Hybodont sharks from the Early Cretaceous of Thailand. (original) (raw)
Freshwater hybodont sharks from the Lower Cretaceous of Thailand
International Congress on …, 2004
The lower Cretaceous of Thailand has yielded isolated teeth of eight hybodont genera, including Hybodus, Lonchidion, Thaiodus and Heteroptychodus. They are distributed in two successive assemblages, the first one from the Sao Khua Formation (Neocomian), and the second one from the Khok Kruat Formation (Aptian), with only two genera in common between these two assemblages, Hybodus and Heteroptychodus. These sharks show a wide range of diet and many of them were restricted to freshwater environment and thus endemic to the Khorat Plateau. The distribution of Thaiodus and Heteroptychodus, known in other Asian locations, may be explained by a mode of life similar to that of the modern sawfish Pristis perotteti.
A new hybodont with a cutting dentition from the Lower Cretaceous of Thailand
Cretaceous Research, 2009
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).
Shark faunas from the Late Jurassic—Early Cretaceous of northeastern Thailand
Paläontologische Zeitschrift, 2013
A revision of the freshwater shark fauna from the Phu Kradung Formation in NE Thailand allows the recognition of a new species of Acrodus, which represents the youngest occurrence of the genus and confirms its displacement in freshwater environments after the Toarcian. The rest of the shark fauna includes teeth of Hybodus sp., aff. Hybodus sp., hybodontid dermal denticles, Jiaodontus sp., Lonchidion sp. A, Lonchidion sp. B, Heteroptychodus cf. H. kokutensis and dorsal fin spines. The presence of Jaiodontus and of unusual hybodontid dermal denticles suggests a Jurassic age for most of the Phu Kradung Formation, whereas the presence of Heteroptychodus suggests an Early Cretaceous age for the top of the Formation. However, the age of the Phu Kradung Formation is still uncertain, with contradictory signals coming from palynology, detrital zircon thermochronology and vertebrate palaeontology. In any case, it appears that this is the oldest occurrence of the genus Heteroptychodus, and suggests a Thai origin for this genus, which may have replaced Acrodus in the Thai freshwater palaeoecosystems. Together with Acrodus, the presence of Lonchidion sp. A suggests some European affinities for the shark fauna from the Phu Kradung Formation.
Hybodont sharks from the Aptian-Albian of Tunisia and Thailand
Isolated teeth of six hybodont genera, including Hybodus, Thaiodus and Heteroptychodus, are described from the freshwater Lower Cretaceous of Thailand. The presence of the South American hybodont genus Tribodus, based on isolated teeth, is reported from the Lower Cretaceous of Tunisia in a brackish or freshwater environment. The appearance during the Lower Cretaceous among hybodonts of specializations like cutting teeth (Thaiodus, Priohybodus, Pororhiza) and hyostylic jaw suspension (Tribodus) indicates that this lineage was still very successful in freshwater and brackish environments by that time. In terms of number of genera and diversity of diet, the hybodonts were more diversified during the Lower Cretaceous than during the whole Triassic. (2000). -Dinosaurs and other fossil vertebrates from fluvial deposits in the Lower Cretaceous of southern Tunisia. Palaeogeography, Palaeoclimatology, Palaeoecology, 157, 227-246.
PARAPTYCHODUS WASHITAENSIS N. GEN. ET N. SP., OF PTYCHODONTID SHARK FROM THE ALBIAN OF TEXAS, USA.
A new genus and species of Ptychodontiform elasmobranch, Paraptychodus washitaensis n. gen. et n. sp. is described on the basis of 13 teeth from the Middle Albian Duck Creek Formation of the Washita Group in north central Texas, USA. This material is significant as it demonstrates an intermediate tooth form between the Lonchidiidae and Ptychodus with regard to occlusal ornamentation of the crown and tooth root morphology; the new taxon represents the earliest member of the family Ptychodontidae in North America. Analysis of dental characters and stratigraphic occurrences within the family suggests that P. washitaensis is a basal taxon and is the most recent ancestor of Ptychodus. Morphological trends of derived species of Ptychodus demonstrate continuous specialization in tooth crown morphologies. The diagnosis of P. washitaensis from the upper Albian of Texas adjusts the stratigraphic distribution of the genus Ptychodus to lower Cenomanian through lower Campanian.
… Journal of the …, 2009
Extensive sampling of several Barremian and Albian-Cenomanian levels across the Aguilón, Oliete and Aliaga subbasins of the Iberian Basin, north-east Spain, yielded abundant material of new or so far poorly known neoselachians. The faunas consist of 16 different species, five of which represent new species and two new genera: Cantioscyllium brachyplicatum sp. nov., Platypterix venustulus gen. et sp. nov., Ptychotrygon pustulata sp. nov., Ptychotrygon striata sp. nov. and Iberotrygon plagiolophus gen. et sp. nov. In addition, teeth of Heterodontus cf. H. carerens, Lamniformes indet., Pteroscyllium sp., Scyliorhinidae indet., Rhinobatos sp., Spathobatis sp., Belemnobatis sp., Ptychotrygon geyeri, Ptychotrygon sp. and Celtipristis herreroi are described. The new family Ptychotrygonidae is defined. The localities comprise palaeoenvironments ranging from lacustrine and shallow lake to open marine settings. Neoselachians are almost completely absent from continental settings in the Barremian, as a result of prevailing freshwater conditions, but became more abundant in marine strata. The Albian-Cenomanian selachian assemblage is the most profuse and diverse of the three assemblages studied. It is dominated by small, benthic and near-coastal taxa, for instance Cantioscyllium and Ptychotrygon, and contains several new species, including an endemic batoid, Iberotrygon plagiolophus gen. et sp. nov.
First record of hybodont egg capsules from the Jurassic of Thailand
Annales de paléontologie, 2023
Two egg capsules of Palaeoxyris sp. are reported from the Jurassic Phu Kradung Formation in the Khorat Plateau, northeastern Thailand. As the record of this genus remains rare in the Jurassic, it complements its stratigraphic distribution. Most importantly, it represents the first unambiguous evidence that some hybodont sharks from the Mesozoic of Thailand were able to reproduce in fresh waters, even if it is not yet possible to identify which species in particular. RÉSUMÉ Deux capsules ovigères de Palaeoxyris sp. ont été découvertes sur le plateau de Khorat dans le nord-est de la Thaïlande. Les spécimens proviennent de la Formation Phu Kradung, datée du Jurassique. Le registre fossile de ce genre demeurant mal connu au Jurassique, cette découverte permet de compléter sa distribution stratigraphique. Ces capsules ovigères représentent la première preuve indéniable que durant le Mésozoïque certains requins hybodontes se reproduisaient dans les eaux douces thaïlandaises, même s'il n'est pas encore possible d'identifier quelles espèces en particulier.