The Late Jurassic elasmobranch Protospinax annectans is often regarded as a key species to our understanding of crown group elasmobranch interrelationships and the evolutionary history of this group. However, since its first description more than 100 years ago, its phylogenetic position within the Elasmobranchii (sharks and rays) has proven controversial, and a closer relationship between Protospinax and each of the posited superorders (Batomorphii, Squalomorphii, and Galeomorphii) has been proposed over the time. Here we revise this controversial taxon based on new holomorphic specimens from the Late Jurassic Konservat-Lagerstätte of the Solnhofen Archipelago in Bavaria (Germany) and review its skeletal morphology, systematics, and phylogenetic interrelationships. A data matrix with 224 morphological characters was compiled and analyzed under a molecular backbone constraint. Our results indicate a close relationship between Protospinax, angel sharks (Squatiniformes), and saw sharks (Pristiophoriformes). However, the revision of our morphological data matrix within a molecular framework highlights the lack of morphological characters defining certain groups, especially sharks of the order Squaliformes, hampering the phylogenetic resolution of Protospinax annectans with certainty. Furthermore, the monophyly of modern sharks retrieved by molecular studies is only weakly supported by morphological data, stressing the need for more characters to align morphological and molecular studies in the future.

Elasmobranchs, comprising sharks, skates, and rays, have a long evolutionary history extending back into the Palaeozoic. They are characterized by various unique traits including a predominantly cartilaginous skeleton, superficial prismatic phosphatic layer, and permanent tooth replacement. Moreover, they exhibit a more or less marked sexual dimorphism. Especially the morphology of the chondrocranium and the elements of the whole cranial region of extant and extinct chondrichthyans can provide valuable information about corresponding functions, e.g. the feeding apparatus might reflect the diet of the animals. However, studies on sexual dimorphisms are lacking in orectolobiform sharks, therefore, little is known about possible sexual dimorphic characters in the cranial region in this group. For this reason, we present in this study a comprehensive morphological description of the cranial region of the brownbanded bamboo shark Chiloscyllium punctatum Müller & Henle, 1838, with a special focus on its sexual dimorphic characters. Our results reveal clear morphological differences in both sexes of the examined C. punctatum specimens, particularly in the chondrocranium and the mandibular arch. The female specimen shows a comparatively more robust and compact morphology of the chondrocranium. This pattern is also evident in the mandibular arch, especially in the palatoquadrate. The present study is the first to describe the morphology of an orectolobiform shark species in detail using both manual dissection and micro-CT data. The resulting data furthermore provide a starting point for pending studies and are intended to be a first step in a series of comparative studies on the morphology of the cranial region of orectolobiform sharks, including the determination of possible sexual dimorphic characteristics.

In this study, we apply a two‐step (untreated and soft tissue stained) diffusible iodine‐based contrast‐enhanced micro‐computed tomography array to a wet‐collection Lantern Shark specimen of Etmopterus lucifer. The focus of our scanning approach is the head anatomy. The unstained CT data allow the imaging of mineralized (skeletal) tissue, while results for soft tissue were achieved after staining for 120 h in a 1% ethanolic iodine solution. Three‐dimensional visualization after the segmentation of hard as well as soft tissue reveals new details of tissue organization and allows us to draw conclusions on the significance of organs in their function. Outstanding are the ampullae of Lorenzini for electroreception, which appear as the dominant sense along with the olfactory system. Corresponding brain areas of these sensory organs are significantly enlarged as well and likely reflect adaptations to the lantern sharks' deep‐sea habitat. While electroreception supports the capture of living prey, the enlarged olfactory system can guide the scavenging of these opportunistic feeders. Compared to other approaches based on the manual dissection of similar species, CT scanning is superior in some but not all aspects. For example, fenestrae of the cranial nerves within the chondrocranium cannot be identified reflecting the limitations of the method, however, CT scanning is less invasive, and the staining is mostly reversible and can be rinsed out.

The modern diversity of sharks, skates, and rays (Neoselachii) is the result of various diversification and extinction events during the Mesozoic (252–66 Ma). However, the key drivers of their diversity patterns remain poorly understood despite all the progress that has been accomplished in recent years. Here, we show that the interplay of climatic- and tectonic-linked trajectories, resulting in a high shallow marine habitat availability and lower atmospheric CO₂ concentration, were significant drivers and sustainers of Mesozoic neoselachian diversity. We show, for the first time, that higher atmospheric CO₂ content negatively affected neoselachian diversity in the past. The recognized gradual faunal changes throughout the Mesozoic and the two major diversification events during the Jurassic and Cretaceous, respectively, ultimately cumulated in an all-time diversity high in the Palaeogene despite the events during the end-Cretaceous extinction event, highlighting their remarkable resilience and adaptability despite severe environmental challenges. We thus provide novel perspectives on the processes underlying neoselachian diversification since the Mesozoic that contribute importantly to a better understanding of the selective forces that have shaped the long-term evolution and diversification of neoselachians. Given their vital role in modern ecosystems, our results provide information about possible future trends in the face of the current climate crisis.

Sharks, rays and their immediate extinct ancestors (Neoselachii) are some of the ecologically most impactful marine vertebrates. Despite their evolutionary success, the deep-time patterns of neoselachian diversity and turnover as a response to environmental perturbations remain understudied. Past studies have focussed on taxonomic richness while neglecting changes in faunal composition and ecological strategies, limiting our understanding of macroevolutionary resilience and vulnerability of neoselachians. Consequently, the extent to which major Cenozoic environmental shifts affected neoselachian diversity and turnover remain elusive. Here, we present a sampling-standardised analysis of Cenozoic neoselachian genus diversity and faunal composition change, using high-resolution fossil occurrence data and ecological and environmental variables. We demonstrate a milder impact of the KPg mass extinction on neoselachians than previously suggested, followed by a radiation culminating in an Eocene diversity peak, which is systematically documented and described for the first time using sampling-standardised data. Additionally, we identify two distinct faunal shifts during the Miocene. Shallow, heterogeneous habitats emerged as the primary diversification driver, although responses varied across ecological and taxonomic groups. These findings shed light on the evolutionary and ecological dynamics that shaped modern neoselachian diversity and provide critical context for assessing their vulnerability to ongoing anthropogenic pressures and informing conservation strategies.

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.