RESUMEN
This study describes and illustrates the jaws, teeth, and tooth microstructure of the Prickly Dogfish Oxynotus bruniensis. Detailed accounts of the dental morphology of O. bruniensis are rare and have not addressed the tissue arrangement or microstructure of the teeth. These features are documented and discussed in the contexts of interspecific comparisons with other elasmobranchs and the dietary specialization of O. bruniensis. The overall tooth morphology of O. bruniensis is similar to those of other closely related members in the order Squaliformes, as is the tissue arrangement, or histotype. Oxynotus bruniensis exhibits a simplified enameloid microstructure, which we compare with previously documented enameloid microstructures of other elasmobranchs. Though subtle interspecific differences in dental characters are documented, neither overall tooth morphology nor histotype and microstructure are unique to O. bruniensis. We conclude that in the case of O. bruniensis, dietary specialization is facilitated by behavioral rather than morphological specialization.
Asunto(s)
Cazón/anatomía & histología , Diente/anatomía & histología , Animales , Dieta , Femenino , Maxilares/anatomía & histología , Maxilares/diagnóstico por imagen , Masculino , Diente/diagnóstico por imagen , Microtomografía por Rayos XRESUMEN
This study examines the feeding behaviour and kinematics of three sub-adult sand tiger sharks Carcharias taurus on display at Mystic Aquarium (Mystic, Connecticut, USA). Using high-speed video data from 52 bites, we identify kinematic variables associated with the expansive and compressive phases of the bite. The mean bite duration from the onset of the expansive phase to the conclusion of the compressive phase is mean (± SE) 0.14 ± 0.01 s and across the 10 fastest bites of each individual, the maximum performance average is 0.13 ± 0.01 s. Values of maximum performance do not vary significantly among individuals. When compared with kinematic bite data from species studied previously, these results indicate that body size is not the only determinant factor of bite duration. This study also provides detailed descriptions of feeding behaviours in C. taurus and presents documentation of tooth loss both prior to and during feeding, suggesting that there are multiple mechanisms of tooth loss and use in C. taurus. Finally, we discuss the behavioural and ecological components of prey capture in C. taurus and suggest points of consideration to facilitate interspecific comparisons of prey capture performance in ram-feeding, macrophagous elasmobranchs.
Asunto(s)
Conducta Alimentaria , Tiburones/fisiología , Animales , Fenómenos BiomecánicosRESUMEN
Booralana nickorum sp. nov. is described from the deep-water slope of the Exuma Sound, The Bahamas, from depths of 540 to 560 metres. It is the fourth species to be assigned to the genus and the second species described from the Western North Atlantic. The species can be distinguished from Booralana tricarinata Camp and Heard, 1988 and the other species by the sub-triangular pleotelson and the uropodal exopod of mature males being far longer than endopod, with both rami extending well beyond the posterior margin of the pleotelson. Additionally, pleopods 3 and 4 lack a prominent angle at midpoint of ramus.
Asunto(s)
Isópodos , Masculino , Animales , Bahamas , CrustáceosRESUMEN
When novel or extreme morphologies arise, they are oft met with the burden of functional trade-offs in other aspects of anatomy, which may limit phenotypic diversification and make particular adaptive peaks inaccessible. Bramids (Perciformes: Bramidae) comprise a small family of 20 extant species of fishes, which are distributed throughout pelagic waters worldwide. Within the Bramidae, the fanfishes (Pteraclis and Pterycombus) differ morphologically from the generally stout, laterally compressed species that typify the family. Instead, Pteraclis and Pterycombus exhibit extreme anterior positioning of the dorsal fin onto the craniofacial skeleton. Consequently, they possess fin and skull anatomies that are radically different from other bramid species. Here, we investigate the anatomy, development, and evolution of the Bramidae to test the hypothesis that morphological innovations come at functional (proximate) and evolutionary (ultimate) costs. Addressing proximate effects, we find that the development of an exaggerated dorsal fin is associated with neurocrania modified to accommodate an anterior expansion of the dorsal fin. This occurs via reduced development of the supraoccipital crest (SOC), providing a broad surface area on the skull for insertion of the dorsal fin musculature. While these anatomical shifts are presumably associated with enhanced maneuverability in fanfishes, they are also predicted to result in compromised suction feeding, possibly limiting the mechanisms of feeding in this group. Phylogenetic analyses suggest craniofacial and fin morphologies of fanfishes evolved rapidly and are evolutionarily correlated across bramids. Furthermore, fanfishes exhibit a similar rate of lineage diversification as the rest of the Bramidae, lending little support for the prediction that exaggerated medial fins are associated with phylogenetic constraint. Our phylogeny places fanfishes at the base of the Bramidae and suggests that nonfanfish bramids have reduced medial fins and re-evolved SOCs. These observations suggest that the evolution of novel fin morphologies in basal species has led to the phylogenetic coupling of head and fin shape, possibly predisposing the entire family to a limited range of feeding. Thus, the evolution of extreme morphologies may have carryover effects, even after the morphology is lost, limiting ecological diversification of lineages.
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Cuando surgen morfologías nuevas o extremas, a menudo se encuentran con la carga de compensaciones funcionales en otros aspectos de la anatomía, lo que puede limitar la diversificación fenotípica y hacer inaccesibles los picos adaptativos particulares. Las bramidas (Perciformes: Bramidae) comprenden una pequeña familia de 20 especies de peces existentes, que se distribuyen en las aguas pelágicas de todo el mundo. Dentro de los Bramidae, los fanfishes (Pteraclis y Pterycombus) difieren morfológicamente de las especies generalmente robustas y comprimidas lateralmente que caracterizan a la familia. En cambio, Pteraclis y Pterycombus exhiben una posición anterior extrema de la aleta dorsal sobre el esqueleto craneofacial. En consecuencia, poseen anatomías de aletas y cráneo que son radicalmente diferentes de otras especies de bramidas. Aquí, investigamos la anatomía, el desarrollo y la evolución de Bramidae para probar la hipótesis de que las innovaciones morfológicas tienen un costo funcional (próximo) y evolutivo (último). Al abordar los efectos inmediatos, encontramos que el desarrollo de una aleta dorsal exagerada se asocia con neurocráneo modificado para adaptarse a una expansión anterior de la aleta dorsal. Esto ocurre a través del desarrollo reducido de la cresta supraoccipital (SOC), proporcionando una amplia área de superficie en el cráneo para la inserción de la musculatura de la aleta dorsal. Si bien estos cambios anatómicos presumiblemente están asociados con una mayor maniobrabilidad en los peces fanfishes, también se predice que darán como resultado una alimentación por succión comprometida, lo que posiblemente limite los mecanismos de alimentación en este grupo. Los análisis filogenéticos sugieren que las morfologías craneofaciales y de aletas de los fanfishes evolucionaron rápidamente y están correlacionadas evolutivamente entre las bramidas. Además, los fanfishes exhiben una tasa similar de diversificación de linajes que el resto de los Bramidae, lo que brinda poco apoyo a la predicción de que las aletas mediales exageradas están asociadas con restricciones filogenéticas. Nuestra filogenia coloca a los peces abanico en la base de las Bramidae y sugiere que las bramidas que no son peces abanico tienen aletas mediales reducidas y SOC reevolucionado. Estas observaciones sugieren que la evolución de nuevas morfologías de aletas en especies basales ha llevado al acoplamiento filogenético de la forma de la cabeza y la aleta, lo que posiblemente predisponga a toda la familia a un rango limitado de alimentación. Por lo tanto, la evolución de morfologías extremas puede tener efectos de arrastre, incluso después de que se pierde la morfología, lo que limita la diversificación ecológica de los linajes.
Quando surgem morfologias novas ou extremas, muitas vezes enfrentam o fardo de compensações funcionais em outros aspectos da anatomia, que podem limitar a diversificação fenotípica e tornar determinados picos adaptativos inacessíveis. Bramids (Perciformes: Bramidae) compreendem uma pequena família de 20 espécies existentes de peixes, que estão distribuídos em águas pelágicas em todo o mundo. Dentro dos Bramidae, os fanfishes (Pteraclis e Pterycombus) diferem morfologicamente das espécies geralmente robustas e comprimidas lateralmente que tipificam a família. Em vez disso, Pteraclis e Pterycombus exibem posicionamento anterior extremo da nadadeira dorsal no esqueleto craniofacial. Conseqüentemente, eles possuem anatomias de barbatana e crânio que são radicalmente diferentes de outras espécies de bramida. Aqui, investigamos a anatomia, o desenvolvimento e a evolução dos Bramidae para testar a hipótese de que as inovações morfológicas têm custos funcionais (proximais) e evolutivos (finais). Abordando os efeitos imediatos, descobrimos que o desenvolvimento de uma nadadeira dorsal exagerada está associado a neurocrania modificada para acomodar uma expansão anterior da nadadeira dorsal. Isso ocorre por meio do desenvolvimento reduzido da crista supraoccipital (SOC), proporcionando uma ampla área de superfície no crânio para a inserção da musculatura da nadadeira dorsal. Embora essas mudanças anatômicas estejam presumivelmente associadas a maior capacidade de manobra em peixes-leque, também se prevê que resultem em alimentação de sucção comprometida, possivelmente limitando os mecanismos de alimentação neste grupo. As análises filogenéticas sugerem que as morfologias craniofaciais e das nadadeiras de fanfishes evoluíram rapidamente e estão evolutivamente correlacionadas entre as bramidas. Além disso, fanfishes exibem uma taxa semelhante de diversificação de linhagem como o resto dos Bramidae, emprestando pouco suporte para a previsão de que nadadeiras mediais exageradas estão associadas a restrições filogenéticas. Nossa filogenia coloca fanfishes na base dos Bramidae e sugere que bramids não fanfish possuem nadadeiras mediais reduzidas e SOCs re-evoluídos. Essas observações sugerem que a evolução de novas morfologias de nadadeiras em espécies basais levou ao acoplamento filogenético da forma da cabeça e da nadadeira, possivelmente predispondo toda a família a uma faixa limitada de alimentação. Assim, a evolução de morfologias extremas pode ter efeitos de transporte, mesmo após a perda da morfologia, limitando a diversificação ecológica das linhagens.
RESUMEN
Prior to European contact, South Pacific islanders used serrated shark teeth as components of tools and weapons. They did this because serrated shark teeth are remarkably effective at slicing through soft tissues. To understand more about the forms and functions of serrated shark teeth, we examined the morphology and histology of tooth serrations in three species: the Tiger Shark (Galeocerdo cuvier), Blue Shark (Prionace glauca), and White Shark (Carcharodon carcharias). We show that there are two basic types of serrations. A primary serration consists of three layers of enameloid with underlying dentine filling the serration's base. All three species studied have primary serrations, although the dentine component differs (orthodentine in Tiger and Blue Sharks; osteodentine in the White Shark). Smaller secondary serrations are found in the Tiger Shark, formed solely by enameloid with no contribution from underlying dentine. Secondary serrations are effectively "serrations within serrations" that allow teeth to cut at different scales. We propose that the cutting edges of Tiger Shark teeth, equipped with serrations at different scales, are linked to a diet that includes large, hard-shelled prey (e.g., sea turtles) as well as smaller, softer prey such as fishes. We discuss other aspects of serration form and function by making analogies to man-made cutting implements, such as knives and saws.
Asunto(s)
Tiburones/anatomía & histología , Diente/ultraestructura , Animales , Microscopía Electrónica de Rastreo , Especificidad de la EspecieRESUMEN
Elasmobranchs exhibit two distinct arrangements of mineralized tissues in the teeth that are known as orthodont and osteodont histotypes. Traditionally, it has been said that orthodont teeth maintain a pulp cavity throughout tooth development whereas osteodont teeth are filled with osteodentine and lack a pulp cavity when fully developed. We used light microscopy, scanning electron microscopy, and high-resolution micro-computed tomography to compare the structure and development of elasmobranch teeth representing the two histotypes. As an example of the orthodont histotype, we studied teeth of the blue shark, Prionace glauca (Carcharhiniformes: Carcharhinidae). For the osteodont histotype, we studied teeth of the great white shark, Carcharodon carcharias (Lamniformes: Lamnidae). We document similarities and differences in tooth development and the microstructure of tissues in these two species and review the history of definitions and interpretations of elasmobranch tooth histotypes. We discuss a possible correlation between tooth histotype and tooth replacement and review the history of histotype differentiation in sharks. We find that contrary to a long held misconception, there is no orthodentine in the osteodont teeth of C. carcharias.