Although selachian fossil remains have been studied for nearly three centuries, little is known about their evolutionary history. Recent studies have suggested different timings of early ...diversification events in the Late Triassic, Jurassic, and Early Cretaceous. However, Late Cretaceous selachian diversity has remained little explored despite numerous and diversified selachian assemblages known from this time interval. Sampling standardization, origination/extinction rates, and raw ordinal diversity were examined based on taxonomic occurrences in three data sets representing distinct geographical areas (Anglo-Paris Basin, northwestern Europe, and Western Interior Seaway) spanning the Cenomanian-Campanian interval. This examination allowed the identification of regional diversity events, previously reported for some invertebrate groups, but presented for the first time for a marine vertebrate group. The local mid-Cenomanian diversity drop (Anglo-Paris Basin) is interpreted as a possible consequence of changes in bottom seawater conditions related to the rapid mid-Cenomanian transgression. The Cenomanian/Turonian faunal turnover is likely to be due to various sampling biases (Anglo-Paris Basin and northwestern Europe), but a genuine extinction in the Western Interior Seaway cannot be excluded. The Santonian diversity peak synchronous with a marked global increase in seawater temperatures contrasts with the rapid temperature decrease linked with low diversity in the early Campanian.
Age-structured demographic models were constructed based on empirical estimates of longevity and maturity for five deepwater Bering Sea skates to investigate how observed differences in life history ...parameters affect population growth rates. Monte Carlo simulations were used to incorporate parameter uncertainty. Estimated population growth rates ranged from 1.045 to 1.129 yr-1 and were lower than those reported for other Alaskan skates and most chondrichthyans. Population growth rates of these and other high-latitude skates increased with relative reproductive lifespan, but displayed no significant relationship with body size or depth distribution, suggesting that assemblage shifts may be difficult to predict for data-poor taxa. Elasticity analyses indicated that juvenile and adult survival had greater per-unit effects on population growth rates than did egg-case survival or fecundity. Population growth rate was affected more by uncertainty in age at maturity than maximum age. The results of this study indicate that if skates are deemed to be a management concern, gear modifications or depth-specific effort controls may be effective.
Abstract The objective of this study was to describe the histology and histochemistry of the integument covering the back and stinger of the freshwater stingray Potamotrygon rex, endemic to the ...Middle Upper Tocantins River. The species has a dark back and yellowish circular spots that extend to the tail, which has one to two stings located in the median portion of the tail. Through histological study it was observed that the epithelia of the back and stinger are composed of non-keratinized stratified pavement epithelial tissue, and are organized in three layers: basal, intermediate and superficial. The differences between the tissues are related to the cell types that compose them. The back is organized with epithelial cells, mucus cells, granulocyte cells and chromatophores. The mucus cells are distributed in different layers along the animal's back, influencing the thickness of the tissue. The tissue that covers the stinger is composed of epithelial cells, chromatophores and specialized cells in protein synthesis. In the histochemistry, the stinger epithelial cells were stained with Bromophenol Blue, especially those of the intermediate layer, which were called specialized cells. In the back the epithelial cells were stained with Bromophenol Blue, Alcian Blue and PAS, and the mucous cells with PAS. In both tissues the presence of protein reserves was detected, areas so called because they are stained strongly with Bromophenol Blue. The results show that the stinger presents activity directed to the production of proteins, and that the back is organized to produce different components, which constitute the cuticle that covers the animal's body.
Resumo O objetivo deste estudo foi descrever a histologia e histoquímica do tegumento que reveste o dorso e o ferrão da arraia de água doce Potamotrygon rex, endêmica do Médio Alto Tocantins. A espécie possui o dorso escuro e manchas circulares amareladas que se estendem até a cauda, que possui de um a dois ferrões localizados na porção mediana da cauda. Através do estudo histológico observou-se que os epitélios do dorso e do ferrão são compostos por tecido epitelial pavimentoso estratificado não queratinizado, e estão organizados em três camadas: basal, intermediária e superficial. As diferenças entre os tecidos estão relacionadas aos tipos de células que os compõem. O dorso é organizado com células epiteliais, células mucosas, células de granulócitos e cromatóforos. As células mucosas estão distribuídas em diferentes camadas ao longo do dorso do animal, influenciando na espessura do tecido. O tecido que reveste o ferrão é composto por células epiteliais, cromatóforos e células proteicas. Na histoquímica, as células epiteliais do ferrão foram coradas com Azul de Bromofenol, principalmente as da camada intermediária, que foram denominadas células proteicas. No dorso as células epiteliais foram coradas com Azul de Bromofenol, Azul Alcian e PAS, e as células mucosas com PAS. Em ambos os tecidos também foi detectada a presença de reservatórios de proteínas, áreas assim denominadas por estarem fortemente coradas com Azul de Bromofenol. Os resultados mostram que o ferrão apresenta atividade direcionada à produção de proteínas, e que o dorso se organiza para produzir diferentes componentes que constituem a cutícula que reveste o corpo do animal.
Three species assigned to the same nominal genus of Paleozoic xenacanthiform shark have been combined with the name Orthacanthus gracilis (Chondrichthyes, Xenacanthiformes, Orthacanthidae). ...Orthacanthus gracilis (Giebel, 1848), which was originally combined as Chilodus gracilis Giebel, 1848, is the senior synonym; it has priority over both Orthacanthus gracilis (Newberry, 1857), which was originally combined as Diplodus gracilis Newberry, 1857, and Orthacanthus gracilis Newberry, 1875a. Proposed species-group replacement names are Orthacanthus lintonensis nom. nov. for O. gracilis (Newberry, 1857) and Orthacanthus adamas nom. nov. for O. gracilis Newberry, 1875a. Chilodus gracilis Giebel, 1848 is designated as the type species of Chilodus Giebel, 1848; this species becomes the type species for Giebelodus Whitley, 1940, which is a replacement name for Chilodus Giebel, 1848 (preoccupied by Chilodus Müller & Troschel, 1844, Actinopterygii). Giebelodus Whitley, 1940 is a junior subjective synonym of Orthacanthus Agassiz, 1843.
Leptocharias smithii has been poorly explored in anatomical terms. This species bears a mosaic of morphological characters and is considered to represent an intermediate condition between other ...carcharhiniform clades. In the present paper, the anatomy of the appendicular skeleton of the species is thoroughly investigated and compared with other representatives of the order Carcharhiniformes. Leptocharias bears exclusive characteristics, such as the visible separation of the pro‐ and mesopterygia but it also has an aplesodic pectoral fin, a condition shared with carcharhiniforms placed at the base of the phylogenetic tree and at the same time a chevron‐shaped coracoid bar, a condition characteristic of charcharhiniforms placed at the apex of the phylogenetic tree. Additionally, in an attempt to understand the evolution of its appendicular skeleton and of other carcharhiniforms, 20 characters of the paired fins and girdles are explored and discussed in light of two recent phylogenetic hypotheses. Most of these characters were not previously explored and support not only the monophyly of Carcharhiniformes, such as the mesopterygium overlapping the metapterygium in ventral view, but also the monophyly of the less inclusive clade Hemigaleidae + (Galeocerdonidae + (Carcharhinidae+Sphyrnidae)), such as the morphology and arrangement of the distal radials, which are pointed and spaced.
The appendicular skeleton of Leptocharias smithii is comparatively analyzed in relation to other carcharhiniforms. The evolution of the paired fins within Carcharhiniformes is discussed in light of two recent phylogenetic hypotheses. The appendicular skeleton is a rich source of phylogenetic information.
The structure of marine communities is affected by both fishing and climate variability. The Argentinean-Uruguayan Common Fishing Zone (AUCFZ) comprising the Rio de la Plata and its oceanic front (SW ...Atlantic, 34degrees 30' to 39degrees 30' S) has a high environmental variability. Intensive trawling activity results in the bycatch of many chondrichthyan species. Using generalized linear mixed models, we analyzed the effects of commercial fishing effort, sea surface thermal anomalies (SSTA) and depth on the spatiotemporal dynamics of chondrichthyan species richness and total number of individuals in 3 zones of the AUCFZ between 1984 and 2009. Species richness increased with fishing effort in warmer years in the northern zone but displayed the opposite trend in the river and southern zones. While the total number of individuals decreased in the coldest years and at greater depths in the northern zone, these 2 variables had opposite effects in the southern zone. Depth had a stronger effect on both chondrichthyan species richness and the total number of individuals than the other 2 explanatory variables. While SSTA and depth had statistically significant effects on species richness and the total number of individuals, commercial fishing effort was significantly related only with species richness. The spatial variability of both response variables was greater than their temporal variation during the study period. These findings contribute to a greater understanding of the spatio-temporal dynamics of demersal chondrichthyans in the AUCFZ and are of relevance to the longterm sustainable management of chondrichthyans in this area and elsewhere.
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