New findings of stegosaurs from the Lower Cretaceous Luohandong Formation in the Ordos Basin, Inner Mongolia

The Early Cretaceous Zhidan Group in the northern Ordos Basin of Inner Mongolia yielded a large number of tetrapods, which included turtles, choristoderes, crocodyliforms, psittacosaurs, stegosaurs, ankylosaurs, theropods, birds and primitive mammals. A well-preserved stegosaurian sacrum with paired ilia found from the Luohandong Formation, a middle-upper unit of Zhidan Group, is referred to as Wuerhosaurus ordosensis. The new findings give some additional characteristics to the pelvic girdle in W.ordosensis, such as both concave anterior margin and concave medio-posterior margin of the supra-acetabular flange. Based on comparison of Wuerhosaurus ordosensis with W. homheni known from Xinjiang, the authors point out the differences in ilia between the two species:① a relatively short anterior iliac process in W.ordosensis; ② the anterior iliac process with arched posterior portion of the dorsal margin in W.ordosensis, and anterior iliac process with nearly parallel dorsal and ventral margins in W. homheni; ③ the relatively small angle between anterior iliac processes and midline in W.ordosensis. These characteristics further provide the evidence that W.ordosensis and W. homheni are different species.