Résumé
dagger Siamamia naga, gen. et sp. nov, is described on the basis of three partly articulated skulls and a collection of isolated ossifications from a continental Early Cretaceous Formation of northeastern Thailand. The new taxon is a dagger sinamiid halecomorph as demonstrated by the median parietal and other cranial characters. dagger Sinamiidae is hitherto known by two genera occurring in Early Cretaceous freshwater deposits in China. Although a complete revision of all species within the family is necessary, the Thai material shows characters justifying a new genus. It is the first dagger sinamiid found outside eastern Asia (South and North Chinese blocks, plus small Central Asian terranes), thus validating the close paleogeographical affinities between mainland Asia and SE Asia in the Early Cretaceous. A preliminary phylogenetic assessment of the new taxon with the data matrix of Grande and Bemis (1998) with the addition of data for dagger Siamamia and dagger Tomognathus provides a strict consensus tree similar to the phylogenetic hypothesis of Halecomorphi proposed by these authors, except the basal-most amiids which show a lower resolution in our hypothesis. The dagger Sinamiidae appear as a monophyletic clade, but the four taxa included in the analysis form a polytomy.