Frederik H. Mollen

Orectolobiform sharks are predominantly benthic, and members of the genus Hemiscyllium are further distinguished by a unique walking locomotion driven by coordinated movements of the paired pectoral and pelvic fins. Although this locomotion has been described repeatedly in the epaulette shark, Hemiscyllium ocellatum (Bonnaterre, 1788), a morphological framework linking musculoskeletal structures to these movement patterns is still lacking. Here, we combine manual dissection with diffusible iodine-based contrast-enhanced computed tomography (diceCT) to describe the cranial and locomotory musculature and the associated skeletal system of H. ocellatum, with particular emphasis on the pectoral, pelvic and dorsal fin musculature and adjacent axial structures. Both the pectoral and pelvic fins possess a well-developed musculature with robust skeletal support, consistent with a weight-bearing role during substrate-based locomotion. Although not in contact with the substrate, the dorsal fins possess a likewise well-developed and clearly differentiated musculature, the musculi inclinatores dorsales, suggesting a functional specialisation beyond passive stabilisation. These findings expand current knowledge of locomotor adaptations in orectolobiform sharks and establish a morphological basis for future comparative and functional studies on fin-assisted locomotion in neoselachians. They may further provide insight into morphological adaptations analogous to the fin-to-limb transition in early tetrapods.

Documenting past trophic relationships is crucial to understand deep time changes in the ecology and geographic distribution of large marine predators. Though bite marks on cetacean bones are a useful source of information to assess shark-whale predator-prey relationships, in many cases the identity of the prey and/or predator cannot be precisely determined. In this work, we investigate two cetacean specimens from the Kattendijk Formation (Lower Pliocene, north of Belgium): (i) the partial cranium of a small balaenid (right whale) that we describe and refer to Balaenella brachyrhynus and (ii) the previously described partial skeleton of a monodontid (family of beluga and narwhal), attributed here to the genus Casatia. Shark bite marks observed on the bones of the two specimens are described and the tip of a shark tooth found embedded in each cranium is visualized through micro-CT imaging. A comparison with shark species recorded in the Kattendijk Formation allows for the identification of the author of at least one bite for each cetacean: the bluntnose sixgill shark Hexanchus griseus for B. brachyrhynus and the large lamnid shark Carcharodon plicatilis for Casatia sp. Based on the position and topology of the marks, the H. griseus bite on B. brachyrhynus may have occurred on an upside down, floating carcass, a hypothesis that could indicate a scavenging event. Bite marks on the monodontid cranium suggest an attempt by C. plicatilis to sever the head from the rest of the body and point to the forehead region as a main targeted area. These new Early Pliocene records of shark-cetacean trophic relationships constitute a first step towards the exploration of the possible link between changes through time in the availability of prey in the southern North Sea and the local loss of large predatory sharks, which occurred in the Late Pliocene to Pleistocene time interval.

Basking sharks, Cetorhinus maximus (Gunnerus, Brugden [Squalus maximus], Det Kongelige Norske Videnskabers Selskabs Skrifter, 1765, vol. 3, pp. 33–49), feed by gaping their mouths and gill slits, greatly reorienting their cranial skeletons to filter food from water. The 3D biomechanics of this behavior, however, are exceptionally difficult to study due to the size, elusiveness, and CITES status of these animals and the rarity of well‐preserved specimens. To overcome these challenges, we integrated anatomical, digital design, and computer imaging approaches to reconstruct bio‐realistic and poseable 3D skeletal models of feeding basking sharks. The skeleton, segmented from CT scans of intact heads, was first abstracted as a rigging for guiding skeletal positioning in 3D space. Directed by the anatomies of museum specimens and dissected beached animals, the digital scaffolding was used to virtually correct skeletal distortions (e.g., from specimen collapse), resetting the skeleton to closed‐mouth symmetry. Open‐mouthed feeding postures were recreated by repositioning skeletal joints to biologically relevant destination coordinates defined from videos of feeding sharks, exploiting the basking shark's steady feeding posture to build 3D photogrammetry models from successive video frames. The resultant “digital puppet” bridges diverse imaging data while capturing the coordinated motion of “hidden” cranial joints, deconstructing complex form‐function relationships into computationally controllable parameters for exploring 3D skeletal movement. The input data gathered for our model provides new perspectives on basking shark cranial anatomy, while the model's biological fidelity gives insights into dynamic feeding processes impossible to observe in the laboratory. Branchial arch mechanics are comparatively poorly studied in sharks; our model can act as a platform for future kinematic modeling (e.g., of individual variation, other species), while demonstrating interdisciplinary approaches for studying large and elusive wildlife.

A new species of hornshark is described from northwestern Australia based on six whole specimens and a single egg case. Heterodontus marshallae n. sp. was previously considered to be conspecific with H. zebra from the Western Pacific. The new species differs from H. zebra in the sequence of its NADH2 gene, several morphological characters, egg case morphology and key coloration features. Despite the coloration being similar between H. marshallae n. sp. and H. zebra, i.e., pale background with 22 dark brown bands and saddles, they differ consistently in two key aspects. Firstly, the snout of H. marshallae n. sp. has a dark semicircular bar, usually bifurcated for most of its length vs. a pointed, triangular shaped dark marking in H. zebra. Secondly, H. zebra has a dark bar originating below the posterior gill slits and extending onto anterior pectoral fin, which is absent in H. marshallae n. sp. The Heterodontus marshallae n. sp. is endemic to northwestern Australia and occurs in deeper waters (125–229 m) than H. zebra (0–143 m).

The Bull Shark (Carcharhinus leucas) faces varying levels of exploitation around the world due to its coastal distribution. Information regarding population connectivity is crucial to evaluate its conservation status and local fishing impacts. In this study, we sampled 922 putative Bull Sharks from 19 locations in the first global assessment of population structure of this cosmopolitan species. Using a recently developed DNA‐capture approach (DArTcap), samples were genotyped for 3400 nuclear markers. Additionally, full mitochondrial genomes of 384 Indo‐Pacific samples were sequenced. Reproductive isolation was found between and across ocean basins (eastern Pacific, western Atlantic, eastern Atlantic, Indo‐West Pacific) with distinct island populations in Japan and Fiji. Bull Sharks appear to maintain gene flow using shallow coastal waters as dispersal corridors, whereas large oceanic distances and historical land‐bridges act as barriers. Females tend to return to the same area for reproduction, making them more susceptible to local threats and an important focus for management actions. Given these behaviors, the exploitation of Bull Sharks from insular populations, such as Japan and Fiji, may instigate local decline that cannot readily be replenished by immigration, which can in turn affect ecosystem dynamics and functions. These data also supported the development of a genetic panel to ascertain the population of origin, which will be useful in monitoring the trade of fisheries products and assessing population‐level impacts of this harvest.

Sharks occupy all living environments of the marine realm as well as some freshwater systems. They display varied and flexible feeding behaviours, but understanding their diet remains challenging due to their elusive ecology and the invasiveness of stomach content analyses in regard of their threatened status. As a potential alternative, we discuss the variability in δ^44/42Ca values recorded in the tooth enamel of size‐graded individuals belonging to three species of large sharks with distinct diets (Isurus oxyrinchus, Hexanchus griseus and Carcharodon carcharias). The preliminary results highlight shifts in diet linked to ontogeny (I. oxyrinchus and H. griseus) and spatial distribution (C. carcharias) characterizing feeding behaviour in these species at individual and population level. These outcomes agree with the results of traditional stomach analyses supporting that nontraditional stable isotopes thus represent new perspectives for the study of modern and extinct shark ecology. In addition, for the first time, the Sr/Ca elemental ratios measured in H. griseus reflect sexual differences that could be interpreted in terms of spatial segregation or physiological heterogeneities.

The application of high-resolution X-ray computed tomography permits an appraisal of historically and newly collected specimens of Belosaepia (Belosaepiidae, Coleoidea, Cephalopoda) from the Ypresian (Early Eocene) of Belgium and provides resolution into the taxonomy of stem-group sepiids. The new finds are from the basal beds of the Egemkapel Clay Member (Tielt Formation) in the Ampe claypit at Egem and in the middle of the Roubaix Clay Member (Kortrijk Formation) in the Koekelberg claypit at Marke (province of West-Flanders, Belgium). Combining the historically and newly collected material allows us to conclude that only a single species can be positively identified, namely Belosaepia tricarinata (Watelet, 1851), and that all currently documented occurrences are restricted to the middle Ypresian (NP11-NP12). This seems to correspond well with the occurrence of Belosaepia tricarinata in the Paris, London, and Hampshire basins. Micro-CT imaging is an excellent, non-destructive tool in the study of the calcified remains. In the Belosaepia skeleton, this method allowed us to identify growth lines, ontogenetic changes, and resorption. Utilised in conjunction with a biostratigraphic assessment, this technology has the potential to be a major aid in taxonomic assignments and revisions. In the current study, it also highlighted stratigraphically important fossils (e.g. Nummulites) retained in the residual sediment attached to the specimens. This provides additional stratigraphic information that may otherwise be lost, or not recorded in older samples.

Synopsis: From large ventral pleats of humpback whales to nanoscale ridges on flower petals, wrinkled structures are omnipresent, multifunctional, and found at hugely diverse scales. Depending on the particulars of the biological system—its environment, morphology, and mechanical properties—wrinkles may control adhesion, friction, wetting, or drag; promote interfacial exchange; act as flow channels; or contribute to stretching, mechanical integrity, or structural color. Undulations on natural surfaces primarily arise from stress-induced instabilities of surface layers (e.g., buckling) during growth or aging. Variation in the material properties of surface layers and in the magnitude and orientation of intrinsic stresses during growth lead to a variety of wrinkling morphologies and patterns which, in turn, reflect the wide range of biophysical challenges wrinkled surfaces can solve. Therefore, investigating how surface wrinkles vary and are implemented across biological systems is key to understanding their structure–function relationships. In this work, we synthesize the literature in a metadata analysis of surface wrinkling in various terrestrial and marine organisms to review important morphological parameters and classify functional aspects of surface wrinkles in relation to the size and ecology of organisms. Building on our previous and current experimental studies, we explore case studies on nano/micro-scale wrinkles in biofilms, plant surfaces, and basking shark filter structures to compare developmental and structure-vs-function aspects of wrinkles with vastly different size scales and environmental demands. In doing this and by contrasting wrinkle development in soft and hard biological systems, we provide a template of structure–function relationships of biological surface wrinkles and an outlook for functionalized wrinkled biomimetic surfaces.

Here we report on four highly peculiar skate teeth from Arcille and Certaldo, two Pliocene localities of Tuscany (central Italy). While being attributable to Rajiformes and somewhat reminiscent ofDipturusandRostroraja, these specimens display an unusual multicuspid tooth design that does not match any extinct or extant skate taxon known to date. The studied teeth are thus referred to a new genus and species of Rajiformes,Nebriimimus wardigen. et sp. nov., which is here tentatively assigned to the family Rajidae. Based on pronounced morphological similarities between the rather large-sized teeth of the latter and those of extant nurse sharks, we hypothesise thatN. wardimight have been capable of actively foraging upon relatively large food items compared to other rays. This extinct skate species was likely not a common component of the Pliocene Tuscan marine vertebrate assemblages. The palaeoenvironmental scenarios thatN. wardiinhabited were marginal-marine and open shelf settings characterised by tropical climate conditions. AsN. wardiis currently known only from lower to mid-Pliocene deposits of the Mediterranean Basin, it is tempting to speculate that its speciation dates back to an earliest Pliocene phase of diversification that also contributed to the emergence of the Mediterranean endemic stock of extant skate species.