus, Sepia and Spirula. These taxa differ in their external/internal hardparts, life spans, trophic levels, habitat depth, hinterland geology, and resulting runoff. In a second step, we have put these concepts to the test and explore the calcium isotope signatures of Lower Cretaceous (lower Albian) well-preserved cephalopods (nautiloids, ammonoids and belemnites) and bivalve shells from Madagascar. In the sense of a methodological comparison, two measurement approaches (double spike (δ44/40Ca, TIMS) and bracketing standard (δ44/42Ca, MC-ICP-MS) techniques are applied. Calcium from organic matter and intra-shell variations on bulk δ44/40Ca isotope values are explored. Four protocols (H2O2, NaOH, HClO4, incineration up to 250 °C including subsequent rinsing with deionised water and Ca removal) are applied to destroy organic matter in the shell material and to dissolve any non‑carbonate bound Ca, i.e., its metastable secondary Ca reservoir. These are equally successful, and the Ca isotope values of the purified carbonate phase plot on the equilibrium mass fractionation line. Samples not treated to destroy or remove their organic matter do not fall on the equilibrium mass fractionation line. Limitations of sample pre-treatment are reflected by a slight shift towards lower values in the case of incineration experiments at 650 °C. This feature is best explained in the context of a mineralogical phase transformation of aragonite to calcite. Calcium isotope values show no significant variability when sampling hardparts with different microstructures (callus, nacre, prismatic layer) and mineralised during different ontogenetic phases (outer shell, septa). Perhaps most relevant, mean δ44/40Ca (‰ SRM-915a) isotope values for Nautilus (0.72‰ ±0.19 2SD), Sepia (0.79‰ ±0.18 2SD), and Spirula (0.50‰ ±0.18 2SD) lack evidence for a significant control by trophic levels. Nitrogen isotope data and known diets for all three cephalopods serve as a litmus test for these data, which do not correlate with this dietary proxy information. These results are considered encouraging and suggest that Ca isotope values of cephalopod shells are proxies for their ambient seawater Ca isotope signatures. According to our data, however, it remains unclear to which extend cephalopod hardparts record the Ca isotopic composition of past seawater. Specifically, the data from three different modern species point to a mean Δ44/40Ca(ceph-seawater) fractionation of −1.21‰ (± 0.15 2SD). Based on our work, we present a best practice guide for cephalopod Ca isotope analysis and interpretation.

Buoyancy control in ammonoid cephalopods refined by complex internal shell architecture

The internal architecture of chambered ammonoid conchs profoundly increased in complexity through geologic time, but the adaptive value of these structures is disputed. Specifically, these cephalopods developed fractal-like folds along the edges of their internal divider walls (septa). Traditionally, functional explanations for septal complexity have largely focused on biomechanical stress resistance. However, the impact of these structures on buoyancy manipulation deserves fresh scrutiny. We propose increased septal complexity conveyed comparable shifts in fluid retention capacity within each chamber. We test this interpretation by measuring the liquid retained by septa, and within entire chambers, in several 3D-printed cephalopod shell archetypes, treated with (and without) biomimetic hydrophilic coatings. Results show that surface tension regulates water retention capacity in the chambers, which positively scales with septal complexity and membrane capillarity, and negatively scales with size. A greater capacity for liquid retention in ammonoids may have improved buoyancy regulation, or compensated for mass changes during life. Increased liquid retention in our experiments demonstrate an increase in areas of greater surface tension potential, supporting improved chamber refilling. These findings support interpretations that ammonoids with complex sutures may have had more active buoyancy regulation compared to other groups of ectocochleate cephalopods. Overall, the relationship between septal complexity and liquid retention capacity through surface tension presents a robust yet simple functional explanation for the mechanisms driving this global biotic pattern.

The ammonite septum is not an adaptation to deep water: re-evaluating a centuries-old idea.

The shells of ammonoid cephalopods are among the most recognizable fossils, whose fractally folded, internal walls (septa) have inspired many hypotheses on their adaptive value. The enduring explanation for their iterative evolution is that they strengthen the shell against pressure at increasing water depths. The fossil record does not definitively support this idea and much of the theoretical mechanical work behind it has suffered from inaccurate testing geometries and conflicting results. By using a different set of mathematical methods compared with previous studies, I generate a system of finite-element models that explore how different parameters affect the shell's response to water pressure. Increasing the number of initial folds of the septa ultimately has little to no effect on the resulting stress in the shell wall or the septum itself. The introduction of higher-order folds does reduce the tensile stress in the shell wall; however, this is coupled with a higher rate of increase of tensile stress in the septum itself. These results reveal that the increase in complexity should not be expected to have a significant effect on the shell's strength and suggests that the evolution of ammonitic septa does not reflect a persistent trend towards deeper-water habitats.

A Nature’s Curiosity: The Argonaut “Shell” and Its Organic Content

Molluscs are known for their ability to produce a calcified shell resulting from a genetically controlled and matrix-mediated process, performed extracellularly. The occluded organic matrix consists of a complex mixture of proteins, glycoproteins and polysaccharides that are in most cases secreted by the mantle epithelium. To our knowledge, the model studied here—the argonaut, also called paper nautilus—represents the single mollusc example where this general scheme is not valid: the shell of this cephalopod is indeed formed by its first dorsal arms pair and it functions as an eggcase, secreted by females only; furthermore, this coiled structure is fully calcitic and the organization of its layered microstructures is unique. Thus, the argonautid shell appears as an apomorphy of this restricted family, not homologous to other cephalopod shells. In the present study, we investigated the physical and biochemical properties of the shell of Argonauta hians, the winged argonaut. We show that the shell matrix contains unusual proportions of soluble and insoluble components, and that it is mostly proteinaceous, with a low proportion of sugars that appear to be mostly sulfated glycosaminoglycans. Proteomics performed on different shell fractions generated several peptide sequences and identified a number of protein hits, not shared with other molluscan shell matrices. This may suggest the recruitment of unique molecular tools for mineralizing the argonaut’s shell, a finding that has some implications on the evolution of cephalopod shell matrices.

Bioerosion in fossil cephalopods: a case study from the Upper Carboniferous Buckhorn Asphalt Quarry Lagerstätte, Oklahoma, USA

The mid-Pennsylvanian (Desmoinesian–Virgilian) deposits from the Buckhorn Asphalt Quarry Lagerstatte near Sulphur, Oklahoma, are characterized by siliciclastic–carbonate rocks. One of these deposits is the ‘cephalopod coquina’ that contains a large amount of orthocerid and coiled nautiloid, and ammonoid shell remains. These were used for a detailed study on bioerosion in cephalopod shells in order to help in the reconstruction of the paleoenvironment and to increase the general knowledge on bioerosion in fossil cephalopods. More than 50 shell fragments were cast and investigated. The shells cast and investigated in this study comprise a diverse set of ichnotaxa-/forms. Besides chlorophyte and cyanobacterial traces, also rhodophyte, fungal, and spongal traces are present as well as those of unknown origin. In addition, there are six ichnoforms that might have foraminiferans as producers. In orthoceratids, Ichnoreticulina elegans and a curly morphotype of Scolecia isp. are most common while the abundance in coiled cephalopods is dominated by the ‘superthin form’, the ‘extremely thin form’, andFlagrichnus profundus. In total, 22 ichnotaxa and -forms were recognized and 12 of these have their oldest record in the Carboniferous. The succession of ichnotaxa/-forms in the casts of orthocones suggests deposition in the deep euphotic to dysphotic zone of the Buckhorn sea while shells of coiled specimens had drifted for a while; they were therefore more prone to bioerosion by autotrophs until they sank to the seafloor.

Conellae, enigmatic structures on cephalopod shells – shapes, distribution and formation

Conellae, enigmatic structures on cephalopod shells – shapes, distribution and formation

From pristine aragonite to blocky calcite: Exceptional preservation and diagenesis of cephalopod nacre in porous Cretaceous limestones.

Aragonite (along with calcite) is one of the most common polymorphs of the crystalline calcium carbonate that forms the skeletal structures of organisms, but it has relatively low preservation potential. Under ambient conditions and in the presence of water, aragonite transforms into calcite, the stable polymorph. Aragonite is also more soluble therefore, in water-permeable siliceous limestones (opokas) that are typical of Upper Cretaceous deposits of Poland and Ukraine, the primary aragonitic skeletons are either entirely dissolved and found as moulds and casts or transformed into secondary calcite, whereas the primary calcitic shells remain well preserved. Contrary to the common notion of the lack of aragonite in such porous carbonate deposits, we show that relics of aragonite can be preserved as a nacreous lining on cephalopod moulds or as thin, lenticular structures entrapped in neomorphic calcite. Based on the observed intermediate steps of aragonite alteration, we propose an extended model of nacre diagenesis. Among the originally aragonitic biota, only nautilids and ammonites have retained relics of pristine skeletons. Such selective preservation of only some aragonitic structures (nacre but not the prismatic aragonitic layers) points to the role of microstructural and biochemical differences between cephalopod shell layers that may set a threshold for the dissolution, dissolution/precipitation or preservation of original biomineral structures.

A novel multiproxy approach to reconstruct the paleoecology of extinct cephalopods

Reconstructing marine paleoenvironments from the skeletal hardparts of nektic organisms is often hampered by their unknown migrational pathways involving different water masses and their corresponding physico-chemical parameters. Despite significant progress over the last years, the reconstruction of migration patterns of extinct ammonoids is difficult because both, vertical and horizontal ones lead to an intricate combination of reconstructed seawater temperatures. Paleonvironmental data retrieved from exceptionally well-preserved lower Albian (Douvilleiceras mammillatum ammonite zone, uppermost CC8a nannofossil zone, 110.5–111.0 Ma) cephalopod shells from Madagascar (Mahajanga Basin, 40–42° southern latitude) are reconstructed based on a novel multi-proxy approach. Here we combine and contrast: (i) nacre tablet-paleobathymetry, (ii) Westermann Morphospace, and (iii) shell isotope geochemistry analysis. Results obtained allow for a robust reconstruction of habitat depth, paleo-seawater temperatures, and paleoecology of extinct cephalopod taxa. The discocone nautiloid Cymatoceras is regarded as vertical migrant with a maximum habitat depth of 250 m and a mean habitat water temperature of 20–21 °C. All three ammonoid taxa (Cleoniceras, Desmoceras, and Eogaudryceras) share a platycone to planorbicone shell shape suggesting a demersal life habit at maximal water depths of 450–500 m and temperatures of 19–21 °C for Cleoniceras and Desmoceras, and the deepest (525 m) and coolest (14 °C) habitat for Eogaudryceras. Circumstantial evidence from benthic mollusk shells from the same stratigraphic interval as well as sedimentological and paleopathological data provide further support for habitat reconstructions. Reconstructed paleotemperatures shown here provide well-constrained evidence for the thermal structure of past oceanic water masses and have significance for Cretaceous paleoceanography in general.

Postmortem transport in fossil and modern shelled cephalopods.

The chambered shells of cephalopod mollusks, such as modern Nautilus and fossil ammonoids, have the potential to float after death, which could result in significant postmortem transport of shells away from living habitats. Such transport would call into question these clades’ documented biogeographic distributions and therefore the many (paleo)biological interpretations based on them. It is therefore imperative to better constrain the likelihood and extent of postmortem transport in modern and fossil cephalopods. Here, I combine the results of classic experiments on postmortem buoyancy with datasets on cephalopod shell form to determine that only those shells with relatively high inflation are likely to float for a significant interval after death and therefore potentially experience postmortem transport. Most ammonoid cephalopods have shell forms making postmortem transport unlikely. Data on shell forms and geographic ranges of early Late Cretaceous cephalopod genera demonstrate that even genera with shell forms conducive to postmortem buoyancy do not, in fact, show artificially inflated biogeographic ranges relative to genera with non-buoyant morphologies. Finally, georeferenced locality data for living nautilid specimens and dead drift shells indicate that most species have relatively small geographic ranges and experience limited drift. Nautilus pompilius is the exception, with a broad Indo-Pacific range and drift shells found far from known living populations. Given the similarity of N. pompilius to other nautilids in its morphology and ecology, it seems unlikely that this species would have a significantly different postmortem fate than its close relatives. Rather, it is suggested that drift shells along the east African coast may indicate the existence of modern (or recently extirpated) living populations of nautilus in the western Indian Ocean, which has implications for the conservation of these cephalopods.

First possible evidence of parasite infestation in Upper Devonian Discosorida (Nautiloidea)

The small, but rather deep pit in the internal mould of the body chamber of Upper Devonian Cyclopoceras (nom. nov.) abundans (Taxyceratidae, Discosorida) from Central Russia is described in this paper. Similar pits are known to exist on internal moulds of Paleozoic cephalopod shells including nautiloids and Devonian ammonoids, and are interpreted as imprints of blister pearls: nacreous projections on the inner shell surface formed by mollusk for isolation of parasites. The pit studied herein corresponds with asymmetry of the muscle attachment scars and deformation of the last septum: the largest central pair of the muscle scars are shifted from the center of the ventral side, whereas the last septum is curved apically above the pit. These deformations indicate an abnormal growing of the shell at the latest stages of its development, giving a base for assumption that the pit was caused by a parasitic disease. The assumption of an appearance of this abnormality due to an attack by a drilling predator seems less likely. This finding is the first known possible imprint of blister pearls in Discosorida.

First Middle–Late Jurassic gladius vestiges provide new evidence on the detailed origin of incirrate and cirrate octopuses (Coleoidea)

Limpet-like and non-mineralized fossils from the upper Kimmeridgian Nusplingen Plattenkalk are identified as internal shells of coleoid cephalopods, more specifically as octobrachian gladii. The significantly reduced median field provokes us to consider this new gladius type to be shorter than the mantle length. It is consequently seen as a vestigial gladius. The first recognition of an unpaired gladius vestige in the fossil record sheds new light on the evolutionary history of the gladius vestiges of incirrate and cirrate Octopoda. Patelloctopus ilgi sp. nov. is most similar to Callovian Pearceiteuthis buyi in having a rudimentary median field with an extraordinary large opening angle and radiating ribs on the lateral fields. Both P. ilgi sp. nov. and P. buyi are therefore combined in the new family Patelloctopodidae. The patella-shaped lateral fields of the gladius vestige exposes Patelloctopus and Pearceiteuthis as members of the superfamily Muensterelloidea, which includes, apart from Patelloctopodidae, the Muensterellidae and Enchoteuthidae. The unpaired patelloctopodid gladius vestige is morphologically intermediate between the muensterelloid gladius type and the paired (bipartite) gladius vestige of Late Cretaceous Palaeoctopodidae (Palaeoctopus, Keuppia). The gladius vestige morphology suggests that the mode of locomotion and the life style of these shallow water inhabitants were similar to those of extant deep-sea octopods (Cirrata) and that the Patelloctopodidae represents the stem group of the Octopoda (Cirrata and Incirrata), although Patelloctopus ilgi sp. nov. might alternatively be a stem incirrate.

Direct chitin conversion to N-doped amorphous carbon nanofibers for high-performing full sodium-ion batteries

Currently, renewable and low-cost electrode materials are being intensively pursued to meet the development of sustainable electrochemical energy-storage systems. Chitin, which is the second most abundant biopolymer throughout the natural world and can be sourced cheaply from the exoskeletons of arthropods and shells of cephalopods, has many attractive properties such as renewability, nontoxicity, intrinsically fibrous structure and high nitrogen content. In this study, nitrogen-doped amorphous carbon nanofibers (NACF) fabricated by direct pyrolysis of chitin, were used as the anode material in sodium-ion batteries (SIBs) for the first time. The NACF electrode delivered a high reversible capacity of 320.6mAhg−1 with excellent rate capability and long cyclability. The superior electrochemical performance can mainly be attributed to synergistic effects of the unique one-dimensional mesoporous nanofibers facilitating the transmission of electrons/electrolyte, and the N-doped amorphous nanostructure increasing electrical conductivity and number of active sites. Furthermore, a sodium-ion full cell was constructed by coupling the NACF electrode with a Prussian blue cathode, and it delivered 115mAhg−1 while retaining 90% of the capacity after 200 cycles. Our work will hopefully inspire the research community to explore other advanced materials with value-added attributes that can be generated by appropriate treatment of renewable bio-waste.

‘Serpent stones’: myth and medical application

Abstract ‘Serpent stones’ have been credited with medical efficacy since antiquity. Likely having their root in ancient traditions from India, accounts are now widespread across much of the world. Serpent stones are known by many names and descriptions of their appearance and medical uses are diverse; however, they commonly have a legendary association with serpents and are most frequently considered efficacious in the alexipharmic treatment of snakebite. This work presents and details five broad categories of serpent stone: a round white stone (thought to be extracted from the head of a dragon), a smooth lens-shaped black stone (purported to be taken from the head of a snake, but artificially manufactured of burnt bone or horn), ammonites (the fossilized shells of extinct cephalopods), glass or vitreous paste in the form of rings or beads, and serpentinite.

Comparative cephalopod shell strength and the role of septum morphology on stress distribution.

The evolution of complexly folded septa in ammonoids has long been a controversial topic. Explanations of the function of these folded septa can be divided into physiological and mechanical hypotheses with the mechanical functions tending to find widespread support. The complexity of the cephalopod shell has made it difficult to directly test the mechanical properties of these structures without oversimplification of the septal morphology or extraction of a small sub-domain. However, the power of modern finite element analysis now permits direct testing of mechanical hypothesis on complete, empirical models of the shells taken from computed tomographic data. Here we compare, for the first time using empirical models, the capability of the shells of extant Nautilus pompilius, Spirula spirula, and the extinct ammonite Cadoceras sp. to withstand hydrostatic pressure and point loads. Results show hydrostatic pressure imparts highest stress on the final septum with the rest of the shell showing minimal compression. S. spirula shows the lowest stress under hydrostatic pressure while N. pompilius shows the highest stress. Cadoceras sp. shows the development of high stress along the attachment of the septal saddles with the shell wall. Stress due to point loads decreases when the point force is directed along the suture as opposed to the unsupported chamber wall. Cadoceras sp. shows the greatest decrease in stress between the point loads compared to all other models. Greater amplitude of septal flutes corresponds with greater stress due to hydrostatic pressure; however, greater amplitude decreases the stress magnitude of point loads directed along the suture. In our models, sutural complexity does not predict greater resistance to hydrostatic pressure but it does seem to increase resistance to point loads, such as would be from predators. This result permits discussion of palaeoecological reconstructions on the basis of septal morphology. We further suggest that the ratio used to characterize septal morphology in the septal strength index and in calculations of tensile strength of nacre are likely insufficient. A better understanding of the material properties of cephalopod nacre may allow the estimation of maximum depth limits of shelled cephalopods through finite element analysis.