- Functional morphologist, museum lover, & stingray enthusiast. Interested in the evolution of biodiversity, feeding sy... moreFunctional morphologist, museum lover, & stingray enthusiast. Interested in the evolution of biodiversity, feeding systems, and the co-evolution of predator and prey morphologies, materials, and behaviors.edit
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Abstract Three complete mitochondrial genomes of South American electric fishes (Gymnotiformes), derived from high-throughput RNA sequencing (RNA-Seq), are reported herein. We report the complete mitochondrial genome of the bluntnose... more
Abstract Three complete mitochondrial genomes of South American electric fishes (Gymnotiformes), derived from high-throughput RNA sequencing (RNA-Seq), are reported herein. We report the complete mitochondrial genome of the bluntnose knifefish Brachyhypopomus n.sp. VERD, determined from newly sequenced data. We also provide the complete mitochondrial genomes for Sternopygus arenatus and the electric eel Electrophorus electricus, assembled from previously published transcriptome data. The mitochondrial genomes of Brachyhypopomus n.sp. VERD, Sternopygus arenatus and Electrophorus electricus have 13 protein-coding genes, 1 D-loop, 2 ribosomal RNAs and 22 transfer RNAs, and are 16,547, 16,667 and 16,906 bp in length, respectively. Phylogenetic analysis of the eight available mitochondrial genomes of gymnotiform fishes shows Apteronotus to be the sister lineage of other gymnotiformes, contradicting the “Sinusoidea” hypothesis that Apteronotidae and Sternopygidae are sister taxa.
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Evolutionary transitions between marine and freshwater ecosystems have occurred repeatedly throughout the phylogenetic history of fishes. The theory of ecological opportunity predicts that lineages that colonize species-poor regions will... more
Evolutionary transitions between marine and freshwater ecosystems have occurred repeatedly throughout the phylogenetic history of fishes. The theory of ecological opportunity predicts that lineages that colonize species-poor regions will have greater potential for phenotypic diversification than lineages invading species-rich regions. Thus, transitions between marine and freshwaters may promote phenotypic diversification in trans-marine/freshwater fish clades. We used phylogenetic comparative methods to analyze body size data in nine major fish clades that have crossed the marine/freshwater boundary. We explored how habitat transitions, ecological opportunity, and community interactions influenced patterns of phenotypic diversity. Our analyses indicated that transitions between marine and freshwater habitats did not drive body size evolution, and there are few differences in body size between marine and freshwater lineages. We found that body size disparity in freshwater lineages is not correlated with the number of independent transitions to freshwaters. We found a positive correlation between body size disparity and overall species richness of a given area, and a negative correlation between body size disparity and diversity of closely related species. Our results indicate that the diversity of incumbent freshwater species does not restrict phenotypic diversification, but the diversity of closely related taxa can limit body size diversification. Ecological opportunity arising from colonization of novel habitats does not seem to have a major effect in the trajectory of body size evolution in trans-marine/freshwater clades. Moreover, competition with closely related taxa in freshwaters has a greater effect than competition with distantly related incumbent species.
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Abstract. Herbivorous fishes feed on stems, leaves, flowers, seeds, fruits, and nuts of diverse aquatic plants, as well as algae. Pacus are the herbivorous cousins of piranhas and consume a myriad of diets comprised of these plant... more
Abstract. Herbivorous fishes feed on stems, leaves, flowers, seeds, fruits, and nuts of diverse aquatic plants, as well as algae. Pacus are the herbivorous cousins of piranhas and consume a myriad of diets comprised of these plant products, but a few species are phytophages, herbivores that feed almost exclusively on rapids-dwelling (rheophilic) riverweed plants from the family Podostemaceae. The degree to which pacus feed on riverweed varies from obligate year-round consumption to strictly seasonal, facultative feeding. Obligate phytophages feed heavily on riverweed and strictly occur in river rapids, while facultative phytophages only consume riverweed during seasons with low flow. Does ecological specialization (diet) beget morphological specialization in the feeding apparatus and/or body shape of phytophages? Under a phylogenetic framework, we used micro-computed tomography (µCT) scanning to compare functional feeding traits among 26 species of serrasalmids, four of which are obligate phytophages. We also compared body shape between pacus using geometric morphometrics to identify potential locomotor adaptations for rheophily. Obligate phytophages have dentitions and slicing jaws well-suited for shearing fleshy plant material relative to other pacus, which are equipped with fruit and seed crushing morphologies. Unrelated obligate phytophages have also converged on a similar body shape that is distinct from sympatric congeneric herbivores. Phytophagy involves more consistent changes to body shape than to feeding morphology, suggesting that body shape has more important ties to diet.
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Research Interests: Functional Morphology, Biology, CNC Machine tools, Diet, Medicine, and 15 moreBiological Sciences, Bite force, Gastropoda, Bivalvia, Predation, Animals, Viperidae, Jaw, Feeding Behavior, Feeding Biology, Myliobatiformes, Stingrays, Experimental Biology, Biomechanical Phenomena, and Medical and Health Sciences
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Habitat transitions are key potential explanations for why some lineages have diversified and others have not—from Anolis lizards to Darwin's finches. The ecological ramifications of marine-to-freshwater transitions for fishes suggest... more
Habitat transitions are key potential explanations for why some lineages have diversified and others have not—from Anolis lizards to Darwin's finches. The ecological ramifications of marine-to-freshwater transitions for fishes suggest evolutionary contingency: some lineages maintain their ancestral niches in novel habitats (niche conservatism), whereas others alter their ecological role. However, few studies have considered phenotypic, ecological, and lineage diversification concurrently to explore this issue. Here, we investigated the macroevolutionary history of the taxonomically and ecologically diverse Neotropical freshwater river rays (subfamily Potamotrygoninae), which invaded and diversified in the Amazon and other South American rivers during the late Oligocene to early Miocene. We generated a time-calibrated, multi-gene phylogeny for Potamotrygoninae and reconstructed evolutionary patterns of diet specialization. We measured functional morphological traits relevant for ...
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Biological armors are potent model systems for understanding the complex series of competing demands on protective exoskeletons; after all, armored organisms are the product of millions of years of refined engineering under the harshest... more
Biological armors are potent model systems for understanding the complex series of competing demands on protective exoskeletons; after all, armored organisms are the product of millions of years of refined engineering under the harshest conditions. Fishes are no strangers to armor, with various types of armor plating common to the 400 million years of evolution in both jawed and jawless fishes. Here we focus on the poachers (Agonidae), a family of armored fishes native to temperate waters of the Pacific rim. We examined armor morphology, body stiffness, and swimming performance in the Northern Spearnose Poacher (Agonopsis vulsa) over ontogeny. As juveniles, these fishes make frequent nocturnal forays into the water column in search of food, while heavily armored adults are bound to the benthos. Most armor dimensions and density increase with body length, as does body stiffness. Juvenile poachers have enlarged spines on their armor whereas adults invest more mineral in armor plate ba...
Evolutionary transitions between ecosystems are rare, and yet in lineages that have made these transitions we observe drastic changes in their diversity and richness as they adapt to novel habitats and novel resources. The main goal of my... more
Evolutionary transitions between ecosystems are rare, and yet in lineages that have made these transitions we observe drastic changes in their diversity and richness as they adapt to novel habitats and novel resources. The main goal of my dissertation is to examine how transitions among diets and habitats have molded the evolution of predator traits. To test hypotheses regarding how prey materials have shaped the evolution of predators, I examined predator feeding biomechanics using experimental methods and deep-time approaches. Using 3D printing, computational milling, and computed tomography scanning, I compared the biomechanical performance of jaw shape for durophagous stingrays which prey on mollusks with shells of drastically different material and structural properties. I found that all of these jaw morphologies were equally well-suited to crushing the entire breadth of prey mollusk diversity, establishing equifinality of anatomical form stemming from convergent feeding mechan...
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The subfamily Potamotrygoninae, the only extant clade of elasmobranchs exclusive to freshwater environments, encompasses four genera and 38 species distributed across almost every major South American river basin. Despite their importance... more
The subfamily Potamotrygoninae, the only extant clade of elasmobranchs exclusive to freshwater environments, encompasses four genera and 38 species distributed across almost every major South American river basin. Despite their importance in the ornamental fish trade, the taxonomy and evolutionary relationships within potamotrygonines have not yet been resolved. Here, we present a comprehensive molecular phylogeny for the Neotropical freshwater stingrays, based on extensive species and population sampling (35 species and > 350 individuals from drainages across South America). Our phylogeny corroborates the monophyly of the genera Paratrygon and Heliotrygon and the monophyly of the Potamotrygon + Plesiotrygon clade. Within the Potamotrygon + Plesiotrygon clade, we identify a core Potamotrygon clade characterized by short branches, low nodal support and incongruence with current species-level taxonomy. In the core Potamotrygon clade, specimens of widespread species, such as Potamot...
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Aim: Paleogeographic changes have had profound effects on the evolution and diversity of the Neotropical biota. However, the influence of marine incursions on the origin, diversification, and distribution of fishes is still incompletely... more
Aim: Paleogeographic changes have had profound effects on the evolution and diversity of the Neotropical biota. However, the influence of marine incursions on the origin, diversification, and distribution of fishes is still incompletely understood. We investigate the biogeographical and chronological patterns of diversification for the marine-derived Neotropical freshwater stingrays (subfamily Potamotrygoninae) at a continental scale. Location: Neotropics, South America. Taxa: Neotropical freshwater stingrays. Subfamily Potamotrygoninae (Myliobatiformes: Chondrichthyes). Methods: We generated a time-calibrated phylogeny for 35 of the 38 valid species of Neotropical freshwater stingrays, from most of the major river basins of South America, using four genes. We used BEAST2 to determine the chronology of population and species divergence events, and "BioGeoBEARS" to infer historical biogeo-graphic patterns. Results: The Potamotrygoninae originated during the early/middle Miocene in the upper Amazon region. We recover clades associated with particular geographic areas and detect a recurrent pattern of upper Amazon clades sister to clades in adjacent basins. The timing of dispersals from the upper Amazon to adjacent areas corresponds with the end of the Pebas wetlands. Lower Amazon and Shield associated taxa are relatively young. Main conclusions: We propose that the origin of the Neotropical freshwater sting-rays is related to marine incursions that occurred during the Oligocene/Miocene. Subsequent diversification of Potamotrygoninae occurred in the Pebas wetland system in the upper Amazon with colonization of adjacent basins. These movements were generally unidirectional, with few lineages returning to the upper Amazon, and we speculate that ecological factors drove this pattern. We observed a burst of
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Although rare within the context of 30 000 species of extant fishes, scale-feeding as an ecological strategy has evolved repeatedly across the teleost tree of life. Scale-feeding (lepidophagous) fishes are diverse in terms of their... more
Although rare within the context of 30 000 species of extant fishes, scale-feeding as an ecological strategy has evolved repeatedly across the teleost tree of life. Scale-feeding (lepidophagous) fishes are diverse in terms of their ecology, behaviour, and specialized morphologies for grazing on scales and mucus of sympatric species. Despite this diversity, the underlying ontogenetic changes in functional and biomechanical properties of associated feeding morphologies in lepidophagous fishes are less understood. We examined the ontogeny of feeding mechanics in two evolutionary lineages of scale-feeding fishes: Roeboides , a characin, and Catoprion , a piranha. We compare these two scale-feeding taxa with their nearest, non-lepidophagous taxa to identify traits held in common among scale-feeding fishes. We use a combination of micro-computed tomography scanning and iodine staining to measure biomechanical predictors of feeding behaviour such as tooth shape, jaw lever mechanics and jaw...
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Chewing, characterized by shearing jaw motions and high-crowned molar teeth, is considered an evolutionary innovation that spurred dietary diversification and evolutionary radiation of mammals. Complex prey-processing behaviours have been... more
Chewing, characterized by shearing jaw motions and high-crowned molar teeth, is considered an evolutionary innovation that spurred dietary diversification and evolutionary radiation of mammals. Complex prey-processing behaviours have been thought to be lacking in fishes and other vertebrates, despite the fact that many of these animals feed on tough prey, like insects or even grasses. We investigated prey capture and processing in the insect-feeding freshwater stingray Potamotrygon motoro using high-speed videography. We find that Potamotrygon motoro uses asymmetrical motion of the jaws, effectively chewing, to dismantle insect prey. However, CT scanning suggests that this species has simple teeth. These findings suggest that in contrast to mammalian chewing, asymmetrical jaw action is sufficient for mastication in other vertebrates. We also determined that prey capture in these rays occurs through rapid uplift of the pectoral fins, sucking prey beneath the ray's body, thereby d...
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The cownose ray is a source of controversy and increasing media attention due to interactions with commercial fisheries and on-bottom aquaculture operations for bivalves such as oysters, clams, and bay scallops. Claims of increases in the... more
The cownose ray is a source of controversy and increasing media attention due to interactions with commercial fisheries and on-bottom aquaculture operations for bivalves such as oysters, clams, and bay scallops. Claims of increases in the population of cownose rays coupled with increases in damage to shellfish culture, grow-out, and restoration operations have led to the development of commercial harvesting for cownose rays in regions such as Chesapeake Bay, though no stock assessments have been completed and no management plans exist. We seek to empirically evaluate the jaw biomechanics of the cownose ray relative to the mechanical properties of commercial bivalve in order to inform management and stakeholders and perhaps suggest alternative means of mitigating interactions. Preliminary studies indicate cownose rays are bite force and gape limited suggesting bivalve susceptibility to predation decreases ontogenetically. Gape size limitation hinders or restricts the ability of a pre...
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The subfamily Potamotrygoninae, the only extant clade of elasmobranchs exclusive to freshwater environments, encompasses four genera and 38 species distributed across almost every major South American river basin. Despite their importance... more
The subfamily Potamotrygoninae, the only extant clade of elasmobranchs exclusive to freshwater environments, encompasses four genera and 38 species distributed across almost every major South American river basin. Despite their importance in the ornamental fish trade, the taxonomy and evolutionary relationships within potamotrygonines have not yet been resolved. Here, we present a comprehensive molecular phylogeny for the Neotropical freshwater stingrays, based on extensive species and population sampling (35 species and > 350 individuals from drainages across South America). Our phylogeny corroborates the monophyly of the genera Paratrygon and Heliotrygon and the monophyly of the Potamotrygon + Plesiotrygon clade. Within the Potamotrygon + Plesiotrygon clade, we identify a core Potamotrygon clade characterized by short branches, low nodal support and incongruence with current species-level taxonomy. In the core Potamotrygon clade, specimens of widespread species, such as Potamotrygon motoro and Potamotrygon orbignyi, do not form monophyletic lineages; instead, specimens from these species are often closely related to those of other species from the same river basins. These patterns could be caused by inaccurate taxonomy, hybridization, incomplete lineage sorting and rapid diversification. We discuss the conservation of Neotropical freshwater stingrays from a phylogenetic perspective and suggest ways to prioritize potamotrygonid conservation efforts with respect to endemism and evolutionary distinctiveness.
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The Amazon and neighboring South American river basins harbor the world’s most diverse assemblages of freshwater fishes. One of the most prominent South American fish families is the Serrasalmidae (pacus and piranhas), found in nearly... more
The Amazon and neighboring South American river basins harbor the world’s most diverse assemblages of freshwater fishes. One of the most prominent South American fish families is the Serrasalmidae (pacus and piranhas), found in nearly every continental basin. Serrasalmids are keystone ecological taxa, being some of the top riverine predators as well as the primary seed dispersers in the flooded forest. Despite their widespread occurrence and notable ecologies, serrasalmid evolutionary history and systematics are controversial. For example, the sister taxon to serrasalmids is contentious, the relationships of major clades within the family are inconsistent across different methodologies, and half of the extant serrasalmid genera are suggested to be non-monophyletic. We analyzed exon capture to reexamine the evolutionary relationships among 63 (of 99) species across all 16 serrasalmid genera and their nearest outgroups, including multiple individuals per species to account for cryptic...
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Biological armours are potent model systems for understanding the complex series of competing demands on protective exoskeletons; after all, armoured organisms are the product of millions of years of refined engineering under the harshest... more
Biological armours are potent model systems for understanding the complex series of competing demands on protective exoskeletons; after all, armoured organisms are the product of millions of years of refined engineering under the harshest conditions. Fishes are no strangers to armour, with various types of armour plating common to the 400–500 Myr of evolution in both jawed and jawless fishes. Here, we focus on the poachers (Agonidae), a family of armoured fishes native to temperate waters of the Pacific rim. We examined armour morphology, body stiffness and swimming performance in the northern spearnose poacher ( Agonopsis vulsa ) over ontogeny. As juveniles, these fishes make frequent nocturnal forays into the water column in search of food, while heavily armoured adults are bound to the benthos. Most armour dimensions and density increase with body length, as does body stiffness. Juvenile poachers have enlarged spines on their armour whereas adults invest more mineral in armour pl...
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A fundamental challenge for both sustainable fisheries and biodiversity protection in the Neotropics is the accurate determination of species identity. The biodiversity of the coastal sharks of Guyana is poorly understood, but these... more
A fundamental challenge for both sustainable fisheries and biodiversity protection in the Neotropics is the accurate determination of species identity. The biodiversity of the coastal sharks of Guyana is poorly understood, but these species are subject to both artisanal fishing as well as harvesting by industrialized offshore fleets. To determine what species of sharks are frequently caught and consumed along the coastline of Guyana, we used DNA barcoding to identify market specimens. We sequenced the mitochondrial co1 gene for 132 samples collected from six markets, and compared our sequences to those available in the Barcode of Life Database (BOLD) and GenBank. Nearly 30% of the total sample diversity was represented by two species of Hammerhead Sharks (Sphyrna mokarran and S. lewini), both listed as Endangered by the International Union for Conservation of Nature (IUCN). Other significant portions of the samples included Sharpnose Sharks (23% - Rhizoprionodon spp.), considered Vu...
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The evolution of sexual weaponry is thought to have marked effects on the underlying static allometry that builds them. These weapons can negatively affect organismal survivability by creating trade-offs between trait size and... more
The evolution of sexual weaponry is thought to have marked effects on the underlying static allometry that builds them. These weapons can negatively affect organismal survivability by creating trade-offs between trait size and performance. Here we use three-dimensional geometric morphometrics to study the static allometry of two species of sexually dimorphic electric fishes (Apteronotus rostratus and Compsaraia samueli) in which mature males grow elongate jaws used in agonistic male-male interactions. We quantify jaw mechanical advantage between the sexes of both species to track changes in velocity and force transmission associated with the development of sexual weaponry. We find evidence for trade-offs between skull shape and mechanical advantage in C. samueli, where males with longer faces exhibit lower mechanical advantages, suggesting weaker bite forces. In contrast, males, and females of A. rostratus exhibit no difference in mechanical advantage associated with facial elongati...
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All stingrays in the family Myliobatidae are durophagous, consuming bivalves and gastropods, as well as decapod crustaceans. Durophagous rays have rigid jaws, flat teeth that interlock to form pavement-like tooth plates, and large muscles... more
All stingrays in the family Myliobatidae are durophagous, consuming bivalves and gastropods, as well as decapod crustaceans. Durophagous rays have rigid jaws, flat teeth that interlock to form pavement-like tooth plates, and large muscles that generate bite forces capable of fracturing stiff biological composites (e.g. mollusk shell). The relative proportion of different prey types in the diet of durophagous rays varies between genera, with some stingray species specializing on particular mollusk taxa, while others are generalists. The tooth plate module provides a curved occlusal surface on which prey is crushed, and this curvature differs significantly among myliobatids. We measured the effect of jaw curvature on prey-crushing success in durophagous stingrays. We milled aluminum replica jaws rendered from computed tomography scans, and crushed live mollusks, three-dimensionally printed gastropod shells, and ceramic tubes with these fabricated jaws. Our analysis of prey items indic...
Research Interests: Functional Morphology, Feeding Biomechanics (Engineering), CNC Machine tools, Diet, Biological Sciences, and 13 moreBite force, Gastropoda, Bivalvia, Animals, Jaw, Feeding Behavior, Feeding Biology, 3-D printing, Myliobatiformes, Stingrays, Experimental Biology, Biomechanical Phenomena, and Medical and Health Sciences
Aim: Paleogeographic changes have had profound effects on the evolution and diversity of the Neotropical biota. However, the influence of marine incursions on the origin, diversification, and distribution of fishes is still incompletely... more
Aim: Paleogeographic changes have had profound effects on the evolution and diversity of the Neotropical biota. However, the influence of marine incursions on the origin, diversification, and distribution of fishes is still incompletely understood. We investigate the biogeographical and chronological patterns of diversification for the marine-derived Neotropical freshwater stingrays (subfamily Potamotrygoninae) at a continental scale. Location: Neotropics, South America. Taxa: Neotropical freshwater stingrays. Subfamily Potamotrygoninae (Myliobatiformes: Chondrichthyes). Methods: We generated a time-calibrated phylogeny for 35 of the 38 valid species of Neotropical freshwater stingrays, from most of the major river basins of South America, using four genes. We used BEAST2 to determine the chronology of population and species divergence events, and "BioGeoBEARS" to infer historical biogeo-graphic patterns. Results: The Potamotrygoninae originated during the early/middle Miocene in the upper Amazon region. We recover clades associated with particular geographic areas and detect a recurrent pattern of upper Amazon clades sister to clades in adjacent basins. The timing of dispersals from the upper Amazon to adjacent areas corresponds with the end of the Pebas wetlands. Lower Amazon and Shield associated taxa are relatively young. Main conclusions: We propose that the origin of the Neotropical freshwater sting-rays is related to marine incursions that occurred during the Oligocene/Miocene. Subsequent diversification of Potamotrygoninae occurred in the Pebas wetland system in the upper Amazon with colonization of adjacent basins. These movements were generally unidirectional, with few lineages returning to the upper Amazon, and we speculate that ecological factors drove this pattern. We observed a burst of
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Although rare within the context of 30 000 species of extant fishes, scale-feeding as an ecological strategy has evolved repeatedly across the teleost tree of life. Scale-feeding (lepidophagous) fishes are diverse in terms of their... more
Although rare within the context of 30 000 species of extant fishes, scale-feeding as an ecological strategy has evolved repeatedly across the teleost tree of life. Scale-feeding (lepidophagous) fishes are diverse in terms of their ecology, behaviour, and specialized morphologies for grazing on scales and mucus of sympatric species. Despite this diversity, the underlying ontogenetic changes in functional and biomechanical properties of associated feeding morphologies in lepidophagous fishes are less understood. We examined the ontogeny of feeding mechanics in two evolutionary lineages of scale-feeding fishes: Roeboides, a characin, and Catoprion, a piranha. We compare these two scale-feeding taxa with their nearest, non-lepidophagous taxa to identify traits held in common among scale-feeding fishes. We use a combination of micro-computed tomography scanning and iodine staining to measure biomechanical predictors of feeding behaviour such as tooth shape, jaw lever mechanics and jaw musculature. We recover a stark contrast between the feeding morphology of scale-feeding and non-scale-feeding taxa, with lepidophagous fishes displaying some paedomorphic characters through to adulthood. Few traits are shared between lepidophagous characins and piranhas, except for their highly-modified, stout dentition. Given such variability in development, morphology and behaviour, ecological diversity within lepidophagous fishes has been underestimated.
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The various configurations of the jaws, anterior branchial arches and neurocranium provide some of the fundamental synapomorphies, distinguishing the major lineages of sharks, rays and ratfishes. For the Neotropical freshwater stingrays... more
The various configurations of the jaws, anterior branchial arches and neurocranium provide some of the fundamental synapomorphies, distinguishing the major lineages of sharks, rays and ratfishes. For the Neotropical freshwater stingrays (family Potamotrygonidae), putatively unique skeletal elements, the angular cartilages, are intermediate between the hyomandibula and the lower jaw. These skeletal elements have been proposed as a synapomorphy for the potamotrygonids, but confidence in this character has been limited by poor sampling and taxonomic uncertainty, particularly regarding their ontogeny and homology. The morphology of the angular cartilages across the family is described, and the nomenclature of these structures is standardized. In addition, developmental and functional hypotheses for the origins of the angular cartilages are proposed. These cartilages, formed within the hyomandibu-lar–Meckelian ligament, are suggested to be fibrocartilaginous in origin and aid in jaw kinesis. The angular cartilages are corroborated as a synapomorphy for Potamotrygonidae, although there is great variation within the family and similar structures have arisen independently in other extinct and extant batoid lineages. In potamotrygonines, the angular cartilages appear to have been lost in piscivorous Heliotrygon and Paratrygon, while additional angular cartilages were gained, typically one at a time, in some lineages of Potamotrygon.