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.

Abstract We describe a new elasmobranch fauna from the lower part of the Khlong Min Formation in Thailand. The fauna includes Hybodus sp., Asteracanthus sp., Lonchidion reesunderwoodi sp. nov., Belemnobatis aominensis sp. nov., and possibly a second species of Belemnobatis. This fauna supports a Bathonian–Callovian age for the Khlong Min Formation, and suggests a close taxonomic relationship between the Middle Jurassic elasmobranch faunas of Europe and Thailand. The presence of a monolayered enameloid in Belemnobatis aominensis sp. nov. and other primitive batoids is interpreted as the retention of a primitive character for neoselachians, which would suggest a divergence time between the batoids and the rest of the neoselachian sharks as early as the Carboniferous–Permian boundary.