New materials of Chalicotherium brevirostris (Perissodactyla, Chalicotheriidae) from the Tunggur Formation, Inner Mongolia

Chalicotherium brevirostris was named by Colbert based on a skull lacking mandibles from the late Middle Miocene Tunggur Formation, Tunggur, Inner Mongolia, China. Here we describe new mandibular materials collected from the same area. In contrast to previous expectations, the new mandibular materials show a long snout, long diastema, a three lower incisors and a canine. C. brevirostris shows some sexual dimorphism and intraspecific variation in morphologic characters. The new materials differ from previously described C. cf. brevirostris from Cixian County (Hebei Province) and the Tsaidam Basin, which may represent a different, new species close to C. brevirostris. The diagnosis of C. brevirostris is revised.