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).