Shark Genus Research Articles

First report on a diverse Neogene cartilaginous fish fauna from Borneo (Ambug Hill, Brunei Darussalam)

The highest biodiversity of marine fishes occurs in South-east Asia in the Indo-Australian Archipelago (IAA). However, the fossil record of fishes is very sparse and extremely incomplete in the IAA. Here we present a diverse fossil cartilaginous fish fauna from Borneo, found in late Miocene sediments in Brunei Darussalam. This fauna provides the first insight into the types of fishes that existed in the IAA region about 6.5–8 million years ago. The chondrichthyan remains belong to 24 selachian and batoid taxa. The shark fauna is dominated by Carcharhiniformes, comprising three families with at least 12 taxa, most related to modern species: Hemigaleidae (one species), Carcharhinidae (nine) and Sphyrnidae (two). In addition, the teeth of one Lamniformes shark, the extinct giant macro-predator Otodus (Megaselachus) megalodon, are present in the fauna. The batoids are dominated by Myliobatiformes from the following families: Dasyatidae (three species), Aetobatidae (one), Myliobatidae (three), Rhinopteridae (one), while three taxa of the order Rhinopristiformes were also recovered: Pristidae (one species), and Rhinidae (two). Such diversity of fossil cartilaginous fish has never before been reported from the tropical region of South-east Asia. The dominance of the carcharhinid sharks and small rays suggests a shallow marine, coastal palaeoenvironment. The presence of the freshwater shark genus Glyphis indicates a nearby fluvial influence. Some species of the ray genera, such as Himantura or Pastinachus, have also been reported from estuaries and fresh water. The lack of some generally common Neogene taxa, such as Odontaspididae, Lamnidae and Alopidae, may be linked to such local factors and the coastal shallow-water environment.

First record of the hexanchoid shark genus Crassodontidanus (Chondrichthyes: Hexanchiformes) from the Jurassic of Hungary (Mecsek Mts, Southern Hungary), with a summary of the hexanchiform fossil record of Hungary

First record of the hexanchoid shark genus Crassodontidanus (Chondrichthyes: Hexanchiformes) from the Jurassic of Hungary (Mecsek Mts, Southern Hungary), with a summary of the hexanchiform fossil record of Hungary

Molecular diversity and distribution of eastern Atlantic and Mediterranean dogfishes Squalus highlight taxonomic issues in the genus

The alpha taxonomy of the globally distributed shark genus Squalus has been under intense investigation recently, and many new species have been described over the last decade. However, taxonomic uncertainty remains about several taxa. Without consistent nomenclature and the ability to reliably distinguish between the different Squalus species, basic data collection, downstream conservation and management efforts are seriously compromised. To aid in clarifying the taxonomic status of Squalus species in the eastern Atlantic and Mediterranean, we assessed species diversity at the molecular level and evaluated the consistency in species identification in the region. Samples from all nominal Squalus species recognized in the above regions were collected in an international effort and sequenced for regions of the mitochondrial COI and ND2 genes. These data were further analysed alongside publicly available sequences, including 19 of the 26 Squalus species globally recognized, to compare the regional genus‐level diversity with that found elsewhere. Our results confirm inconsistent species identification in the eastern Atlantic and Mediterranean Squalus, particularly concerning S. blainville and S. megalops, and reinforce the need to revise the status of S. megalops and S. mitsukurii as they may include several distinct species distributed around the world. The status of S. blainville is also discussed in the light of the current findings and its problematic taxonomic history.

Revision of Isanodus paladeji (Elasmobranchii, Hybodontiformes) from the Lower Cretaceous of Thailand

Microremains from the Lower Cretaceous Phu Phan Thong locality, Nong Bua Lam Phu Province, northeastern Thailand, yielded ten tooth morphotypes of the freshwater shark genus Isanodus, which allow the revision of this genus. Two new morphotypes assigned to anterolateral and posterolateral teeth possess shared characters with anterior and posterior teeth of Isanodus paladeji whereas its former anterolateral and posterolateral teeth appear to belong to a new species, Isanodusnongbualamphuensis sp. nov. The pattern of ornamentation in some teeth of I. paladeji and I. nongbualamphuensis is quite similar to that observed in the genus Heteroptychodus, suggesting these two genera are closely related.

Molecular phylogeny of Squaliformes and first occurrence of bioluminescence in sharks.

BackgroundSqualiform sharks represent approximately 27 % of extant shark diversity, comprising more than 130 species with a predominantly deep-dwelling lifestyle. Many Squaliform species are highly specialized, including some that are bioluminescent, a character that is reported exclusively from Squaliform sharks within Chondrichthyes. The interfamiliar relationships within the order are still not satisfactorily resolved. Herein we estimate the phylogenetic interrelationships of a generic level sampling of “squaloid” sharks and closely related taxa using aligned sequences derived from a targeted gene capture approach. The resulting phylogenetic estimate is further used to evaluate the age of first occurrence of bioluminescence in Squaliformes.ResultsOur dataset comprised 172 putative ortholog exon sequences. Phylogenetic estimates result in a fully resolved tree supporting a monophyletic lineage of Squaliformes excluding Echinorhinus. Non-luminous Squalidae are inferred to be the sister to a clade comprising all remaining Squaliform families. Our results suggest that the origin of photophores is coincident with an elevated diversification rate and the splitting of families Dalatiidae, Etmopteridae, Oxynotidae and Somniosidae at the transition of the Lower to the Upper Cretaceous. The presence of luminous organs was confirmed for the Sleeper shark genus Zameus. These results indicate that bioluminescence in sharks is not restricted solely to the families Etmopteridae and Dalatiidae as previously believed.ConclusionsThe sister-clade to non-luminous Squalidae comprises five families. The presence of photophores is reported for extant members of three out of these five families based on results of this study, i.e. Lantern sharks (Etmopteridae), Kitefin sharks (Dalatiidae) and Sleeper sharks (Somniosidae). Our results suggest that the origin of luminous organs arose during the rapid diversification event that gave rise to the extant Squaliform families. These inferences are consistent with the idea of diversification of Squaliform sharks being associated with the emergence of new deep-sea habitats in the Lower Cretaceous, which may have been facilitated by the evolution of bioluminescence.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0446-6) contains supplementary material, which is available to authorized users.

Ictiofauna del Mioceno Inferior de la localidad de Pacuare de Tres Equis, Formación Río Banano, provincia de Cartago, Costa Rica, y descripción de un nuevo género y una nueva especie de Scaridae

A studied of the Lower Miocene fish fauna of the Pacuare de Tres Equis locality is made. In this area it is recorded 8 genera of sharks: Heptranchias, Megaselachus, Isurus, Carcharias, Mitsukurina, Hemipristis, Negaprion and Carcharhinus; and 6 families of osteichthyans, Sparidae, Acanthuridae, Scaridae, Labridae, Sphyraenidae and Tetraodontidae. This fish assemblage points out to infra-littoral-neritic, tropical warming waters environments with normal salinity.

The chondrichthyan fauna from the Middle Triassic (Ladinian) of the Iberian Range (Spain)

ABSTRACT Here we present for the first time a detailed taxonomic study of a diverse chondrichthyan fauna from the Middle Triassic of the Iberian Range (Spain). The assemblage consists of isolated remains of seven species of five non-neoselachian shark genera (Palaeobates, Hybodus, Pseudodalatias, Prolatodon, gen. nov., and Lissodus), including a new species of hybodontiform shark, Hybodus bugarensis, sp. nov. In addition, a new homalodontid genus, Prolatodon, sp. nov., is erected for the taxa ‘Polyacrodus’ bucheri and ‘Polyacrodus’ contrarius. The chondrichthyans of the Iberian Range represent a heterogeneous group from a paleogeographic point of view made up of common components of Middle Triassic shark faunas of northern Europe (Hybodus plicatilis and Palaeobates angustisimus) together with species only known previously from North America and China (Prolatodon bucheri, comb. nov., and Prolatodon contrarius, comb. nov.), as well as several ‘endemic’ taxa (Pseudodalatias henarejensis, Hybodus bugarensis, sp. nov., and Lissodus aff. L. lepagei). This fauna demonstrated adaptation for a wide diversity of feeding strategies, implying that non-neoselachian sharks dominated among the predator community of Middle Triassic coastal ecosystems of Iberia. The co-occurrence with bivalves, ammonoids, and conodonts allows us to date the chondrichthyan assemblage as ‘Longobardian’ (upper Ladinian).

A new species of the sclerorhynchid sawfish Borodinopristis from the Campanian (Upper Cretaceous) of North Carolina, USA

Elasmobranch fossils recovered from Campanian marine exposures at Elizabethtown, Bladen County, NC, include species from at least seven genera of sharks and four genera of batoids. Of particular interest is the recovery of multiple isolated rostral spines from a new sclerorhynchid sawfish, Borodinopristis shannoni, sp. nov. Species of Borodinopristis are known from oral teeth and/or rostral spines (‘rostral teeth’ for some authors). In species known from the latter, the spines differ from those of other sclerorhynchids by the presence of one or more ‘collared’ barbs on the posterior margin of the crown. Unlike the previously described B. schwimmeri, the rostral spines of the new species have well-developed hooked barbs with collars (curved, connected crests) extending asymmetrically onto the dorsal and ventral surfaces of the spine, as well as small, rudimentary barbs. Also unlike B. schwimmeri, the anterior margin of the spine is strongly convex and there is no enamelled collar at the base of the crown. The new species also occurs in the Upper Cretaceous of the Gulf Coastal Plain.

The ichthyosaur in the room

The ichthyosaur in the room

A new hyperapolytic species, Trilocularia eberti sp. n. (Cestoda: Tetraphyllidea), from Squalus cf. mitsukurii (Squaliformes: Squalidae) off South Africa with comments on its development and fecundity

A new species of tetraphyllidean cestode in the genus Trilocularia is described from an undescribed shark species, Squalus cf. mitsukurii, off the coast of South Africa. Trilocularia eberti sp. n. is the second known member of its genus, and like its congener, T. gracilis (Olsson, 1866-1867) Olsson, 1869, is extremely hyperapolytic, dropping proglottids from its strobila while they are still very immature. Characteristic of the genus, it possesses a distinctive scolex with triloculated bothridia, but differs conspicuously from its congener in its possession of an anterior loculus that is much larger in width relative to the paired posterior loculi, and also in its possession of an anterior, enlarged region of its free proglottids that is triangular with a slit-like ventral aperture, rather than rounded and cup-like. This anterior region of the free proglottid is used in attachment, and its development is described. For assessment of fecundity, an attempt was made to record all free proglottids of all ages found in both host individuals, and yielded an average estimate of 362 free proglottids being produced per individual worm of T. eberti sp. n. Both Trilocularia species parasitize sharks of the genus Squalus, and given the host specificity typically exhibited by tetraphyllideans and preliminary examinations of other members of this shark genus, it is likely that other Squalus species will be found to host additional new Trilocularia species.

Genetic divergence, speciation and biogeography of Mustelus (sharks) in the central Indo-Pacific and Australasia

The shark genus Mustelus is speciose, commercially important and systematically troublesome. We use a molecular approach combining inter and intra-specific data to investigate Mustelus species in the central Indo-Pacific and Australasia. Our analysis supports two Mustelus clades, one comprising species with no white spots and a placental reproductive mode and a second clade of white spotted, aplacental species. Levels of genetic divergence are low, especially among species in the white spotted, aplacental clade and this should be taken into account when employing molecular data to delineate species. Our data support the hypothesis of a radiation following dispersal from a northern hemisphere ancestor. Molecular dating suggests that localised speciation in Australasia may have occurred during the Pleistocene. We propose that some of the difficulties associated with Mustelus systematics relate to a recent radiation, particularly in the Australasian region.

Morphology and control of photogenic structures in a rare dwarf pelagic lantern shark ( Etmopterus splendidus)

The shark genus Etmopterus encompasses numerous deep-sea species that are widely distributed throughout the world's oceans and share the capability to emit light thanks to numerous tiny epidermal photogenic organs called photophores. Despite the potential wide ecological interest of this light emission, it is still a poorly studied aspect of shark biology, mostly due to the challenges inherent to the study of uncommon deep-sea animals. During a collection trip in waters around Okinawa Island, we had the opportunity to collect, maintain and study specimens of Etmopterus splendidus, a small pelagic lantern shark that was not previously known from this area. Analyses show that (i) the photophore density of this species varies according to the different parts of the body, which led to a heterogeneous photogenic pattern; (ii) photophore harbour the classical structure found in other etmopterid sharks, i.e. a cluster of photocytes enclosed in a pigmented sheath and surmounted by pigmented and lens cells; (iii) the physiological control of these photophores appears similar to what was found in the distantly related Etmopterus spinax, i.e. including hormonal and neural inputs as well as the action of pigmented cells overlying the photocytes. These results indicate that E. splendidus luminescence is probably used for more than one purpose, and support the idea that the physiological control of lantern shark photophores was selected early in the evolution of these sharks.

A new genus and species of fossil myliobatoid ray from the Fishburne Formation (lower Eocene/Ypresian) of Berkeley County, South Carolina, USA

Elasmobranch fossils recovered from the Fishburne Formation (lower Eocene/Ypresian) of Berkeley County, South Carolina, USA, include species from four genera of sharks and six genera of rays. Of particular interest was the recovery of multiple isolated teeth from a new genus and species of the cownosed ray family Rhinopteridae, which is the focus of this study. The unique crown morphology separates this genus and species from Rhinoptera. Eorhinoptera grabdai, gen. et sp. nov., is represented by small, bar-shaped teeth in the shape of greatly elongated hexagons. These teeth are the isolated elements of a dental plate. The holotype, with 12 wide root lobes, is the most elongated in the sample being 1 cm long and 1.5 mm wide, indicating an origin in the central region of the plate. Paratypes are less elongated, have 4–8 root lobes and are from more lateral rows. The crown is smooth and has a distinctly convex occlusal surface. Eorhinoptera is only the second genus of cow-nosed ray. Its distinctive crown morphology may have allowed it to exploit different kinds of prey than those favoured by rays that lacked convex tooth crowns.

Mouth-Size Estimation of a Primitive Lamniform Shark,Protolamna: Low Trophic Position in Lamniform Shark Origin

Abstract. The Lamniformes are a shark clade which occupies the highest trophic-level regimes in extant marine ecosystems, and includes the largest fish-eating shark, Carcharodon carcharias. However, the ancestor of this taxon is thought to be a small shark. In order to evaluate the trophic position of the lamniform shark ancestor, I first developed a new method to estimate the mouth size of fossil lamniform sharks from isolated teeth, and then estimated the mouth size of the oldest recorded lamniform shark genus, Protolamna. This method can predict the mouth size of a fossil lamniform shark if the original tooth position within a jaw or the most closely related extant species is unknown. The result suggests that the mouth size of Protolamna was smaller than most extant Lamniformes. This estimate indicates that they likely fed on small prey, considering that mouth size determines the upper limit of prey size. This finding indicates that extant lamniform sharks evolved from lower trophic-level ancestors.

Marine vertebrates from the ‘middle’ Cretaceous (early Cenomanian) of South India

ABSTRACT Vertebrate fossils have been known from South India's Cauvery Basin since the 1840s, but records of marine vertebrates from the late Albian to Turonian Karai Formation have been limited to a single set of ichthyosaur remains. Recent surface collecting and sieving of lower Cenomanian glauconitic mudstones has yielded the first ichthyosaur material reported in India over the last 140 years, as well as a diverse and previously unrecorded shark assemblage. The ichthyosaur material, including several teeth and vertebrae, is assigned to the sole described Cretaceous genus Platypterygius and to the species P. indicus (Lydekker, 1879). Eight species of shark (one squaliformes, two hexanchiformes, and five lamniformes) are recorded. A new hexanchiform genus Gladioserratus is erected, and two new species (Gladioserratus magnus, gen. et sp. nov., and Dwardius sudindicus, sp. nov.) are named. Many of the shark genera within this largely species-level endemic fauna are known from high paleolatitudes elsewhere, with many showing an antitropical distribution, but are absent in Tethyan areas. This first description of the Karai Formation marine fauna documents the previously unappreciated diversity and unique character of India's Cretaceous marine vertebrates, and indicates a cool-water paleoenvironment for the marine vertebrate assemblage.

Protocotyle euzetmaillardi n. sp. (Monogenea: Hexabothriidae) from the bigeye sixgill shark Hexanchus nakamurai Teng (Elasmobranchii: Hexanchidae) off New Caledonia

Protocotyle euzetmaillardi n. sp. is described from the gills of the sixgill shark Hexanchus nakamurai Teng caught in deep-sea off New Caledonia, South Pacific. The new species is compared with the two other species of the genus (both from the only other species in this shark genus, H. griseus (Bonn.)), namely P. grisea (Cerfontaine, 1899) Euzet & Maillard, 1974, redescribed from vouchers, and P. taschenbergi (Maillard & Oliver, 1966) Euzet & Maillard, 1974, redescribed from its type-specimens. The anatomy of the reproductive system is detailed; all three species have a characteristic oötype with longitudinal cells ('ootype côtelé' of Euzet & Maillard). The following unique combination of characters differentiates the new species from its two congeners: posterior lobe of seminal vesicle absent, diverticulum of oviduct present and small body size. Furthermore, its tubular ovary does not include a region with sperm, which is present in both of the other species, and its eggs have only one filament, whereas eggs in the uterus have one or two filaments in P. grisea and one filament in P. taschenbergi. The latter features differ from existing diagnoses of Protocotyle, in which eggs with two filaments and the presence of a tubular ovary dilated with sperm are key characteristics.

Review of the deep sea squaloid shark genus Scymnodon of Japan, with a description of a new species

Review of the deep sea squaloid shark genus Scymnodon of Japan, with a description of a new species

Review of the enigmatic Eocene shark genus Xiphodolamia (Chondrichthyes, Lamniformes) and description of a new species recovered from Angola, Iran and Jordan

Little is known about the extinct Xiphodolamia, a peculiar lamnid shark which inhabited the Eocene seas. The reexamination of a large set of fossilized teeth specimens from the Ypresian of Kazakhstan has enabled the reconstitution of the tooth series of this enigmatic taxa of lamnid shark. Five distinct tooth morphologies seem to occur in X. ensis Leidy [Leidy, J., 1877. Description of vertebrate remains, chiefly from the phosphate beds of South Carolina. Journal of the Academy of Natural Sciences of Philadelphia 8, 209–261] species revealing a weak ontogenetic variation. Such specific variation in tooth shape means that the other described species may be their junior synonyms. Dental morphology perfectly conforms with a Lamniforme but does not prove the current attribution to the Lamnidae family due to some inconsistent dental features observed, such as the presence of symphysial teeth. This genus could be regarded as an old lineage branched from the stem group of Lamnidae, close to the Isuroids sharks. Several Xiphodolamia teeth, originating both from old collections and new acquisitions, are reported and illustrated in order to provide information about a new species described here: Xiphodolamia serrata nov. sp. This species, currently limited to deposits in Angola, Jordan and Iran and dated at the Late Eocene, is easily distinguishable from the Early-Middle Eocene material belonging to the genus by the presence of serrated cutting edges. Adding to the type species considered here as the only valid taxa during the Early-Middle Eocene period, the temporal range of this genus extends to the Late Eocene, thus setting its upper stratigraphic limit prior to its disappearance as enigmatic as its appearance in the Early Eocene was.

Comments on the selachian genus Cladodus Agassiz, 1843

ABSTRACT The claim that the Carboniferous chondrichthyan genus Cladodus Agassiz, 1843, is a nomen vanum is critically examined. The teeth of C. mirabilis, the type species of the genus, are re-examined from Agassiz's syntypes and other material. It is concluded that C. mirabilis offers a suite of characters adequate for definition of the genus Cladodus. Comparison of the teeth of Cladodus with those of other Carboniferous shark genera confirms its status as a valid taxon. From this revision it is concluded that C. marginatus, C. vanhornei, C. bellifer, and C. elegans should all be included within Cladodus, while C. striatus Agassiz is placed in the new genus Saivodus. Both Cladodus and Saivodus are considered to belong in the Ctenacanthiformes.

A New Genus and Species of Tetraphyllidean Cestode from the Spadenose Shark, Scoliodon laticaudus, in Malaysian Borneo

One of 23 specimens of the Spadenose shark, Scoliodon laticaudus (Elasmobranchii: Carcharhiniformes: Carcharhinidae), necropsied for tapeworms in Mukah, Sarawak, in Malaysian Borneo between 2002 and 2003 was found to host a new genus and species of tetraphyllidean tapeworm belonging to the family Phyllobothriidae. Ruhnkecestus latipi n. g., n. sp. is described from 4 specimens, 3 prepared as whole mounts and 1 from which the strobila was prepared as a whole mount, and the scolex prepared for examination with scanning electron microscopy. The genus is unique among phyllobothriids in that each bothridium bears 1 anterior, 3 central, and 2 posterior facial loculi. Its microthrix pattern, proglottid anatomy, and host associations suggest that its affinities are with the Phyllobothriinae. Among the Phyllobothriinae it most closely resembles species of Paraorygmatobothrium in its possession of a scutellate neck and serrated microtriches on its proximal bothridial surfaces, as well as a tetralobed ovary and vitellaria that are interrupted by the ovary. This represents the first report of a tetraphyllidean tapeworm from the monotypic shark genus Scoliodon.