Acristatherium

Acristatherium yanensis is an extinct basal eutherian from the Early Cretaceous (early Aptian, about 125 million years ago) Lujiatun Bed of the Yixian Formation. 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. The specimen comprises a partial skull, 25 mm (0.98 in) long. It appears to possess a vestige of a septomaxilla, a feature only otherwise seen in nonmammalian therapsids.