Abstract:  A new non-hadrosaurid hadrosauroid dinosaur (Datonglong tianzhenensis gen. et sp. nov.) is reported. The new taxon is recovered from the Upper Cretaceous Huiquanpu Formation of Tianzhen County, Shanxi Province in northern China, and represented by an almost complete right dentary with dentition. Different from all other hadrosauroids, Datonglong possesses two functional teeth in each alveolus, and the pattern of ridge development on the lingual surface of its dentary crown shows a unique combination of character states (for example: distally offset primary ridge; well-developed secondary ridge; no additional ridge(s); slightly distally curved apical half of primary ridge). Comparative studies indicate advanced non-hadrosaurid hadrosauroids experienced a complex pattern in the evolution of their dentary, especially dentary dentition. Derived hadrosaurid features occurred frequently in these taxa, such as high height/width ratio of tooth crown in Bactrosaurus, one primary and one faint ridges inGilmoreosaurus, median placed primary ridge in Zhanghenglong, rostrally inclined coronoid process in Nanningosaurus, and two functional teeth in each alveolus in Datonglong. This implies incredible diversities and attempts close to the origin of Hadrosauridae and difficulties to elucidate their phylogenetic relationships.