Sharks are cartilaginous fish that appeared 245 million years ago and became a highly diversified group, occupying several niches successfully. On the coast of Rio Grande do Sul, Brazil, shark ...fossils are commonly found ex situ associated with accumulations of biodetrital gravels along the current beach line. The present study consisted of a faunistic and paleobiologic survey of sharks from the Quaternary in the southern region of the Rio Grande do Sul Coastal Plain (RSCP), southern Brazil. Based on taxonomy, about 3611 fossilized shark teeth collected on the beaches of Cassino and Hermenegildo were analyzed. A total of 13 taxa were identified, among them cf. Carcharhinus brachyurus, cf. Carcharhinus leucas, cf. Carcharhinus longimanus, Carcharhinus sp., Carcharias taurus, Carcharodon carcharias, Galeocerdo cuvier, Galeorhinus galeus, Isurus oxyrinchus, Notorynchus cepedianus, Rhizoprionodon sp., Sphyrna sp. and Squatina sp. Besides the already known species, here we also report the presence of Carcharhinus brachyurus, Carcharhinus longimanus, Galeorhinus galeus, Rhizoprionodon sp. and Squatina sp. as the first fossil record in the Pleistocene of Brazil for these taxa in the region. The study showed that the fossil taxa identified are similar to those extant taxa that inhabit the coast of Rio Grande do Sul. Evidence of climate oscillations that occurred during the Quaternary can be seen throughout the presence of the species Carcharhinus leucas, Carcharodon carcharias, and Galeocerdo cuvier (when compared to the composition of the modern shark fauna). Since, currently, the occurrence of these species are given as rare in the region. The present study expanded the occurrence of fossil species on the coast of the state of Rio Grande do Sul and confirmed the occurrence of populations of Carcharias taurus, Carcharodon carcharias, Carcharhinus sp., and Carcharhinus leucas during the Quaternary.
•13 shark fossil taxa from the Quaternary were identified in the Rio Grande do Sul Coastal Plain.•There are similarities between the fossil and recent Quaternary shark fauna on the east coast of Rio Grande do Sul, Brazil.•Climatic fluctuations during the Quaternary would alter the distribution of shark taxa.
•All sharks studied to date are cone monochromats and likely colour blind.•A reversion to cone monochromacy has occurred independently at least three times.•Opsin loss may represent convergent ...evolution in eye design in marine predators.•Rays are cone dichromats and capable of seeing colour.•Elasmobranchs are a valuable counterpoint for vision studies in other vertebrates.
The visual sense of elasmobranch fishes is poorly studied compared to their bony cousins, the teleosts. Nevertheless, the elasmobranch eye features numerous specialisations that have no doubt facilitated the diversification and evolutionary success of this fascinating taxon. In this review, I highlight recent discoveries on the nature and phylogenetic distribution of visual pigments in sharks and rays. Whereas most rays appear to be cone dichromats, all sharks studied to date are cone monochromats and, as a group, have likely abandoned colour vision on multiple occasions. This situation in sharks mirrors that seen in other large marine predators, the pinnipeds and cetaceans, which leads us to reassess the costs and benefits of multiple cone pigments and wavelength discrimination in the marine environment.
Chondrichthyan species are considered highly susceptible to fishing activities and as “indicator species” for overfishing and ecosystem stability. In European waters, chondrichthyes have become a ...focus of conservation actions due to the abundance declines of several species.
In the present study, fishery independent data obtained from the Mediterranean International Trawl Surveys (MEDITS) in the Aegean and E. Ionian Seas (eastern Mediterranean) were coupled with bottom trawl fishing effort data obtained from vessel monitoring systems (VMS) in order to evaluate the effect of fishing on biomass variations of demersal chondrichthyan species. The study focused on commonly captured species such as Raja clavata, Galeus melastomus, Scyliorhinus canicula and Squalus spp, as well as to the total chondrichthyan biomass. The effect of fishing effort on biomass indices, expressed in terms of kg per square km of swept area, was examined by means of Generalized Additive Model techniques, using also the sampling position, year and depth as co-variates.
Overall findings suggested a biomass decline of chondrichthyan species with increasing fishing effort. Nevertheless, it was also found that certain species (e.g G. melastomus in both areas and S. canicula in the Aegean Sea) can withstand fishing pressure and it is likely that discard survival rates, depth preferences and fisheries exploitation patterns, are the main drivers explaining variations regarding the impact of fishing on the different stocks.
Gladbachus adentatus is a putative chondrichthyan, known only from the holotype specimen, which comprises an articulated endoskeleton complete from head to pelvic region with the squamation also ...preserved. The scales superficially resemble those of placoderms more than sharks, in having a similar gross morphology, lamellar cellular bone forming the base and upright dentinous tubercles comprising the crown. The odontocytic mesodentine in the tubercles is comparable to that in the Osteostraci and in some acanthodian taxa, known only from isolated scales, and is probably the plesiomorphic form of dentine for Gnathostomata.
Recent studies have uncovered mosaic patterns of allometric and isometric growth underlying ontogenetic shifts in the body form of elasmobranch species (shark and rays). It is thought that shifts in ...trophic and spatial ecology through ontogeny drive these morphological changes; however, additional hypotheses relating to developmental constraints have also been posed. The bull shark (Carcharhinus leucas) is a large‐bodied coastal shark that exhibits strong ontogenetic shifts in trophic and spatial ecology. In this study, we utilise a large data set covering a large number of morphological structures to reveal ontogenetic shifts in the body form of C. leucas, stratifying analyses by sex and size classes to provide fine‐scale, more ecomorphologically relevant results. Our results indicate shifts in functional demands across the body through ontogeny, driven by selective pressures relating to trophic and spatial ecology driving the evolution of allometry. We also find significant differences in scaling trends between life stages, and between the sexes, highlighting the importance of utilising large, diverse datasets that can be stratified in this way to improve our understanding of elasmobranch morphological evolution. Ultimately, we discuss the implications of these results for existing ecomorphological hypotheses regarding the evolution of specific morphological structures, and pose novel hypotheses where relevant.
Bull sharks display shifts in functional demands across the body through ontogeny. Morphological scaling differs between life stages and sexes. These results highlight the importance of large sample sizes in studies of shark morphometry.
During field and laboratory investigation of the phosphate nodules that are eroding from the Excello Shale of the Senora Formation, Cabaniss Group, Desmoinesian, of Middle Pennsylvanian age of Rogers ...County in northeastern Oklahoma has produced numerous vertebrate, invertebrate, and plant fossils. The vertebrate material recovered include the dermal denticles of Petrodus patelliformis and Listracanthus hystrix, along with teeth of Cladodus occidentals, Caseodus eatoni, Edestus sp, Lisgodus serratus, and a spine from the spine-brush complex of Stethacanthus sp. Previously, the only known vertebrates reported from the Excello Shale of Oklahoma were Edestus and Petrodus. This report thus increases the number of known vertebrates from the Excello Shale of northeastern Oklahoma.
Occurrence, abundance and size trends of 25 demersal Chondrichthyes (10 Sharks: 3 Carcharhiniformes, 2 Hexanchiformes, 5 Squaliformes; 14 Batoids: 3 Myliobatiformes, 8 Rajiformes, 3 Torpediniformes ...and 1 Holocephalan: 1 Chimaeriformes) collected from 22 years (1994–2015) of Mediterranean International Trawl Surveys (MEDITS) around Sardinian seas, were given. Data relative to two strata, the continental shelf (10–200m), the slope (201–800m), and the overall (10–800m), were analyzed in order to identify the general species distribution of their habitat preference. From the gathered data it appeared that the shelf was mostly inhabited by batoids while the slope by sharks. Only the small-spotted catshark Scyliorhinus canicula and the thornback skate Raja clavata were equally distributed with high values of occurrence and abundance both in the shelf and in the slope. All the other species showed a preferential distribution only in one stratum (shelf or slope). In general, temporal trends of abundance indexes were stable or increasing in all strata. GAM analysis also confirmed a stable trend. Almost all species displayed stable in size structure analysis, apart from R. brachyura and Dipturus oxyrinchus that showed a statistically increasing trend. Although the investigated chondrichthyan species seemed to display a not alarming status of conservation in Sardinian seas, more investigation should be done to assure a proper management of this threatened resource.
The deep-sea can act as a sink for legacy contaminants such as organochlorines (OCs), causing damages in its inhabitants for their persistence and their prolonged effects in the organisms. HCB, DDT ...and its isomers, and 28 PCBs congeners were detected in muscle and embryonic tissues of three deep-sea chondrichthyes Chimaera monstrosa (n = 16), Dalatias licha (n = 12) and Etmopterus spinax (n = 51) sampled in Ligurian and Tyrrhenian Sea (Mediterranean Sea). Contaminant distribution in E. spinax and C. monstrosa was PCBs > DDTs ≫ HCB while in D. licha was DDTs > PCBs ≫ HCB. Statistically significant differences were highlighted in OC levels among the species, but no such differences were found among sexes. Ratios between DDT isomers highlighted an historical input of the pesticide in the environment. For the first time was also demonstrated maternal transfer in deep water chondrichthyes, specifically in E. spinax where was highlighted that transfer of contaminants increases with increasing compound's Log Kow.
•OC pattern in sampled species was HCB < DDTs < PCBs.•OC burden in the species was made up of OCs with EDC properties.•OCs maternal transfer was documented for the first time in deep sea chondrichthyes.•OCs with higher LogKow showed greater maternal transfer in E. spinax.•Legacy contaminants are still a threat to deep-sea biodiversity conservation.
The central tenet of ecomorphology links ecological and morphological variation through the process of selection. Traditionally used to rationalise morphological differences between taxa, an ...ecomorphological approach is increasingly being utilised to study morphological differences expressed through ontogeny. Elasmobranchii (sharks, rays and skates) is one clade in which such ontogenetic shifts in body form have been reported. Such studies are limited to a relatively small proportion of total elasmobranch ecological and morphological diversity, and questions remain regarding the extent to which ecological selection are driving observed morphometric trends. In this study, we report ontogenetic growth trajectories obtained via traditional linear morphometrics from a large data set of the brown smoothhound shark (Mustelus henlei). We consider various morphological structures including the caudal, dorsal and pectoral fins, as well as several girth measurements. We use an ecomorphological approach to infer the broad ecological characteristics of this population and refine understanding of the selective forces underlying the evolution of specific morphological structures. We suggest that observed scaling trends in M. henlei are inconsistent with migratory behaviour, but do not contradict a putative trophic niche shift. We also highlight the role of predation pressure and sex‐based ecological differences in driving observed trends in morphometry, a factor which has previously been neglected when considering the evolution of body form in sharks.
Ontogenetic shifts in body form have been reported in a number of shark species and are primarily thought to result from differences in trophic ecology or habitat usage between life stages. However, existing studies are taxonomically and ecologically restricted, meaning ontogenetic scaling trends across Elasmobranchii (sharks and rays) are poorly understood. We report ontogenetic morphometric trajectories in the brown smoothhound shark (Mustelus henlei), using existing theory to predict basic ecological characteristics of the population in question. We also highlight potential roles of sexual dimorphism and predation pressure in driving ontogenetic changes in body form.”
This study describes the feeding ecology, spatial distribution of each ontogenetic phase and the corresponding plastic debris contamination, in the Caribbean sharpnose shark, Rhizoprionodon porosus ...as a function of spatial-temporal parameters in the Western South American coastal region. The density and biomass of all individuals, captured in a surface drift gillnet fishery, were 1.3 ± 0.3 ind.day −1 and 877 ± 232 g.day −1, respectively. Neonates, and juveniles were captured during all seasons. Adults were largely caught during the late rainy and early dry seasons, probably moving offshore to adjacent open waters during the late dry season. The diet of R. porosus consisted mainly of fish (FO = 71.8%). All ontogenetic phases were contaminated by plastic debris (FO = 100%). Among the plastic debris detected in R. porosus, 91.6% were microplastics (MP) (<5 mm), of which blue fibers contributed 53.7%. The MP samples were identified as polyethylene by Optical microscopy (OM), Fourier Transform Infrared spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and by Energy dispersion X-ray spectroscopy (EDS). R. porosus has a high gut concentration of MP compared to fishes of lower trophic levels. In addition, many fishes within the stomach contents of R. porosus were themselves contaminated with MP (e.g., Eugerres brasilianus, Harengula clupeola, Rhinosardinia bahiensis, Anchovia clupeoides, Monacanthus ciliatus, Polydactylus virginicus, Trachinocephalus myops, Eucinostomus melanopterus, and Lutjanus analis). The piscivorous diet of R. porosus likely leads to accumulation of MP contamination in this top predator through trophic transfer.
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•Density and biomass of R. porosus fluctuated with the seasonal changes.•Blue fiber is the most frequent microplastic contaminant for coastal top predator.•The main source of microplastic is related to artisanal fishery activities.•The piscivorous feeding habit is responsible for the microplastic trophic transfer.
