Extensive bulk-sampling of the continuous K-Pg succession at Byala (Central Tethys) provides high-resolution insights into elasmobranch responses to the end-Cretaceous mass extinction of a deep-marine environmental setting. The studied section represents a rhythmic alternation of marls and marly limestones of the Byala Formation, which shows exceptionally well-preserved Milankovitch cyclicity in combination with a deepening-upward trend. The sampled interval comprises one horizon from the uppermost Maastrichtian (Zone CC26), the boundary clay, and five horizons from the lowermost Danian (Zone NP1), which combined yielded a total of 535 elasmobranch teeth. The Maastrichtian assemblage is moderately diverse but strongly dominated by squaliform sharks, including Centrophoridae, Somniosidae, and Etmopteridae. Although most teeth are poorly preserved, limiting accurate estimates of original diversity, several genera typical of deep-marine Maastrichtian environments (e.g., Deania, Centrodeania, Cretascymnus, Protoxynotus, Incognitorapax) were recovered. The sampled Danian interval shows higher elasmobranch diversity compared to the undisturbed pre-extinction environment of the Maastrichtian and a pronounced faunal turnover is described, which is marked by the appearance of Hexanchiformes (Chlamydoselachidae, Hexanchidae), Lamniformes (Carchariidae, Mitsukurinidae), and Carcharhiniformes (Triakidae). The Danian assemblages include teeth of Squalidae (Squalus) and Dalatiidae (Angoumeius), with the latter extending its fossil record into the earliest Paleocene and now spanning from the Danian to the Middle Miocene. Notably, Cretascymnus is reported for the first time in the Danian, indicating that this genus survived the end-Cretaceous extinction event. Comparison with previously studied K-Pg successions from the Northern Tethyan and Boreal realms indicates that elasmobranch extinction intensity was moderate in deep-marine and high-latitude settings, while shallower environments experienced stronger ecological restructuring.

Echinorhiniformes and Echinorhinidae are a distinct order and family of sharks comprising two species showing several outstanding morphological characteristics, such as their tooth morphologies. Their teeth display unique shapes among sharks with main and secondary cusps which also allow tracking the fossil record of Echinorhinidae. In this study, we review the dental morphological characters of Echinorhinus spp. and further analyse intraspecific morphological variation in a population tentatively identified as E. cf. brucus from the Indian Ocean. Previously suggested hypotheses of intra- and interspecific morphological variations are critically tested, i.e., we examine ontogenetic changes in dental morphologies in E. cf. brucus and test for species-specific differences of dental morphologies between E. brucus, E. cf. brucus, and E. cookei. Results show that within and between species dental variation is limited. Neither tooth size nor cusp angle are jaw position specific. An ontogenetic change in cusplet numbers is detected. Species-specific dental morphological differences within the examined specimens of Echinorhinus were not found; however, the overall tooth formula may be a useful character for species identification. Further, our tooth measurements are useful for estimating the average total length of specimens, which, in combination with the detected ontogenetic change in cusplet numbers, we suggest using for the characterization of the fossil record of Echinorhinus.

Summary Estimating deep-time diversification patterns and the establishment of extant biodiversity represent major challenges in macroevolution. Fossil record data provide essential information to address these topics, but their heterogeneous temporal and geographical distributions require using analytical approaches to process these data. Gardiner et al. 1 (hereafter GEA) used a deep-learning model 2 and a fossil-occurrences dataset 3 to estimate neoselachian richness over the last 145 myr. Results and Discussion GEA 1 found that neoselachian diversity increased throughout the Cretaceous, was little impacted by the Cretaceous-Paleogene (K/Pg) mass extinction (~10% species loss), and peaked in the mid-Eocene but declined until the Present. While the Cretaceous increase in neoselachian richness is well known 4 , the other findings of GEA 1 are at odds with current knowledge. With the exception of lamniform sharks, the perceived decrease in species richness in the recent past is most likely due to a drop in available fossil record data combined with difficulties in identifying extant species in the fossil record 5 . Similarly, all previous analyses of the impact of the K/Pg mass extinction on elasmobranch diversification have reported high extinction rates, a marked diversity drop, and delayed recovery 6–7 , despite heterogeneity across clades, ecology, and geographical distribution 7 . Taking the K/Pg as an example, we demonstrate that the discrepancies between GEA 1 ’s results and current consensus is most likely due to a combination of incomplete, unverified, and incorrect fossil-occurrence data with inappropriate methodology.

Trophic interactions play pivotal roles in marine vertebrate ecology and evolution. Yet, these parameters are especially difficult to determine in fossil communities. To elucidate past trophic palaeoecology, we apply the zinc isotope proxy in a comprehensive analysis of 19 taxa from an early Miocene marine ecosystem, including the megatooth sharks Otodus megalodon/chubutensis. We find substantial resource partitioning among these taxa, with at least three distinct trophic positions and a general increase in body size of taxa towards the top of the food web. The white shark (Carcharodon carcharias) ancestor Carcharodon hastalis had a distinctly different trophic ecology compared to modern C. carcharias, corresponding to the evolutionary gain of tooth serrations between the two species. A comparison among fossil assemblages indicates that megatooth Otodus sharks possessed a higher dietary flexibility on a population level than previously understood, suggesting that they were opportunistic supercarnivores capable of foraging throughout the food web.

Reconstructing ancient food web structures and trophic interactions of extinct taxa is challenging and typically relies on rare fossil evidence such as preserved bite marks, stomach content or faeces. In addition, trophic and diet inferences may be drawn from an anatomical approach, i.e., functional morphology. Yet none of these methods alone can decisively identify the overall diet nor can they quantify a species’ trophic position. To address these uncertainties we utilize new geochemical methods to identify an animal’s trophic position on timescales of millions of years from the analyses of dental enamel(oid). Here we focus on zinc isotope ratios (66Zn/64Zn), reported as δ66Zn value, a trophic-level proxy that is increasingly being applied in archaeological and palaeobiological research. Specifically, we use enamel(oid) δ66Zn values to investigate ancient marine food web structures and the roles of their inhabitants in them, including gigantic extinct predators. Extinct gigantic Mesozoic and Cenozoic marine predators reaching sizes beyond any macropredatory animal existing today have no apparent modern counterparts. Indeed their size alone may imply a very different resource use for these animals or ecosystem structures vastly different from present ones. The diet and trophic position of the megatooth shark Otodus megalodon is still subject of debate and is often linked to its evolution towards gigantism and its extinction. Here we present novel Early Miocene megatoothed shark δ66Zn values from the enameloid of O. megalodon and Otodus chubutensis teeth from two time-equivalent localities in the Paratethys in comparison to the isotopic composition of 20 other sympatric marine vertebrate species with variable trophic ecology and dietary preferences. The inclusion of a larger number of taxa permits a more robust reconstruction of food web dynamics amongst its inhabitants, along with greater insight into the ecological roles of dietary-ambiguous extinct taxa and related length of extinct food chains. We thus contextualise the trophic position of O. megalodon/chubutensis within its food web in greater detail than previously possible. In general, our results support the notion that O. megalodon/chubutensis occupied a high trophic position, though possibly not as high as previously estimated. Perhaps more importantly in terms of its evolution, our findings suggest that Otodus possessed a higher dietary flexibility on a population level than previously understood.

This study reports on a rare assemblage of deep-marine elasmobranchs from the middle Badenian (Langhian) of Austria, which has been recovered by extensive bulk sampling of sediment deposited in the Krems embayment. The applied multidisciplinary approach enabled an age assignment, placing the assemblage around the mid Badenian flooding event (14.59 +/- 0.2 Ma). Palaeoenvironmental reconstruction, based on a well-preserved foraminifera assemblage and fish otoliths, indicates predominantly oxic to suboxic with partially dysoxic conditions of a rather deep-marine (>100 m) setting, which align with the recovered elasmobranch taxa. Despite analyzing 180 kilograms of sediment, only five elasmobranch teeth were recovered. The low number of teeth and the extraordinarily well-preserved foraminifera argue for an autochthonous deposition and point to high sedimentation rates associated with the flooding event. The teeth represent five different elasmobranch orders (Squaliformes, Squatiniformes, Carcharhiniformes, Torpediniformes, and Myliobatiformes) with a wide range of feeding behaviors, providing new insights into the ecological structure of this deep-marine environment. Despite common genera known from other marine settings of the Paratethyan realm (e.g., Squatina, Scyliorhinus, and Centrophorus), this study documents the first distinct records of Torpedo and Mobula from Austria, expanding the known palaeogeographic distribution of these taxa.

The ecological upheavals produced by the Cretaceous-Paleogene mass extinction event (K-Pg, -66 Ma) have been mostly studied at large scale with emphasis on clades' diversity dynamics. How this event affected the structure of paleocommunities is comparatively less investigated, especially within large vertebrate clades like fish. Here, we quantified changes in the contribution of elasmobranchs (sharks, skates, rays) and actinopterygians (ray-finned fishes) to the fish community across the K-Pg extinction by analyzing ichthyolith (fossil teeth and denticles) abundance through time. Based on extensive sampling of 20 horizons from two outcrops spanning the K-Pg event in Austria (>4 tons of rock, >9,000 ichthyoliths), we show that the K-Pg event fostered elasmobranch abundance while reducing actinopterygian density in the Tethys Ocean. Elasmobranch ichthyolith dominance in postextinction communities is not driven by estimated local environmental change (paleobathymetry, bottom-water oxygenation) and may relate to the greater independence of this clade from lower trophic levels in their ecology and early life stages than actinopterygians. We further measured the size structure of ichthyolith assemblages and found that the K-Pg event initiated an increase in the range of ecological niche space occupied by elasmobranchs simultaneously to the demise of actinopterygians in postextinction communities. Finally, using the fine taxonomic resolution of the elasmobranch fossil record, we demonstrate that local environmental fluctuations controlled elasmobranch community structure and richness, which are decoupled from global-scale upheavals. Our results challenge previous hypotheses and provide insights into global and regional environmental forcing over the structure of fish communities across a mass extinction event.

Otodus megalodon (Lamniformes: Otodontidae) is an iconic Neogene shark, but the lack of well-preserved skeletons has hampered our understanding of various aspects of its biology. Here, we reassess some of its biological properties using a new approach, based on known vertebral specimens of O. megalodon and 165 species of extinct and extant neoselachian sharks across ten orders. Using the median neurocranial and caudal fin proportions relative to the trunk proportion among non-mitsukurinid/non-alopiid lamniforms, we show that O. megalodon could have had a slender body and possibly reached about 24.3 m in length. Allometric considerations indicate that a stout body plan like the extant white shark (Carcharodon carcharias) for O. megalodon could have incurred excessive hydrodynamic costs, further supporting the interpretation that O. megalodon likely had a slenderer body than C. carcharias. A 24.3-m-long O. megalodon may have weighed around 94 t, with an estimated cruising speed of 2.1-3.5 km h-1. A reanalysis of vertebral growth bands suggests a size at birth of 3.6-3.9 m for O. megalodon, supporting the previous interpretations of its ovoviviparity and embryos' intrauterine oophagous behavior, but less likely the need for nursery areas. Additional inferred growth patterns corroborated by the known fossil record support the hypothesis that the emergence of C. carcharias during the Early Pliocene is at least partly responsible for the demise of O. megalodon due to competition for resources. These interpretations are working hypotheses expected to serve as reasonable reference points for future studies on the biology of O. megalodon.

The Paleozoic represents a key time interval in the origins and early diversification of chondrichthyans (cartilaginous fishes), but their diversity and macroevolution are largely obscured by heterogenous spatial and temporal sampling. The predominantly cartilaginous skeletons of chondrichthyans pose an additional limitation on their preservation potential and hence on the quality of their fossil record. Here, we use a newly compiled genus-level dataset and the application of sampling standardization methods to analyze global total-chondrichthyan diversity dynamics through time from their first appearance in the Ordovician through to the end of the Permian. Subsampled estimates of chondrichthyan genus richness were initially low in the Ordovician and Silurian but increased substantially in the Early Devonian. Richness reached its maximum in the middle Carboniferous before dropping across the Carboniferous/Permian boundary and gradually decreasing throughout the Permian. Sampling is higher in both the Devonian and Carboniferous compared with the Silurian and most of the Permian stages. Shark-like scales from the Ordovician are too limited to allow for some of the subsampling techniques. Our results detect two Paleozoic radiations in chondrichthyan diversity: the first in the earliest Devonian, led by acanthodians (stem-group chondrichthyans), which then decline rapidly by the Late Devonian, and the second in the earliest Carboniferous, led by holocephalans, which increase greatly in richness across the Devonian/Carboniferous boundary. Dispersal of chondrichthyans, specifically holocephalans, into deeper-water environments may reflect a niche expansion following the faunal displacement in the aftermath of the Hangenberg extinction event at the end of the Devonian.

The megatooth shark, dagger Otodus megalodon, which likely reached at least 15 m in total length, is an iconic extinct shark represented primarily by its gigantic teeth in the Neogene fossil record. As one of the largest marine carnivores to ever exist, understanding the biology, evolution, and extinction of dagger O. megalodon is important because it had a significant impact on the ecology and evolution of marine ecosystems that shaped the present-day oceans. Some attempts inferring the body form of dagger O. megalodon have been carried out, but they are all speculative due to the lack of any complete skeleton. Here we highlight the fact that the previous total body length estimated from vertebral diameters of the extant white shark (Carcharodon carcharias) for an dagger O. megalodon individual represented by an incomplete vertebral column is much shorter than the sum of anteroposterior lengths of those fossil vertebrae. This factual evidence indicates that dagger O. megalodon had an elongated body relative to the body of the modern white shark. Although its exact body form remains unknown, this proposition represents the most parsimonious empirical evidence, which is a significant step towards deciphering the body form of dagger O. megalodon.

Extensive bulk-sampling of the continuous Cretaceous-Paleogene boundary section at Gams (Styria, Austria) allows for the first time the description of the elasmobranch communities inhabiting the bathyal environment of this well-known section. The sampled succession comprises six horizons from the uppermost Maastrichtian (upper part of Nephrolites frequens Zone CC26) and five horizons from the lowermost Danian (Zone NP1), which yielded a total of 1852 elasmobranch teeth. Although the majority of the teeth are not well preserved, this study enabled the description of at least 16 taxa of the orders Hexanchiformes, Squaliformes, Orectolobiformes, Lamniformes and Carcharhiniformes, providing a rare snapshot of elasmobranch diversity of this specific environmental setting. Beside minor diversity fluctuations between the assemblages, the extensive bulk-sampling of this section did not reveal a marked diversity decline related to the end-Cretaceous mass extinction event. However, a noteworthy correlation between the deepening upward trend of the section with the appearance of frilled and goblin sharks points to changes in palaeobathymetry, which is also reflected in the increase of the total proportion of squaliform teeth in the uppermost sampled horizon. Furthermore, teeth of the extinct triakid Palaeogaleus were recovered exclusively from the Danian deeper deposits, expanding the palaeoecological range of the genus down to fairly deep marine environments. In addition, this study provides the first record of the lamniform Cretolamna ex gr. borealis from the Danian of the Tethyan Realm expanding the palaeogeographic distribution of this group.

This study reports elasmobranch remains from two fossil-rich horizons in the earliest Danian Olching Formation at Waidach, Austria. These outer neritic assemblages complement previous fine-scale bulk-sampling of latest Maastrichtian horizons at Waidach and document a regional elasmobranch faunal turnover across the Cretaceous-Palaeogene (K-Pg) boundary. The Danian assemblages show homogeneity in species richness and are dominated by squaliforms. The fauna comprises 16 species belonging to 12 genera including several new taxa (Centrodeania rugosa gen. et sp. nov., Centrodeania annae gen. et sp. nov., Incognitorapax fernsebneri gen. et sp. nov., Scyliorhinus alaformis sp. nov.). Comparison with latest Maastrichtian assemblages from Waidach revealed a marked faunal turnover across the K-Pg boundary associated with an increase in species richness and shift in abundance from Squaliformes to Carcharhiniformes. This is associated with marked environmental changes from a deep marine, dysoxic setting in the Maastrichtian to a more oxygenated, shallower environment in the earliest Danian. The turnover was driven by environmentally induced regional changes in species geographic ranges. High diversity in the Danian fauna suggests that the habitability of the corresponding palaeoenvironment was preserved or recovered immediately after the K-Pg event. Comparison with other elasmobranch assemblages across the K-Pg boundary highlights a strong control of local palaeoenvironmental settings over the timing and magnitude of the turnover. Our study emphasizes the importance of successive sampling to disentangle local from general patterns of faunal turnover during the K-Pg event and to better assess the consequences of this extinction event over elasmobranch diversity.

The previously known occurrences of Protoxynotus were stratigraphically disjunct with the first occurrence in the Turonian being separated by a gap of about 6 Myr from the Campanian occurrences. The new record of isolated teeth from the Late Santonian of Lebanon described in this study narrows this gap down to about 3 Myr with a hiatus spanning the Coniacian. Although the famous Lebanese Konservat-Lagerstatten are well known for its exquisitely preserved articulated elasmobranch specimens, previous studies paid little attention to recover isolated teeth exclusively found by acid processing of rock samples. In this study, we present for the first time isolated teeth, which were extracted from about two kilograms of rock matrix by acid processing. This study highlights the importance and potential of acid processing even of small sample sizes for unlocking the stratigraphic and palaeogeographic occurrence of elasmobranchs through time, providing essential data for global diversity analyses of this group. Furthermore, this study documents the first record of Protoxynotus in the southern Tethyan Realm and pointing towards the occupation of overlapping or similar habitats of the deep-water somniosids Protoxynotus and Cretascymnus during the Late Cretaceous.

This study describes for the first time a number of distinct fossil teeth documenting several deep-sea shark species from the Eocene, which were previously not recorded from the North Sea Basin, including Apristurus sp., Orthechinorhinus cf. pfeili, Deania cf. angoumeensis, Squaliolus sp., Etmopterus cf. cahuzaci and Paraetmopterus nolfi. Our findings significantly increase the deep-sea shark diversity documented from this area so far. Despite the fact that the North Sea Basin had already lost direct connections to the neighbouring marine areas in the Eocene, the fauna shows highest similarities with documented Eocene deep-sea faunas of France, Austria and northern Morocco using cluster analysis.

Extensive bulk sampling of seven horizons of a continuous succession deposited in an outer neritic environment of the latest Maastrichtian yielded more than three thousand ichthyoliths, including 1347 elasmobranch teeth. The sampled succession represents a characteristic deep-water fauna dominated by small squaliform sharks with an increase of species richness towards the end of the Cretaceous. The multidisciplinary approach of precise sampling in combination with a well-founded biostratigraphic classification of seven assemblages provides rare and direct evidence of diversity fluctuations within the latest Maastrichtian, immediately before the bolide impact triggered the severe mass extinction event at the K/Pg boundary. Although squaliform sharks dominate the fauna, a conspicuous heterogeneity of species abundance between the assemblages is observed and a noteworthy correlation between squa-liform species richness and the abundance of Parasquatina zitteli (Orectolobiformes) might indicate clade competition for ecological niches. Among 15 elasmobranch species, this study describes one new genus (Fredipristis gen. nov.) and four new squaliform species (F. eximia gen. et sp. nov., Eoetmopterus davidi sp. nov., Proetmopterus lukasi sp. nov., and Cretascymnus beauryi sp. nov.), which highlights the importance and potential of bulk sampling for reconstructing elasmobranch diversity of deep-marine realms through time.(c) 2022 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Due to the peculiar combination of dental features characteristic for different squaliform families, the position of the Late Cretaceous genera Protoxynotus and Paraphorosoides within Squaliformes has long been controversial. In this study, we revise these genera based on previously known fossil teeth and new dental material. The phylogenetic placement of Protoxynotus and Paraphorosoides among other extant and extinct squaliforms is discussed based on morphological characters combined with DNA sequence data of extant species. Our results suggest that Protoxynotus and Paraphorosoides should be included in the Somniosidae and that Paraphorosoides is a junior synonym of Protoxynotus. New dental material from the Campanian of Germany and the Maastrichtian of Austria enabled the description of a new species Protoxynotus mayrmelnhofi sp. nov. In addition, the evolution and origin of the characteristic squaliform tooth morphology are discussed, indicating that the elongated lower jaw teeth with erected cusp and distinct dignathic heterodonty of Protoxynotus represents a novel functional adaptation in its cutting-clutching type dentition among early squaliform sharks. Furthermore, the depositional environment of the tooth bearing horizons allows for an interpretation of the preferred habitat of this extinct dogfish shark, which exclusively occupied shelf environments of the Boreal- and northern Tethyan realms during the Late Cretaceous.

Repeated bulk sampling for over a decade in an indurated glauconitic sandy marl horizon at St. Pankraz Salzburg, Austria, has yielded a diverse assemblage of 37 elasmobranchs (sharks and rays) from the early middle Eocene (Lutetian). This elasmobranch fauna is dominated by epipelagic and mesopelagic taxa known today to preferentially inhabit the middle or outer continental shelf and upper slope, indicating that the depositional environment of the top Member of Kressenberg Formation in Austria has a more complex bathymetric history than previously thought. As these new occurrences fill a substantial gap in the sporadic fossil record of Eocene mesopelagic elasmobranchs, comparisons of this assemblage with the coeval mesopelagic faunas indicate that this northwestern Tethyan realm association shares considerable similarities with those recovered from the North Sea Basin and the northeastern Atlantic. This suggests that the faunal homogeneity observed in neritic and coastal elasmobranch communities during the warm early middle Eocene is also characterised in mesopelagic habitats.

The Carboniferous is characterized by drastic climatic and environmental fluctuations, which include multiple phases of glaciation resulting in an icehouse climate. Additionally, dynamic continental reconfigurations forced the contraction of the Rheic Ocean resulting in the closure of the Rheic–Tethyan Gateway, which precluded further faunal exchanges between the North American and Eurasian marine realms. Interestingly, cartilaginous fishes seem to be relatively immune to these drastic climatic and environmental changes. The Eurasian fossil record of Paleozoic sharks is strongly biased towards intensively sampled localities from England, Ireland, Scotland, and the Russian Platform. Here we present rare dental material from the Serpukhovian (early Carboniferous) of Austria, adding new information to the paleogeographic distribution of ctenacanthiform sharks. The new material revealed the first record of the genus Saivodus in Central Europe and allowed us to recognize a new species, Cladodus gailensis sp. nov., and a remnant of fossilized cartilage. In an attempt to identify possible linkages between climatic or environmental fluctuations on shark diversity throughout the Carboniferous, we provide a synopsis of the distribution and diversity of elasmobranchs based on primary literature. This preliminary assessment at genus level indicates two pronounced events of extinction, with the first one occurring during the latest Mississippian and the second one towards the end of the Pennsylvanian. The first extinction event distinctly correlates with the known diversity decline of other marine inhabitants and the second occurred during an unstable period of multiple phases of glaciation.

ABSTRACT Based on a shark-bitten partial skeleton of an immature sirenian (Metaxytherium cf. medium) from the middle Miocene of the Styrian Basin (Austria), we report on the oldest predator–prey interaction between tiger sharks and dugongs. The bite mark-bearing ribs and vertebrae are associated with seven teeth of Galeocerdo aduncus, which are otherwise rare in the fossil record of the Styrian Basin. The unique tooth morphology of the genus Galeocerdo is reflected by an unambiguous pattern of bite marks, which is repeatedly detected on one rib fragment. Similar bite marks were reproduced experimentally by using clay instead of bone. The obtained pattern is consistent with the observed bite marks on the sirenian rib fragment, which demonstrates that tiger sharks fed upon the Metaxytherium carcass. Furthermore, we also report on the first record of the angel shark Squatina sp. within the Styrian Basin.