Comparative neurocranial morphology of angelsharks from the south‐western Atlantic Ocean (Chondrichthyes, Elasmobranchii, Squatinidae): implications for taxonomy and phylogeny
Abstract:de Carvalho MR., Faro C. and Gomes UL. 2010. Comparative neurocranial morphology of angelsharks from the south‐western Atlantic Ocean (Chondrichthyes, Elasmobranchii, Squatinidae): implications for taxonomy and phylogeny. —Acta Zoologica (Stockholm) 00:1–13
Neurocrania of three species of angelsharks from the south‐western Atlantic Ocean, occurring off south‐eastern and southern Brazil, are described. A detailed morphological description is provided of the neurocranium of Squatina guggenheim and compared with … Show more
“… Figure 6 Rate of morphological evolution for selected modules on the neurocranium of the angel sharks, circles indicate the analysis on the complete data set and squares the dataset with only living angel sharks. Modules defined after de Carvalho et al 27 Mod1: Rostrum; Mod2: Nasal capsules; Mod3: Orbit; Mod4: Otic capsules; Mod5: Occipital. …”
Section: Resultsmentioning
confidence: 99%
“…Angel sharks, which show a very consistent dorso-ventrally compressed body plan since their first occurrence in the fossil record during the Late Jurassic 22 , 23 , 25 , apparently have experienced three major radiations 46 finally resulting in their current taxonomic diversity and spatial distribution 17 . However, it is still difficult to clearly differentiate extant angel shark species on the basis of morphological characters, which has led to uncertainty in species designation 27 – 30 , 47 . Similarly, many fossil species, which are in most cases based on isolated teeth only, remain dubious 23 , 25 , 48 , highlighting their highly conserved morphological nature in their dental traits.…”
Section: Discussionmentioning
confidence: 99%
“…In particular the SAM species have been difficult to distinguish 29 . However, de Carvalho et al 27 considered traits like the rostral projections and the anterior fontanelle outline as discrete morphological features suitable for use in species differentiation. In our study, we found that both of these structures display variation enough only to separate the analysed clades, but not at species level.…”
Section: Discussionmentioning
confidence: 99%
“…One of the most prominent features of the neurocranium of Squatiniformes are the massive postorbital processes, which in † Pseudorhina are slender and in extant Squatina spp. display a wide variety of forms 22 , 23 , 27 , 48 . This trait also can be interpreted as a derived feature for modern angel sharks 48 .…”
Section: Discussionmentioning
confidence: 99%
“…Despite the remarkable features of the body plan of angel sharks, little attention has been paid to its possible origins as well as other aspects of their biology 26 . A previous work on the skeletal morphology of angel sharks has demonstrated that the neurocranial traits are useful to determine species 27 . Differences in the neurocranium are mainly expressed in the shape of the rostral region, which can be anteriorly extended.…”
Elasmobranchii (i.e., sharks, skates, and rays) forms one of the most diverse groups of marine predators. With a fossil record extending back into the Devonian, several modifications in their body plan illustrate their body shape diversity through time. The angel sharks, whose fossil record dates back to the Late Jurassic, some 160 Ma, have a dorsoventrally flattened body, similar to skates and rays. Fossil skeletons of this group show that the overall morphology was well established earlier in its history. By examining the skull shape of well-preserved fossil material compared to extant angel sharks using geometric morphometric methods, within a phylogenetic framework, we were able to determine the conservative skull shape among angel sharks with a high degree of integration. The morphospace occupation of extant angel sharks is rather restricted, with extensive overlap. Most of the differences in skull shape are related to their geographic distribution patterns. We found higher levels of disparity in extinct forms, but lower ones in extant species. Since angel sharks display a highly specialized prey capture behaviour, we suggest that the morphological integration and biogeographic processes are the main drivers of their diversity, which might limit their capacity to display higher disparities since their origin.
“… Figure 6 Rate of morphological evolution for selected modules on the neurocranium of the angel sharks, circles indicate the analysis on the complete data set and squares the dataset with only living angel sharks. Modules defined after de Carvalho et al 27 Mod1: Rostrum; Mod2: Nasal capsules; Mod3: Orbit; Mod4: Otic capsules; Mod5: Occipital. …”
Section: Resultsmentioning
confidence: 99%
“…Angel sharks, which show a very consistent dorso-ventrally compressed body plan since their first occurrence in the fossil record during the Late Jurassic 22 , 23 , 25 , apparently have experienced three major radiations 46 finally resulting in their current taxonomic diversity and spatial distribution 17 . However, it is still difficult to clearly differentiate extant angel shark species on the basis of morphological characters, which has led to uncertainty in species designation 27 – 30 , 47 . Similarly, many fossil species, which are in most cases based on isolated teeth only, remain dubious 23 , 25 , 48 , highlighting their highly conserved morphological nature in their dental traits.…”
Section: Discussionmentioning
confidence: 99%
“…In particular the SAM species have been difficult to distinguish 29 . However, de Carvalho et al 27 considered traits like the rostral projections and the anterior fontanelle outline as discrete morphological features suitable for use in species differentiation. In our study, we found that both of these structures display variation enough only to separate the analysed clades, but not at species level.…”
Section: Discussionmentioning
confidence: 99%
“…One of the most prominent features of the neurocranium of Squatiniformes are the massive postorbital processes, which in † Pseudorhina are slender and in extant Squatina spp. display a wide variety of forms 22 , 23 , 27 , 48 . This trait also can be interpreted as a derived feature for modern angel sharks 48 .…”
Section: Discussionmentioning
confidence: 99%
“…Despite the remarkable features of the body plan of angel sharks, little attention has been paid to its possible origins as well as other aspects of their biology 26 . A previous work on the skeletal morphology of angel sharks has demonstrated that the neurocranial traits are useful to determine species 27 . Differences in the neurocranium are mainly expressed in the shape of the rostral region, which can be anteriorly extended.…”
Elasmobranchii (i.e., sharks, skates, and rays) forms one of the most diverse groups of marine predators. With a fossil record extending back into the Devonian, several modifications in their body plan illustrate their body shape diversity through time. The angel sharks, whose fossil record dates back to the Late Jurassic, some 160 Ma, have a dorsoventrally flattened body, similar to skates and rays. Fossil skeletons of this group show that the overall morphology was well established earlier in its history. By examining the skull shape of well-preserved fossil material compared to extant angel sharks using geometric morphometric methods, within a phylogenetic framework, we were able to determine the conservative skull shape among angel sharks with a high degree of integration. The morphospace occupation of extant angel sharks is rather restricted, with extensive overlap. Most of the differences in skull shape are related to their geographic distribution patterns. We found higher levels of disparity in extinct forms, but lower ones in extant species. Since angel sharks display a highly specialized prey capture behaviour, we suggest that the morphological integration and biogeographic processes are the main drivers of their diversity, which might limit their capacity to display higher disparities since their origin.
Batoids (skates and rays) are the most speciose group of cartilaginous fishes. Their body plan represents diverse ecologies and swimming modes. Early skeletal fossil remains, and recent phylogenetic analyses suggest that convergence has occurred within the batoids several times independently. The drivers for such disparity patterns and possible association with modularity and phenotypic integration among batoids are not fully understood. Here we used geometric morphometrics and phylogenetic comparative methods to characterize the evolutionary trends of the basal fin skeleton of batoids and sharks. Our analyses show that the morphological variation has a strong phylogenetic signal. Interestingly, the most speciose orders of batoids display low morphological disparity. Reef and freshwater species, show increased evolutionary rates. Meanwhile, the swimming mode shows different rates depending on the fin structure analyzed. A higher modularity and integration signal suggest that the pectoral fin of batoids has experienced mosaic evolution. The low morphological disparity might be associated with high integration. We find support for convergence between Jurassic, Cretaceous, and Extant guitarfishes, however, not completely between sharks and batoids. Our findings suggest that habitats and swimming mode have shaped the pectoral fin evolution among batoids, and at the same time batoids have constrained their basal fin skeleton.
Angel sharks (Squatina spp.) are distributed in warm temperate to tropical waters around the world. Many species occur in shelf seas and exhibit seasonal inshoreoffshore migrations, moving inshore to give birth. Consequently, there can be high spatial overlap of angel shark populations with fisheries and other human activities. Their dorso-ventrally flattened body shape, large size (most species attain >100 cm total length, L T) and demersal nature means that they may be taken in a variety of demersal fishing gears from birth. Available data indicate that angel sharks typically have a biennial reproductive cycle, with litter sizes generally <20 and the young born at c. 20-30 cm. The biological characteristics of angel sharks render them susceptible to overexploitation, as exemplified by the decline of Squatina squatina from many parts of its former range in the northeast Atlantic and Mediterranean Sea. Currently, half of the 22 recognized extant species of angel shark are classed as Threatened on the International Union for Conservation of Nature (IUCN) Red List (with a further three classified as Data Deficient). Given the biological vulnerability of angel sharks, and that many species are data-limited, the current paper provides a review of available biological information and fisheries data pertaining to this family.
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