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354 results for “elasmobranch”

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dryad36/100

Data from: The early elasmobranch Phoebodus: phylogenetic relationships, ecomorphology, and a new time-scale for shark evolution

Anatomical knowledge of early chondrichthyans and estimates of their phylogeny are improving, but many taxa are still known only from microremains. The nearly cosmopolitan and regionally abundant Devonian genus Phoebodus has long been known solely from isolated teeth and fin spines. Here, we report the first skeletal remains of Phoebodus from the Famennian (Late Devonian) of the Maïder region of Morocco, revealing an anguilliform body, specialized braincase, hyoid arch, elongate jaws and rostrum, complementing its characteristic dentition and ctenacanth fin spines preceding both dorsal fins. Several of these features corroborate a likely close relationship with the Carboniferous species Thrinacodus gracia, and phylogenetic analysis places both taxa securely as members of the elasmobranch stem lineage. Identified as such, phoebodont teeth provide a plausible marker for range extension of the elasmobranchs into the Middle Devonian, thus providing a new minimum date for the origin of the chondrichthyan crown-group. Among pre-Carboniferous jawed vertebrates, the anguilliform body shape of Phoebodus is unprecedented, and its specialized anatomy is, in several respects, most easily compared with the modern frilled shark Chlamydoselachus. These results add greatly to the morphological, and by implication ecological, disparity of the earliest elasmobranchs.

opencc-zeroSep 2019View details →

dryad36/100

The impact of the Pull of the Recent in extant elasmobranchs

Modern elasmobranchs have a long evolutionary history and an abundant fossil record. Many fossil taxa have living representatives. However, the representation of extant taxa in the fossil record is unknown. To begin to understand the geological history of extant elasmobranchs, here we assess the quality of their fossil record. We do so by assessing the Pull of the Recent (herein, POR). The POR can bias the fossil record because the rather complete record of living taxa allows palaeontologists tobridge time bins where fossils are absent. We assessed the impact of the POR by quantifying the proportion of extant elasmobranchs that have a fossil record, but do not occur in the last 5 million years. We found that the POR does not affect orders and families, but it does affect 24% of elasmobranch genera. Although modest, the impact of the POR in extant elasmobranch genera is higher than that found in other taxa. Overall, the geological history of elasmobranchs contradicts the usual assumption that the fossil record becomes worse backwards in time. This is the case across geographical regions and tooth size, further suggesting that sampling intensity and outcrop availability can help explain the POR effect on sharks and rays.

opencc-zeroFeb 2020View details →

dryad36/100

Using protein isolation on elasmobranch blood plasma for ecological research and stable isotope analysis

Stable isotope analysis is a useful tool for studying the ecology of elasmobranchs. Analysis of elasmobranch blood plasma provides insight into an individual's ecology on a small temporal scale. However, plasma is a systemic transport vessel containing many dissolved constituents in variable amounts, which may bias analyses and ecological conclusions based on that data. In this study, we develop a new method of protein precipitation using ethanol and acetonitrile to isolate the protein fraction of plasma from Sandbar Sharks, and examine its effects on carbon and nitrogen stable isotope values. We also tested these solvent precipitations on bovine serum albumin as a control to assess the introduction of exogenous sources of C and N. Protein isolation resulted in a significant decrease in δ13C values and a significant increase in C:N compared to untreated plasma. Isolated proteins were not significantly different in δ15N value compared to untreated plasma. We observed no change in isotope composition in bovine serum albumin samples, indicating protein precipitation does not itself affect isotope analysis. These results suggest that the preparation of blood plasma is necessary for stable isotope analysis, to eliminate the biasing effects of other dissolved compounds. We find that solvent precipitation is an effective method of isolating proteins for stable isotope studies.

opencc-zeroMar 2024View details →

dryad36/100

Exceptionally preserved shark fossils from Mexico elucidate the long-standing enigma of the Cretaceous elasmobranch Ptychodus

The fossil fish Ptychodus Agassiz, 1834, characterized by a highly distinctive grinding dentition and an estimated gigantic body size, has remained one of the most enigmatic extinct elasmobranchs (i.e. sharks, skates, and rays) for nearly two centuries. This widespread Cretaceous taxon is common in Albian to Campanian deposits from almost all continents. However, specimens mostly consist of isolated teeth or more or less complete dentitions, whereas cranial and post-cranial skeletal elements are very rare. Here we describe newly discovered material from the early Late Cretaceous of Mexico, including complete articulated specimens with preserved body outline, which reveals crucial information on the anatomy and systematic position of Ptychodus. Our phylogenetic and ecomorphological analyses indicate that ptychodontids were high-speed (tachypelagic) durophagous lamniforms (mackerel sharks), occupying a specialized predatory niche previously unreported among both extant and extinct elasmobranchs. Our results support the view that lamniforms were ecomorphologically highly diverse and represented the dominant group of sharks in Cretaceous marine ecosystems. Ptychodus may have fed predominantly on nektonic hard-shelled prey items such as ammonites and sea turtles rather than on benthic invertebrates, and its extinction during the Campanian, well before the end-Cretaceous crisis, might have been related to competition with emerging blunt-toothed globidensine and prognathodontine mosasaurs.

opencc-zeroMar 2024View details →

dryad36/100

Population and seascape genomics of a critically endangered benthic elasmobranch, the blue skate Dipturus batis

The blue skate (Dipturus batis) has a patchy distribution across the North-East Atlantic Ocean, largely restricted to occidental seas around the British Isles following fisheries-induced population declines and extirpations. The viability of remnant populations remains uncertain, and could be impacted by continued fishing and bycatch pressure and the projected impacts of climate change. We genotyped 503 samples of D. batis, obtained opportunistically from the widest available geographic range, across 6,350 single nucleotide polymorphisms (SNPs) using a reduced-representation sequencing approach. Genotypes were used to assess the species' contemporary population structure, estimate effective population sizes, and identify putative signals of selection in relation to environmental variables using a seascape genomics approach. We identified genetic discontinuities between inshore (British Isles) and offshore (Rockall and Faroe Island) populations, with differentiation most pronounced across the deep waters of the Rockall Trough. Effective population sizes were largest in the Celtic Sea and Rockall, but low enough to be of potential conservation concern among Scottish and Faroese sites. Among the 21 candidate SNPs under positive selection was one significantly correlated with environmental variables predicted to be affected by climate change, including bottom temperature, salinity, and pH. The paucity of well annotated elasmobranch genomes precluded us from identifying a putative function for this SNP. Nevertheless, our findings suggest that climate change could inflict a strong selective force upon remnant populations of D. batis, further constraining its already restricted habitat. Furthermore, the results provide fundamental insights on the distribution, behaviour, and evolutionary biology of D. batis in the North-East Atlantic that will be useful for the establishment of conservation actions for this and other critically endangered elasmobranchs.

opencc-zeroDec 2021View details →

dryad36/100

Barriers in a sea of elasmobranchs

Background The interplay of animal dispersal and environmental heterogeneity is fundamental for the distribution of biodiversity on earth. In the ocean, the interaction of physical barriers and dispersal has primarily been examined for organisms with planktonic larvae. Animals that lack a planktonic life stage and depend on active dispersal are however likely to produce distinctive patterns. Methods We used available literature on population genetics and phylogeography of elasmobranchs (sharks, rays and skates), to examine how marine barriers and dispersal ecology shape genetic connectivity in animals with active dispersal. We provide a global geographic overview of barriers extracted from the literature and synthesize the geographic and hydrologic factors, spatial and temporal scales to characterize different types of barriers. The three most studied barriers were used to analyse the effect of elasmobranch dispersal potential and barrier type on genetic connectivity. Results We characterized nine broad types of marine barriers, with the three most common barriers being related to ocean bathymetry. The maximum depth of occurrence, maximum body size and habitat of each species were used as proxies for dispersal potential, and were important predictors of genetic connectivity with varying effect depending on barrier type. Environmental tolerance and reproductive behaviour may also play a crucial role in population connectivity in animals with active dispersal. However, we find that studies commonly lack appropriate study designs based on a priori hypotheses to test the effect of physical barriers while accounting for animal behaviour. Main conclusions Our synthesis highlights the relative contribution of different barrier types in shaping elasmobranch populations. We provide a new perspective on how barriers and dispersal ecology interact to rearrange genetic variation of marine animals with active dispersal. We illustrate methodological sources that can bias the detection of barriers and provide potential solutions for future research in the field.

opencc-zeroJul 2022View details →

zenodo36/100

Diving into the vertical dimension of elasmobranch movement ecology

Knowledge of the three-dimensional movement patterns of elasmobranchs is vital to understanding their ecological roles and exposure to anthropogenic pressures. To date, comparative studies among species at global scales have mostly focused on horizontal movements. Our study addresses the knowledge gap of vertical movements by compiling the first global synthesis of vertical habitat use by elasmobranchs from data obtained by deployment of 989 biotelemetry tags on 38 elasmobranch species. Elasmobranchs displayed high intra- and interspecific variability in vertical movement patterns. Significant vertical overlap was observed for many epipelagic elasmobranchs, indicating an increased likelihood to display spatial overlap, biologically interact, and share similar risk to anthropogenic threats that vary on a vertical gradient. We highlight the critical next steps towards incorporating vertical movement into global management and monitoring strategies for elasmobranchs, emphasising the need to address geographic and taxonomic biases in deployments and to concurrently consider both horizontal and vertical movements.

opencc-by-4.0Dec 2021View details →

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FIGURE 2 in Trophic relationships in the Early Miocene Upper Marine Molasse of Baden-Württemberg, Southwest Germany, with special emphasis on the elasmobranch fauna

FIGURE 2. Map showing the fossiliferous localities studied herein.

opencc-by-4.0Dec 2023View details →

zenodo36/100

Figure 1 in Short Communication First record of two Myliobatid Elasmobranchs from West Bengal, northern east coast of India

Figure 1. Rhinoptera javanica collected from West Bengal coast.

opencc-by-4.0Dec 2020View details →

dryad36/100