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. [ABSTRACT FROM AUTHOR]