A second hadrosauroid dinosaur from the early Late Cretaceous of Zuoyun, Shanxi Province, China

A second basal hadrosauroid dinosaur, <i>Zuoyunlong huangi</i> gen. et sp. nov., is reported from the early Late Cretaceous Zhumapu Formation in Zuoyun County, Shanxi Province, northern China. <i>Zuoyunlong</i> preserves a partial right ilium and ischium and is unique in having a very short postacetabular process 50% as long as the iliac central plate. Our cladistic analysis recovers <i>Zuoyunlong</i> as the most basal Late Cretaceous hadrosauroid, with a sister taxon relationship with <i>Probactrosaurus</i> from the late Early Cretaceous of Inner Mongolia. Including <i>Zuoyunlong</i>, four Cenomanian basal hadrosauroids have been recorded, and the two taxa in North America (<i>Eolambia</i> and <i>Protohadros</i>) represent the earliest known hadrosauroids outside of Asia. In the light of the proposed phylogenetic topology and biogeographic data, the discovery of <i>Zuoyunlong</i> indicates that the first dispersal of hadrosauroids from Asia to North America probably happened around the boundary between the Early and Late Cretaceous.