New data on Cretaceous freshwater hybodont sharks from Guangxi Province, South China

Abstract : The Lower Cretaceous Xinlong Formation in Guangxi Zhuang Autonomous region, which was deposited in a non-marine, fluvial environment, has yielded a diverse assemblage of vertebrates. The study of the shark teeth from the Xinlong Formation revealed the presence of teeth of Acrorhizodus khoratensis that do not appear to correspond to a jaw position retrieved in Thailand. It also provides a new understanding of the systematic affinities of the species \textquotedblleftHybodus\textquotedblright aequitridentatus. The latter does not belong to te genus Hybodus but to a new genus belonging to the family Thaiodontidae. The material found in the Xinlong Formation also questions our understanding of the heterodonty pattern of the genus Acrorhizodus and highlights how peculiar this genus is among Hybodontiformes. As only two teeth differ significantly from the material retrieved in Thailand, it is difficult to assess whether the Chinese material includes a species different from the Thai one, but it certainly calls for a careful reappraisal of all the available material to better assess the heterodonty pattern of this genus.