New basal hadrosauroid (Dinosauria: Ornithopoda) from the Lower Cretaceous Kitadani Formation, Fukui, central Japan
Abstract
A new basal hadrosauroid, Koshisaurus katsuyama, from the Lower Cretaceous Kitadani Formation in Fukui, central Japan, is reported. The new taxon is distinguished by an autapomorphy and a unique combination of maxillary, vertebral, pubic and femoral characters. A phylogenetic analysis indicates thatKoshisaurusis positioned as a basal member of Hadrosauroidea and is more derived than the contemporaneousFukuisaurus, which is a non-hadrosauroid hadrosauriform. The presence of the antorbital fossa on the maxilla and at least three subsidiary ridges on the labial side of maxillary tooth crown implies thatKoshisaurus was among the most basal hadrosauroids. This discovery indicates a higher diversity of hadrosauroids along the eastern margin of the Asian continent in the Early Cretaceous.