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Quaternary fossil diversity of Stingrays (Chondrichthyes: Myliobatiformes) from the eastern coast of South America, Brazil, Southwestern Atlantic
Abstract and Figures
Sharks, rays, and chimeras have a limited fossil record compared to other taxa due to their predominantly cartilaginous skeletal structure. Fossilization tends to
preserve anatomic structures such as teeth, scales, cephalic and caudal fins, and other fins. The Myliobatiformes order, derived from rays, is characterized by
viviparity and distinctive serrated stings, with some species exhibiting hexagonal dental plates. These marine organisms inhabit coastal zones globally. This study
aims to enhance understanding of Quaternary biodiversity and paleoecology in southern Brazil, focusing on fossils from the Myliobatiformes order, specifically dental
plates and stings. Material from biodetrital deposits at Concheiros and Hermenegildo beaches in Santa Vitoria ´ do Palmar, Rio Grande do Sul, Brazil, were analyzed.
Six taxa were identified from fossil teeth, including Myliobatis ridens, Myliobatis freminvillei, Myliobatis goodei, and Myliobatis sp. (Morphotypes 1 and 2), marking their
first Pleistocene fossil record in Brazil. Most teeth couldn’t be classified at the species level, but genera were discerned. Fossil stings were described, possibly
associated with Myliobatiformes. Results revealed notable differences between identified fossil taxa and their modern counterparts in the western Atlantic Ocean,
currently considered common. M. ridens was the most frequent species in the fossil samples, followed by M. freminvillei, with fewer records for M. goodei. Conversely,
the current scenario shows M. goodei as the most abundant, followed by M. freminvillei, while M. ridens is Critically Endangered. This investigation expands knowledge
of fossil species on the southern Brazilian coast, confirming the presence of M. ridens, M. freminvillei, and M. goodei during the Quaternary.
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A atual estrutura geológica e geográfica da Terra foi formada ao longo de 4,5 bilhões de anos. Os últimos 2 milhões de anos (Quaternário)-cerca de 0,05% dessa história-foram marcados por forte oscilações climáticas e pelo surgimento do homem, que passou a ser um agente importante na modificação do ambiente natural. As mudanças impostas pelo clima e pelo homem resultaram em profundas alterações ambientais, que ficaram gravadas na história do planeta. O Quaternário do Brasil é uma obra que traz o estado da arte dos estudos desse importante período geológico realizados no país, o que deverá influenciar a própria dinâmica da pesquisa e a docência nessa área do conhecimento. Apenas uma compreensão ampla e adequada da história do Quaternário, incluindo a dinâmica dos ambientes naturais e as relações do homem com esses ambientes, poderá evitar uma ação devastadora sobre o que é um dos nossos maiores tesouros-nossa própria casa.
This newly described chondrichthyan fauna from the late Miocene Chucunaque Formation of Lago Bayano reveals a prolific and highly diverse assemblage from Panama, and one of the richest shark faunas from the Neotropics. Strontium geochronology indicates an age of 10–9.5 Ma for the chonrichthyan-bearing strata. Field efforts resulted in 1429 identifiable specimens comprising at least 31 taxa, of which at least eight are new to the documented fossil record of Panama. With this information an analysis of functional diversity was conducted, indicating ecosystems dominated by generalist species feeding upon a wide range of organisms, from plankton to marine mammals. A probabilistic approach of paleobathymetric estimation suggests a neritic environment. Previous studies based on foraminifera have suggested that the Chucunaque Formation had a greater Pacific Ocean affinity, making this the first Miocene chondrichthyan fauna described from the Pacific shelf of Panama. However, our geographic comparisons show that this fauna has mixed Caribbean and Pacific biogeographic affinities, which likely supports the previously purported connection between chondrichthyan faunas during the late Miocene.
The objective of the present work is to compare the presence of Pleistocene vertebrate fossils from the central and southern sectors of the Coastal Plain of Rio Grande do Sul, quantifying and qualifying the taphonomy, and taxonomic group and skeletal remains representativeness. A total of 2,820 fossils was collected, among them 95% were collected in the southern sector and 5% in the central sector. In both sectors were identified two populations of bioclasts: non-identified fossils (85%) and identified fossils (15%). The same taxonomic groups and skeletal remains were identified in both sectors, except for some due to the different amount of fossils collected. The two populations of bioclasts identified represent greater (85% non-identified) or less (15% identified) reworking by waves. The hypothesis for the different amount of fossils collected is the availability of fossils on the shoreface and inner continental shelf. The presence of several submerged sedimentary rocks and records of paleolagoons and paleochannels on the shoreface and inner continental shelf of the southern sector indicates probably the source-areas where the skeletal remains were once fossilized and now are being eroded.
A new Middle Miocene (Langhian – early Serravallian) assemblage with shark and ray teeth from Nyirád (Hungary, Transdanubia, Veszprém County) consists of nine families, with 15 different species. The assemblage shares many common genera with other Middle Miocene assemblages in the Paratethys (Notorynchus, Carcharias, Otodus, Cosmopolitodus, Hemipristis, Galeocerdo, Carcharhinus, and Aetobatus), and reflects a subtropical climate and a close connection with the Mediterranean Sea. However, a detailed faunal compilation of Miocene selachians reveals that several taxa that were still present in the Mediterranean or lived in the Paratethys during the Lower Miocene disappeared or became very rare by the Middle Miocene in the Central Paratethys (e.g., Isistius, Centrophorus, Mitsukurina, Carcharoides, Parotodus, Alopias). The taxa that went locally extinct in the Paratethys are mainly represented by deep-water or pelagic forms. Their disappearance is most probably related to the gradual separation of the Paratethys from the Mediterranean. The common presence of some large, rather pelagic sharks (e.g., Otodus, Cosmopolitodus) in the Central Paratethys during the Middle Miocene is explained here by the widespread occurrence of their potential prey
represented by marine mammals (e.g., whales and dolphins).
Please visit the authors' website for this book: https://sites.google.com/view/fishes-of-the-world-5/welcome.
Fishes of the World, Fifth Edition is the only modern, phylogenetically based classification of the world’s fishes. The updated text offers new phylogenetic diagrams that clarify the relationships among fish groups, as well as cutting-edge global knowledge that brings this classic reference up to date. With this resource, you can classify orders, families, and genera of fishes, understand the connections among fish groups, organize fishes in their evolutionary context, and imagine new areas of research. To further assist your work, this text provides representative drawings, many of them new, for most families of fishes, allowing you to make visual connections to the information as you read. It also contains many references to the classical as well as the most up-to-date literature on fish relationships, based on both morphology and molecular biology.
The study of fishes is one that certainly requires dedication—and access to reliable, accurate information. With more than 30,000 known species of sharks, rays, and bony fishes, both lobe-finned and ray-finned, you will need to master your area of study with the assistance of the best reference materials available. This text will help you bring your knowledge of fishes to the next level.
- Explore the anatomical characteristics, distribution, common and scientific names, and phylogenetic relationships of fishes
- Access biological and anatomical information on more than 515 families of living fishes
- Better appreciate the complexities and controversies behind the modern view of fish relationships
- Refer to an extensive bibliography, which points you in the direction of additional, valuable, and up-to-date information, much of it published within the last few years.
711 pages, Index, Bibliography
Vertebrate marine fossils were collected between Cassino beach and Barra do Chuí beach, and continental inner shelf (20 m) in Southern of Brazil; between 1989 and 1994. Ten taxa were identified: Carcharodon carcharias, Carcharias taurus, Galeocerdo cuvieri, Isurus oxyrinchus, Notorynchus cepedianus, Heptranchias perlo, Carcharhinus sp. Netuma sp., Pogonias cromis, and Pontoporia blainvillei. The identification showed an ictiofauna similar to the recent due, except from Galeocerdo cuvieri and Carcharodon carcharias. The great number of specimens of Carcharodon carcharias suggest that there was a paleo-population. The occurrence of pontoporia blainvillei is evidence of the existence of little cetaceans, which could have been the main alimentary source for Carcharodon carcharias. The vertebrate marine fossils are found concentrated always associated to submersed geomorphology features in continental shelf. That are composed by beachrock ledges and biodetritic gravel deposits. This relict features are reworked by actual dinamics and this fossil (palimpsest) are transported onshore to the beach face; along the open ocean beaches, RS, Brazil.
Resumo As variações do nível do mar durante o Quaternário no Brasil têm sido estudadas desde trabalhos pioneiros do século XIX. Desde então, centenas de trabalhos têm contribuído para melhor entendê-las. Apesar disto, o conhecimento ainda é incompleto e controvérsias persistem na literatura. Deste modo, para contribuir no conhecimento das variações do nível do mar no Quaternário no Brasil, foi realizada a revisão conceitual dos indicadores de paleoníveis marinhos utilizados em trabalhos anteriores. Na revisão, é apresentada proposta de classificação dos indicadores, descrição de suas características e discussão das incertezas e erros de interpretação. Finalmente, sugere-se a elaboração de mais e mais precisas curvas locais e regionais de nível relativo do mar para poder discriminar as diversas componentes das variações eustáticas e aparentes do nível do mar. Palavras-chave: Holoceno; nível do mar; costão rochoso; fácies sedimentares. Abstract The Quaternary sea-level changes along the Brazilian coast have been studied since 19 th century pioneer works. Since then hundreds of works have been contributed to the understanding the sea-level changes. However, their knowledge is still incomplete and some controversies could be found at previous works. Therefore, to contribute with the understanding of the Quaternary sea-level changes along the Brazilian coast there was performed the conceptual review of the paleo-sea level indicators found at previous works. At the review is presented a proposal of classification of paleo-sea level indicators, the description of their characteristics and the discussion of their uncertainness and misinterpretations. Finally is suggested the construction of more and more precise local and regional relative sea-level curves to distinguish the several components of eustatic and apparent sea-level changes.
Remains of selachians (sharks and rays) and other icthiolites have been collected from the Upper Mio-cene locality of San Gerardo of Limoncito. Three new records of fossil species of sharks are described for Central America and the Caribbean Region: Carcharhinus longimanus (Poey, 1861), Isogomphodon caneullensis (Cappetta, 1970) and Sphyrna arambourgi (Cappetta, 1970). The fauna of the Curré Formation is notable for the strong Tethisian affinity with the paleomediterranean faunas.
The exact affinities of the fossil teeth attributed to the devilrays (mobulids) are critical for resolving the debated origin of these giant pelagic rays amongst Myliobatiformes and the timing of their evolution toward planktivory. We performed the first detailed comparative description of teeth belonging to most of the living and fossil mobulids. Based on a survey of living devilrays, three dental morphologies are newly identified as cobblestone tooth plates, comb-like teeth, and peg-like teeth. In addition, all extinct mobulid species are reviewed with comments on their dentition, fossil record, and geographical distribution. As a result, three fossil mobulid taxa are newly described from the Late Eocene of south-west Morocco (Argoubia barbei gen. et sp. nov., Oromobula dakhlaensis gen. et sp. nov., and Eoplinthicus underwoodi sp. nov.). This has permitted the first assessment of the phylogenetic positions of extinct and extant species of mobulids, using cladistic analyses and a combined data set of nondental anatomical characters from the literature and the dental characters defined here. Our new results support the monophyly of mobulids including all living and most extinct species and indicate that mobulids are closely related to rhinopterids. They also indicate that there was a recent split within Mobulidae into the three tooth morphology groups that we describe in this paper. This work provides clues to the evolutionary history of this clade since the Early Eocene, including the gradual lack in tooth interlocking toward the filter-feeding strategy, whereas the preservation of cusped teeth without feeding function in modern filter-feeder mobulids is interpreted as a tool for precopulatory purposes.
Past studies have suggested that increases in cownose ray (Rhinoptera bonasus) abundance may pose problems for fisheries management due to their specialized diet of exploitable mollusks. However, more
recent work has identified cownose rays as opportunistic generalists, consuming mainly non-commercial prey (e.g. soft-bodied
invertebrates) most abundant in their locale. To better assess the generalist vs. specialist foraging behaviors of cownose
rays, including their impact to commercial shellfish of the north-central Gulf of Mexico, we conducted gut content analysis
on 201 individuals from coastal Alabama. Prey items were analyzed for frequency of occurrence and percent composition by weight,
which were used to develop an index of importance. Our diet analysis indicated a minimal impact of cownose rays to exploitable
shellfish species of coastal Alabama. Further, we observed important spatial and ontogenetic diet variability: adult diets
were dominated by crustaceans along barrier islands and open waters of the Gulf of Mexico, whereas juvenile and young-of-the-year
individuals almost exclusively consumed bivalves in riverine and estuarine areas. Individual cownose ray diets were primarily
monotypic (54.3%) and appeared selective for amphipods (i.e. Haustorius sp.) when hyperabundant along gulf barrier islands and bivalves at estuarine sites regardless of ambient densities. While
this study highlights the importance of locality in determining dietary composition of cownose rays, we do not suggest this
species is opportunistic or completely mollusk-specialized. Alternatively, we propose cownose rays exhibit a continuum of
foraging behaviors between specialization and generalization, depending on locale and prey availability.
ICHNOFOSSILS (PALEO-BURROWS AND CROTOVINES) ATTRIBUTED TO EXTINCT MAMMALS IN SOUTHEASTERN AND SOUTH BRAZIL. This work presents information regarding tunnels which are attributed to large extinct mammals. These structures can be found in several places in southeastern and southern Brazil, in different types of substrate, occurring as hollow structures (paleo-burrows) or those filled with sediments (crotovines). The dimensions and osteoderm and claw imprints found along the internal walls of the paleo-burrow found on aluvial fan deposits near the town of Cristal (Rio Grande do Sul State) suggest that a dasypodid xenarthran might have dug this structure. Comparison with similar structures found in Argentina can provide more detailed information regarding the paleoecology and biostratigraphy of the organisms that made these burrows. RESUMO – Neste trabalho são apresentadas informações sobre túneis atribuídos a grandes mamíferos extintos. Essas estruturas são encontradas em diversos locais do sudeste e sul do Brasil, ocorrendo em diferentes tipos de substratos, desobstruídas (paleotocas) ou preenchidas por sedimentos (crotovinas). A paleotoca encontrada no município de Cristal (RS) foi escavada nos depósitos de leques aluviais terciários e marcas de garras e impressões da carapaça podem ser vistas ao longo da superfície interna da galeria. As dimensões da estrutura, as marcas de escavação e marcas de osteodermos presentes ao longo das paredes da paleotoca sugerem que tenha sido produzida por um xenartro dasipodídeo. A comparação com estruturas similares encontradas na Argentina pode fornecer informações mais detalhadas a respeito da paleoecologia e bioestratigrafia dos organismos responsáveis por sua escavação.
This paper demonstrates the link between the evolution of a coastal barrier in southern Brazil during the Late Holocene and the formation of a large volume of eolian disseminated heavy mineral deposits. Our data set is based on an earlier heavy mineral prospecting campaign (1991) and on 10 new shallow vibrocores, 2–5 m long. The model presented has three main steps of barrier evolution. The first step is the recycling of coastal plain deposits during the Postglacial Marine Transgression, which ended at 5.6 ka when heavy minerals were incorporated into beach and washover facies of a transgressive barrier. The second step is the shoreward retreat of the barrier, under a slow and small sea-level fall, during the last 5.6 ka. This second step eroded and recycled sediments from the Pleistocene substrate, which acted as an extra source of heavy minerals. Heavy minerals were concentrated in backshore deposits by wave action during barrier recession. The third step is the erosion and transport of backshore sands by onshore winds into an inter-barrier depression in the form of transgressive dune deposits. These deposits contain an average of 4.66±1.02% disseminated heavy minerals (1494 samples). This eolian placer deposit has started to form 1 ka ago and is still under formation.
Two species of Myliobatis, the southern eagle ray M. goodei Garman and the bullnose eagle ray
M. freminvillii Le Sueur, have long been recognized to occur in coastal Argentinean waters. Several unusual
specimens belonging to the family Myliobatidae were recently collected off Buenos Aires Province, Argentina.
These specimens clearly belong to the genus Myliobatis, since they have a broad disk with long sharply pointed
pectoral fins, a projecting snout, a very long and thin tail, and a smaller dorsal fin set farther back on the tail,
well beyond the pelvic fins. However, the specimens were distinct from all sympatric congeners in several
characters, and they are described here as a new species. Myliobatis ridens sp. nov. is distinguished from M.
goodei in having a relatively shorter snout, a wider interorbital space, a wider mouth, and different shapes of the
ventral and dorsal marginal cartilages of the claspers than the latter; and from M. freminvillii by having smaller
eyes, a smaller dorsal fin, a plain dorsal coloration, and a different shape of the dorsal marginal cartilage of the
claspers. In order to test this morphological differentiation, cytochrome c oxidase subunit I (COI) sequence
data were obtained from the new species and compared to those of its congeners. Analysis of COI sequences
showed a congeneric sequence divergence of > 6%, supporting species differentiation. Therefore combining
both traditional taxonomy and DNA barcoding, a new eagle ray species, M. ridens sp. nov., from the Southwest
Atlantic Ocean was discovered.
Freshwater stingrays from the Fossil Butte Member of the late early Eocene Green River Formation of Wyoming are reviewed, and a new genus and species of fossil stingray is described. †Asterotrygon maloneyi, n.gen., n.sp. is remarkably well preserved and is known from articulated skeletons of juveniles and adults, both males and females. It is distinguished from all Recent and fossil stingrays, including †Heliobatis radians from the same formation, by the unique presence of a dorsal fin covered with dermal denticles directly anterior to the caudal stings. Other characters that in combination distinguish the new fossil genus from all other stingrays include: retention of separate, individual vertebrae extending to the tail extremity instead of a cartilaginous rod posterior to caudal stings; dorsal surface of disc and tail covered by numerous, closely packed, minute denticles; tail relatively stout at base; and relative proportions of disc and tail. †Asterotrygon, n.gen. shares with certain stingray genera postorbital processes of neurocranium separated from a supraorbital process by a small notch in the supraorbital shelf, presence of both dorsal and ventral tail-folds posterior to caudal stings (and internally supported by rudimentary radial elements), and hyomandibulae separated from lower jaws by a gap that originally contained the hyomandibular-Meckelian ligament. A calcified angular cartilage between the hyomandibula and Meckel's cartilage is tentatively identified in †Asterotrygon, n.gen. as well. †Asterotrygon, n.gen. is unquestionably a stingray, presenting many myliobatiform synapomorphies including caudal stings on the dorsal aspect of tail, lack of jugal arches in neurocranium, a thoracolumbar synarcual cartilage posterior to scapulocoracoid, absence of thoracic ribs, and laterally expanded, shelflike postorbital processes. †Asterotrygon, n.gen. and †Heliobatis primitively retain a narrow and slightly arched puboischiadic girdle and primitively lack calcified rostral elements in adults.A phylogenetic analysis of 23 stingray genera, two outgroups, and 44 informative morphological characters resulted in 35 equally most parsimonious trees. The strict consensus reveals the following hierarchical structure: Hexatrygon + (†Asterotrygon, n.gen., Plesiobatis, Urolophidae + (Urotrygonidae + (†Heliobatis + (Potamotrygonidae + (amphi-American Himantura, Pteroplatytrygon, Himantura, Taeniura, Dasyatis + (Gymnuridae + Myliobatidae)))))). Our resulting tree has nodes in common with previous phylogenetic analyses of stingrays (e.g., Hexatrygon is the most basal stingray genus; gymnurids and myliobatids [pelagic stingrays] are well-supported sister-groups), but includes novel components, such as a clade that includes all dasyatid genera (as a polytomy) and the component Gymnuridae + Myliobatidae. “Dasyatidae” is not monophyletic in any of the minimum-length trees obtained; Urolophidae (Urolophus and Trygonoptera) and Urotrygonidae (Urobatis and Urotrygon) are both monophyletic, but are not sister-groups. †Asterotrygon, n.gen. forms a clade with urolophids in 21 of the 35 equally most parsimonious trees. Successive approximations weighting adds only one additional node in relation to the strict consensus, which unites Pteroplatytrygon, Dasyatis, and Himantura sensu stricto (in a polytomy) with Gymnuridae + Myliobatidae. The resulting stingray phylogeny is at odds with previous phylogenies mostly regarding the affinities of amphi-American Himantura and Taeniura, which do not form a monophyletic group with the South American freshwater stingrays (Potamotrygonidae) in any of the minimum-length trees obtained. Similar to most elasmobranch groups, stingrays display much character conflict, and cladogram topologies are very sensitive to changes in character coding. Due to a high degree of character variation present in certain generic-level terminal taxa, a more fully representative species-level phylogeny is necessary to clarify the systematic importance of tail-fold configuration, ceratobranchial fusion patterns, and other characters discussed in our study. Three additional synapomorphies of stingrays were uncovered by our study, pertaining to the configuration of the basihyal, first pair of hypobranchial cartilages, and to the forward extension of the basibranchial copula. Our phylogenetic results imply the following biogeographic patterns: the relationships of †Asterotrygon, n.gen. demonstrate a strong Indo-west Pacific historical correlation, while †Heliobatis displays an affinity with the Americas; the node containing the greatest diversity of modern stingrays (“Dasyatidae” + (Gymnuridae + Myliobatidae)) evolved only after an American stingray lineage was established sometime earlier than the early Eocene; and potamotrygonids date at least from the late early Eocene, and not the Miocene, as previous studies have implied. The mechanism responsible for the invasion of the potamotrygonid ancestor into South America could indeed have been a marine transgression as advocated by other authors, albeit a much earlier (pre-Miocene) one, during either the Late Cretaceous or the late Paleocene to early Eocene.
Cartilaginous fishes continuously replace their teeth throughout their life (polyphyodonty) and often show a sexually dimorphic dentition that was previously thought to be an invariant sex character. Radial vector analysis of tooth shape in the polyphyodontic stingray Dasyatis sabina across a consecutive 24 month period shows a stable molariform morphology for females but a periodic shift in male dentition from a female-like molariform to a recurved cuspidate form during the reproductive season. The grip tenacity of the male dentition is greater for the cuspidate form that occurs during the mating season than for the molariform dentition that occurs during the non-mating season. Dental sexual dimorphism and its sex-dependent temporal plasticity probably evolved via polyphyodontic preadaptation under selective pressures on both sexes for increased feeding efficiency and sexual selection in males to maximize mating success. These phenomena are important considerations for the identification and classification of cartilaginous fishes and possibly other polyphyodontic vertebrates in the fossil record.
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.
This paper presents a brief review of the structure , stratigraphy and mineral resources of the Rio Grande do Sul Coastal Province, especially with regard to its outcropping surface units as well as a new approach proposition based on data gathered in a systematic geological mapping which has been carried out in the region. Based on this new approach, which is mainly supported on geomorphological evidences, a new scheme of paleogeographic evolution has been proposed.
Although many sharks have a rather general vertebrate body plan, they display a number of specializations for feeding that belie the notion that they are "primitive." These specializations include a battery of highly developed exteroceptive systems such as vision, olfaction, acoustico-lateralis sense and electroreception; and a cranial morphology that has been molded into a number of functionally adaptive forms. These forms result in grasping, sucking, crushing, gouging, cutting and filtering systems of feeding. With relatively few exceptions elasmobranch feeding mechanisms share such features as subterminal or inferior mouths, a dynamic tooth replacement system, hyostylic jaw suspension and a kinetic, protractile upper jaw. The importance of each of these components is discussed. The evolution of the high diversity of mechanical feeding systems in such a small group of vertebrates has probably been facilitated by the morphological simplicity of the basic feeding mechanism. This radiation was accomplished by modifications in jaw length, the length and supporting angle of the hyomandibula, the size of the gape, dentition and changes in the relative size of the cranial musculature. The evolutionary pattern of shark feeding mechanisms is complex, there being several examples of both parallelism and convergence. A long-jawed, grasping form (similar to, but not identical with Chlamydoselachus) is here considered primitive. From a subsequent benthic sucking and grasping ancestor, similar in many respects to some living batoids,radiated crushing, ray-like forms; cutting, squaloid forms; and gouging, lamniform and carcharhiniform types. From the latter developed sucking and grasping, or crushing forms such as modern orectolobiforms, triakids and heterodontiform sharks. From several levels (primary crushing, secondary crushing and gouging) there emerged filter-feeding forms represented today by mobulids, rhiniodontids and cetorhin.
In the last few years, estimates of the patterns and timing of the evolution of the pelagic, durophagous stingrays (Myliobatidae) have improved through new comparative data from morphology, the fossil record, and DNA sequences. These recent studies are here reviewed and a conservative summary of myliobatid diversification and origins is presented. The interrelationships and morphological evolution of the durophagous stingrays are discussed, including the nature of devil rays as derived myliobatids. An exploration of myliobatid origins includes estimates of the timing of their diversification and an assessment of gymnurids as a possible sister group. The prevailing signal suggests that the most recent common ancestor of extant myliobatids was a Late Cretaceous oscillating swimmer with a pavement-like dentition. The devil ray lineage began the transition to planktivory by at least the Oligocene, with dentition gradually reduced from grinding plates of interlocking elements to long rows of homodont teeth. Finally, the validity of the genera Manta (Bancroft, 1829) and Pteromylaeus (Garman, 1913) are called into question.
Chondrichthyans (sharks, batoids, and chimaeras) have simple feeding mechanisms owing to their relatively few cranial skeletal elements. However, the indirect association of the jaws to the cranium (euhyostylic jaw suspension) has resulted in myriad cranial muscle rearrangements of both the hyoid and mandibular elements. We examined the cranial musculature of an abbreviated phylogenetic representation of batoid fishes, including skates, guitarfishes and with a particular focus on stingrays. We identified homologous muscle groups across these taxa and describe changes in gross morphology across developmental and functional muscle groups, with the goal of exploring how decoupling of the jaws from the skull has effected muscular arrangement. In particular, we focus on the cranial anatomy of durophagous and nondurophagous batoids, as the former display marked differences in morphology compared to the latter. Durophagous stingrays are characterized by hypertrophied jaw adductors, reliance on pennate versus fusiform muscle fiber architecture, tendinous rather than aponeurotic muscle insertions, and an overall reduction in mandibular kinesis. Nondurophagous stingrays have muscles that rely on aponeurotic insertions onto the skeletal structure, and display musculoskeletal specialization for jaw protrusion and independent lower jaw kinesis, relative to durophagous stingrays. We find that among extant chondrichthyans, considerable variation exists in the hyoid and mandibular muscles, slightly less so in hypaxial muscles, whereas branchial muscles are overwhelmingly conserved. As chondrichthyans occupy a position sister to all other living gnathostomes, our understanding of the structure and function of early vertebrate feeding systems rests heavily on understanding chondrichthyan cranial anatomy. Our findings highlight the incredible variation in muscular complexity across chondrichthyans in general and batoids in particular. J. Morphol., 2014. © 2014 Wiley Periodicals, Inc.
Described species: Apristurus laurussonii, Asymbolus analis, Atelomycterus marmoratus, Aulohalaelurus labiosus, Cephaloscyllium isabellum, Cephalurus cephalus, Cephalurus cf. cephalus, Galeus melastomus, Halaelurus (Bythaelurus) canescens, Halaelurus (Halaelurus) bürgeri, Haploblepharus edwardsii, Holohalaelurus regani, Parmaturus pilosus, Poroderma pantherinum, Schroederichthys maculatus, Scyliorhinus canicula
A set of hypotheses are developed for the origin of living sharks and rays and the interrelationships of their major groups, using some methods of cladistic analysis to relate groups with shared derived characters. Comparative studies on living sharks and rays combined with new data on fossil sharks suggests that the living groups ultimately stem from a common ancestral group of “neoselachian” sharks with many modern characters. Reinterpretations of “amphistyly” in modern sharks is presented on new data.
Shark teeth are the most common vertebrate fossils found along the western shore of Chesapeake Bay at Calvert Cliffs in Maryland. The stratigraphic distribution of teeth within the cliffs has not yet been documented. We utilized museum collections of in situ teeth to access their distribution within stratigraphic beds and a large selection of float teeth retrieved from Calvert County beaches as a proxy for the distribution of teeth within stratigraphic beds and across underlying beaches. Museum collections provide 1,866 teeth recorded in situ; float collections yield a total of 24,409 teeth. These data sets offer different, but complementary, results. Miocene sediments along Calvert Cliffs comprise the Calvert, Choptank, and St. Marys formations. Over 96% of all teeth in the in situ data set derive from the Calvert Formation, likely due to favorable paleoenvironmental conditions for sharks. The non-uniform stratigraphic distribution of teeth is further supported by an uneven distribution of teeth collected on beaches below the cliffs. Samples from northern localities contained more float specimens; cliffs in this area are composed almost entirely of the Calvert Formation. Fifteen genera are represented in the in situ and float collections. The main constituents are Carcharhinus spp., Hemipristis serra, Galeocerdo spp., Isurus spp., and Carcharias spp. Most of these genera exhibit significant unidirectional trends in the proportional abundance of teeth across Calvert Cliffs beaches. Factors influencing these variations remain unclear, but the overall dominance of carcharhiniforms over lamniform and other sharks observed for the Miocene persists in modern nearshore environments.
The Azores Archipelago is a group of isolated islands located in the North Atlantic Ocean. One of these oceanic islands - Santa Maria - exhibits marine fossiliferous sediments of late Miocene/early Pliocene and also of Pleistocene age. Recent research provided new selachian fossil material, with three new records (Carcharias acutissima, Megaselachus megalodon, and Carcharhinus cf. leucas) increasing the number of fossil sharks reported from the Azores (Santa Maria Island) to seven species (Notorynchus primigenius, C. acutissima, Cosmopolitodus hastalis, Paratodus benedenii, Isurus oxyrinchus, M. megalodon, and C. cf. leucas). So far, no teeth of batoids or small sharks have been found despite the screen-washing of several sediment samples from Santa Maria. The Azorean Mio-Pliocene selachian fauna clearly differs from those described from sediments deposited on continental shelves, in which batoids and small benthic sharks (e.g., scyliorhinids) are usually well represented. During the late Miocene/early Pliocene, subtropical to warm-temperate seas were prevalent in the area of the Azores, as deduced from palaeontological, geological and isotopic data, all indicating a warmer climate than in the present.
Shoreline sedimentation during the last interglacial highstand on the Rio Grande do Sul Coastal Plain, southern Brazil, is represented by a sandy barrier that extends almost uninterrupted for hundreds of kilometers along the coast. Facies analyses of high quality exposures in several sandpits situated in the northern part of the coastal plain provided an opportunity to examine the stratigraphic nature of these deposits. Based on distinct assemblages of physical and biogenic sedimentary structures, the vertical sequence of facies reveals a regressive (prograded) barrier with vegetated coastal dune sands overlying beach and shallow marine sediments. Progradation was probably promoted by abundant supplies of nearshore sand during the highstand and early fall of sea level (forced regression) associated with the last interglacial period, around 125 ka. As indicated by elevations of Ophiomorpha burrows, the maximum level reached by the sea was around 7 m above the present sea level. Paleocurrent data suggest that, in the studied area, shoreline orientation, hydrodynamics and sediment transport during the last interglacial highstand were similar to present-day conditions.
Skates, rays and allies (Batoidea) comprise more than half of the species diversity and much of the morphological disparity among chondrichthyan fishes, the sister group to all other jawed vertebrates. While batoids are morphologically well characterized and have an excellent fossil record, there is currently no consensus on the interrelationships of family-level taxa. Here we construct a resolved, robust and time-calibrated batoid phylogeny using mitochondrial genomes, nuclear genes, and fossils, sampling densely across taxa. Data partitioning schemes, biases in the sequence data, and the relative informativeness of each fossil are explored. The molecular phylogeny is largely congruent with morphology crownward in the tree, but the branching orders of major batoid groups are mostly novel. Body plan convergence appears to be widespread in batoids. A depressed, rounded pectoral disk supported to the snout tip by fin radials, common to skates and stingrays, is indicated to have been derived independently by each group, while the long, spiny rostrum of sawfishes similarly appears to be convergent with that of sawsharks, which are not batoids. The major extant batoid lineages are inferred to have arisen relatively rapidly from the Late Triassic into the Jurassic, with long stems followed by subsequent radiations in each group around the Cretaceous/Tertiary boundary. The fossil record indicates that batoids were affected with disproportionate severity by the end-Cretaceous extinction event.
The stingray family Myliobatidae contains five durophagous (hard prey specialist) genera and two planktivorous genera. A suite of morphological features makes it possible for the hard prey specialists to crush mollusks and crustaceans in their cartilaginous jaws. These include: 1) flat, pavement-like tooth plates set in an elastic dental ligament; 2) multiple layers of calcified cartilage on the surface of the jaws; 3) calcified struts running through the jaws; and 4) a lever system that amplifies the force of the jaw adductors. Examination of a range of taxa reveals that the presence of multiple layers of calcified cartilage, previously described from just a few species, is a plesiomorphy of Chondrichthyes. Calcified struts within the jaw, called "trabecular cartilage," are found only in the myliobatid genera, including the planktivorous Manta birostris. In the durophagous taxa, the struts are concentrated under the area where prey is crushed, thereby preventing local buckling of the jaws. Trabecular cartilage develops early in ontogeny, and does not appear to develop as a direct result of the stresses associated with feeding on hard prey. A "nutcracker" model of jaw function is proposed. In this model, the restricted gape, fused mandibular and palatoquadrate symphyses, and asynchronous contraction of the jaw adductors function to amplify the closing force by 2-4 times.
Selachorum tabula analytica
- Bonaparte
Beachcombing for fossils
- Craven
Interrelationships of living elasmobranchs
- Compagno
Central America. Myliobatis goodei garman
- Garman
Analyse morphostructurale et evolution paleogeographique de la plate-forme continentale atlantique sudbresilienne (Rio Grande Do Sul - Bresil)
- I C S Corrêa
- P Last
- G Naylor
- B Séret
- W White
- M De Carvalho
- M Stehmann
Types of morphogenesis of the dermal skeleton in fossil sharks
- Reif
Stiffening the stingray skeleton – an investigation of durophagy in myliobatid stingrays (Chondrichthyes, Batoidea, Myliobatidae)
- Suguio
On the application of the laws of evolution to the arrangement of the Vertebrata, and more particularly of the Mammalia: Proceedings of the Scientific Meetings of the Zoological Society of London
- T H Huxley
Cape Cod to Brazil; not uncommon
- LeSueur