A new symmetrodont mammal from the Early Cretaceous Jehol Biota of Ningcheng Basin, Inner Mongolia, Northeast China

Recently, a dinosaur assemblage with three-dimensional preservation of the Early Cretaceous Jehol Biota has been discovered in the Ningcheng Basin, Inner Mongolia, China. Of the vertebrate fossils, a new spalacotherioid "symmetrodont" mammal is described here as Ningchengodon foxi gen. et sp. nov. The specimen is an incomplete right dentary characterized by a lower dental formula of i3/c1/p3/m5, with molar cusps in acute-triangulation. Cusps e and f embraced cusp d of the preceding molar forming a molar interlocking, reported here for the first time for acute-angled spalacotherioids. Phylogenetically, the new taxon is placed in the clade of Spalacotherioidea, and clustered at the base of the paraphyletic zhangheotheriids although its relationship is not further resolved with other zhangheotheriids. Additionally, the ultimate premolar replacement is simultaneous with the m5 eruption as in Origolestes lii and Zhangheotherium quinquecuspidens . This discovery enriches the biodiversity of spalacotherioids, and further highlights the complexity of the Zhangheotheriidae in evolution.