Hybodont Shark Research Articles

New Hybondontoid Shark from the Permocarboniferous (Gzhelian—Asselian) of Guardia Pisano (Sardinia, Italy)

Numerous isolated teeth, fin spine fragments and dermal denticles of a hybodont shark from a lacustrine limestone horizon at the top of lithofacies B of the Late Carboniferous to Early Permian succession of the Guardia Pisano Basin (Sulcis area, southwestern Sardinia, Italy) are assigned to a new species of the genus Lissodus Brough, 1935. Lissodus sardiniensis sp. nov. is erected on the basis of about 500 teeth, which show a unique feature of only one pair of lateral cusps that are bent in the direction of the prominent central cusp. Weak heterodonty allows distinction of symphyseal, mesial to anterolateral, and lateral teeth. Lissodus sardiniensis sp. nov. was a freshwater-adapted durophagous shark of bottom dwelling habit, an interpretation supported by general construction of the dentition and the morphology of the dermal denticles. The association with Acanthodes, diplodoselachid sharks and branchiosaurs allows the reconstruction of a five-level trophic chain for the Guardia Pisano Basin. The discove...

Fossil vertebrate remains from Kut Island (Gulf of Thailand, Early Cretaceous)

The Mesozoic vertebrate fauna from Kut Island includes hybodont sharks ( Hybodus sp., Isanodus paladeji, a new species of Heteroptychodus), actinopterygians (Semionotiformes indet., Lepidotes sp.), indeterminate turtles, goniopholidid crocodiles, cf. Theriosuchus sp. and theropod dinosaurs. The new hybodont species is also present in the Sao Khua Formation and maybe also in the Phu Kradung Formation on the Khorat Plateau in northeastern Thailand. The occurrence of both I. paladeji and the new hybodont, together with heavily ornamented Semionotiformes teeth strongly suggest that this fauna is of the same age as the Sao Khua Formation one. Deposits from Kut Island are therefore younger than usually considered, and not older than Berriasian.

Morphology of the Braincase in the Cretaceous Hybodont Shark Tribodus limae (Chondrichthyes: Elasmobranchii), Based on CT Scanning

The braincase of the Lower Cretaceous hybodont shark Tribodus limae is examined using high-resolution CT scanning, and its internal and external morphology is described based on three-dimensional digital reconstructions. This study represents the first in-depth examination of a hybodont braincase using CT scanning and digital imaging technology. The braincase of an additional Lower Cretaceous hybodont, Egertonodus basanus, is also digitally reconstructed and compared to Tribodus. A reconstruction of cranial nerves and blood vessels in Tribodus is presented on the basis of preserved foramina. The braincase of Tribodus shares many features with those of Egertonodus and neoselachians, providing further support for the sister-group relationship between hybodonts and extant elasmobranchs. CT scans confirm that in both Tribodus and Egertonodus the glossopharyngeal and vagus canals converge and exit from a common foramen (also found in Chlamydoselachus). In both of the hybodonts examined, the trochlear nerve exits the braincase anterior to the optic nerve, a possible hybodont synapomorphy. Separate foramina for the two rami of the octaval nerve are present in both Tribodus and Egertonodus, and may represent an additional hybodont synapomorphy. Also, both taxa have three separate foramina for the trigeminal, facial, and anterodorsal lateral line nerves, apparently including an individual foramen for the superficial ophthalmic complex. However, the basicranial arterial system in Tribodus differs considerably from that of Egertonodus in that in the former the internal carotid arteries enter the braincase much farther posteriorly and through paired foramina rather than a single median foramen. The median ventral basicranial process in Tribodus is similar in structure and position to median ventral processes seen in some extant neoselachians (e.g., Etmopterus) and in embryonic Torpedo (although in the latter this structure disappears during development), and thus may have had a similar ontogenetic origin.

First unequivocal record of the hybodont shark egg capsule Palaeoxyris in the Mesozoic of North America

The hybodont shark egg capsule Palaeoxyris humblei n. sp. is described here from four specimens collected from flood plain deposits in the Blue Mesa Member of the Chinle Formation of Late Triassic (Norian) age in Petrified Forest National Park, Arizona. This find is the first unequivocal record of Palaeoxyris in the Mesozoic of North America. The species differs from previously known taxa, especially other Triassic forms in size and banding. It also is one of the smallest species assigned to the genus. This find offers the rare opportunity of plausibly assigning these egg capsules to the hybodont nonmarine shark Lonchidion humblei as the most probable source since its disarticulated remains (teeth, fin spines) have been found at a closely adjacent locality. Originally, these eggs were deposited in special spawning grounds in the river that deposited the Newspaper Sandstone Bed. There they became attached by tendrils to a piece of drift wood or perhaps the stem or branches of a horsetail such as Neocalamites or Equisetites that grew in the shallow waters of the stream. However, the stream overflowed its banks and the egg capsules together with masses of plant debris and various invertebrates were washed onto the adjacent floodplain where they were buried and eventually fossilized.

New hybodont shark assemblage from the Early Cretaceous of the Basque-Cantabrian Basin

Hybodont remains from the Early Cretaceous of the Basque-Cantabrian Basin (Cantabric Range) in the North of Spain are described for the first time. This assemblage represents a highly diversified shark fauna adapted to different feeding habits. Isolated remains of six hybodont genera, namely Hybodus, Egertonodus, Planohybodus, Lonchidion, Parvodus, and Lissodus, have been recovered and described from the freshwater Vega de Pas Formation in the locality of Vega de Pas (Cantabria, Northern Spain). Most of these taxa are known from the English Wealden, making the shark fauna of the Vega de Pas 1 site the most similar assemblage to English Wealden shark fauna among any other site known in Europe.

Pectoral anatomy of Tribodus limae (Elasmobranchii: Hybodontiformes) from the Lower Cretaceous of northeastern Brazil

ABSTRACT New, undescribed material of the hybodont shark Tribodus limae, from the Lower Cretaceous of northeastern Brazil, provides new information on the pectoral endoskeleton in this taxon. This allows for a revision of its pectoral morphology, which may be broadly applicable to other Hybodontoidei. Four new specimens of Tribodus with well-preserved pectoral girdles are described, including the first complete, three-dimensionally preserved hybodont scapulocoracoid and partial pectoral fin. These specimens permit examination of the posterior surface of the scapulocor-acoid, not visible in previously described hybodonts. Overall pectoral morphology of Tribodus is similar to that of other hybodontiforms and neoselachians. However, the new material shows that the pectoral articulation in Tribodus comprises an oblique posterior ridge on the scapulocoracoid, unlike previous reconstructions of pectoral anatomy in Tribodus and other hybodonts based on two-dimensionally preserved specimens. However, other elasmobranchs, including many neoselachians, Orthacanthus, and ctenacanths, also have an oblique posterior articulation, indicating that this feature may be primitive for elasmobranchs. The pectoral articulation of Tribodus differs noticeably from that of Cladoselache and similar Paleozoic chondrichthyans, which have an elongated, laterally positioned articular process, and from the outgroup (osteichthyans, acanthodians and placoderms). Tribodus also differs from the Paleozoic hybodontiform Ony-choselache in which the articular region comprises a laterally positioned glenoid fossa and posterior condyle. Tribodus has an additional diazonal foramen not found in other hybodonts. Other pectoral features of Tribodus are in agreement with previous phylogenetic hypotheses, supporting the position of Tribodus within Hybodontoidei.

A new hybodont with a cutting dentition from the Lower Cretaceous of Thailand

A new species of hybodont shark with a cutting dentition, Mukdahanodus trisivakulii gen. nov. et sp. nov., from the Lower Cretaceous Sao Khua Formation of Thailand is described. After a turn-over in hybodont faunas in Thailand, it was apparently replaced in the Aptian/Albian ecosystem by Thaiodus ruchae. A comparative study indicates that cutting dentitions with serrated teeth appeared four times independently within the hybodont sharks over a rather short period of time, from the Late Jurassic to the Albian. Moreover, such a dentition occurred only in species spending at least part of their life cycle in fresh waters. Two main kinds of cutting dentition can be identified among hybodonts: high-crowned ( Priohybodus) and low-crowned ( Mukdahanodus gen. nov., Thaiodus and Pororhiza).

Early Middle Jurassic vertebrate microremains from the Three Gorges area, southern China

Vertebrate microremains were collected from the Middle Jurassic freshwater deposits of the Lower Member of the Xietan Formation in the Three Gorges area, Hubei Province, People's Republic of China. They include remains of hybodont sharks (Hybodus aff. “H.” parvidens, Hybodus sp., cf. Parvodus sp., Polyacrodus sp. and Hubeiodus ziguiensis gen. et sp. nov.), an actinopterygian fish, and a crocodyliform. The diversity of hybodont sharks in the Xietan Formation and the appearance of a peculiar pattern of tooth morphology in Hubeiodus ziguiensis suggest the adaptive radiation of these sharks in freshwater systems in China during the Middle Jurassic. This diversification led to the rich endemic hybodont faunas of the Lower Cretaceous in Asia.

Hybodont sharks from the lower Cretaceous Khok Kruat Formation of Thailand, and hybodont diversity during the Early Cretaceous

Abstract Isolated teeth of five hybodont species are described from the Khok Kruat Formation (Aptian): Hybodus aequitridentatus nov. sp., Heteroptychodus steinmanni , Thaiodus ruchae, Khoratodus foreyi nov. gen. et nov. sp., and Acrorhizodus khoratensis . A new family, Thaiodontidae is also erected for Thaiodus and Khoratodus. Two species are recognized inside the genus Heteroptychodus, H. steinmanni and H. chuvalovi nov. comb. These sharks show a wide range of diet and many of them appear to be restricted to a freshwater environment and thus are probably endemic to the Khorat Plateau. However, Thaiodus and Heteroptychodus are also found in deltaic and/or marine environments outside Thailand, but are nevertheless restricted to the Asian continent. It seems that the appearance of three different palaeobiogeographical provinces (Europe, Asia and Africa–South America) around the Tethys during the Early Cretaceous led to the highest diversity at the generic level in the history of hybodont sharks.

HYBODONT SHARKS OF THE ENGLISH BATHONIAN AND CALLOVIAN (MIDDLE JURASSIC)

Abstract: Recent bulk sampling and study of museum collections has revealed a high diversity of hybodont sharks from the English Bathonian, with 15 species being recognised. In addition, study of dental and skeletal material from the English Callovian has allowed the diagnosis of a new genus and species, Planohybodus peterboroughensis gen. et sp. nov., allowing the Bathonian species Hybodus grossiconus Agassiz to be referred to Planohybodus. Two additional new genera, Secarodus and Frangerodus, are erected for the Bathonian taxa Hybodus polyprion Agassiz and Strophodus lingualis Woodward, respectively. Egertonodus duffini sp. nov. is described and the diagnosis of Egertonodus based on dental material is discussed. The previously unrecorded Hybodus sp., Parvodus sp., and Lonchidion sp. are recognised but left in open nomenclature. Asteracanthus medius (Owen) is recorded in the British Bathonian for the first time, and the status of Bathonian nominal species of Asteracanthus are assessed. Bathonian hybodonts showed great diversity in trophic ecology and many of the species are specific to particular palaeoenvironments.

Dinosaurs and other fossil vertebrates from the Late Jurassic and Early Cretaceous of the Galve area, NE Spain

Since 1950, diverse assemblages of Mesozoic vertebrates have been described from the Galve area (Teruel Province, NE Spain). More than fifty taxa have been noted, including fishes, crocodyliforms, pterosaurs, dinosaurs and mammals. The Galve fossil sites occur in an Upper Jurassic to Lower Cretaceous succession spanning some 30 myr, divided into five formations, representing marginal marine and continental settings, with a Tithonian–early Barremian regression and a transgression from the Barremian onwards. New discoveries include teeth of the hybodont shark Lonchidion microselachos, spinosaurine theropods, Eusauropoda and the dryosaurid Valdosaurus. The 30-myr succession shows some possible evolutionary shifts, with a predominance of sauropods as herbivores in older strata, and ornithopods commoner in younger beds. There are some possible replacements among mammals in the latter part of the succession, with trechnotheres, such as spalacotheriids and dryolestoids, dominant in the El Castellar Formation, and multituberculates in the Camarillas Formation. Matching of the vertebrates from the Galve succession with those from age-equivalent units throughout Europe shows close similarity with the Purbeck–Wealden succession of southern England, among others. There are many similarities with dinosaur faunas from North America and Africa, but continent-scale faunal differentiation had clearly begun.

A new hybodont shark assemblage from the Lower Cretaceous of Thailand

Isolated teeth of five hybodont taxa (Hybodus sp., Parvodus sp., Lonchidion khoratensis nov. sp., Isanodus paladeji nov. gen., nov. sp., Heteroptychodus steinmanni) are described from the freshwater Sao Khua Formation of Thailand (Lower Cretaceous). This Early Cretaceous fauna appears less endemic, with some European affinities, than the hybodont fauna found in Thailand in the more recent Aptian/Albian Khok Kruat Formation. Teeth of Isanodus paladeji (Lonchidiidae) and Heteroptychodus steinmanni (Ptychodontidae) share an unusual ornamentation pattern suggesting that the origin of the family Ptychodontidae is nested among Asian Lonchidiidae.

Hybodont sharks from the Middle Jurassic of the Inner Hebrides, Scotland

ABSTRACTNon-marine Bathonian (Middle Jurassic) strata on the Isles of Eigg and Skye in Scotland have yielded fossil remains of eight hybodont shark taxa. Faunas from several horizons within the Lealt Shale and Valtos Formation on the Isle of Eigg include six species: Hybodus grossiconus, Hybodus sp. 1, Hybodus sp. 2, Lissodus leiodus, L. leiopleurus and Parvodus pattersoni. Large collections of teeth of L. leiodus and L. leiopleurus enable a better understanding of the dentitional patterns of the two species and their differential diagnosis. Surface-collecting from exposures of the Kilmalaug Formation on the Isle of Skye yielded hybodont teeth of two taxa: Hybodus sp. 3 and Acrodus caledonicus sp. nov. The occurrence of Acrodus in the Bathonian of Scotland is one of the youngest known occurrences of this genus, and the only non-marine record in the European Jurassic. Collectively, the hybodont assemblages from the Scottish Bathonian provide evidence that non-marine faunas of the group were specifically diverse in the Middle Jurassic.

Hybodont sharks from the Middle Jurassic of the Inner Hebrides, Scotland

Hybodont sharks from the Middle Jurassic of the Inner Hebrides, Scotland

First record of the hybodont shark genus, “Polyacrodus” sp., (Chondrichthyes; Polyacrodontidae) from the Kiowa Formation (Lower Cretaceous) of McPherson County, Kansas

Abstract Three unassociated tooth fragments of the hybodont shark, Polyacrodus sp., were recovered from a quarry in the Kiowa Formation (Lower Cretaceous, Albian), McPherson County, Kansas, in June of 2003. The teeth of this shark represent a new record for the poorly known vertebrate marine paleofauna of the Kiowa. The fragments were discovered in association with the teeth of another hybodont, two lamniform sharks, a ray, and a pycnodont fish; a turtle vertebra; a plesiosaur tooth fragment; and bone, osteoscute, and tooth fragments of crocodilians. The teeth are the first recognized occurrence of “Polyacrodus” in Kansas, and further document the diversity of this near-shore paleofauna in the Western Interior Sea during the Early Cretaceous.

Teeth of enigmatic neoselachian sharks and an ornithischian dinosaur from the uppermost Triassic of Lons-le-Saunier (Jura, France)

Shark teeth and an ornithischian dinosaur tooth are described from a new palynologically dated Rhaetian locality at Lons-le-Saunier (Jura, France). The structure of the enameloid of the teeth ofSynechodus rhaeticus has been studied, but this appears quite different from the usual pattern seen in neoselachian sharks, making the precise relationships of this species difficult to determine. On the other hand,‘Hybodus’ minor, which has long be thought to be a hybodont shark, is included among the Synechodontiformes. The find of the tooth of an ornithischian dinosaur is also reported. Study of the Lonsle-Saunier site seems to indicate a change in the marine faunas during the Rhaetian transgression, preferentially affecting the neoselachian sharks, which increase in abundance, and thedurophasous bony fishes, which become dominated bySareodon tomicus.

Late Cretaceous hybodont sharks from the Kristianstad Basin, southern Sweden

Late Cretaceous hybodont sharks from the Kristianstad Basin, southern Sweden

Sedimentology and vertebrate taphonomy of bone-bearing facies from the Clockhouse Rock Store (Weald Clay, late Hauterivian), Capel, Surrey, UK

The Clockhouse Rock Store [TQ 174 384] has for the past twenty years been a major source of Wealden insect fossils, but the presence of vertebrate remains has only been briefly documented. Nine distinct vertebrate-bearing facies are described here. Sedimentary structures in the sandstones indicate fluvial deposition. Taxa recorded include hybodont sharks, holostean-grade and teleost fish and goniopholidid crocodiles. The vertebrate fossils show taphonomic features confirming deposition by rivers.

Nouvelles données sur l'anatomie et la position systématique de tribodus limae Brito & Ferreira, 1989 (Chondrichthyes, Elasmobranchii) du Crétacé inférieur de la Chapada do Araripe (N-E Brésil)

The recent discovery of new specimens of Tribodus limae, hybodont shark from the Santana Formation, Lower Cretaceous of the Chapada do Araripe (North-East Brazil), permitted us to describe its cranial anatomy (neurocranium and visceral skeleton) and post-cranial (axial skeleton). These new elements, along with a more complete knowledge of its dentition which presents differentiated foramina in the root, confirm the validity of this genus and the systematic position of Tribodus within the hybodontidae along with new elements which permit us to relate this shark to the subfamily Acrodontinae.

A new hybodont shark from the Lower Cretaceous of Thailand

A new hybodont shark from the Lower Cretaceous of Thailand