Acristatherium yanensis is an extinct basal eutherian from the Early Cretaceous (early Aptian, about) Lujiatun Bed of the Yixian Formation.[1] It was described on the basis of a single specimen (holotype) from Beipiao, Liaoning, China, by Yaoming Hu, Jin Meng, Chuankui Li, and Yuanqing Wang in 2010.[1] The specimen comprises a partial skull, 25mm long. It appears to possess a vestige of a septomaxilla, a feature only otherwise seen in nonmammalian therapsids.[1]